CN113622891A - Dredging type fracturing method for high-order coal reservoir - Google Patents
Dredging type fracturing method for high-order coal reservoir Download PDFInfo
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- 239000003245 coal Substances 0.000 title claims abstract description 296
- 238000000034 method Methods 0.000 title claims abstract description 46
- 239000012530 fluid Substances 0.000 claims abstract description 208
- 238000006073 displacement reaction Methods 0.000 claims abstract description 9
- 239000007788 liquid Substances 0.000 claims abstract description 7
- 239000011259 mixed solution Substances 0.000 claims abstract description 7
- 239000004576 sand Substances 0.000 claims description 77
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 claims description 44
- 239000004927 clay Substances 0.000 claims description 26
- 239000003381 stabilizer Substances 0.000 claims description 25
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 24
- 239000001103 potassium chloride Substances 0.000 claims description 22
- 235000011164 potassium chloride Nutrition 0.000 claims description 22
- 239000003795 chemical substances by application Substances 0.000 claims description 16
- 238000002347 injection Methods 0.000 claims description 11
- 239000007924 injection Substances 0.000 claims description 11
- 239000003583 soil stabilizing agent Substances 0.000 claims description 2
- 230000009466 transformation Effects 0.000 abstract description 3
- 206010017076 Fracture Diseases 0.000 description 111
- 208000010392 Bone Fractures Diseases 0.000 description 86
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 74
- 239000002245 particle Substances 0.000 description 36
- 238000005086 pumping Methods 0.000 description 25
- 230000008569 process Effects 0.000 description 11
- 239000006004 Quartz sand Substances 0.000 description 8
- 230000015572 biosynthetic process Effects 0.000 description 8
- 230000000694 effects Effects 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 5
- 230000035699 permeability Effects 0.000 description 5
- 238000010276 construction Methods 0.000 description 4
- 238000001914 filtration Methods 0.000 description 4
- 239000011435 rock Substances 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000009471 action Effects 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 230000003628 erosive effect Effects 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- 208000006670 Multiple fractures Diseases 0.000 description 1
- 125000003277 amino group Chemical group 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- UXYBXUYUKHUNOM-UHFFFAOYSA-M ethyl(trimethyl)azanium;chloride Chemical compound [Cl-].CC[N+](C)(C)C UXYBXUYUKHUNOM-UHFFFAOYSA-M 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
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- 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
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
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- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/60—Compositions for stimulating production by acting on the underground formation
- C09K8/80—Compositions for reinforcing fractures, e.g. compositions of proppants used to keep the fractures open
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- 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
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
- E21B43/267—Methods for stimulating production by forming crevices or fractures reinforcing fractures by propping
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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Abstract
The invention provides a dredging type fracturing method for a high-rank coal reservoir, which comprises the following steps: determining the depth range of the raw coal in the high-order coal reservoir according to the logging data; perforating in the middle area of the depth range of the primary coal of the corresponding high-order coal reservoir in the shaft, and forming a plurality of perforations on the inner wall of the shaft; injecting a first fracturing fluid through a plurality of perforations to form a first fracture in the virgin coal of the higher-rank coal reservoir; injecting a second fracturing fluid through a plurality of holes to form a second fracture in the raw coal of the high-order coal reservoir, wherein the first fracture is communicated with the second fracture, and the second fracturing fluid is a mixed solution of the first fracturing fluid and a fracture proppant; injecting a displacement fluid from a shaft, and displacing the first fracturing fluid and the second fracturing fluid in the raw coal of the high-order coal reservoir; stopping injecting liquid into the shaft, and directly flowing back without closing the well. The method can be used for performing fracturing transformation on the primary coal in the high-order coal reservoir and improving the gas yield of the gas well.
Description
Technical Field
The disclosure relates to the technical field of coal bed gas exploitation, in particular to a dredging type fracturing method for a high-order coal reservoir.
Background
The hydraulic fracturing technology is an important means for improving high-order coal reservoirs. The hydraulic fracturing utilizes the pressure conduction performance of fracturing fluid, the fracturing fluid is pumped into a well based on a ground high-pressure pump set, and when the bottom hole pressure is greater than the ground stress near the well wall and the tensile strength of reservoir rock, the stratum is fractured to generate cracks. Then pumping sand carrying liquid containing sand proppant to fill the cracks and extend the cracks, forming sand filling cracks with high flow conductivity at the bottom of the well, increasing the permeability and achieving the purpose of increasing the yield.
Due to the influence of stress in the formation process of the high-rank coal reservoir, the high-rank coal reservoir can be broken to different degrees, and different types of coal body structures can be developed and formed in the reservoir. The coal body structure of the high-rank coal reservoir comprises raw coal and tectonic coal. Wherein, the raw coal is hard coal with higher strength, while the structural coal has poor cementation property, low strength and easy breakage.
During hydraulic fracturing, the fracturing fluid firstly breaks through weak tectonic coal, and a high-diversion seepage zone is formed at the position of the tectonic coal. And the pressure in the shaft can not reach the fracture pressure intensity of the primary coal, so the primary coal can not realize reservoir transformation. Because the gas content of the constructed coal is low, the gas production rate of the gas well after hydraulic fracturing is less.
Disclosure of Invention
The embodiment of the disclosure provides a dredging type fracturing method for a high-rank coal reservoir, which can perform fracturing transformation on primary coal in the high-rank coal reservoir and improve the gas yield of a gas well. The technical scheme is as follows:
the embodiment of the disclosure provides a dredging type fracturing method for a high-rank coal reservoir, which comprises the following steps: determining the depth range of the raw coal in the high-order coal reservoir according to the logging data; perforating in the middle area of the depth range of the primary coal of the high-rank coal reservoir in the shaft, and forming a plurality of perforations on the inner wall of the shaft; injecting a first fracturing fluid through the plurality of perforations to form a first fracture in the virgin coal of the higher-order coal reservoir; injecting a second fracturing fluid through the plurality of holes to form a second fracture in the raw coal of the high-order coal reservoir, wherein the first fracture is communicated with the second fracture, and the second fracturing fluid is a mixed solution of the first fracturing fluid and a fracture proppant; injecting a displacement fluid from a shaft, and displacing the first fracturing fluid and the second fracturing fluid in raw coal of the high-rank coal reservoir; stopping injecting liquid into the shaft, and directly flowing back without closing the well.
In one implementation of the embodiment of the present disclosure, the determining, according to the well log data, a depth range of raw coal in the high-rank coal reservoir includes: obtaining the logging data of different areas in the high-rank coal reservoir, wherein the logging data comprises: at least one of resistivity of the high-rank coal reservoir, sonic moveout of the high-rank coal reservoir, natural gamma value of the high-rank coal reservoir, and density log of the high-rank coal reservoir; and determining the depth range of the raw coal in the high-rank coal reservoir according to the logging data.
In another implementation of the embodiment of the present disclosure, the determining a depth range of raw coal in the higher-rank coal reservoir according to the well log data includes: if the well logging data satisfies the region of the first determined relationship, determining the depth range of all the regions satisfying the first determined relationship in the high-rank coal reservoir as the depth range of the raw coal in the high-rank coal reservoir, wherein the first determined relationship comprises at least one of the following: the resistivity is larger than 3000 omega-m, the sound wave time difference is between 370 mu s/m and 410 mu s/m, the natural gamma value is between 30API and 80API, and the density logging is between 1.3g/cm3 and 1.6g/cm 3.
In another implementation of the embodiments of the present disclosure, the perforating at the middle region of the wellbore corresponding to the depth range of the native coal of the higher-rank coal reservoir comprises: and performing concentrated perforation in the middle area of the depth range of the primary coal of the high-rank coal reservoir in the shaft, wherein the perforation density is 10-20 holes/m, the perforation depth is 2.5-3.0 m, and the perforation direction is vertical to the direction of the minimum principal stress of the coal bed.
In another implementation of the embodiment of the present disclosure, before the injecting the second fracturing fluid through the plurality of perforations forms a second fracture in the raw coal of the higher-rank coal reservoir, the dredging fracturing method further includes: injecting a third fracturing fluid from the plurality of perforations, so that a fracture proppant in the third fracturing fluid props the first fracture, wherein the third fracturing fluid is a mixed solution of the first fracturing fluid and the fracture proppant, and the content of the fracture proppant in the third fracturing fluid is lower than that of the fracture proppant in the second fracturing fluid; the injecting a second fracturing fluid through the plurality of perforations to form a second fracture in the virgin coal of the higher-order coal reservoir comprises: injecting the second fracturing fluid from the plurality of perforations, causing the second fracturing fluid to form the second fracture in the virgin coal of the higher-order coal reservoir and causing fracture proppants within the second fracturing fluid to prop the second fracture.
In another implementation of the disclosed embodiment, said injecting the second fracturing fluid from the plurality of perforations comprises: injecting the second fracturing fluid from the plurality of perforations into the first fracture in a manner that gradually increases the rate of injection of the second fracturing fluid and the mass percent of fracture proppant in the second fracturing fluid.
In another implementation of the disclosed embodiment, the injecting the second fracturing fluid from the plurality of perforations into the first fracture in a manner that gradually increases the rate of injection of the second fracturing fluid and the percentage by mass of fracture proppant in the second fracturing fluid includes: and injecting the second fracturing fluid into the first fracture sequentially and continuously according to a first speed, a second speed and a third speed, wherein the first speed is lower than the second speed, the second speed is lower than the third speed, when the second fracturing fluid is injected according to the first speed, the mass percentage of the fracture propping agent of the second fracturing fluid is a first content, when the second fracturing fluid is injected according to the second speed, the mass percentage of the fracture propping agent of the second fracturing fluid is a second content, when the second fracturing fluid is injected according to the third speed, the mass percentage of the fracture propping agent of the second fracturing fluid is a third content, the first content is lower than the second content, and the second content is lower than the third content.
In another implementation of an embodiment of the present disclosure, the tri-fracturing fluid includes: the crack proppant comprises potassium chloride, a clay stabilizer, a crack proppant and water, wherein the mass percent of the potassium chloride is 1.0-2.0%, the mass percent of the clay stabilizer is 0.2-0.5%, the mass percent of the crack proppant is 6.0-8.0%, and the balance is water; the second fracturing fluid comprises: the crack proppant comprises potassium chloride, a clay stabilizer, the crack proppant and water, wherein the mass percent of the potassium chloride is 1.0-2.0%, the mass percent of the clay stabilizer is 0.2-0.5%, the mass percent of the crack proppant is 12-20%, and the balance is water.
In another implementation manner of the embodiment of the present disclosure, the fracture proppant is a sand proppant, the sand proppant of the second fracturing fluid includes three types of propping sands with different particle sizes, where a mass percentage of the propping sand with the smallest particle size is 16.7%, a mass percentage of the propping sand with the largest particle size is 33.3%, a mass percentage of the propping sand with the largest particle size located between the propping sand with the smallest particle size and the propping sand with the largest particle size is 50.0%, and a particle size of the sand proppant of the third fracturing fluid is the propping sand with the smallest particle size located between the propping sand with the smallest particle size and the propping sand with the largest particle size in the sand proppant of the second fracturing fluid.
In another implementation of an embodiment of the present disclosure, the first fracturing fluid includes: the soil stabilizer comprises potassium chloride, a clay stabilizer and water, wherein the potassium chloride accounts for 1.0-2.0% by mass, the clay stabilizer accounts for 0.2-0.5% by mass, and the balance is water.
In another implementation manner of the embodiment of the present disclosure, the dredging type fracturing method further includes: measuring wellhead pressure, and determining flowback parameters according to the wellhead pressure; the determining of the flowback parameter according to the wellhead pressure comprises: if the pressure of the well mouth is more than 20Mpa, a nozzle tip with the diameter of 6mm is adopted for backflow; if the pressure of the well head is 10MPa to 20MPa, a choke with the diameter of 10mm is adopted for backflow; if the pressure of the well head is 5MPa to 10MPa, a nozzle tip with the diameter of 12mm is adopted for backflow; and if the pressure of the well head is less than 5MPa, adopting a 14mm oil nozzle for backflow.
The beneficial effects brought by the technical scheme provided by the embodiment of the disclosure at least comprise:
the dredging type fracturing method of the high-order coal reservoir disclosed by the embodiment comprises the steps of firstly judging and identifying the coal body structure development characteristics of the high-order coal reservoir based on logging data, locking the development layer section of raw coal in the high-order coal reservoir, and determining the position of the raw coal in the high-order coal reservoir; and then, perforating in the middle area of the depth range of the primary coal of the high-rank coal reservoir in the shaft, and forming a plurality of perforations on the inner wall of the shaft. After the holes are formed in the shaft, first fracturing fluid is injected into the high-order coal reservoir from the holes, so that first fractures are formed at the original coal positions in the high-order coal reservoir, the seepage resistance of the reservoir is initially reduced, and the yield is increased. And simultaneously injecting a second fracturing fluid into the first fracture from the plurality of holes to further expand the trend and the depth of the first fracture in the reservoir, so that a second fracture is formed to a deeper part of the reservoir on the basis of the first fracture in the reservoir, and a long fracture is formed in the high-rank coal reservoir. And propping the long fractures with the fracture proppant in the second fracturing fluid. Under the action of the second fracturing fluid, a plurality of sub-cracks extend out of the main crack in the reservoir along different lateral directions of the main crack to form a net-shaped crack system, so that the crack forming effect is improved, and the seepage resistance of the reservoir is reduced. And then, injecting a displacing fluid into the shaft, and displacing the first fracturing fluid and the second fracturing fluid in the raw coal of the high-order coal reservoir, so that the first fracturing fluid and the second fracturing fluid can completely support the first fracture and the second fracture, and a reticular fracture system can be more stable. Finally, after the displacement fluid is injected by the pump, the non-closed well is adopted to directly carry out flowback, so that the pressure of the reservoir can be quickly reduced to the original formation pressure, the filtration loss of the fracturing fluid and the degree of pollution to the reservoir are reduced, the high-pressure fluid and the coal powder are guided to be quickly discharged, the crack is kept clean, and the rising of the pressure of the reservoir and the range of erosion and expansion of the fracturing fluid to the periphery are effectively relieved.
According to the method and the device, the depth range of the raw coal in the high-rank coal reservoir is determined through the logging data, and then the perforation is carried out in the position, corresponding to the depth, of the raw coal in the shaft, so that the condition that a fracturing fluid easily forms a high-diversion seepage zone at a coal construction position in the fracturing process of the related technology is avoided. The raw coal in a high-order coal reservoir is reformed, and the gas production rate of a gas well can be improved; meanwhile, a net-shaped crack system is formed by respectively injecting the first fracturing fluid and the second fracturing fluid, so that the crack forming effect is improved, and the yield is increased.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present disclosure, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a flow chart of a dredging fracturing method for a high-rank coal reservoir provided by an embodiment of the disclosure;
fig. 2 is a flow chart of another dredging fracturing method for a high-rank coal reservoir provided by an embodiment of the disclosure.
Detailed Description
To make the objects, technical solutions and advantages of the present disclosure more apparent, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.
Fig. 1 is a flowchart of a dredging fracturing method for a high-rank coal reservoir provided by an embodiment of the disclosure. As shown in fig. 1, the fracturing method comprises:
s101: and determining the depth range of the raw coal in the high-rank coal reservoir according to the logging data.
S102: perforating in the middle area of the depth range of the primary coal of the corresponding high-rank coal reservoir in the shaft, and forming a plurality of perforations on the inner wall of the shaft.
S103: a first fracture is formed in the virgin coal of the higher-rank coal reservoir by injecting a first fracturing fluid through the plurality of perforations.
S104: injecting a second fracturing fluid through the plurality of perforations to form a second fracture in the virgin coal of the higher-order coal reservoir.
The first fracture is communicated with the second fracture, and the second fracturing fluid is a mixed solution of the first fracturing fluid and a fracture proppant.
S105: and injecting a displacement fluid from the shaft, and displacing the first fracturing fluid and the second fracturing fluid in the raw coal of the high-rank coal reservoir.
S106: stopping injecting liquid into the shaft, and directly flowing back without closing the well.
According to the dredging type fracturing method of the high-order coal reservoir disclosed by the embodiment, firstly, the depth position of raw coal in the high-order coal reservoir is determined according to logging data, namely, the fracturing method judges the coal body structure development characteristics of the high-order coal reservoir based on the logging data, the development interval of the raw coal in the high-order coal reservoir is locked, and the position of the raw coal in the high-order coal reservoir is determined; then, perforating in the middle area of the depth range of the primary coal of the high-rank coal reservoir in the shaft, and forming a plurality of holes on the inner wall of the shaft, namely forming dense holes. Because the boundary region of the depth range of the primary coal is mostly weak-strength structural coal, if the perforation position completely corresponds to the position of the whole primary coal, the fracturing fluid can enter the structural coal, a high-diversion seepage zone is formed at the position of the structural coal, and the hydraulic fracturing reformation of the primary coal is not facilitated. After dense holes are formed in a shaft, first fracturing fluid is injected into the high-order coal reservoir from the holes, when the first fracturing fluid is subjected to pressure holding at the bottom of the shaft, and the pressure is higher than the strength of raw coal in the high-order coal reservoir where the holes are located, the raw coal in the high-order coal reservoir generates cracks (namely first cracks), and the first cracks formed at the raw coal in the high-order coal reservoir are used for preliminarily reducing the seepage resistance of the reservoir, increasing the permeability and realizing yield increase. Meanwhile, second fracturing fluid is injected into the first fractures from the plurality of holes, the trend and the depth of the first fractures in the reservoir are further expanded by the second fracturing fluid, so that second fractures are formed in the reservoir deeper on the basis of the first fractures in the reservoir, the second fractures are communicated with the first fractures, long fractures are formed in a high-order coal reservoir, meanwhile, the long fractures are supported by fracture propping agents in the second fracturing fluid, so that the long fractures are more stable, the fractures in the reservoir continue to extend into the reservoir under the action of the second fracturing fluid, a plurality of sub-fractures extend along different lateral directions of the main fractures on the basis of taking the first fractures and the second fractures as main fractures, so that a plurality of dendritic fractures are formed, namely, the main fractures and the sub-fractures are mutually crossed to jointly form a reticular fracture system, so that the seepage resistance of a reticular fracture system formed at the original coal in the high-order coal reservoir can be further reduced, so as to increase the permeability and realize the yield increase. And then, injecting a displacing fluid from the shaft, and displacing the first fracturing fluid and the second fracturing fluid in the raw coal of the high-order coal reservoir to ensure that the first fracturing fluid and the second fracturing fluid can completely support the first fracture and the second fracture, so that a reticular fracture system formed at the raw coal in the high-order coal reservoir can be more stable and reliable. Finally, in the embodiment of the disclosure, after the displacement fluid is injected by the pump, the non-closed well is adopted to directly carry out flowback, so that the reservoir pressure can be quickly reduced to the original formation pressure, the filtration loss of the fracturing fluid and the degree of pollution to the reservoir are reduced, the high-pressure fluid and the pulverized coal are guided to be quickly discharged, the crack is kept clean, and the lifting of the reservoir pressure and the range of erosion and expansion of the fracturing fluid to the periphery are effectively relieved. Therefore, compared with the construction process of hydraulically fracturing and then flowback, the dredging type fracturing method provided by the embodiment of the disclosure can control the pressure rise of the reservoir, reduce the filtration loss of the fracturing fluid and the degree of polluting the reservoir, and effectively improve the yield of the coal bed methane reservoir. When fracturing is carried out, the depth position of the raw coal in the high-order coal reservoir is determined through the logging data, and then perforation is carried out in the position, corresponding to the depth, of the raw coal in the shaft, so that the condition that a high-diversion seepage zone is formed at the position of the constructed coal due to the fact that fracturing fluid easily breaks through the weak-strength constructed coal at first in the fracturing process of the related technology is avoided, and the raw coal in the high-order coal reservoir is reformed; meanwhile, a reticular fracture system taking the first fracture and the second fracture as main fractures is formed by respectively injecting the first fracturing fluid and the second fracturing fluid, so that the fracture forming effect is improved, the seepage resistance of the area where the raw coal is in the high-order coal reservoir is reduced, the permeability is increased, and the yield is increased.
Fig. 2 is a flow chart of another dredging fracturing method for a high-rank coal reservoir provided by an embodiment of the disclosure. As shown in fig. 2, the fracturing method comprises:
s201: and determining the depth range of the raw coal in the high-rank coal reservoir according to the logging data.
The logging data can be measured by a productivity test well before the gas well is used, various data can be measured by the productivity test well, and in the embodiment of the disclosure, the distribution position of the coal body structure in the high-order coal reservoir is identified and judged by using one or more data in the logging data.
Because the coal body structure of the high-rank coal reservoir comprises raw coal and tectonic coal, the tectonic coal comprises broken coal, crushed coal and minced coal. And the response relations between the coal body structures of different types and the four kinds of logging data are different, so that the coal body structure of the high-order coal reservoir can be judged according to the combination of the four kinds of logging data, namely resistivity, acoustic time difference, natural gamma value and density logging.
The well logging data for identifying and determining the distribution position of the coal body structure in the higher-rank coal reservoir in S201 may include: at least one of resistivity of the higher-rank coal reservoir, sonic moveout of the higher-rank coal reservoir, natural gamma value of the higher-rank coal reservoir, and density log of the higher-rank coal reservoir.
The coal body structure of the high-rank coal reservoir in the embodiment of the disclosure can be determined according to the following data table:
when the position of the raw coal in the high-rank coal reservoir is determined according to the logging data, firstly, the logging data of different areas in the high-rank coal reservoir are obtained, and the depth position of the raw coal in the high-rank coal reservoir is determined according to the logging data. In combination with the above table, if there are regions in the high-rank coal reservoir that satisfy the first determined relationship, the depth range of all the regions in the high-rank coal reservoir that satisfy the first determined relationship is determined as the depth position of the raw coal in the high-rank coal reservoir. Wherein the first determined relationship may include at least one of: the resistivity is more than 3000 omega-m, the sound wave time difference is between 370 mu s/m and 410 mu s/m, the natural gamma value is between 30API and 80API, and the density logging is between 1.3g/cm3 and 1.6g/cm 3. And if the areas meeting the second determined relation exist in the high-rank coal reservoir, determining the depth range of all the areas meeting the second determined relation in the high-rank coal reservoir as the depth position of the fractured coal in the high-rank coal reservoir. Wherein the second determining relationship comprises: resistivity is between 1000 Ω · m and 3000 Ω · m, acoustic time difference is greater than 380 μ s/m, natural gamma value is less than 60API, density logging is at 1.2g/cm3To 1.35g/cm3In the meantime. And if the areas meeting the third determined relation exist in the high-rank coal reservoir, determining the depth range of all the areas meeting the third determined relation in the high-rank coal reservoir as the depth positions of the crushed coal or the minced coal in the high-rank coal reservoir. Wherein the third determining relationship comprises: resistivity is more than 1000 omega.m, acoustic wave time difference is more than 410 mu s/m, natural gamma value is less than 60API, density logging is positioned at 1.1g/cm3To 1.25g/cm3In the meantime.
S202: perforating in the middle area of the depth range of the primary coal of the corresponding high-rank coal reservoir in the shaft, and forming a plurality of perforations on the inner wall of the shaft.
S202 may include: and performing centralized perforation at the position of the primary coal of the high-rank coal reservoir in the shaft. Wherein the perforation density is 16 holes/m, and the perforation depth is 2.5m to 3.0 m. The centralized perforation is to make the pressure of hydraulic fracturing more centralized and facilitate the creation of long seams in the fracturing process. In the disclosed embodiment, the perforation direction can be selected to be perpendicular to the direction of the minimum principal stress of the coal seam. The perforation direction is set to be perpendicular to the direction of the minimum main stress of the coal seam, so that the resistance in the process of fracturing fracture expansion is relatively small, and the purpose of forming long fractures is achieved.
S203: a first fracture is formed in the virgin coal of the higher-rank coal reservoir by injecting a first fracturing fluid into the higher-rank coal reservoir through the plurality of perforations.
S203 may include: and pumping the first fracturing fluid into the area of the raw coal in the high-rank coal reservoir through a plurality of holes. And when the pressure of the first fracturing fluid at the bottom of the well is greater than the strength of the raw coal in the high-rank coal reservoir at the positions of the plurality of holes, the first fracturing fluid generates a first fracture in the raw coal region in the high-rank coal reservoir. The first fracturing fluid is active water fracturing fluid and can comprise 1.0-2.0% by mass of potassium chloride, 0.2-0.5% by mass of clay stabilizer and the balance of water. The active water fracturing fluid with the components is low in cost, can effectively solve the problem of expansion of coal rock and clastic rock clay, and further reduces the damage of the fracturing process to a reservoir. The clay stabilizer may be various clay stabilizers such as 2-ethyltrimethyl ammonium chloride, quaternary amine clay stabilizers, and the like, and the embodiments of the present disclosure are not limited thereto.
In S203, the pumping speed of the first fracturing fluid may be 4.0m3Min to 5.0m3Min, pump injection can be 70m3To 100m3. Illustratively, the pumping speed of the first fracturing fluid may be 4.0m3Min to 4.5m3Min, the pump injection can be 90m3. The pumping speed and the pumping quantity of the first fracturing fluid can controllably form seams at the position of the primary coal of the high-rank coal reservoir, and can further extend to other positions in the high-rank coal reservoir, such as weak surfaces of the combination of the construction coal position and other rocks.
S204: injecting a third fracturing fluid into the first fracture through the plurality of perforations such that the fracture proppant in the third fracturing fluid propps the first fracture.
The third fracturing fluid is a mixed solution of the first fracturing fluid and a fracture propping agent, and the content of the fracture propping agent of the third fracturing fluid is lower than that of the fracture propping agent of the second fracturing fluid. Illustratively, the third fracturing fluid may include: potassium chloride, clay stabilizer, fracture proppant and water. The weight percentage of the potassium chloride is 1.0-2.0%, the weight percentage of the clay stabilizer is 0.2-0.5%, the weight percentage of the crack propping agent is 6.0-8.0%, and the rest is water.
The pumping speed of the third fracturing fluid in S204 is 2.5m3Min to 4.5m3Min, the pump injection can be 150m3To 200m3The amount of the fracture proppant can be 5m3To 15m3. Illustratively, the pumping speed of the third fracturing fluid may be 3.0m3Min to 4.0m3Min, pump injection 180m3The amount of the fracture proppant may be 10m3. The pumping speed and the pumping quantity of the third fracturing fluid can further expand the trend and the depth of the first fracture in the coal bed, so that the first fracture penetrates into the coal bed, and a long seam is formed in the coal bed. The fracture proppant can be sand proppant, and the sand proppant in the third fracturing fluid can be natural quartz sand with the particle size of 20-40 meshes. Therefore, the first fracture is filled and supported by the natural quartz sand in the third fracturing fluid, so that the first fracture is more stable and reliable.
S205: injecting a second fracturing fluid into the first fracture through the plurality of perforations, causing the second fracturing fluid to form a second fracture in the virgin coal of the higher-order coal reservoir and causing a fracture proppant within the second fracturing fluid to prop the second fracture.
Wherein the second fracturing fluid may include: potassium chloride, clay stabilizer, fracture proppant and water. The weight percentage of the potassium chloride is 1.0-2.0%, the weight percentage of the clay stabilizer is 0.2-0.5%, the weight percentage of the sand proppant is 12-20%, and the balance is water. That is, in the disclosed embodiments, the third fracturing fluid and the second fracturing fluid each include a fracture proppant, and the fracture proppant content of the third fracturing fluid is lower than the fracture proppant content of the second fracturing fluid.
In S205, the second fracturing fluid pump injection amount may be 200m3To 250m3. For example, the second fracturing fluid pump injection may be 220m3. The second fracturing fluid based on the pump injection amount can support fracturing and crack formation, can ensure that the formed cracks are filled with crack propping agents, and effectively improves the crack formation effect.
And S205, continuously pumping the second fracturing fluid into the reservoir through the plurality of holes, so that a second fracture communicated with the first fracture is formed in the primary stratum of the high-rank coal reservoir, the fracture can continuously extend towards the inside of the high-rank coal reservoir, and a plurality of dendritic fractures filled with fracture propping agents are formed in the high-rank coal reservoir. The branch-shaped crack is a plurality of sub-cracks which take the first crack and the second crack as main cracks and extend along different directions, the main cracks and the sub-cracks can be mutually crossed to jointly form a net-shaped crack system, so that the crack making effect is improved, the seepage resistance of the area where the raw coal in a high-order coal reservoir is located is reduced, the permeability is increased, and the yield is increased.
Optionally, the fracture proppant in the second fracturing fluid may be a sand proppant, and the sand proppant of the second fracturing fluid may include: the support sand comprises three support sands with different particle sizes, wherein the support sand with the smallest particle size is 16.7% by mass, the support sand with the largest particle size is 33.3% by mass, and the support sand with the largest particle size between the support sand with the smallest particle size and the support sand with the largest particle size is 50.0% by mass. Illustratively, the sand-based proppant in the second fracturing fluid may be a combination of multi-particle size sand-based proppants including coarse, medium, and fine particle size natural quartz sand. That is, the sand proppant combination with multiple particle sizes comprises supporting sand with the smallest particle size, supporting sand with the particle size between the supporting sand with the smallest particle size and the supporting sand with the largest particle size, and the supporting sand with the largest particle size. And according to the mass percentage, the supporting sand with the smallest particle size, the supporting sand with the particle size between the supporting sand with the smallest particle size and the supporting sand with the largest particle sizeThe sand supporting rate is 16.7%: 50.0%: 33.3 percent. Wherein the particle size of the support sand with the smallest particle size is 12 meshes to 20 meshes, the particle size of the support sand between the support sand with the smallest particle size and the support sand with the largest particle size is 20 meshes to 40 meshes, and the particle size of the support sand with the largest particle size is 40 meshes to 70 meshes. And the dosage of the sand proppant in the second fracturing fluid can be 25m3To 35m3。
The supporting sand in the implementation mode can be natural quartz sand, so that the second crack and the plurality of dendritic cracks are filled and supported by the natural quartz sand in the second fracturing fluid, and the second crack and the formed reticular crack system are more stable and reliable. In the embodiment of the disclosure, the second fracturing fluid combined by the sand proppant with multiple particle sizes is used for water conservancy fracturing modification process, so that the sand proppant can be filled into multiple fractures formed in a high-order coal reservoir, and a long-distance extending reticular fracture system is formed in the high-order coal reservoir, so that fractures of all levels are effectively supported, and the smoothness of fractured fractures is kept.
In S205, injecting the second fracturing fluid through the plurality of apertures may include: and injecting second fracturing fluid into the first fracture in sequence according to the first speed, the second speed and the third speed, wherein the first speed is smaller than the second speed, the second speed is smaller than the third speed, when the second fracturing fluid is injected according to the first speed, the mass percentage of the sand propping agent of the second fracturing fluid is first content, when the second fracturing fluid is injected according to the second speed, the mass percentage of the sand propping agent of the second fracturing fluid is second content, when the second fracturing fluid is injected according to the third speed, the mass percentage of the sand propping agent of the second fracturing fluid is third content, the first content is smaller than the second content, and the second content is smaller than the third content. Illustratively, the first speed is 3.0m3Min to 4.5m3Min, second speed 5.0m3Min to 6.5m3Min, third speed 7.0m3Min to 8.5m3Min, and the first content is 12% to 14%, the second content is 15% to 17%, and the third content is 18% to 20%. In the embodiment of the disclosure, the second fracturing fluid is pumped by adopting a variable speed method for gradually increasing the pumping speed, and the pumping process is as follows: controlling the pumping rate of the second fracturing fluidIs 3.0m in sequence3Min to 4.5m3/min，5.0m3Min to 6.5m3/min，7.0m3Min to 8.5m3Min, and the pumping speed is 4.0m in sequence3/min，5.5m3/min，7.5m3And/min. Accordingly, the sand proppant in the second fracturing fluid is controlled to be 12% to 14%, 15% to 17%, 18% to 20% by mass, for example, the sand proppant in the second fracturing fluid may be 13%, 16%, 18% by mass. According to the embodiment of the invention, the second fracturing fluid is pumped in a mode of improving the pumping speed in a stepped mode, the extending distance of the main seam is ensured, the pumping speed of the sand-carrying fluid and the content of the sand proppant are gradually improved, the extending range of the branch seams near the main seam is further expanded, the fracturing modification range is improved, and a long-distance supporting seam net is formed in the coal seam.
S206: and injecting a displacement fluid from the shaft, and displacing the first fracturing fluid and the second fracturing fluid in the raw coal of the high-rank coal reservoir.
In S206, the displacement fluid may include 1.0% to 2.0% by mass of potassium chloride, 0.2% to 0.5% by mass of a clay stabilizer, and the balance water. And the third fracturing fluid and the second fracturing fluid remained in the shaft can be replaced into the high-rank coal storage layer through the displacement fluid.
S207: stopping injecting liquid into the shaft, and directly flowing back without closing the well.
In S207, well head pressure can be measured during the flow back, and flow back parameters are determined according to the well head pressure. In order to completely and completely return in the embodiment of the present disclosure, the return process may be implemented as follows: if the pressure of the well mouth is more than 20Mpa, adopting an oil nozzle with the diameter of 6mm to carry out backflow; if the pressure of the well head is 10MPa to 20MPa, a choke with the diameter of 10mm is adopted for backflow; if the pressure of the well head is 5MPa to 10MPa, a nozzle tip with the diameter of 12mm is adopted for backflow; and if the pressure at the well head is less than 5MPa, a 14mm oil nozzle is adopted for backflow. According to the embodiment of the invention, the well is not closed after fracturing, the formation pressure is quickly reduced to the original formation pressure, the filtration loss of fracturing fluid and the degree of polluting a reservoir are reduced, high-pressure liquid and coal powder are guided to be quickly discharged, the fracture is kept clean, and the lifting of the formation pressure and the range of the expansion of the fracturing fluid to the periphery are effectively relieved.
Taking the high-rank coal reservoir of the Zhenzhuang district in the south of Shanxi as an example for illustration, the depth range of the high-rank coal reservoir is 703.65 meters to 709.65 meters, the thickness of the high-rank coal reservoir is 6 meters, the top and bottom plates of the high-rank coal reservoir are mudstone and sandy mudstone, the middle part of the high-rank coal reservoir develops into primary coal, and both sides are accompanied by cracked coal and a small amount of crushed coal.
Firstly, a coal body structure recognition model is established by utilizing response characteristics between logging data and different types of coal body structures, the primary coal of the high-order coal reservoir is determined to be distributed in the depth range of 704.85-708.35 m according to the logging data, the thickness of the primary coal is 3.50 m, most of the top of the high-order coal reservoir is broken coal, and the bottom of the high-order coal reservoir is broken coal and a small amount of crushed coal. And then, perforating in the middle area of the depth range of the primary coal of the high-rank coal reservoir in the shaft, and forming a plurality of perforations on the inner wall of the shaft. And the perforation density is controlled to be 16 holes/m, the perforation thickness is 3 m, the perforation depth is 705.0 m to 708.0 m (namely the middle area of the depth range), and the number of the perforations is 48. Then, pumping a first fracturing fluid, wherein the first fracturing fluid comprises 1.0% of KCl, 0.2% of clay stabilizer and the balance of water by mass percent, and the pumping speed of the first fracturing fluid is controlled to be 4.5m3Min, pumping 90m into the high-order coal reservoir through a plurality of holes3The first fracturing fluid is used for fracturing construction, and a first fracture is formed in a high-order coal reservoir. And then, pumping and injecting a third fracturing fluid, wherein the third fracturing fluid comprises 1.0 mass percent of KCl, 0.2 mass percent of clay stabilizer, 8.0 mass percent of natural quartz sand and the balance of water. Controlling the pumping speed of the third fracturing fluid to be 3.5m3Min, pump 180m into the first fracture3The third fracturing fluid of (1). The sand proppant in the third fracturing fluid is Lanzhou quartz sand with the grain diameter of 20 meshes to 40 meshes, and the dosage of the sand proppant is 10m3Thereby allowing it to enter the first fracture and prop the fracture. Then, pumping a second fracturing fluid, wherein the second fracturing fluid comprises 1.0% of KCl, 0.2% of clay stabilizer and sand proppant combination in percentage by mass, and the sand proppant combination comprises 13% of sand proppant combination in percentage by mass16 percent and 18 percent of natural quartz sand, the sand proppant combination comprises coarse sand with the grain diameter of 15 meshes, medium sand with the grain diameter of 30 meshes and fine sand with the grain diameter of 60 meshes, and the dosage of the sand proppant combination is 30m3. Controlling the pumping speed of the second fracturing fluid to be 4.0m in sequence during pumping3/min，5.5m3/min，7.5m3Min, correspondingly, controlling the mass percentage of the sand proppant in the second fracturing fluid to be 13%, 16% and 18% in sequence, and the amount of the second fracturing fluid pumped to be 220m3. And then, replacing the third fracturing fluid and the second fracturing fluid remained in the shaft into the high-order coal storage layer by using a replacing fluid which comprises 1.0 mass percent of KCl, 0.2 mass percent of clay stabilizer and the balance of water. Stopping the pump, not closing the well, measuring the pressure to reasonably control the flowback parameters, quickly flowback, and controlling the pressure rise and pollution of the reservoir. By the fracturing method, the single-well gas production rate of the coal bed gas reaches 1800m3To 3200m3Average single well daily gas production 2100m3Compared with the adjacent old well in the same region, the stable gas yield of the gas well adopting the fracturing method is 2.5-3 times of that of the old well, and the accumulated gas yield is 156 ten thousand meters3The stable production period reaches 11-23 months, the dredging type fracturing improving process effectively improves the yield of a single well and improves the overall development effect of a block.
The above description is meant to be illustrative of the principles of the present disclosure and not to be taken in a limiting sense, and any modifications, equivalents, improvements and the like that are within the spirit and scope of the present disclosure are intended to be included therein.
Claims (11)
1. A dredging type fracturing method for a high-order coal reservoir is characterized by comprising the following steps:
determining the depth range of the raw coal in the high-order coal reservoir according to the logging data;
perforating in the middle area of the depth range of the primary coal of the high-rank coal reservoir in the shaft, and forming a plurality of perforations on the inner wall of the shaft;
injecting a first fracturing fluid through the plurality of perforations to form a first fracture in the virgin coal of the higher-order coal reservoir;
injecting a second fracturing fluid through the plurality of holes to form a second fracture in the raw coal of the high-order coal reservoir, wherein the first fracture is communicated with the second fracture, and the second fracturing fluid is a mixed solution of the first fracturing fluid and a fracture proppant;
injecting a displacement fluid from a shaft, and displacing the first fracturing fluid and the second fracturing fluid in raw coal of the high-rank coal reservoir;
stopping injecting liquid into the shaft, and directly flowing back without closing the well.
2. The method for dredging fracturing of a higher-rank coal reservoir according to claim 1, wherein the determining a depth range of raw coal in the higher-rank coal reservoir according to the log data comprises:
obtaining the logging data of different areas in the high-rank coal reservoir, wherein the logging data comprises: at least one of resistivity of the high-rank coal reservoir, sonic moveout of the high-rank coal reservoir, natural gamma value of the high-rank coal reservoir, and density log of the high-rank coal reservoir;
and determining the depth range of the raw coal in the high-rank coal reservoir according to the logging data.
3. The method of claim 2, wherein determining a depth range of virgin coal in the higher-rank coal reservoir from the well log data comprises:
if the logging data meet the region of the first determined relationship, determining the depth range of all the regions meeting the first determined relationship in the high-rank coal reservoir as the depth range of the raw coal in the high-rank coal reservoir,
the first determined relationship comprises at least one of: the resistivity is larger than 3000 omega-m, the sound wave time difference is between 370 mu s/m and 410 mu s/m, the natural gamma value is between 30API and 80API, and the density logging is between 1.3g/cm3 and 1.6g/cm 3.
4. The dredging fracturing method for the higher-rank coal reservoir according to claim 1, wherein the perforating in the middle area of the depth range of the primary coal of the higher-rank coal reservoir in the shaft comprises the following steps:
and performing concentrated perforation in the middle area of the depth range of the primary coal of the high-rank coal reservoir in the shaft, wherein the perforation density is 10-20 holes/m, the perforation depth is 2.5-3.0 m, and the perforation direction is vertical to the direction of the minimum principal stress of the coal bed.
5. The method of claim 1, wherein the injecting the second fracturing fluid through the plurality of perforations further comprises, prior to forming a second fracture in the virgin coal of the higher-rank coal reservoir:
injecting a third fracturing fluid from the plurality of perforations, so that a fracture proppant in the third fracturing fluid props the first fracture, wherein the third fracturing fluid is a mixed solution of the first fracturing fluid and the fracture proppant, and the content of the fracture proppant in the third fracturing fluid is lower than that of the fracture proppant in the second fracturing fluid;
the injecting a second fracturing fluid through the plurality of perforations to form a second fracture in the virgin coal of the higher-order coal reservoir comprises:
injecting the second fracturing fluid from the plurality of perforations, causing the second fracturing fluid to form the second fracture in the virgin coal of the higher-order coal reservoir and causing fracture proppants within the second fracturing fluid to prop the second fracture.
6. The method of dredging fracturing for a higher-rank coal reservoir as claimed in claim 5, wherein said injecting the second fracturing fluid from the plurality of perforations comprises:
injecting the second fracturing fluid from the plurality of perforations into the first fracture in a manner that gradually increases the rate of injection of the second fracturing fluid and the mass percent of fracture proppant in the second fracturing fluid.
7. The method of dredging a higher-order coal reservoir of claim 6, wherein the injecting the second fracturing fluid from the plurality of perforations into the first fracture in a manner that gradually increases the rate of injection of the second fracturing fluid and the percentage by mass of fracture proppant in the second fracturing fluid comprises:
injecting the second fracturing fluid into the first fracture continuously and sequentially according to a first speed, a second speed and a third speed, wherein the first speed is lower than the second speed, the second speed is lower than the third speed,
when the second fracturing fluid is injected according to the first speed, the mass percentage of the fracture propping agent of the second fracturing fluid is a first content, when the second fracturing fluid is injected according to the second speed, the mass percentage of the fracture propping agent of the second fracturing fluid is a second content, when the second fracturing fluid is injected according to the third speed, the mass percentage of the fracture propping agent of the second fracturing fluid is a third content, the first content is less than the second content, and the second content is less than the third content.
8. The dredging type fracturing method for high-rank coal reservoirs according to claim 5, wherein the three fracturing fluids comprise: the crack proppant comprises potassium chloride, a clay stabilizer, a crack proppant and water, wherein the mass percent of the potassium chloride is 1.0-2.0%, the mass percent of the clay stabilizer is 0.2-0.5%, the mass percent of the crack proppant is 6.0-8.0%, and the balance is water;
the second fracturing fluid comprises: the crack proppant comprises potassium chloride, a clay stabilizer, the crack proppant and water, wherein the mass percent of the potassium chloride is 1.0-2.0%, the mass percent of the clay stabilizer is 0.2-0.5%, the mass percent of the crack proppant is 12-20%, and the balance is water.
9. The dredging fracturing method for high-order coal reservoirs according to claim 5, wherein the fracture proppant is a sand proppant, the sand proppant of the second fracturing fluid comprises three kinds of propping sands with different grain sizes, wherein the mass percent of the propping sand with the smallest grain size is 16.7%, the mass percent of the propping sand with the largest grain size is 33.3%, the mass percent of the propping sand with the largest grain size between the propping sand with the smallest grain size and the propping sand with the largest grain size is 50.0%,
the grain size of the sand proppant of the third fracturing fluid is the supporting sand with the grain size between the supporting sand with the minimum grain size and the supporting sand with the maximum grain size in the sand proppant of the second fracturing fluid.
10. The dredging fracturing method for high-rank coal reservoirs according to any one of claims 1 to 9, wherein the first fracturing fluid comprises: the soil stabilizer comprises potassium chloride, a clay stabilizer and water, wherein the potassium chloride accounts for 1.0-2.0% by mass, the clay stabilizer accounts for 0.2-0.5% by mass, and the balance is water.
11. The dredging fracturing method for high-rank coal reservoirs according to any one of claims 1 to 9, characterized in that the dredging fracturing method further comprises:
measuring wellhead pressure, and determining flowback parameters according to the wellhead pressure;
the determining of the flowback parameter according to the wellhead pressure comprises:
if the pressure of the well mouth is more than 20Mpa, a nozzle tip with the diameter of 6mm is adopted for backflow;
if the pressure of the well head is 10MPa to 20MPa, a choke with the diameter of 10mm is adopted for backflow;
if the pressure of the well head is 5MPa to 10MPa, a nozzle tip with the diameter of 12mm is adopted for backflow;
and if the pressure of the well head is less than 5MPa, adopting a 14mm oil nozzle for backflow.
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