US20140069721A1 - Magnetic ranging while drilling using an electric dipole source and a magnetic field sensor - Google Patents
Magnetic ranging while drilling using an electric dipole source and a magnetic field sensor Download PDFInfo
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- US20140069721A1 US20140069721A1 US14/083,236 US201314083236A US2014069721A1 US 20140069721 A1 US20140069721 A1 US 20140069721A1 US 201314083236 A US201314083236 A US 201314083236A US 2014069721 A1 US2014069721 A1 US 2014069721A1
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- 238000005553 drilling Methods 0.000 title claims abstract description 72
- 238000000034 method Methods 0.000 claims abstract description 33
- 238000005259 measurement Methods 0.000 claims abstract description 20
- 230000004907 flux Effects 0.000 claims description 46
- 238000013459 approach Methods 0.000 claims description 27
- 238000010796 Steam-assisted gravity drainage Methods 0.000 claims description 19
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- 230000008901 benefit Effects 0.000 description 3
- 239000000696 magnetic material Substances 0.000 description 3
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- 238000011084 recovery Methods 0.000 description 3
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- 238000010793 Steam injection (oil industry) Methods 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
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- 229910000952 Be alloy Inorganic materials 0.000 description 1
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- E21B47/02216—
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/24—Enhanced recovery methods for obtaining hydrocarbons using heat, e.g. steam injection
- E21B43/2406—Steam assisted gravity drainage [SAGD]
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/02—Determining slope or direction
- E21B47/022—Determining slope or direction of the borehole, e.g. using geomagnetism
- E21B47/0228—Determining slope or direction of the borehole, e.g. using geomagnetism using electromagnetic energy or detectors therefor
Definitions
- the present invention relates generally to well drilling operations and, more particularly, to well drilling operations using magnetic field measurements from an electric dipole to ascertain the relative location of a new well to an existing well.
- Heavy oil may be too viscous in its natural state to be produced from a conventional well.
- a variety of techniques may be employed, including, for example, Steam Assisted Gravity Drainage (SAGD), Cross Well Steam Assisted Gravity Drainage (X-SAGD), or Toe to Heel Air Injection (THAI). While SAGD wells generally involve two parallel horizontal wells, X-SAGD and THAI wells generally involve two or more wells located perpendicular to one another.
- X-SAGD and THAI techniques function by employing one or more wells for steam injection or air injection, respectively, known as “injector wells.”
- the injector wells pump steam or air into precise locations in a heavy oil formation to heat heavy oil.
- One or more lower horizontal wells known as “producer wells,” collect the heated heavy oil.
- the injector well is a horizontal well located above and oriented perpendicular to the producer well.
- the injector well is a vertical well located near and oriented perpendicular to the producer well.
- Steam or air from an injector well in an X-SAGD or THAI well pair should be injected at a precise point in the heavy oil formation to maximize recovery. Particularly, if steam is injected too near to a point of closest approach between the injector well and the producer well, steam may be shunted out of the formation and into the producer well. Using many conventional techniques, the point of closest approach between the two wells may be difficult to locate or the location of the point of closest approach may be imprecise.
- the relative distance between the injector and producer wells of an X-SAGD or THAI well pair may affect potential recovery.
- the wells should be located sufficiently near to one another such that heavy oil heated at the injector well may drain into the producer well. However, if the wells are located too near to one another, steam or air from the injector well may shunt into the producer well, and if the wells are located too far from one another, the heated heavy oil may not extend to the producer well. Using conventional techniques, it may be difficult to accurately drill one well perpendicular to another well.
- a method of drilling a new well in a field having an existing well includes drilling the new well using a bottom hole assembly (BHA) having a drill collar divided by an insulated gap, generating a current on the drill collar of the BHA, and measuring from the existing well a magnetic field caused by the current on the drill collar of the BHA. Using measurements of the magnetic field, the relative position of the new well to the existing well may be determined.
- BHA bottom hole assembly
- FIG. 1 is a schematic of a well drilling operation using magnetic ranging while drilling for a parallel well
- FIG. 2 is a schematic of a more detailed view of the well drilling operation of FIG. 1 ;
- FIG. 3 is a cross-sectional view of an existing well taken along cut lines 3 - 3 in the well drilling operation of FIG. 1 ;
- FIG. 4 is a schematic depicting a well drilling operation for drilling a Toe to Heel Air Injection (THAI) well using magnetic ranging while drilling in accordance with an embodiment of the invention
- THAI Toe to Heel Air Injection
- FIG. 5 is a flowchart describing an embodiment of a method of performing the well drilling operation of FIG. 4 ;
- FIG. 6 is a flowchart depicting another embodiment of a method of performing the well drilling operation of FIG. 4 ;
- FIG. 7 is a schematic depicting a well drilling operation for drilling a Cross Well Steam Assisted Gravity Drainage (X-SAGD) well in accordance with an embodiment of the invention
- FIG. 8 is a flowchart describing an embodiment of a method of performing the well drilling operation of FIG. 7 ;
- FIG. 9 is a schematic side view of the well drilling operation of FIG. 4 ;
- FIG. 10 is a schematic top view of the well drilling operation of FIG. 4 ;
- FIG. 11 is a schematic end view of the well drilling operation of FIG. 4 ;
- FIG. 12 is a plot of sensor noise of a plurality of available magnetometers for a variety of magnetic field frequencies
- FIG. 13 is a diagram of an electric dipole formed as an electric current passes through a bottom hole assembly (BHA) divided by an insulated gap;
- BHA bottom hole assembly
- FIG. 14 is a plot of the magnitude of magnetic flux density as a function of distance along a BHA using magnetic ranging while drilling for a variety of offsets in the x-axis;
- FIG. 15 is a plot of magnetic flux density in the x-axis as a function of distance in the y-axis from a BHA using magnetic ranging while drilling for a variety of offsets in the x-axis;
- FIG. 16 is a plot of magnetic flux density in the y-axis as a function of distance in the y-axis from a BHA using magnetic ranging while drilling for a variety of offsets in the x-axis;
- FIG. 17 is a flowchart describing a method of obtaining the relative positions between two perpendicular wells in accordance with an embodiment of the invention.
- FIG. 18 is a schematic depicting a well drilling operation in which the relative positions between two wells may be ascertained when the two wells are not necessarily perpendicular;
- FIG. 19 is a plot of transverse magnetic flux density as a function of distance along the existing well depicted in FIG. 18 ;
- FIG. 20 is a plot of parallel magnetic flux density as a function of distance along the existing well depicted in FIG. 18 ;
- FIG. 21 is a flowchart describing a method of obtaining the relative positions of two non-parallel wells in accordance with an embodiment of the invention.
- first well refers to a generally horizontal existing well
- vertical well refers to a generally vertical existing vertical well
- second well refers to a secondary well drilled in the vicinity of either the first well 12 or the vertical well 52 . It should be appreciated, however, that the wells may be drilled in any order and that the terms are used to clarify the figures discussed below.
- FIG. 1 depicts a well drilling operation 10 involving magnetic ranging while drilling.
- an existing first well 12 and a new second well 14 extend from the surface through a formation 16 into a heavy oil zone 18 .
- the first well 12 is cased with casing 20 and completed with tubing 22 .
- a drill string 24 is used to drill the second well 14 .
- the drill string 24 includes a bottom hole assembly (BHA) 26 having a drill bit 28 and a steerable system 30 .
- the BHA 26 may also include a variety of drilling tools such as a measurement while drilling (MWD) tool or a logging while drilling (LWD) tool.
- MWD measurement while drilling
- LWD logging while drilling
- a tool in the BHA 26 generates an electric current 32 on both sides of an insulated gap 34 in the outer drill collar.
- the current 32 generates an azimuthal magnetic field 36 around the BHA 26 .
- FIG. 1 depicts the magnetic field 36 centered on the insulated gap 34 , but it should be understood that the magnetic field 36 extends along the length of the BHA 26 and beyond.
- a wireline magnetometer 38 may be deployed into the first well 12 using a tractor or a coiled tubing system, with which the strength of the magnetic field 36 may be measured at a variety of locations along the first well 12 . With measured magnetic field 36 strength data obtained by the wireline magnetometer 38 , the relative position between first well 12 and second well 14 may be ascertained.
- FIG. 2 provides a more detailed view 40 of the well drilling operation 10 of FIG. 1 .
- the BHA 26 includes an electric current driving tool 42 , which may be a component of a measurement while drilling (MWD) tool such as Schlumberger's E-Pulse or E-Pulse Express tool or a standalone tool.
- the electric current driving tool 42 generates the electric current 32 on an outer drill collar 44 located on the opposite side of the insulated gap 34 .
- the more detailed view 40 also illustrates that when the first well 12 and the second well 14 are parallel, the magnetic field 36 generated by the electric current 32 may not necessarily be detected by the wireline magnetometer 38 .
- the casing 20 is composed of a magnetic material such as alloy steel, the magnetic field 36 may be significantly attenuated and may not effectively penetrate the casing 20 .
- FIG. 3 a cross-sectional view 46 of the first well 12 , depicted from along the cut lines 3 - 3 of FIG. 1 , illustrates the attenuation of the magnetic field 36 which may occur when the first well 12 and the second well 14 are parallel and the casing 20 is composed of a magnetic material.
- the wireline magnetometer 38 is deployed within the tubing 22 and surrounded by the casing 20 , which may be assumed to be alloy steel.
- the azimuthal magnetic field 36 from the second well 14 will be perpendicular to the first well 12 .
- the magnetic field 36 may be significantly attenuated.
- a re-directed magnetic field path 48 may effectively route the magnetic field 36 around the casing 20 of the first well 12 , largely preventing its detection by the wireline magnetometer 38 .
- FIG. 4 illustrates a well drilling operation 50 for drilling a horizontal well perpendicular to a vertical well.
- the magnetic field 36 may be largely undiminished by the presence of magnetic casing.
- many applications may benefit from an accurate placement of perpendicular wells, and though the well drilling operation 50 depicted relates primarily to Toe to Heel Air Injection (THAI), the methods described herein may be well suited to developing a variety of such applications.
- THAI Toe to Heel Air Injection
- THAI is an in situ combustion process involving horizontal wells for producing oil and combustion by-products and vertical wells for injecting air into the heavy oil zone 18 .
- the injected air causes some heavy oil in the heavy oil zone 18 to combust, which heats the surrounding heavy oil, reducing its viscosity.
- some upgrading of the heavy oil to lighter oil may occur.
- Gravity causes the heated heavy oil and upgraded oil to collect in the horizontal wells below.
- One approach to THAI is depicted in the well drilling operation 50 of FIG. 4 . First, a vertical well 52 , known as an injector well, is drilled and cased with casing 54 .
- the horizontal second well 14 known as a producer well, is subsequently drilled.
- the magnetic field 36 may be measured from a wireline magnetometer 38 within the vertical well 52 . Using measurements of the magnetic field 36 at various locations from within the vertical well 52 , the precise location of the second well 14 relative to the vertical well 52 may be obtained. The trajectory of the BHA 26 may be properly adjusted such that the second well 14 is drilled at the proper distance and orientation from the vertical well 52 .
- the well drilling operation 50 and, specifically, the spatial relationships of the second well 14 and the vertical well 52 will be described further below with respect to FIGS. 9-11 .
- a flow chart 56 describes one method for drilling the THAI well depicted in the well drilling operation 50 of FIG. 4 .
- first step 58 the vertical well 52 is drilled and cased with casing 54 .
- Step 60 involves drilling the second well 14 .
- magnetic field measurements may be obtained while the second well 14 is being drilled.
- the electric current driving tool 42 generates the electric current 32 on the drill collar of the BHA 26
- an electric dipole is effectively formed from the two sides of the BHA 26 surrounding the insulated gap 34 , producing the azimuthal magnetic field 36 .
- the gravity deployed wireline magnetometer 38 may measure the strength of the magnetic field 36 at a variety of points in the vertical well 52 .
- step 64 based on the measurements of the magnetic field, the relative position of the vertical well 52 and the second well 14 may be determined according to a technique discussed below.
- FIG. 6 depicts an alternative flow chart 66 describing a method of drilling horizontal wells in fields having existing vertical wells.
- a series of horizontal wells drilled among existing vertical wells may increase recovery.
- the existing vertical wells may be employed as steam injector wells, and the new horizontal wells may be employed as producer wells.
- a horizontal well such as the second well 14 begins being drilled in a field with a plurality of existing vertical wells such as the vertical well 52 .
- magnetic field measurements may be obtained while the second well 14 is being drilled.
- the wireline magnetometer 38 is gravity deployed into a first of the existing vertical wells such as vertical well 52 .
- the wireline magnetometer may measure the magnetic field 36 at a variety of points in the vertical well 52 . Based on the measurements of the magnetic field 36 , the relative position of the vertical well 52 and the second well 14 may be determined according to a technique discussed below.
- decision block 76 if the horizontal second well 14 will cross another vertical well 52 in the field of existing vertical wells, the process returns to step 70 for drilling beyond the subsequent vertical well 52 . If not, the process ends at step 78 .
- a well drilling operation 80 depicts drilling two perpendicular wells for use in Cross Well Steam Assisted Gravity Drainage (X-SAGD) wells.
- a first horizontal well 12 is drilled through the formation 16 and into the heavy oil zone 18 before completion with casing 20 and tubing 22 .
- a second well 14 is subsequently drilled above and perpendicular to the first well 12 .
- Periodically, magnetic field measurements may be obtained while the second well 14 is being drilled.
- the electric current 32 on the drill collar of the BHA 26 may form an electric dipole from the two sides of the BHA 26 surrounding the insulated gap 34 , producing the azimuthal magnetic field 36 .
- the magnetic field 36 may be detected by the magnetometer 38 with little attenuation.
- a flowchart 84 depicts a method of drilling the X-SAGD well depicted in FIG. 7 .
- the first horizontal well 12 is drilled and completed with casing 20 and tubing 22 .
- Step 88 involves drilling the perpendicular horizontal second well 14 .
- Periodically, magnetic field measurements may be obtained while the second well 14 is being drilled.
- the electric current 32 on the drill collar of the BHA 26 may form an electric dipole from the two sides of the BHA 26 surrounding the insulated gap 34 , producing the azimuthal magnetic field 36 .
- step 90 the wireline magnetometer 38 is deployed in the first well 12 using a mud pump to push it down inside the tubing 22 , or in case there is no tubing present, using a tractor, coiled tubing, or other means.
- step 92 the magnetic field 36 may be detected by the wireline magnetometer 38 at a variety of locations along the first well 12 .
- the data obtained by the wireline magnetometer 38 may be subsequently used in step 94 to determine the relative position of the first well 12 to the second well 14 using techniques described further below.
- the decision block 96 if the second well 14 will cross another horizontal well 12 , the process returns to step 90 for drilling beyond the subsequent horizontal well 12 . If not, the process ends at step 98 .
- FIGS. 9 , 10 , and 11 depict three different views of the well drilling operation 50 as depicted in FIG. 4 to illustrate the spatial relationship between the vertical well 52 and the second well 14 .
- FIG. 9 depicts a side view 100 of the well drilling operation 50 of FIG. 4 .
- the second well 14 is perpendicular to the vertical well 52 .
- the second well is aligned with the z-axis.
- the vertical well 52 is aligned with the y-axis.
- the intensity of the magnetic field 36 may be defined as a function of distance along the y-axis.
- FIG. 10 depicts a top view 104 of the well drilling operation 50 of FIG. 4 .
- the second well 14 is depicted as being offset from the vertical well 52 along the x-axis.
- the closest approach between the second well 14 and the vertical well 52 is correspondingly defined along the x-axis.
- FIG. 11 depicts end view 106 of the well drilling operation 50 of FIG. 4 .
- the magnetometer 38 is raised and lowered along the y-direction by the wireline 102 within the vertical well 52 .
- the intensity of the magnetic field 36 may be measured.
- the magnetometer 38 may detect the magnetic field 36 largely unimpeded by the casing 54 , since the second well 14 is oriented perpendicularly to the vertical well 52 .
- a plot 108 illustrates the sensitivity of available magnetometers for borehole use.
- An ordinate 110 represents sensor noise in units of nanoTesla per root Hertz (nT/ ⁇ square root over (Hz) ⁇ ), while an abscissa 112 represents frequency in units of Hertz (Hz).
- Lines 114 , 116 , 118 , 120 , and 122 respectively indicate the sensitivity of a BF-4 magnetometer, a BF-6 magnetometer, a BF-7 magnetometer, a BF-10 magnetometer, and a BF-17 magnetometer, all of which are manufactured by Schlumberger EMI Technology Center, in Richmond, Calif.
- noise figures may be exceptionally low for many of the BF series magnetometers.
- a magnetometer with one nanoTesla (nT) resolution should be sufficient to accurately estimate a distance of one well to another from at least fifty meters apart.
- the noise figures for the magnetometers described in the plot 108 achieve picoTesla (pT) noise levels per root Hertz (pT/ ⁇ square root over (Hz) ⁇ ).
- pT picoTesla
- an electric dipole 124 is depicted.
- the electric dipole 124 models the electric dipole which forms on the BHA 26 surrounding the insulated gap 34 .
- the portion of the BHA 26 from the insulated gap to the drill bit 28 is noted in FIG. 13 as a first electric pole 126 .
- the portion of the BHA 26 from the insulated gap through the drill string 24 is noted in FIG. 13 as a second electric pole 128 .
- the second electric pole 128 on the BHA 26 is longer than the first electric pole 126 on the BHA 26 , since the electric current 32 can extend onto the drill string 24 above the BHA 26 .
- the azimuthal magnetic field 36 strength created by the electric dipole 124 may be described by the following relationship:
- d 1 represents the length of the first electric pole 126
- d 2 represents the length of the second electric pole 128
- s represents a distance from the center of the insulated gap 34 to the outer drill collar.
- ⁇ represents angular frequency
- ⁇ represents the permeability of free space
- ⁇ represents permittivity of the surrounding formation 18
- ⁇ represents electrical conductivity of the surrounding formation 18
- I 0 represents the magnitude of the electric current 32 at the insulated gap 34 .
- Equation (1) may be simplified as the frequency approaches zero, i.e., for frequencies of a few hundred Hertz or lower. Assuming the insulated gap 34 to be negligible in length compared to the length of the arms of the dipoles, in a limit when the frequency ⁇ approaches zero, equation (1) may be rewritten as follows:
- H ⁇ I 0 ⁇ y 4 ⁇ ⁇ [ ⁇ - d 2 0 ⁇ d 2 + z ′ d 2 ⁇ ⁇ ⁇ ⁇ exp ⁇ ( - j ⁇ ⁇ kR ) ⁇ ⁇ ⁇ z ′ + ⁇ 0 d 1 ⁇ d 1 - z ′ d 1 ⁇ ⁇ ⁇ ⁇ exp ⁇ ( - j ⁇ ⁇ kR ) ⁇ ⁇ z ′ ] . ( 2 )
- a vector magnetic field B at an arbitrary location (x, y, z) may be defined according to the following equation:
- this calculation does not include the attenuating effect that the casing 22 or 54 may have in the first well 12 or the vertical well 52 .
- the field intensity may be reduced if the magnetometer 38 is concealed within magnetic casing.
- attenuation due to the casing 22 generally has a constant value, and this effect may be removed by calibration.
- Equation (4) may be used to calculate the magnetic field and existing wellbore for any trajectory of a well being drilled at any angle and distance.
- plot 132 illustrates magnetic flux density as measured by the magnetometer 38 in the first well 12 for a variety of x-direction offsets of the second well 14 .
- An ordinate 134 represents the absolute magnitude of magnetic flux density in units of nanoTesla (nT)
- an abscissa 136 illustrates the distance in meters (m) along the z-direction from the insulated gap 34 on the BHA 26 .
- Lines 142 , 144 , 146 , 148 , and 150 illustrate respectively the magnitude of magnetic flux density along the axial direction in the z-direction for offsets in the x-direction of 50 m, 30 m, 10 m, 5 m, and 2 m.
- the coordinate system described in the plot 132 moves with the BHA 26 .
- different values of z correspond to the position of the wireline magnetometer 38 in the first well 12 relative to the insulated gap 34 on the BHA 26 in the second well 14 .
- a magnetometer with 1 nT resolution should be able to accurately estimate the distance from the first well 12 to the BHA 26 drilling the second well 14 from at least 50 m away.
- available magnetometers are capable of such a resolution.
- the relative positions of the first well 12 and the second well 14 may be used for quality control or to plan production methods such as steam injection. For example, in X-SAGD, solid casing might be used near the crossing point to avoid a short path for the steam to travel between the two wells.
- the corresponding location on the abscissa 136 , at point 138 indicates that the magnetic field intensity is ambiguous, as the curves overlap for the various x-direction offset distances between the two wells.
- the drill bit 28 of the BHA 26 in the second well 14 has not yet reached the point of closest approach of the first well 12 .
- the lines of plot 132 are well resolved for different x-direction offset distances between the two wells.
- the magnetic flux density is very small, approaching 0.4 nT.
- the magnetic flux density is instead 4.5 nT.
- the change in the magnetic flux density as the BHA 26 continues to drill may also be used to estimate a transverse distance between the first well 12 and the second well 14 .
- observing the rate of change in magnetic flux density in drilling ten meters may be used to estimate the relative separation of the first well 12 and second well 14 .
- the magnetometer should have a resolution of at least 0.1 nT to perform such measurements of the drill bit 28 . As indicated by plot 108 of FIG. 12 , this resolution is within the capability of EMI EF magnetometers.
- FIGS. 15 and 16 represent plots obtained from the well drilling operation 50 of FIGS. 4 and 9 - 11 .
- a plot 152 illustrates magnetic flux density B x (y) in the x-direction as measured by the magnetometer 38 for a variety of x-direction offset locations for the first well 12 .
- An ordinate 154 represents the magnetic flux density B x (y) in units of nanoTesla (nT), and an abscissa 156 represents the distance in meters (m) along the y-direction from the insulated gap 34 on the BHA 26 .
- Lines 158 , 160 , 162 , 164 , and 166 illustrate respectively the magnitude of magnetic flux density B x (y) measured along the y-direction inside the first well 12 for offsets in the x-direction of 20 m, 10 m, 5 m, 2 m, and 1 m.
- a plot 170 illustrates magnetic flux density B y (y) in the y-direction as measured by the magnetometer 38 for a variety of x-direction offset locations for the first well 12 .
- An ordinate 172 represents magnetic flux density B y (y), and an abscissa 174 represents the distance in meters (m) along the y-direction from the insulated gap 34 on the BHA 26 .
- Lines 176 , 178 , 180 , 182 , and 184 illustrate respectively the magnitude of magnetic flux density B y (y) measured along the y-direction inside the first well 12 for offsets in the x-direction of 20 m, 10 m, 5 m, 2 m, and 1 m.
- the magnetic flux density B x (y) will be attenuated and may not provide sufficient data to be useful. However, the magnetic flux density B y (y) is not attenuated by the casing 20 . Thus, when the casing 22 of the first well 12 is magnetic, the peak amplitude located at local maximum 186 on plot 170 may be used to determine the distance between the two wells.
- FIG. 17 represents a flowchart 188 for determining the location and distance of perpendicular wells as depicting in the well drilling operation 50 of FIGS. 4 and 9 - 11 .
- the gravity deployed magnetometer 38 is lowered into the vertical well 52 to measure the magnetic field density of the magnetic field 36 , which arises from the electric current 32 on the BHA 26 in the second well 14 .
- the magnetic flux densities B x (y) and B y (y) may be observed.
- Step 194 of FIG. 17 illustrates that a distance between the vertical well 52 and the second well 14 at the point of closest approach may be obtained from the observed magnetic flux density B y (y).
- distances associated with given values of magnetic flux density B y (y) may be obtained and developed into a table or algorithm.
- the distance between the vertical well 52 and the second well 14 at the point of closest approach may be ascertained.
- FIG. 18 depicts a well drilling operation 196 for use when the second well 14 is not perpendicular to the first well 12 .
- the wireline magnetometer 38 measures the normal and axial components of magnetic field density (B n and B ⁇ ) along a magnetometer trajectory 198 . From observed values of magnetic field density B n and B ⁇ , distances r 1 and r 2 having respective angles ⁇ 1 and ⁇ 2 may be determined at points along the magnetometer trajectory 198 , allowing an accurate establishment of the relative location between the first well 12 and the second well 14 . Additionally, in a manner similar to that of the flowchart 188 of FIG. 17 , the observed values of magnetic field density B n and B ⁇ may offer a precise location and distance between the first well 12 and the second well 14 at a point of closest approach, as discussed below.
- FIGS. 19 and 20 illustrate plots of magnetic field density data obtained in the well drilling operation 196 of FIG. 18 .
- a plot 200 illustrates a normal (i.e., perpendicular to the magnetometer trajectory 198 ) component of magnetic flux density B n as measured by the wireline magnetometer 38 for two possible variations of the trajectory of the second well 14 relative to the first well 12 .
- An ordinate 202 represents the normal component of magnetic flux density B n in units of nanoTesla (nT) and an abscissa 204 represents the distance in meters (m) along the scan length of the magnetometer trajectory 198 in the first well 12 .
- the curves of the plot 200 are not symmetric about the point of closest approach. This result is expected because lines 206 and 208 illustrate a case when the magnetometer trajectory 198 of the first well 12 is not perpendicular to the axis of the second well 14 .
- a plot 210 illustrates an axial (i.e., parallel to the magnetometer trajectory 198 ) component of magnetic flux density B ⁇ as measured by the wireline magnetometer 38 for the two variations of the trajectory of the second well 14 relative to the first well 12 plotted in FIG. 19 .
- An ordinate 212 represents the axial component of magnetic flux density B ⁇ in units of nanoTesla (nT) and an abscissa 214 represents the distance in meters (m) along the scan length of the magnetometer trajectory 198 in the first well 12 .
- line 216 reaches a maximum value at numeral 220 and line 218 reaches a maximum value at numeral 222 when the scan length is 20 m.
- the maxima at numerals 220 and 222 correctly indicate that the point of closest approach between the two wells occurs when the scan length is 20 m.
- measuring the axial component of magnetic flux density B ⁇ can be used to determine the point of closest approach between the two wells.
- FIG. 21 represents a flow chart 224 for determining the relative positions between the first well 12 and the second well 14 for the general case of the well drilling operation 196 of FIG. 18 .
- step 226 the normal component of magnetic flux density B n and the axial component of magnetic flux density B ⁇ are measured along the magnetometer trajectory 198 in the first well 12 .
- step 228 relative positions of the first well 12 to the second well 14 may be determined.
- the determination may take place by comparing measurements of the normal component of magnetic flux density B n and the axial component of magnetic flux density B ⁇ to theoretical models. Such theoretical models may be based on inverting equation (4), disclosed above.
- the measurements of the normal component of magnetic flux density B n and the axial component of magnetic flux density B ⁇ may be compared to tables created using equation (4) and various angles and distances which may be calculated between the two wells or tables created through routine experimentation. It should be further noted that in the general case illustrated by the well drilling operation 196 of FIG.
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Abstract
A system and methods for drilling a well in a field having an existing well are provided. Specifically a method of drilling a new well in a field having an existing well includes drilling the new well using a bottom hole assembly (BHA) having a drill collar divided by an insulated gap, generating a current on the drill collar of the BHA while drilling the new well, and measuring from the existing well a magnetic field caused by the current on the drill collar of the BHA. Using measurements of the magnetic field, a relative position of the new well to the existing well may be determined.
Description
- This application is a divisional application of U.S. patent application Ser. No. 12/105,698 filed Apr. 18, 2008, now U.S. Pat. No. 8,596,382 issued Dec. 3, 2013, which is incorporated herein by reference in its entirety.
- The present invention relates generally to well drilling operations and, more particularly, to well drilling operations using magnetic field measurements from an electric dipole to ascertain the relative location of a new well to an existing well.
- Heavy oil may be too viscous in its natural state to be produced from a conventional well. To produce heavy oil, a variety of techniques may be employed, including, for example, Steam Assisted Gravity Drainage (SAGD), Cross Well Steam Assisted Gravity Drainage (X-SAGD), or Toe to Heel Air Injection (THAI). While SAGD wells generally involve two parallel horizontal wells, X-SAGD and THAI wells generally involve two or more wells located perpendicular to one another.
- X-SAGD and THAI techniques function by employing one or more wells for steam injection or air injection, respectively, known as “injector wells.” The injector wells pump steam or air into precise locations in a heavy oil formation to heat heavy oil. One or more lower horizontal wells, known as “producer wells,” collect the heated heavy oil. For an X-SAGD well pair including an injector well and a producer well, the injector well is a horizontal well located above and oriented perpendicular to the producer well. In contrast, for a THAI well pair including an injector well and a producer well, the injector well is a vertical well located near and oriented perpendicular to the producer well.
- Steam or air from an injector well in an X-SAGD or THAI well pair should be injected at a precise point in the heavy oil formation to maximize recovery. Particularly, if steam is injected too near to a point of closest approach between the injector well and the producer well, steam may be shunted out of the formation and into the producer well. Using many conventional techniques, the point of closest approach between the two wells may be difficult to locate or the location of the point of closest approach may be imprecise.
- Moreover, the relative distance between the injector and producer wells of an X-SAGD or THAI well pair may affect potential recovery. The wells should be located sufficiently near to one another such that heavy oil heated at the injector well may drain into the producer well. However, if the wells are located too near to one another, steam or air from the injector well may shunt into the producer well, and if the wells are located too far from one another, the heated heavy oil may not extend to the producer well. Using conventional techniques, it may be difficult to accurately drill one well perpendicular to another well.
- Certain aspects commensurate in scope with the originally claimed invention are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms of the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.
- In accordance with an embodiment of the invention, a method of drilling a new well in a field having an existing well includes drilling the new well using a bottom hole assembly (BHA) having a drill collar divided by an insulated gap, generating a current on the drill collar of the BHA, and measuring from the existing well a magnetic field caused by the current on the drill collar of the BHA. Using measurements of the magnetic field, the relative position of the new well to the existing well may be determined.
- Advantages of the invention may become apparent upon reading the following detailed description and upon reference to the drawings in which:
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FIG. 1 is a schematic of a well drilling operation using magnetic ranging while drilling for a parallel well; -
FIG. 2 is a schematic of a more detailed view of the well drilling operation ofFIG. 1 ; -
FIG. 3 is a cross-sectional view of an existing well taken along cut lines 3-3 in the well drilling operation ofFIG. 1 ; -
FIG. 4 is a schematic depicting a well drilling operation for drilling a Toe to Heel Air Injection (THAI) well using magnetic ranging while drilling in accordance with an embodiment of the invention; -
FIG. 5 is a flowchart describing an embodiment of a method of performing the well drilling operation ofFIG. 4 ; -
FIG. 6 is a flowchart depicting another embodiment of a method of performing the well drilling operation ofFIG. 4 ; -
FIG. 7 is a schematic depicting a well drilling operation for drilling a Cross Well Steam Assisted Gravity Drainage (X-SAGD) well in accordance with an embodiment of the invention; -
FIG. 8 is a flowchart describing an embodiment of a method of performing the well drilling operation ofFIG. 7 ; -
FIG. 9 is a schematic side view of the well drilling operation ofFIG. 4 ; -
FIG. 10 is a schematic top view of the well drilling operation ofFIG. 4 ; -
FIG. 11 is a schematic end view of the well drilling operation ofFIG. 4 ; -
FIG. 12 is a plot of sensor noise of a plurality of available magnetometers for a variety of magnetic field frequencies; -
FIG. 13 is a diagram of an electric dipole formed as an electric current passes through a bottom hole assembly (BHA) divided by an insulated gap; -
FIG. 14 is a plot of the magnitude of magnetic flux density as a function of distance along a BHA using magnetic ranging while drilling for a variety of offsets in the x-axis; -
FIG. 15 is a plot of magnetic flux density in the x-axis as a function of distance in the y-axis from a BHA using magnetic ranging while drilling for a variety of offsets in the x-axis; -
FIG. 16 is a plot of magnetic flux density in the y-axis as a function of distance in the y-axis from a BHA using magnetic ranging while drilling for a variety of offsets in the x-axis; -
FIG. 17 is a flowchart describing a method of obtaining the relative positions between two perpendicular wells in accordance with an embodiment of the invention; -
FIG. 18 is a schematic depicting a well drilling operation in which the relative positions between two wells may be ascertained when the two wells are not necessarily perpendicular; -
FIG. 19 is a plot of transverse magnetic flux density as a function of distance along the existing well depicted inFIG. 18 ; -
FIG. 20 is a plot of parallel magnetic flux density as a function of distance along the existing well depicted inFIG. 18 ; and -
FIG. 21 is a flowchart describing a method of obtaining the relative positions of two non-parallel wells in accordance with an embodiment of the invention. - One or more specific embodiments of the present invention are described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
- As used herein, the term “first well” (labeled numeral 12) refers to a generally horizontal existing well, “vertical well” (labeled numeral 52) refers to a generally vertical existing vertical well, and “second well” (labeled numeral 14) refers to a secondary well drilled in the vicinity of either the
first well 12 or thevertical well 52. It should be appreciated, however, that the wells may be drilled in any order and that the terms are used to clarify the figures discussed below. -
FIG. 1 depicts a welldrilling operation 10 involving magnetic ranging while drilling. In the welldrilling operation 10, an existingfirst well 12 and a newsecond well 14 extend from the surface through aformation 16 into aheavy oil zone 18. Thefirst well 12 is cased withcasing 20 and completed withtubing 22. Adrill string 24 is used to drill thesecond well 14. Thedrill string 24 includes a bottom hole assembly (BHA) 26 having adrill bit 28 and asteerable system 30. The BHA 26 may also include a variety of drilling tools such as a measurement while drilling (MWD) tool or a logging while drilling (LWD) tool. - A tool in the
BHA 26 generates anelectric current 32 on both sides of an insulatedgap 34 in the outer drill collar. The current 32 generates an azimuthalmagnetic field 36 around the BHA 26.FIG. 1 depicts themagnetic field 36 centered on theinsulated gap 34, but it should be understood that themagnetic field 36 extends along the length of theBHA 26 and beyond. Awireline magnetometer 38 may be deployed into thefirst well 12 using a tractor or a coiled tubing system, with which the strength of themagnetic field 36 may be measured at a variety of locations along thefirst well 12. With measuredmagnetic field 36 strength data obtained by thewireline magnetometer 38, the relative position between first well 12 and second well 14 may be ascertained. -
FIG. 2 provides a moredetailed view 40 of thewell drilling operation 10 ofFIG. 1 . As illustrated in the moredetailed view 40, theBHA 26 includes an electriccurrent driving tool 42, which may be a component of a measurement while drilling (MWD) tool such as Schlumberger's E-Pulse or E-Pulse Express tool or a standalone tool. The electriccurrent driving tool 42 generates the electric current 32 on anouter drill collar 44 located on the opposite side of theinsulated gap 34. The moredetailed view 40 also illustrates that when thefirst well 12 and thesecond well 14 are parallel, themagnetic field 36 generated by the electric current 32 may not necessarily be detected by thewireline magnetometer 38. Particularly, if thecasing 20 is composed of a magnetic material such as alloy steel, themagnetic field 36 may be significantly attenuated and may not effectively penetrate thecasing 20. - Turning to
FIG. 3 , across-sectional view 46 of thefirst well 12, depicted from along the cut lines 3-3 ofFIG. 1 , illustrates the attenuation of themagnetic field 36 which may occur when thefirst well 12 and thesecond well 14 are parallel and thecasing 20 is composed of a magnetic material. In thecross-sectional view 46, thewireline magnetometer 38 is deployed within thetubing 22 and surrounded by thecasing 20, which may be assumed to be alloy steel. When thefirst well 12 and thesecond well 14 are parallel, the azimuthalmagnetic field 36 from thesecond well 14 will be perpendicular to thefirst well 12. To the extent themagnetic field 36 is perpendicular to thecasing 20, themagnetic field 36 may be significantly attenuated. As such, a re-directedmagnetic field path 48 may effectively route themagnetic field 36 around thecasing 20 of thefirst well 12, largely preventing its detection by thewireline magnetometer 38. -
FIG. 4 illustrates awell drilling operation 50 for drilling a horizontal well perpendicular to a vertical well. It should be noted that because the wells depicted inFIG. 4 are not parallel, but perpendicular, themagnetic field 36 may be largely undiminished by the presence of magnetic casing. It should be further noted that many applications may benefit from an accurate placement of perpendicular wells, and though thewell drilling operation 50 depicted relates primarily to Toe to Heel Air Injection (THAI), the methods described herein may be well suited to developing a variety of such applications. - As will be understood, THAI is an in situ combustion process involving horizontal wells for producing oil and combustion by-products and vertical wells for injecting air into the
heavy oil zone 18. The injected air causes some heavy oil in theheavy oil zone 18 to combust, which heats the surrounding heavy oil, reducing its viscosity. In addition, some upgrading of the heavy oil to lighter oil may occur. Gravity causes the heated heavy oil and upgraded oil to collect in the horizontal wells below. One approach to THAI is depicted in thewell drilling operation 50 ofFIG. 4 . First, avertical well 52, known as an injector well, is drilled and cased withcasing 54. The horizontalsecond well 14, known as a producer well, is subsequently drilled. Periodically, during the drilling of thesecond well 14, themagnetic field 36 may be measured from awireline magnetometer 38 within thevertical well 52. Using measurements of themagnetic field 36 at various locations from within thevertical well 52, the precise location of thesecond well 14 relative to thevertical well 52 may be obtained. The trajectory of theBHA 26 may be properly adjusted such that thesecond well 14 is drilled at the proper distance and orientation from thevertical well 52. Thewell drilling operation 50 and, specifically, the spatial relationships of thesecond well 14 and thevertical well 52 will be described further below with respect toFIGS. 9-11 . - Turning to
FIG. 5 , aflow chart 56 describes one method for drilling the THAI well depicted in thewell drilling operation 50 ofFIG. 4 . Infirst step 58, thevertical well 52 is drilled and cased withcasing 54.Step 60 involves drilling thesecond well 14. Periodically, magnetic field measurements may be obtained while thesecond well 14 is being drilled. When the electriccurrent driving tool 42 generates the electric current 32 on the drill collar of theBHA 26, an electric dipole is effectively formed from the two sides of theBHA 26 surrounding theinsulated gap 34, producing the azimuthalmagnetic field 36. Instep 62, the gravity deployedwireline magnetometer 38 may measure the strength of themagnetic field 36 at a variety of points in thevertical well 52. Instep 64, based on the measurements of the magnetic field, the relative position of thevertical well 52 and thesecond well 14 may be determined according to a technique discussed below. -
FIG. 6 depicts analternative flow chart 66 describing a method of drilling horizontal wells in fields having existing vertical wells. Particularly, for heavy oil fields that were originally developed using “huff and puff' or using a steam flood through vertical wells, a series of horizontal wells drilled among existing vertical wells may increase recovery. In such a situation, the existing vertical wells may be employed as steam injector wells, and the new horizontal wells may be employed as producer wells. In afirst step 68, a horizontal well such as thesecond well 14 begins being drilled in a field with a plurality of existing vertical wells such as thevertical well 52. Periodically, magnetic field measurements may be obtained while thesecond well 14 is being drilled. When the electriccurrent driving tool 42 generates the electric current 32 on the drill collar of theBHA 26, an electric dipole is effectively formed from the two sides of theBHA 26 surrounding theinsulated gap 34, producing the azimuthalmagnetic field 36. - In
step 70, thewireline magnetometer 38 is gravity deployed into a first of the existing vertical wells such asvertical well 52. Instep 72, the wireline magnetometer may measure themagnetic field 36 at a variety of points in thevertical well 52. Based on the measurements of themagnetic field 36, the relative position of thevertical well 52 and thesecond well 14 may be determined according to a technique discussed below. Indecision block 76, if the horizontalsecond well 14 will cross anothervertical well 52 in the field of existing vertical wells, the process returns to step 70 for drilling beyond the subsequentvertical well 52. If not, the process ends atstep 78. - Turning to
FIG. 7 , awell drilling operation 80 depicts drilling two perpendicular wells for use in Cross Well Steam Assisted Gravity Drainage (X-SAGD) wells. A firsthorizontal well 12 is drilled through theformation 16 and into theheavy oil zone 18 before completion withcasing 20 andtubing 22. Asecond well 14 is subsequently drilled above and perpendicular to thefirst well 12. Periodically, magnetic field measurements may be obtained while thesecond well 14 is being drilled. The electric current 32 on the drill collar of theBHA 26 may form an electric dipole from the two sides of theBHA 26 surrounding theinsulated gap 34, producing the azimuthalmagnetic field 36. As noted by numeral 82, because the secondhorizontal well 14 is perpendicular to the firsthorizontal well 12, themagnetic field 36 may be detected by themagnetometer 38 with little attenuation. - Turning to
FIG. 8 , aflowchart 84 depicts a method of drilling the X-SAGD well depicted inFIG. 7 . Instep 86, the firsthorizontal well 12 is drilled and completed withcasing 20 andtubing 22.Step 88 involves drilling the perpendicular horizontalsecond well 14. Periodically, magnetic field measurements may be obtained while thesecond well 14 is being drilled. The electric current 32 on the drill collar of theBHA 26 may form an electric dipole from the two sides of theBHA 26 surrounding theinsulated gap 34, producing the azimuthalmagnetic field 36. - Continuing to view the
flowchart 84 ofFIG. 8 , instep 90, thewireline magnetometer 38 is deployed in thefirst well 12 using a mud pump to push it down inside thetubing 22, or in case there is no tubing present, using a tractor, coiled tubing, or other means. Instep 92, themagnetic field 36 may be detected by thewireline magnetometer 38 at a variety of locations along thefirst well 12. The data obtained by thewireline magnetometer 38 may be subsequently used instep 94 to determine the relative position of thefirst well 12 to thesecond well 14 using techniques described further below. Turning to thedecision block 96, if thesecond well 14 will cross anotherhorizontal well 12, the process returns to step 90 for drilling beyond the subsequenthorizontal well 12. If not, the process ends atstep 98. - It should be noted that if the two wells are exactly perpendicular then no current will be generated on the casing of the
first well 12. However, if the two wells are not perpendicular, then a current may be generated on the casing of thefirst well 12. As a result, alternative techniques involving magnetic ranging while drilling from induced magnetic fields may be applied. Such techniques are described in Published Application US 2007/016426 A1, Provisional Application No. 60/822,598, application Ser. No. 11/833,032, and application Ser. No. 11/781,704, each of which is assigned to Schlumberger Technology Corporation and incorporated herein by reference. -
FIGS. 9 , 10, and 11 depict three different views of thewell drilling operation 50 as depicted inFIG. 4 to illustrate the spatial relationship between thevertical well 52 and thesecond well 14.FIG. 9 depicts aside view 100 of thewell drilling operation 50 ofFIG. 4 . As illustrated in theside view 100, thesecond well 14 is perpendicular to thevertical well 52. The second well is aligned with the z-axis. Meanwhile, thevertical well 52 is aligned with the y-axis. As a result, when themagnetometer 38 is raised and lowered on awireline 102, the intensity of themagnetic field 36 may be defined as a function of distance along the y-axis. -
FIG. 10 depicts atop view 104 of thewell drilling operation 50 ofFIG. 4 . In thetop view 104, thesecond well 14 is depicted as being offset from thevertical well 52 along the x-axis. As a result, the closest approach between thesecond well 14 and thevertical well 52 is correspondingly defined along the x-axis. -
FIG. 11 depictsend view 106 of thewell drilling operation 50 ofFIG. 4 . As indicated in the figure, themagnetometer 38 is raised and lowered along the y-direction by thewireline 102 within thevertical well 52. Thus, at various points across the y-axis, the intensity of themagnetic field 36 may be measured. As may be appreciated, for all threeviews magnetometer 38 may detect themagnetic field 36 largely unimpeded by thecasing 54, since thesecond well 14 is oriented perpendicularly to thevertical well 52. - Turning to
FIG. 12 , aplot 108 illustrates the sensitivity of available magnetometers for borehole use. Anordinate 110 represents sensor noise in units of nanoTesla per root Hertz (nT/√{square root over (Hz)}), while anabscissa 112 represents frequency in units of Hertz (Hz).Lines - As apparent in the
plot 108, noise figures may be exceptionally low for many of the BF series magnetometers. As will be discussed below, a magnetometer with one nanoTesla (nT) resolution should be sufficient to accurately estimate a distance of one well to another from at least fifty meters apart. The noise figures for the magnetometers described in theplot 108 achieve picoTesla (pT) noise levels per root Hertz (pT/√{square root over (Hz)}). Thus, the available magnetometers should be sufficient to practice the technique disclosed herein. - Turning to
FIG. 13 , anelectric dipole 124 is depicted. Theelectric dipole 124 models the electric dipole which forms on theBHA 26 surrounding theinsulated gap 34. The portion of theBHA 26 from the insulated gap to thedrill bit 28 is noted inFIG. 13 as a firstelectric pole 126. The portion of theBHA 26 from the insulated gap through thedrill string 24 is noted inFIG. 13 as a secondelectric pole 128. The secondelectric pole 128 on theBHA 26 is longer than the firstelectric pole 126 on theBHA 26, since the electric current 32 can extend onto thedrill string 24 above theBHA 26. For ameasurement point 130, which is located near thefirst pole 126, only a small error is introduced by truncating the length of the secondelectric pole 128. Additionally, since the magnetic field generated by an electric dipole in a conductive medium can be calculated analytically, the result may be used to model themagnetic field 36 generated by theelectric dipole 124 formed by theBHA 26. The azimuthalmagnetic field 36 strength created by theelectric dipole 124 may be described by the following relationship: -
- In the equations above, d1 represents the length of the first
electric pole 126, d2 represents the length of the secondelectric pole 128, and s represents a distance from the center of theinsulated gap 34 to the outer drill collar. Further, ω represents angular frequency, μ represents the permeability of free space, ε represents permittivity of the surroundingformation 18, σ represents electrical conductivity of the surroundingformation 18, and I0 represents the magnitude of the electric current 32 at theinsulated gap 34. - Equation (1) may be simplified as the frequency approaches zero, i.e., for frequencies of a few hundred Hertz or lower. Assuming the
insulated gap 34 to be negligible in length compared to the length of the arms of the dipoles, in a limit when the frequency ω approaches zero, equation (1) may be rewritten as follows: -
- The integral in equation (2) above may be evaluated in closed form, providing the following equation:
-
- Based on the equations above modeling the magnetic field strength Hφ, a vector magnetic field B at an arbitrary location (x, y, z) may be defined according to the following equation:
-
- It should be noted that this calculation does not include the attenuating effect that the
casing first well 12 or thevertical well 52. As a result, the field intensity may be reduced if themagnetometer 38 is concealed within magnetic casing. However, attenuation due to thecasing 22 generally has a constant value, and this effect may be removed by calibration. - Equation (4) may be used to calculate the magnetic field and existing wellbore for any trajectory of a well being drilled at any angle and distance. For the data plotted in
FIGS. 14-16 , 19 and 20, the model parameters are as follows: d1=30 m, d2=80 m, s=0.2 m, and I0=10 A. - Turning to
FIG. 14 ,plot 132 illustrates magnetic flux density as measured by themagnetometer 38 in thefirst well 12 for a variety of x-direction offsets of thesecond well 14. The following discussion applies equally to thevertical well 52 as to thefirst well 12. Anordinate 134 represents the absolute magnitude of magnetic flux density in units of nanoTesla (nT), and anabscissa 136 illustrates the distance in meters (m) along the z-direction from the insulatedgap 34 on theBHA 26.Numeral 138 indicates the location of thedrill bit 28 at z=30 m in theplot 132, and numeral 140 indicates the location on the plot in which theinsulated gap 34 is disposed at z=0 m. TheBHA 26 is located in the x-z plane, i.e., at y=0 m. Themagnetic field 36 is measured at y=0.5 m above the x-z plane.Lines - It should be noted that the magnetic flux density inside the
first well 12 is greatest when thefirst well 12 is exactly opposite theinsulated gap 34 in theBHA 26, which occurs when z=0 m. The coordinate system described in theplot 132 moves with theBHA 26. Hence, different values of z correspond to the position of thewireline magnetometer 38 in thefirst well 12 relative to theinsulated gap 34 on theBHA 26 in thesecond well 14. - In the
plot 132, the magnetic flux density in the first well 12 at z=0 m varies from 1000 nT at an offset distance of 2 m to 20 nT at an offset distance of 50 m. Thus, a magnetometer with 1 nT resolution should be able to accurately estimate the distance from thefirst well 12 to theBHA 26 drilling the second well 14 from at least 50 m away. As discussed above, available magnetometers are capable of such a resolution. - When the
first well 12 is at z=0 meters, thedrill bit 28 is 30 m beyond the point of closest approach to thefirst well 12. Thus, the distance between the two wells could be determined after passing thefirst well 12. This information may be particularly useful for evaluating the relative positions of two wells. The relative positions of thefirst well 12 and thesecond well 14 may be used for quality control or to plan production methods such as steam injection. For example, in X-SAGD, solid casing might be used near the crossing point to avoid a short path for the steam to travel between the two wells. - When the
first well 12 is at z=30 m, thedrill bit 28 is opposite thefirst well 12. The corresponding location on theabscissa 136, atpoint 138, indicates that the magnetic field intensity is ambiguous, as the curves overlap for the various x-direction offset distances between the two wells. Thus, the magnetic field measurements at z=0 m plotted inplot 132 ofFIG. 14 alone may be insufficient to deduce the distance to the first well 12 fromBHA 26 in thesecond well 14. - When the
first well 12 is beyond z=30 m, thedrill bit 28 of theBHA 26 in thesecond well 14 has not yet reached the point of closest approach of thefirst well 12. For example, at z=60 m on theplot 132, the lines ofplot 132 are well resolved for different x-direction offset distances between the two wells. When thefirst well 12 is offset by 2 m from thesecond well 14, the magnetic flux density is very small, approaching 0.4 nT. When thefirst well 12 is offset by 30 m or more from thesecond well 14, the magnetic flux density is instead 4.5 nT. Thus, an approach which may be too close may be detected thirty meters ahead of thedrill bit 28, and corrections may be made to the drilling trajectory by way ofsteerable system 30. - The change in the magnetic flux density as the
BHA 26 continues to drill may also be used to estimate a transverse distance between thefirst well 12 and thesecond well 14. For example, observing the rate of change in magnetic flux density in drilling ten meters (for example, from z=30 m to z=20 m) may be used to estimate the relative separation of thefirst well 12 andsecond well 14. When thefirst well 12 is a substantial distance ahead of thedrill bit 28, the magnetic flux is very weak. Thus, the magnetometer should have a resolution of at least 0.1 nT to perform such measurements of thedrill bit 28. As indicated byplot 108 ofFIG. 12 , this resolution is within the capability of EMI EF magnetometers. -
FIGS. 15 and 16 represent plots obtained from thewell drilling operation 50 of FIGS. 4 and 9-11. Turning first toFIG. 15 , aplot 152 illustrates magnetic flux density Bx(y) in the x-direction as measured by themagnetometer 38 for a variety of x-direction offset locations for thefirst well 12. Thefirst well 12 is located at z=15 m, midway between thedrill bit 28 and theinsulated gap 34 on theBHA 26. Anordinate 154 represents the magnetic flux density Bx(y) in units of nanoTesla (nT), and anabscissa 156 represents the distance in meters (m) along the y-direction from the insulatedgap 34 on theBHA 26.Lines first well 12 for offsets in the x-direction of 20 m, 10 m, 5 m, 2 m, and 1 m. When thewireline magnetometer 38 in thefirst well 12 crosses y=0 m, noted as numeral 168 on theplot 152, the magnetic flux density Bx(y) changes sign. Since the point of closest approach in the y-direction between thefirst well 12 and thesecond well 14 occurs at y=0 m, the point of closest approach may be ascertained by observing the point at which Bx(y) changes sign. - Turning next to
FIG. 16 , aplot 170 illustrates magnetic flux density By(y) in the y-direction as measured by themagnetometer 38 for a variety of x-direction offset locations for thefirst well 12. As above, thefirst well 12 is located at z=15 m, midway between thedrill bit 28 and theinsulated gap 34 on theBHA 26. Anordinate 172 represents magnetic flux density By(y), and anabscissa 174 represents the distance in meters (m) along the y-direction from the insulatedgap 34 on theBHA 26.Lines first well 12 for offsets in the x-direction of 20 m, 10 m, 5 m, 2 m, and 1 m. When thewireline magnetometer 38 in thefirst well 12 crosses y=0 m, the magnetic flux density By(y) reaches alocal maximum 186. Since the point of closest approach in the y-direction between thefirst well 12 and thesecond well 14 occurs at y=0 m, the point of closest approach may be ascertained by observing the point at which By(y) reaches a local maximum. - If the
casing 22 of thefirst well 12 is made of a magnetic material such as steel, the magnetic flux density Bx(y) will be attenuated and may not provide sufficient data to be useful. However, the magnetic flux density By(y) is not attenuated by thecasing 20. Thus, when thecasing 22 of thefirst well 12 is magnetic, the peak amplitude located atlocal maximum 186 onplot 170 may be used to determine the distance between the two wells. -
FIG. 17 represents aflowchart 188 for determining the location and distance of perpendicular wells as depicting in thewell drilling operation 50 of FIGS. 4 and 9-11. Instep 190, the gravity deployedmagnetometer 38 is lowered into thevertical well 52 to measure the magnetic field density of themagnetic field 36, which arises from the electric current 32 on theBHA 26 in thesecond well 14. As the magnetometer moves through thevertical well 52 in the y-direction, the magnetic flux densities Bx(y) and By(y) may be observed. - In
step 192, the observed magnetic flux densities Bx(y) and By(y) may be used to determine a point of closest approach between thesecond well 14 and thevertical well 52. If thecasing 54 on thevertical well 52 is not magnetic, determining the point at which the magnetic flux density Bx(y) changes sign may indicate the point of closest approach (i.e., when y=0 m). Regardless of whether thecasing 54 on thevertical well 52 is magnetic, the magnetic flux density By(y) may also indicate a point of closest approach. As discussed above, the point at which the magnetic flux density By(y) reaches a local maximum indicates the point of closest approach (i.e., when y=0 m). - Step 194 of
FIG. 17 illustrates that a distance between thevertical well 52 and the second well 14 at the point of closest approach may be obtained from the observed magnetic flux density By(y). Through prior experimentation, distances associated with given values of magnetic flux density By(y) may be obtained and developed into a table or algorithm. By comparing the observed value of magnetic flux density By(y) at the point of closest approach with the experimental magnetic flux density By(y), the distance between thevertical well 52 and the second well 14 at the point of closest approach may be ascertained. -
FIG. 18 depicts awell drilling operation 196 for use when thesecond well 14 is not perpendicular to thefirst well 12. In thewell drilling operation 196, thewireline magnetometer 38 measures the normal and axial components of magnetic field density (Bn and Bτ) along amagnetometer trajectory 198. From observed values of magnetic field density Bn and Bτ, distances r1 and r2 having respective angles φ1 and φ2 may be determined at points along themagnetometer trajectory 198, allowing an accurate establishment of the relative location between thefirst well 12 and thesecond well 14. Additionally, in a manner similar to that of theflowchart 188 ofFIG. 17 , the observed values of magnetic field density Bn and Bτ may offer a precise location and distance between thefirst well 12 and the second well 14 at a point of closest approach, as discussed below. -
FIGS. 19 and 20 illustrate plots of magnetic field density data obtained in thewell drilling operation 196 ofFIG. 18 . Turning first toFIG. 19 , aplot 200 illustrates a normal (i.e., perpendicular to the magnetometer trajectory 198) component of magnetic flux density Bn as measured by thewireline magnetometer 38 for two possible variations of the trajectory of thesecond well 14 relative to thefirst well 12. Anordinate 202 represents the normal component of magnetic flux density Bn in units of nanoTesla (nT) and anabscissa 204 represents the distance in meters (m) along the scan length of themagnetometer trajectory 198 in thefirst well 12. In theplot 200,line 206 indicates a magnetometer trajectory from coordinates of (x, y, z)=(5, −20, 40) to (x, y, z)=(5, 20, 40).Line 208 represents themagnetometer trajectory 198 from coordinates of (x, y, z)=(10, −20, 40), to (x, y, z)=(5, 20, 30). Unlike theplot 152 ofFIG. 15 , the curves of theplot 200 are not symmetric about the point of closest approach. This result is expected becauselines magnetometer trajectory 198 of thefirst well 12 is not perpendicular to the axis of thesecond well 14. - Turning to
FIG. 20 , a plot 210 illustrates an axial (i.e., parallel to the magnetometer trajectory 198) component of magnetic flux density Bτ as measured by thewireline magnetometer 38 for the two variations of the trajectory of thesecond well 14 relative to thefirst well 12 plotted inFIG. 19 . Anordinate 212 represents the axial component of magnetic flux density Bτ in units of nanoTesla (nT) and anabscissa 214 represents the distance in meters (m) along the scan length of themagnetometer trajectory 198 in thefirst well 12. In the plot 210,line 216 indicates a magnetometer trajectory from coordinates of (x, y, z)=(5, −20, 40) to (x, y, z)=(5, 20, 40).Line 218 represents themagnetometer trajectory 198 from coordinates of (x, y, z)=(10, −20, 40), to (x, y, z)=(5, 20, 30). From the plot 210,line 216 reaches a maximum value at numeral 220 andline 218 reaches a maximum value atnumeral 222 when the scan length is 20 m. The maxima atnumerals 220 and 222 correctly indicate that the point of closest approach between the two wells occurs when the scan length is 20 m. Hence, measuring the axial component of magnetic flux density Bτ can be used to determine the point of closest approach between the two wells. -
FIG. 21 represents aflow chart 224 for determining the relative positions between thefirst well 12 and thesecond well 14 for the general case of thewell drilling operation 196 ofFIG. 18 . Instep 226, the normal component of magnetic flux density Bn and the axial component of magnetic flux density Bτ are measured along themagnetometer trajectory 198 in thefirst well 12. Instep 228, relative positions of thefirst well 12 to thesecond well 14 may be determined. - As indicated in
step 230, the determination may take place by comparing measurements of the normal component of magnetic flux density Bn and the axial component of magnetic flux density Bτ to theoretical models. Such theoretical models may be based on inverting equation (4), disclosed above. Alternatively, as indicated inalternative step 232, the measurements of the normal component of magnetic flux density Bn and the axial component of magnetic flux density Bτ may be compared to tables created using equation (4) and various angles and distances which may be calculated between the two wells or tables created through routine experimentation. It should be further noted that in the general case illustrated by thewell drilling operation 196 ofFIG. 18 , in which thefirst well 12 and thesecond well 14 are not perpendicular, that the alternative mathematical algorithms described in Published Application US 2007/016426 A1, Provisional Application No. 60/822,598, application Ser. No. 11/833,032, and application Ser. No. 11/781,704 may additionally be applied, as discussed above. - While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. Particularly, though the invention has been described with examples involving THAI wells and X-SAGD wells, the techniques may be applied to any relative orientation between two wells. Moreover, although the invention has been described involving a
wireline magnetometer 38, the magnetometer could also be deployed in another NWD tool or in a coiled tubing tool, or in a slick line. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
Claims (8)
1. A method of drilling a well comprising:
drilling a second horizontal well above a first horizontal well using a bottom hole assembly (BHA) having a drill collar divided by an insulated gap;
generating a current along the drill collar of the BHA while drilling the second horizontal well to form an electric dipole over the insulated gap, the dipole having a first pole and a second pole;
calculating a magnetic field strength for the electric dipole for a range of locations;
on the existing well, measuring a magnetic field caused by the electric dipole on the drill collar of the BHA;
comparing the calculated magnetic field strength to the measured magnetic field;
determining a position of the new well relative to the existing well based on the comparing of the calculated magnetic field strength to the measured magnetic field; and
adjusting a trajectory of the BHA such that the second horizontal well will be drilled substantially perpendicular to the first horizontal well based on measurements of the magnetic field.
2. The method of claim 1 , further comprising locating in the first horizontal well a point of closest approach between the first horizontal well and the second horizontal well based on measurements of the magnetic field.
3. The method of claim 2 , further comprising estimating a distance between the first horizontal well and the second horizontal well at the point of closest approach.
4. The method of claim 1 , further comprising estimating a distance between the first horizontal well and the second horizontal well based on a change in magnetic flux as the BHA moves toward or away from the first horizontal well.
5. The method of claim 1 , wherein the first horizontal well and the second horizontal well are Cross Well Steam Assisted Gravity Drainage (X-SAGD) wells.
6. The method of claim 1 , further comprising deploying a wireline magnetometer into the first horizontal well to measure the magnetic field.
7. The method of claim 6 , further comprising measuring the magnetic field with the wireline magnetometer in a variety of locations along the first horizontal well.
8. The method of claim 1 , further comprising:
drilling a third horizontal well before drilling the first and second horizontal wells;
adjusting a trajectory of the BHA such that the second horizontal well will be drilled substantially perpendicular to the third horizontal well based on measurements of the magnetic field.
Priority Applications (1)
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US14/083,236 US20140069721A1 (en) | 2008-04-18 | 2013-11-18 | Magnetic ranging while drilling using an electric dipole source and a magnetic field sensor |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US12/105,698 US8596382B2 (en) | 2008-04-18 | 2008-04-18 | Magnetic ranging while drilling using an electric dipole source and a magnetic field sensor |
US14/083,236 US20140069721A1 (en) | 2008-04-18 | 2013-11-18 | Magnetic ranging while drilling using an electric dipole source and a magnetic field sensor |
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US12/105,698 Division US8596382B2 (en) | 2008-04-18 | 2008-04-18 | Magnetic ranging while drilling using an electric dipole source and a magnetic field sensor |
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US20140069721A1 true US20140069721A1 (en) | 2014-03-13 |
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US12/105,698 Expired - Fee Related US8596382B2 (en) | 2008-04-18 | 2008-04-18 | Magnetic ranging while drilling using an electric dipole source and a magnetic field sensor |
US14/083,236 Abandoned US20140069721A1 (en) | 2008-04-18 | 2013-11-18 | Magnetic ranging while drilling using an electric dipole source and a magnetic field sensor |
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US12/105,698 Expired - Fee Related US8596382B2 (en) | 2008-04-18 | 2008-04-18 | Magnetic ranging while drilling using an electric dipole source and a magnetic field sensor |
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CA (1) | CA2721443C (en) |
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Also Published As
Publication number | Publication date |
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US20090260879A1 (en) | 2009-10-22 |
US8596382B2 (en) | 2013-12-03 |
WO2009128990A2 (en) | 2009-10-22 |
CA2721443A1 (en) | 2009-10-22 |
WO2009128990A3 (en) | 2011-04-28 |
CA2721443C (en) | 2016-08-30 |
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