CA1183832A - Method of drilling a borehole through cavernous underground formations - Google Patents
Method of drilling a borehole through cavernous underground formationsInfo
- Publication number
- CA1183832A CA1183832A CA000366062A CA366062A CA1183832A CA 1183832 A CA1183832 A CA 1183832A CA 000366062 A CA000366062 A CA 000366062A CA 366062 A CA366062 A CA 366062A CA 1183832 A CA1183832 A CA 1183832A
- Authority
- CA
- Canada
- Prior art keywords
- cavern
- drilling
- borehole
- cement
- density
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 230000015572 biosynthetic process Effects 0.000 title claims abstract description 14
- 238000000034 method Methods 0.000 title claims abstract description 14
- 238000005553 drilling Methods 0.000 title claims description 35
- 238000005755 formation reaction Methods 0.000 title description 12
- 239000004568 cement Substances 0.000 claims abstract description 59
- 239000002002 slurry Substances 0.000 claims abstract description 44
- 239000012530 fluid Substances 0.000 claims description 15
- 239000007788 liquid Substances 0.000 claims description 4
- 238000002347 injection Methods 0.000 claims description 3
- 239000007924 injection Substances 0.000 claims description 3
- 239000004620 low density foam Substances 0.000 claims description 3
- 239000006260 foam Substances 0.000 abstract description 7
- 239000007789 gas Substances 0.000 description 8
- 238000006243 chemical reaction Methods 0.000 description 7
- 239000012267 brine Substances 0.000 description 6
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 description 6
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 239000003795 chemical substances by application Substances 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 238000007789 sealing Methods 0.000 description 4
- 239000004094 surface-active agent Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 238000005086 pumping Methods 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 241000272470 Circus Species 0.000 description 1
- 239000010426 asphalt Substances 0.000 description 1
- 239000000440 bentonite Substances 0.000 description 1
- 229910000278 bentonite Inorganic materials 0.000 description 1
- SVPXDRXYRYOSEX-UHFFFAOYSA-N bentoquatam Chemical compound O.O=[Si]=O.O=[Al]O[Al]=O SVPXDRXYRYOSEX-UHFFFAOYSA-N 0.000 description 1
- 239000001913 cellulose Substances 0.000 description 1
- 229920002678 cellulose Polymers 0.000 description 1
- 239000004927 clay Substances 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000006854 communication Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000008187 granular material Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000011796 hollow space material Substances 0.000 description 1
- 229940090044 injection Drugs 0.000 description 1
- 239000010445 mica Substances 0.000 description 1
- 229910052618 mica group Inorganic materials 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 229920000136 polysorbate Polymers 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 239000004753 textile Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/42—Compositions for cementing, e.g. for cementing casings into boreholes; Compositions for plugging, e.g. for killing wells
-
- 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
- E21B21/00—Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor
- E21B21/003—Means for stopping loss of drilling fluid
-
- 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
- E21B33/00—Sealing or packing boreholes or wells
- E21B33/10—Sealing or packing boreholes or wells in the borehole
- E21B33/13—Methods or devices for cementing, for plugging holes, crevices or the like
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Geology (AREA)
- Mining & Mineral Resources (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Physics & Mathematics (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- Geochemistry & Mineralogy (AREA)
- Chemical & Material Sciences (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Consolidation Of Soil By Introduction Of Solidifying Substances Into Soil (AREA)
Abstract
ABSTRACT
METHOD OF DRILLING A BOREHOLE THROUGH CAVERNOUS
UNDERGROUND FORMATIONS
To pass a cavern in an underground formation through which a borehole is being drilled, a cementing tube is lowered through the hole and into the cavern. A lightweight cement slurry (such as a foam cement slurry) is introduced into the cavern to build up a cement column extending between the floor and the ceiling of the cavity at a location where the borehole should pass the cavity.
METHOD OF DRILLING A BOREHOLE THROUGH CAVERNOUS
UNDERGROUND FORMATIONS
To pass a cavern in an underground formation through which a borehole is being drilled, a cementing tube is lowered through the hole and into the cavern. A lightweight cement slurry (such as a foam cement slurry) is introduced into the cavern to build up a cement column extending between the floor and the ceiling of the cavity at a location where the borehole should pass the cavity.
Description
31~33Z
~ETHOD OF DRILLING A BOREHOLE THROUGH CAVERNOUS
UNDERGROUND FOR~ATIONS
The invention relates to a method of drilling a borehole through cavernous underground formations. Such ~ormations consist of vast caverns also indicated as vugs, cavities or hollow spaces and the mud normally circulated in a borehole that enters such hollow space in the formation will be lost therein, as a result whereof the drilling operation has to be halted and steps have -to be taken -to stop the loss of drilling fluid. Existing techniques of restoring lost circulation such as by pumping down drilling fluid carrying sealing and plugging materials (cellulose flakes, mica, textile fibres, rubber pulp, and many other materials) are of no use as the fluid passages in cavernous formations are so large that the materials will pass therethrough without sealing or plugging the passages. The use of cementing agents that is often successful in sealing off permeable zones with relatively small fluid passages may also be considered. These cementing agents, when applied in permeable zones with relatively small fluid passages, are pumped into these zones in the fluid state and kept stationary therein until they are set, thereby filling the pore space with a solid mass. The large spaces present in cavernous formations, however, require huge amounts of such cementing agents which renders the application thereof unattractive.
5etting of a casing to bridge the height of a cavern that is to be passed by a borehole, is also not attrac-tive, since such setting is an expensive operation. The casing, moreover, will reduce the diameter o~ the production string that should finally be set in the well, which wi]l reduce the oil production capacity of the well. A fur-ther problem is the cemen-tation of such casing in a manner that after setting of the casing there is no fluid communica-tion between the interior of the casing and the cavern.
It will be appreciated that no effective cementation can be carried out under the circumstances existing in the cavernous formation.
The above problems are now solved by the present inven-tion. The drilling method according to the invention allows a quick and certain way of passing the borehole through a cavernous formation, without reducing the di.ameter of the hole, as well as without excessive losses of circu]ation. Dangerous situations that often accompany drilling operations wherein circulation losses are to be faced and which may even lead to loss of control over the well, are also obviated.
The method according to the invention comprises the steps of drilling a borehole through underground formation layers by means of rotary drilling equipment whilst circulating drilling fluid through the drilling equipment and the hole that is being drilled, interrupting the circulation of drilling fluid when the drilling equipment enters a cavern, injecting a low-density cement slurry .into the cavern in a volume sufficient to bridge the distance between the level at which the borehole enters the cavern and the bottom of the cavern r allowing the cement slurry to solidify to a solidified cement, and resuming drilling operations by extending the hole by drilling action through the solidified cement and into the bottom of the cavern.
By the expression "a low-density cement slurry" as used in the specification and claims is to be understood a slurry of which one of the components is a cement, and which slurry has a density that is between 1.0 and 1.4 g/cm3. If the cavern is partly or entirely filled with a liquid, best results will be obtained
~ETHOD OF DRILLING A BOREHOLE THROUGH CAVERNOUS
UNDERGROUND FOR~ATIONS
The invention relates to a method of drilling a borehole through cavernous underground formations. Such ~ormations consist of vast caverns also indicated as vugs, cavities or hollow spaces and the mud normally circulated in a borehole that enters such hollow space in the formation will be lost therein, as a result whereof the drilling operation has to be halted and steps have -to be taken -to stop the loss of drilling fluid. Existing techniques of restoring lost circulation such as by pumping down drilling fluid carrying sealing and plugging materials (cellulose flakes, mica, textile fibres, rubber pulp, and many other materials) are of no use as the fluid passages in cavernous formations are so large that the materials will pass therethrough without sealing or plugging the passages. The use of cementing agents that is often successful in sealing off permeable zones with relatively small fluid passages may also be considered. These cementing agents, when applied in permeable zones with relatively small fluid passages, are pumped into these zones in the fluid state and kept stationary therein until they are set, thereby filling the pore space with a solid mass. The large spaces present in cavernous formations, however, require huge amounts of such cementing agents which renders the application thereof unattractive.
5etting of a casing to bridge the height of a cavern that is to be passed by a borehole, is also not attrac-tive, since such setting is an expensive operation. The casing, moreover, will reduce the diameter o~ the production string that should finally be set in the well, which wi]l reduce the oil production capacity of the well. A fur-ther problem is the cemen-tation of such casing in a manner that after setting of the casing there is no fluid communica-tion between the interior of the casing and the cavern.
It will be appreciated that no effective cementation can be carried out under the circumstances existing in the cavernous formation.
The above problems are now solved by the present inven-tion. The drilling method according to the invention allows a quick and certain way of passing the borehole through a cavernous formation, without reducing the di.ameter of the hole, as well as without excessive losses of circu]ation. Dangerous situations that often accompany drilling operations wherein circulation losses are to be faced and which may even lead to loss of control over the well, are also obviated.
The method according to the invention comprises the steps of drilling a borehole through underground formation layers by means of rotary drilling equipment whilst circulating drilling fluid through the drilling equipment and the hole that is being drilled, interrupting the circulation of drilling fluid when the drilling equipment enters a cavern, injecting a low-density cement slurry .into the cavern in a volume sufficient to bridge the distance between the level at which the borehole enters the cavern and the bottom of the cavern r allowing the cement slurry to solidify to a solidified cement, and resuming drilling operations by extending the hole by drilling action through the solidified cement and into the bottom of the cavern.
By the expression "a low-density cement slurry" as used in the specification and claims is to be understood a slurry of which one of the components is a cement, and which slurry has a density that is between 1.0 and 1.4 g/cm3. If the cavern is partly or entirely filled with a liquid, best results will be obtained
-2~
3~32 when the low-density cement slurry has a density that matches the density of the liquid present in the cavern so that the cement slurry will not segregate upwards or downwards in the cavity under influence of gravity~
The invention will be described by way of example in more detail with reference to Figures 1-5 which all show schematically -2a-~3~3~
a vertical section over a borehole passing -through an underground formation.
Figure 1 shows the situation wherein the borehole is entering a cavern in the forma-tion;
Figure 2 shows a cementing tube having the lower open end thereof close to the floor of the cavern;
Figure 3 shows the initial par-t of the cement injec-tion;
Figure 4 shows the si-tua-tion in which the distance be-tween the borehole and the floor of the cavern is bridged by a column of cement; and Figure 5 shows the borehole extended through the solidified column of cement, and into the floor of the cavern.
The ro-tary drill string 1 and the drill bit 2 shown in the drawing form part of rotary drilling equipment whereof apart from -the string 1 and -the bit 2 only the derrick 3 is shown.
The string 1 and the bit 2 are suspended from the derrick 3 in the hole 4 that extends downwards from the surface 5 in the formation 6 that comprises a brine-filled cavern 7 of unknown size. Figure 1 depicts the situation wherein the bit 2 has entered the cavity 7. As soon as -the bit has penetrated the cavern, it falls to the cavern floor (due to the weight exerted on the bit) and in this situation any drilling fluid that is pumped down the drill string 1 will be lost in the cavern 7.
Circulation of the drilling fluid is then broken and the drilling operation has to be halted.
The mud pumps are subsequently stopped and the drill string 1 and the bit 2 are lifted from the borehole -to the sur~ace. ~
cemen-ting tube ô is -thereafter lowered through the borehole 4 and lnto -the cavern 7. The -tube 8 is positioned with the lower opening thereof close -to -the floor of -the cavern 7. This situation is shown in Figure 2 of the drawing.
~ low-density cement slurry is subsequently made up and pumped down through the cementing -tube 8 into the cavern 7. The slurry has a density that is appro~imately equal -to the densi-ty 3~32 1~
of the brine present in -the cavern 7. A suitable low-density cement slurry is formed by mixing an aqueous cement slurry with a gas (nitrogen or any other gas suitable for the purpose).
Densities in the range of 1.0 and 1.4 g/cm3 can be obtained by varying the amounts of gas added to the aqueous cement slurry .
Since the difference in density between the low-density cement slurry and the brine present in the cavern is very small or almost negligible, the slurry will not flow out over the floor of the cavern, nor move upwards to float on -the brine, but will remain close to the level at which it is leaving the open lower end of the cemen-ting tube 8. By slowly lifting the tube 8 (see arrow 9 in Figure 3) during the cement-injection period, a column 10 of low-densi-ty cement slurry will be built up in the cavern (see also Figure 4)9 which column finally extends from the floor of the cavi-ty 7 to the ceiling thereof, and partly in the lower end of the borehole 4. As the slurry has a certain natural viscosity and thixotropy, and the density thereof is approximately equal to the density of the brine in the cavity, the column will stand up during setting of the cement.
Prior to setting, the cementing tube 8 has been lifted from the borehole 4. After setting, the column 10 forms a firm bridge between the ceiling and the floor of the cavity. Subsequently, the drill string 1 with drill bi-t 2 attached thereto is lowered in the borehole 4 until the bit 2 rests on top of the solidified column 10. The bit is rotated, whilst a pre-determined weight is exerted on the bit, and drilling mud is circulated through the string 1 and the borehole 4. As a result thereof, the solidified cemen-t column 10 is drilled by the bit 2, thereby extending the borehole 4 through the cement column 10 and into the floor of the cavity 7 (see Figure 5). Drilling is continued until the borehole 4 has reached the desired dep-th. If any more caverns are met during the continued drilling operation, the procedure as described hereinabove with reference to Figures 1-5 o~ the dr~ing may be repeated.
3~3~
It will be appreciated -that since the low-density cement is subs-tantially impermeable after solidification thereof, there will be hardly any loss of drilling fluid from the borehole L~
into the cavern 7. Even if the cement col D would show some permeable areas, these areas will be quickly sealed off by the components in the drilling fluid tha-t are added for sealing purposes.
The use of low-density cement slurries is known per se in the cementation oE casing in formations that fracture easily at low pressures. These cement slurries can be made up in various manners, and any one of these known manners may be used for making up the low-density cement slurry to be used in the method of the present invention. The low density of the slurry may be obtained by adding granular material of low density to the cement slurry (such material e.g. consisting of bentonite, coal, asphalt, fired clay and void-con-taining particles that cannot be wetted by water~
In another type of low-density cement, gas is added to the pumpable cement slurry. ~ereby a so-called foam cement is formed.
Such foam cement is partic~arly suitable due to its ability to have sufficient compressive strength in the solidified state thereof, whilst having an extremely low density in the range of 1.0 to 1.1l g/cm3. ~lrthermore, the density can be easily adjusted to the density of the brine by adjusting the cement slurry/gas ratio thereof. The natural viscosity and thixotropy of the foam cement make them in particular suitable for use in the present method. ~he low-density foam cement slurry is made up by mixing cement as used in drilling operations with water to form a pumpable slurry, and injecting this slurry in combination with a controllable volume oE gas (such as air or nitrogen) in-to the drill string. Surfactants are added for obtaining a stable foam.
Also, reaction rate cont~ollers may be added such as acce~rators for increasing the reaction rate between the cement and the water for spee~ing up the solidification of the foam cement column in the cavity. Surfactants and reaction rate controllers are known per se, and are -therefore not described in detail.
In an alternative manner, gas is generated in the aqueous cement slurry by chemical reaction. Gas-generating chemicals are added -to the cemen-t slurry and the gas is generated by the reaction between the chemicals during the downward travel of -the cement slurry through the drill string to the cavern. The reaction rate and pumping rate are controlled such that a low-density foam cement slurry leaves the lower open end of the cement tube. Suitable surfactants, reaction rate controllers and any other chemical compounds required for ob-taining a stable foam cement may be added.
Also, suitable agents may be added for increasing the natural viscosity and thixotropy of the cement slurry to improve the stabilization of the column in the cavity as long as the cement has not solidified.
It will be appreciated that - in case of emergency - low-density cement slurry may also be passed down into the cavern via the drill string. Special care should then be taken to inject the slurry free from cement lumps that might obstruct the nozzles of the bito It will be appreciated that the cross-sectional area of a cement column to be built up in a cavern to bridge the height thereof should be sufficient to allow the borehole to be drilled therethrough. The cross-sectional area is controlled by the rate of supply of the low-density cement slurry to the cavern and -the ra-te at which the cementing tube is raised during the cement supply period.
In case the cavern has a rela-tively small vertical height at the location of the borehole, introduction of the low-density cement slurry may take place via a s-tationary cement tube -that has the outflow opening thereof approximately half~ay the height o~` the cavern.
The invention will be described by way of example in more detail with reference to Figures 1-5 which all show schematically -2a-~3~3~
a vertical section over a borehole passing -through an underground formation.
Figure 1 shows the situation wherein the borehole is entering a cavern in the forma-tion;
Figure 2 shows a cementing tube having the lower open end thereof close to the floor of the cavern;
Figure 3 shows the initial par-t of the cement injec-tion;
Figure 4 shows the si-tua-tion in which the distance be-tween the borehole and the floor of the cavern is bridged by a column of cement; and Figure 5 shows the borehole extended through the solidified column of cement, and into the floor of the cavern.
The ro-tary drill string 1 and the drill bit 2 shown in the drawing form part of rotary drilling equipment whereof apart from -the string 1 and -the bit 2 only the derrick 3 is shown.
The string 1 and the bit 2 are suspended from the derrick 3 in the hole 4 that extends downwards from the surface 5 in the formation 6 that comprises a brine-filled cavern 7 of unknown size. Figure 1 depicts the situation wherein the bit 2 has entered the cavity 7. As soon as -the bit has penetrated the cavern, it falls to the cavern floor (due to the weight exerted on the bit) and in this situation any drilling fluid that is pumped down the drill string 1 will be lost in the cavern 7.
Circulation of the drilling fluid is then broken and the drilling operation has to be halted.
The mud pumps are subsequently stopped and the drill string 1 and the bit 2 are lifted from the borehole -to the sur~ace. ~
cemen-ting tube ô is -thereafter lowered through the borehole 4 and lnto -the cavern 7. The -tube 8 is positioned with the lower opening thereof close -to -the floor of -the cavern 7. This situation is shown in Figure 2 of the drawing.
~ low-density cement slurry is subsequently made up and pumped down through the cementing -tube 8 into the cavern 7. The slurry has a density that is appro~imately equal -to the densi-ty 3~32 1~
of the brine present in -the cavern 7. A suitable low-density cement slurry is formed by mixing an aqueous cement slurry with a gas (nitrogen or any other gas suitable for the purpose).
Densities in the range of 1.0 and 1.4 g/cm3 can be obtained by varying the amounts of gas added to the aqueous cement slurry .
Since the difference in density between the low-density cement slurry and the brine present in the cavern is very small or almost negligible, the slurry will not flow out over the floor of the cavern, nor move upwards to float on -the brine, but will remain close to the level at which it is leaving the open lower end of the cemen-ting tube 8. By slowly lifting the tube 8 (see arrow 9 in Figure 3) during the cement-injection period, a column 10 of low-densi-ty cement slurry will be built up in the cavern (see also Figure 4)9 which column finally extends from the floor of the cavi-ty 7 to the ceiling thereof, and partly in the lower end of the borehole 4. As the slurry has a certain natural viscosity and thixotropy, and the density thereof is approximately equal to the density of the brine in the cavity, the column will stand up during setting of the cement.
Prior to setting, the cementing tube 8 has been lifted from the borehole 4. After setting, the column 10 forms a firm bridge between the ceiling and the floor of the cavity. Subsequently, the drill string 1 with drill bi-t 2 attached thereto is lowered in the borehole 4 until the bit 2 rests on top of the solidified column 10. The bit is rotated, whilst a pre-determined weight is exerted on the bit, and drilling mud is circulated through the string 1 and the borehole 4. As a result thereof, the solidified cemen-t column 10 is drilled by the bit 2, thereby extending the borehole 4 through the cement column 10 and into the floor of the cavity 7 (see Figure 5). Drilling is continued until the borehole 4 has reached the desired dep-th. If any more caverns are met during the continued drilling operation, the procedure as described hereinabove with reference to Figures 1-5 o~ the dr~ing may be repeated.
3~3~
It will be appreciated -that since the low-density cement is subs-tantially impermeable after solidification thereof, there will be hardly any loss of drilling fluid from the borehole L~
into the cavern 7. Even if the cement col D would show some permeable areas, these areas will be quickly sealed off by the components in the drilling fluid tha-t are added for sealing purposes.
The use of low-density cement slurries is known per se in the cementation oE casing in formations that fracture easily at low pressures. These cement slurries can be made up in various manners, and any one of these known manners may be used for making up the low-density cement slurry to be used in the method of the present invention. The low density of the slurry may be obtained by adding granular material of low density to the cement slurry (such material e.g. consisting of bentonite, coal, asphalt, fired clay and void-con-taining particles that cannot be wetted by water~
In another type of low-density cement, gas is added to the pumpable cement slurry. ~ereby a so-called foam cement is formed.
Such foam cement is partic~arly suitable due to its ability to have sufficient compressive strength in the solidified state thereof, whilst having an extremely low density in the range of 1.0 to 1.1l g/cm3. ~lrthermore, the density can be easily adjusted to the density of the brine by adjusting the cement slurry/gas ratio thereof. The natural viscosity and thixotropy of the foam cement make them in particular suitable for use in the present method. ~he low-density foam cement slurry is made up by mixing cement as used in drilling operations with water to form a pumpable slurry, and injecting this slurry in combination with a controllable volume oE gas (such as air or nitrogen) in-to the drill string. Surfactants are added for obtaining a stable foam.
Also, reaction rate cont~ollers may be added such as acce~rators for increasing the reaction rate between the cement and the water for spee~ing up the solidification of the foam cement column in the cavity. Surfactants and reaction rate controllers are known per se, and are -therefore not described in detail.
In an alternative manner, gas is generated in the aqueous cement slurry by chemical reaction. Gas-generating chemicals are added -to the cemen-t slurry and the gas is generated by the reaction between the chemicals during the downward travel of -the cement slurry through the drill string to the cavern. The reaction rate and pumping rate are controlled such that a low-density foam cement slurry leaves the lower open end of the cement tube. Suitable surfactants, reaction rate controllers and any other chemical compounds required for ob-taining a stable foam cement may be added.
Also, suitable agents may be added for increasing the natural viscosity and thixotropy of the cement slurry to improve the stabilization of the column in the cavity as long as the cement has not solidified.
It will be appreciated that - in case of emergency - low-density cement slurry may also be passed down into the cavern via the drill string. Special care should then be taken to inject the slurry free from cement lumps that might obstruct the nozzles of the bito It will be appreciated that the cross-sectional area of a cement column to be built up in a cavern to bridge the height thereof should be sufficient to allow the borehole to be drilled therethrough. The cross-sectional area is controlled by the rate of supply of the low-density cement slurry to the cavern and -the ra-te at which the cementing tube is raised during the cement supply period.
In case the cavern has a rela-tively small vertical height at the location of the borehole, introduction of the low-density cement slurry may take place via a s-tationary cement tube -that has the outflow opening thereof approximately half~ay the height o~` the cavern.
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Method of drilling a borehole comprising the steps of drilling a borehole through underground formation layers by means of rotary drilling equipment whilst circulating drilling fluid through the drilling equipment and the borehole that is being drilled, interrupting the circulation of drilling fluid when the drilling equipment enters a cavern, injecting a low-density cement slurry into the cavern in a volume sufficient to bridge the distance between the location at which the borehole enters the cavern and the bottom of the cavern, allowing the cement slurry to solidify to a solidified cement, and resuming drilling opera-tions by drilling a hole through the solidified cement and into the bottom of the cavern.
2. The method according to claim 1, wherein the slurry is injected into a cavern through a pipe string which initially has the lower end thereof close to the floor of the cavern, and which is displaced upwards during the injection of the slurry.
3. The method according to claim 2, wherein the pipe string is a cementing tube.
4. The method according to any one of the claims 1-3, wherein if the cavern is partly or entirely filled with a liquid the density of the cement slurry is selected to be approximately equal to that of the liquid.
5. The method according to any one of claims 1-3, wherein the low-density cement slurry is a low-density foam cement slurry.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8000010 | 1980-01-02 | ||
| GB8000010A GB2066874B (en) | 1980-01-02 | 1980-01-02 | Method of driling a borehole through cavernous underground formations |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1183832A true CA1183832A (en) | 1985-03-12 |
Family
ID=10510388
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000366062A Expired CA1183832A (en) | 1980-01-02 | 1980-12-03 | Method of drilling a borehole through cavernous underground formations |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1183832A (en) |
| GB (1) | GB2066874B (en) |
| MY (1) | MY8400382A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DD256429A3 (en) * | 1985-12-18 | 1988-05-11 | Freiberg Brennstoffinst | METHOD AND MEDIUM FOR BLOCKING MINERALIZED AND / OR SAEFERING WATER INFLUENCES |
| US5711375A (en) * | 1996-08-02 | 1998-01-27 | Halliburton Company | Well stabilization tools and methods |
| NO318594B1 (en) * | 1996-08-02 | 2005-04-18 | Halliburton Energy Serv Inc | Well stabilization tool and method of stabilizing unstable zone or formation. |
-
1980
- 1980-01-02 GB GB8000010A patent/GB2066874B/en not_active Expired
- 1980-12-03 CA CA000366062A patent/CA1183832A/en not_active Expired
-
1984
- 1984-12-30 MY MY382/84A patent/MY8400382A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| GB2066874A (en) | 1981-07-15 |
| GB2066874B (en) | 1983-07-27 |
| MY8400382A (en) | 1984-12-31 |
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