US20070044969A1 - Perforating a Well Formation - Google Patents
Perforating a Well Formation Download PDFInfo
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- US20070044969A1 US20070044969A1 US11/162,185 US16218505A US2007044969A1 US 20070044969 A1 US20070044969 A1 US 20070044969A1 US 16218505 A US16218505 A US 16218505A US 2007044969 A1 US2007044969 A1 US 2007044969A1
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- 230000015572 biosynthetic process Effects 0.000 title claims abstract description 78
- 238000000034 method Methods 0.000 claims abstract description 36
- 239000012530 fluid Substances 0.000 claims description 71
- 239000011148 porous material Substances 0.000 claims description 47
- 230000001965 increasing effect Effects 0.000 claims description 16
- 238000007789 sealing Methods 0.000 claims description 6
- 230000035699 permeability Effects 0.000 claims description 5
- 230000002706 hydrostatic effect Effects 0.000 claims description 2
- 230000035515 penetration Effects 0.000 description 12
- 239000011435 rock Substances 0.000 description 10
- 238000004891 communication Methods 0.000 description 7
- 238000010586 diagram Methods 0.000 description 4
- 239000011159 matrix material Substances 0.000 description 4
- 230000008901 benefit Effects 0.000 description 3
- 238000013459 approach Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP 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
- E21B21/08—Controlling or monitoring pressure or flow of drilling fluid, e.g. automatic filling of boreholes, automatic control of bottom pressure
Definitions
- the invention generally relates to perforating a well formation.
- the formation typically is perforated from within a wellbore to enhance fluid communication between the reservoir and the wellbore.
- a perforating gun typically is lowered downhole (on a string, for example) inside a casing (that lines the wellbore) to the region of the formation to be perforated; and subsequently, shaped charges of the perforating gun are fired to pierce the well casing and produce corresponding perforations in the formation. All other things being equal, deeper perforations typically lead to greater well productivity (i.e., more oil or gas produced per unit time per unit of extraction energy).
- a technique that is usable with a subterranean well includes reducing a stress on a formation and while the stress is reduced, perforating the formation.
- FIG. 1 is a multicurve graph illustrating perforation penetration depth versus the effective stress of the formation.
- FIGS. 2, 3 , 4 , 7 and 9 are flow diagrams depicting perforating techniques according to different embodiments of the invention.
- FIG. 5 is a schematic diagram of a well depicting a system to increase pore fluid pressure to reduce the effective stress on the formation according to an embodiment of the invention.
- FIG. 6 is a schematic diagram of a well depicting a multibore technique to increase pore fluid pressure to reduce the effective stress on the formation according to an embodiment of the invention.
- FIG. 8 is schematic diagram of a well depicting a technique that uses thermal energy to reduce the stress on the formation according to an embodiment of the invention.
- the depth (herein called the “perforation penetration depth”) to which a shaped charge penetrates a formation typically varies inversely with the effective stress on the formation rock.
- sv represents the vertical component (i.e., the “overburden stress”) of the total stress
- sH represents the maximum horizontal total stress component
- sh represents the minimum horizontal total stress component
- Subterranean rocks that exhibit high effective stress values tend to reduce a shaped charge's penetration effectiveness.
- the perforation penetration depth into the formation may be improved.
- FIG. 1 depicts a perforation penetration depth 2 into a formation versus an effective stress 4 on the formation for different perforating charges (depicted by the different curves 6 ).
- the effect of the formation rock stress is charge dependent, as illustrated by the different curves 6 .
- increasing the effective stress on the formation from zero to 5,000 pounds per square inch (psi) reduces the perforation penetration depth by ten to forty percent.
- the techniques and systems disclosed herein take advantage of this perforation penetration depth versus effective stress relationship to increase the penetration depth.
- FIG. 1 depicts that reducing the effective stress from 5,000 psi to zero should increase the penetration depth by eleven to sixty-seven percent.
- the perforation penetration depth into the formation may be improved.
- the approach that is described herein reduces the effective stress on the formation by increasing the pore fluid pressure.
- the pore fluid pressure may be increased to a value that causes the effective stress to become negative.
- the rock matrix is in a net tensile state, and the penetration depth may be further enhanced.
- the rock stress state accomplished in the techniques that are described herein may approach the stress on the rock, which is created during a hydraulic fracturing operation.
- the operations described herein may include a “pre-perforation” step in which a few perforations are formed in the formation so that fluid may be injected into these pores to increase the local pore fluid pressure.
- the increase in the local pore fluid pressure reduces the effective stress on the formation so that perforation depth is improved.
- These pre-perforation steps may not be performed in other embodiments of the invention.
- the pre-perforation steps may not be performed for an open hole completion, in accordance with some embodiments of the invention.
- a technique 10 may be used for purposes of increasing the perforation penetration depth.
- the effective stress is reduced (block 12 ) on a well formation; and while the effective stress is reduced, the formation is perforated, as depicted in block 14 .
- the reduction of the effective stress on the well formation may be temporary in nature. For example, if the nearby pore fluid pressure is increased by increasing fluid pressure inside the wellbore, the time in which the nearby pore fluid pressure is elevated may depend on the permeability of the formation.
- the initial pressurization establishes a pressure gradient between the nearby pore fluid pressure and the far field pore fluid pressure; and the permeability of the formation establishes the time for the nearby pore fluid pressure to once again equal the far field pore fluid pressure.
- the perforating operation is performed during the time of reduced effective stress, a time in which the nearby pore fluid pressure comes close to or even exceeds the mean total stress of the formation.
- FIG. 3 depicts a technique 20 in accordance with an embodiment of the invention.
- the technique 20 includes reducing (block 22 ) the effective stress on a formation caused by the difference between the mean total stress and the pore fluid pressure by increasing the pore fluid pressure. While the pore fluid pressure is increased, the formation is perforated, as depicted in block 24 .
- FIG. 4 depicts a technique 30 in which preliminary perforations are created (block 34 ) inside an interval of a wellbore to establish communication between a reservoir and the wellbore. This interval is subsequently sealed off, as depicted in block 36 . Next, pressure is applied to the wellbore inside the interval to increase the pore fluid pressure, as depicted in block 38 . Finally, pursuant to the technique 30 , the formation is perforated (block 40 ) in the interval while the fluid pore pressure remains elevated.
- fluid may be pumped from the surface of the well into the interval until the desired pressure (a pressure near the mean total stress, for example) is obtained.
- the fluid flow from the surface then stops, which means the pressure inside the interval gradually reduces due to the permeability of the formation.
- fluid may be continually pumped into the interval to negate the fluid and pressure loss inside the interval and thus, maintain the constant fluid pressure inside the interval nearby.
- an exemplary system 50 to perform at least a portion of the technique 30 may include a string 60 that extends into a wellbore 54 .
- the wellbore 54 may be lined by a casing string 56 .
- the technique that is described herein may be equally applied to uncased wellbores, in other embodiments of the invention.
- the string 60 may include a selectable perforating gun (not depicted in FIG. 5 ), which may be used to from preliminary perforations 72 in a formation 51 from which production is to occur.
- the preliminary perforations 72 may be formed by a perforating gun that is lowered downhole in a prior run.
- the perforations 72 may be pre-existing as part of an older well.
- the preliminary perforations 72 establish fluid communication flow paths 74 into the formation 51 .
- fluid communication is established between the wellbore 54 , through the casing string 56 and into the formation 51 .
- the string 60 includes at least one device to form an annular seal, such as a packer 64 , for example.
- the packer 64 when set, forms the upper boundary of an isolated interval 80 of the well.
- the lower end of the interval 80 may be formed by a sealing device, such as a bridge plug 90 , for example.
- the bridge plug 90 may be set at the lower end of the interval 80 in a prior run.
- the bridge plug 90 may be set in place by a setting tool that is disposed at the lower end of the string 60 .
- the bridge plug 90 may be replaced by a packer that is part of the string 60 . Therefore, many different seal arrangements may be used to form the isolated zone 90 in the various embodiments of the invention.
- the upper packer 64 is set to establish the isolated interval 80 after the formation of the preliminary perforations 72 .
- fluid may then be pumped from the surface of the well through the central passageway of the string 60 .
- the pumped fluid exits the central passageway of the string 60 through radial ports 70 (for example) into the isolated interval 80 .
- the region of the well inside the isolated interval 80 is pressurized.
- the resultant fluid pressure is communicated into the formation 51 to increase the nearby pore fluid pressure. This increase in nearby pore fluid pressure, in turn, reduces the effective stress on the formation 51 near the wellbore 54 , i.e., the portion of the formation 51 in which perforating is to occur.
- shaped charges of a perforating gun 84 are fired to create corresponding extended depth perforations 86 into the formation 51 .
- the perforating gun 84 may be fired by any of a number of different mechanisms, such as tubing conveyed pressure, an inductive coil, an electrical wire, etc.
- the extended depth perforations 86 due to the reduced effective stress, extend deeper into the formation 51 than the preliminary perforations 72 .
- the firing of the shaped charges of the perforating gun 84 occurs during the time interval in which the nearby pore fluid pressure is elevated (near or exceeding the mean total stress, for example).
- FIG. 6 depicts a system 100 to increase the nearby fluid pore pressure in a formation 104 in accordance with an embodiment of the invention.
- the system 100 does not use an increased or high wellbore pressure inside a wellbore 112 (a lateral wellbore in this example) in which extended depth perforations 170 are formed.
- an adjacent wellbore such as an adjacent lateral wellbore 110 , is used as an injector to pressure up the reservoir and increase the local pore fluid pressure near the wellbore 112 .
- the wellbores 110 and 112 share a common vertical wellbore 102 .
- the arrangement that is depicted in FIG. 6 is for purposes of example only.
- the wellbores 110 and 112 may be located in entirely different wells that, although in hydraulic communication through the formation, do not share a common bore or section.
- a string 120 may be inserted into the wellbore 110 for purposes of pressurizing the reservoir and increasing the pore fluid pressure near the wellbore 112 .
- the string 120 may include, for example, a sealing element, such as a packer 122 , for purposes of forming one end of an isolated interval 114 . Another end of the isolated interval 114 may be formed by another seal 124 .
- the seal 122 may be a packer that is set to form an annular seal between the string 120 and the wall of the wellbore 110 ; and the seal 124 may be a bridge plug.
- the bridge plug may be run in separately from the string 120 ; or alternatively, the bridge plug may be run and set by the string 120 .
- radial ports 130 of the string 120 which are located inside the interval 114 , may be used to communicate pumped well fluid from the well surface for purposes of pressurizing the isolation interval 114 and thus, pressurizing the formation near the wellbore 112 .
- one or more preliminary perforations 129 may be formed in the interval 114 to enhance fluid communication between the reservoir and the isolated interval 114 .
- the pressurization of the fluid inside the interval 114 increases the nearby pore fluid pressure of the wellbore 112 .
- shaped charges of a perforating gun 160 may be fired to form extended depth perforations 170 that extend into the formation 104 from the wellbore 112 prior to the pressurization of the interval 114 .
- the perforating gun 160 may be part of another string 150 that is lowered downhole inside the wellbore 102 and inside the lateral wellbore 112 .
- a sealing element 154 such as a packer, may form a seal between the string 150 and the interior wall of the wellbore 112 .
- the strings 120 and 150 are run inside the well.
- the preliminary perforations 129 may be subsequently formed in the wellbore 110 ; or, alternatively, the preliminary perforations 129 may be formed prior to the running of the string 120 into the well.
- the string 120 is then used to form the sealed interval 114 so that fluid pressure may be increased inside the interval 114 to increase the pore fluid pressure near the wellbore 112 . While the pore fluid pressure near the wellbore 112 is elevated (near or exceeding the mean total stress, for example), the perforating gun 160 fires its shaped charges to create the extended depth perforations 170 .
- a technique 180 includes creating preliminary perforations inside an interval of a first wellbore to establish communication between a reservoir and the first wellbore, as depicted in block 184 .
- the interval is sealed off, as depicted in block 186 .
- Pressure is then applied to the first wellbore inside the interval to increase the pore fluid pressure near another second wellbore, as depicted in block 188 .
- the formation is perforated from the second wellbore while the pore fluid pressure remains elevated, as depicted in block 190 .
- annular seal may not be formed in other embodiments of the invention.
- the wellbore may be pressurized using a heavier fluid so that the hydrostatic head of the fluid may be relied on rather than an annular seal to isolate the region of the well in which the perforating occurs.
- a wellbore system 200 includes a string 210 that, in turn, includes one or more heating elements 220 for purposes of altering a pressure balance between the formation rock matrix and the nearby pore fluid. More specifically, the string 210 includes a perforating gun 214 that is lowered downhole inside a wellbore 202 (lined by a casing string 104 in this example) to a position in which extended depth perforations 230 are to be formed.
- the heating elements 220 may be integrated among the perforating charges of the perforating gun 214 , above the perforating gun 214 or below the perforating gun 214 , depending on the particular embodiment of the invention.
- the string 210 may include a sealing element, such as a packer 212 , to form a seal between the outside of the string 210 and the casing 204 .
- the perforating gun 214 is lowered downhole on the string 210 until the perforating gun 214 reaches the proper position. Afterwards, the packer 212 is set and the heater elements 220 is activated to heat up the formation to alter the pressure balance between the rock matrix and the pore fluid. After the pressure balance has been significantly altered, the shaped charges of the perforating gun 214 may then be fired to form the extended depth perforations 230 .
- a technique 250 includes applying (block 252 ) thermal energy inside an interval of a wellbore to alter the pressure balance between a formation rock matrix and pore fluid due to differences in thermal expansion coefficients.
- the formation is perforated (block 256 ) in the interval while the pressure balance remains altered.
- thermal energy assumes that the thermal expansion coefficient of the fluid is greater than the thermal expansion coefficient of the formation. By knowing these thermal expansion coefficients, the temperature needed to be achieved may be determined. Furthermore, knowledge of the relevant heat capacities and heat transfer rates enables determination of the energy and power requirements, respectively.
- the thermal energy may be applied using other arrangements, in other embodiments of the invention.
- the string 210 instead of containing the heater elements 220 , may instead communicate a heated fluid from the surface into an isolated zone to be perforated.
- a chemical reaction may be used to generate the thermal energy.
Abstract
A technique that is usable with a subterranean well includes reducing a stress on a formation in the well. The formation is perforated while the stress is reduced.
Description
- The invention generally relates to perforating a well formation.
- For purposes of producing well fluid from a formation, the formation typically is perforated from within a wellbore to enhance fluid communication between the reservoir and the wellbore. In the perforating operation, a perforating gun typically is lowered downhole (on a string, for example) inside a casing (that lines the wellbore) to the region of the formation to be perforated; and subsequently, shaped charges of the perforating gun are fired to pierce the well casing and produce corresponding perforations in the formation. All other things being equal, deeper perforations typically lead to greater well productivity (i.e., more oil or gas produced per unit time per unit of extraction energy).
- In an embodiment of the invention, a technique that is usable with a subterranean well includes reducing a stress on a formation and while the stress is reduced, perforating the formation.
- Advantages and other features of the invention will become apparent from the following description, drawing and claims.
-
FIG. 1 is a multicurve graph illustrating perforation penetration depth versus the effective stress of the formation. -
FIGS. 2, 3 , 4, 7 and 9 are flow diagrams depicting perforating techniques according to different embodiments of the invention. -
FIG. 5 is a schematic diagram of a well depicting a system to increase pore fluid pressure to reduce the effective stress on the formation according to an embodiment of the invention. -
FIG. 6 is a schematic diagram of a well depicting a multibore technique to increase pore fluid pressure to reduce the effective stress on the formation according to an embodiment of the invention. -
FIG. 8 is schematic diagram of a well depicting a technique that uses thermal energy to reduce the stress on the formation according to an embodiment of the invention. - The depth (herein called the “perforation penetration depth”) to which a shaped charge penetrates a formation typically varies inversely with the effective stress on the formation rock.
- The effective stress is the difference between the mean total stress on the reservoir rock and some multiple of the pore fluid pressure (the multiple generally being one, but perhaps slightly less than one), where the mean total stress is the average of the vertical and two horizontal components of total stress. More specifically, the mean total stress (called “sm”) may be mathematically described as follows:
- where “sv” represents the vertical component (i.e., the “overburden stress”) of the total stress, “sH” represents the maximum horizontal total stress component and “sh” represents the minimum horizontal total stress component.
- The effective stress (called “s_eff”) may be mathematically described as follows:
s — eff=sm−a·Pp Equation 2 - where “Pp” represents the pore pressure, and “a” represents Biot's constant which falls in the range of zero to one (for many cases “a” equals one).
- Subterranean rocks that exhibit high effective stress values tend to reduce a shaped charge's penetration effectiveness. Thus, by decreasing the formation's mean total stress and/or increasing its pore fluid pressure (i.e., reducing the effective stress), the perforation penetration depth into the formation may be improved.
-
FIG. 1 depicts aperforation penetration depth 2 into a formation versus aneffective stress 4 on the formation for different perforating charges (depicted by the different curves 6). The effect of the formation rock stress is charge dependent, as illustrated by thedifferent curves 6. However, as depicted inFIG. 1 , increasing the effective stress on the formation from zero to 5,000 pounds per square inch (psi) reduces the perforation penetration depth by ten to forty percent. The techniques and systems disclosed herein take advantage of this perforation penetration depth versus effective stress relationship to increase the penetration depth. Thus,FIG. 1 depicts that reducing the effective stress from 5,000 psi to zero should increase the penetration depth by eleven to sixty-seven percent. - Therefore, by decreasing the formation's mean total stress and/or increasing its pore fluid pressure (i.e., reducing the effective stress), the perforation penetration depth into the formation may be improved. In accordance with some embodiments of the invention, the approach that is described herein reduces the effective stress on the formation by increasing the pore fluid pressure. In the limit, the pore fluid pressure may be increased to a value that causes the effective stress to become negative. In this state, the rock matrix is in a net tensile state, and the penetration depth may be further enhanced. Thus, the rock stress state accomplished in the techniques that are described herein may approach the stress on the rock, which is created during a hydraulic fracturing operation.
- In accordance with some embodiments of the invention, the operations described herein may include a “pre-perforation” step in which a few perforations are formed in the formation so that fluid may be injected into these pores to increase the local pore fluid pressure. The increase in the local pore fluid pressure, in turn, reduces the effective stress on the formation so that perforation depth is improved. These pre-perforation steps may not be performed in other embodiments of the invention. For example, the pre-perforation steps may not be performed for an open hole completion, in accordance with some embodiments of the invention.
- Referring to
FIG. 2 , as a more specific example, atechnique 10 may be used for purposes of increasing the perforation penetration depth. Pursuant to thetechnique 10, the effective stress is reduced (block 12) on a well formation; and while the effective stress is reduced, the formation is perforated, as depicted inblock 14. The reduction of the effective stress on the well formation may be temporary in nature. For example, if the nearby pore fluid pressure is increased by increasing fluid pressure inside the wellbore, the time in which the nearby pore fluid pressure is elevated may depend on the permeability of the formation. Thus, the initial pressurization establishes a pressure gradient between the nearby pore fluid pressure and the far field pore fluid pressure; and the permeability of the formation establishes the time for the nearby pore fluid pressure to once again equal the far field pore fluid pressure. The perforating operation is performed during the time of reduced effective stress, a time in which the nearby pore fluid pressure comes close to or even exceeds the mean total stress of the formation. - As a more specific example,
FIG. 3 depicts atechnique 20 in accordance with an embodiment of the invention. Thetechnique 20 includes reducing (block 22) the effective stress on a formation caused by the difference between the mean total stress and the pore fluid pressure by increasing the pore fluid pressure. While the pore fluid pressure is increased, the formation is perforated, as depicted inblock 24. - As a more specific example of a way to increase pore fluid pressure,
FIG. 4 depicts atechnique 30 in which preliminary perforations are created (block 34) inside an interval of a wellbore to establish communication between a reservoir and the wellbore. This interval is subsequently sealed off, as depicted inblock 36. Next, pressure is applied to the wellbore inside the interval to increase the pore fluid pressure, as depicted inblock 38. Finally, pursuant to thetechnique 30, the formation is perforated (block 40) in the interval while the fluid pore pressure remains elevated. - It is noted that many different techniques may be used to increase the pressure inside the interval. For example, in some embodiments of the invention, fluid may be pumped from the surface of the well into the interval until the desired pressure (a pressure near the mean total stress, for example) is obtained. The fluid flow from the surface then stops, which means the pressure inside the interval gradually reduces due to the permeability of the formation. However, in other embodiments of the invention, fluid may be continually pumped into the interval to negate the fluid and pressure loss inside the interval and thus, maintain the constant fluid pressure inside the interval nearby. Thus, many variations are possible and are within the scope of the appended claims.
- Referring to
FIG. 5 , anexemplary system 50 to perform at least a portion of thetechnique 30 may include astring 60 that extends into awellbore 54. As depicted inFIG. 5 , thewellbore 54 may be lined by acasing string 56. However, the technique that is described herein may be equally applied to uncased wellbores, in other embodiments of the invention. - The
string 60 may include a selectable perforating gun (not depicted inFIG. 5 ), which may be used to frompreliminary perforations 72 in aformation 51 from which production is to occur. However, in other embodiments of the invention, thepreliminary perforations 72 may be formed by a perforating gun that is lowered downhole in a prior run. Alternatively, in other embodiments of the invention, theperforations 72 may be pre-existing as part of an older well. Thus, many variations are possible and are within the scope of the appended claims. - The
preliminary perforations 72 establish fluidcommunication flow paths 74 into theformation 51. Thus, by the formation of thepreliminary perforations 72, fluid communication is established between the wellbore 54, through thecasing string 56 and into theformation 51. - The
string 60 includes at least one device to form an annular seal, such as apacker 64, for example. In some embodiments of the invention, thepacker 64, when set, forms the upper boundary of anisolated interval 80 of the well. The lower end of theinterval 80, in turn, may be formed by a sealing device, such as abridge plug 90, for example. As an example, thebridge plug 90 may be set at the lower end of theinterval 80 in a prior run. However, in other embodiments of the invention, thebridge plug 90 may be set in place by a setting tool that is disposed at the lower end of thestring 60. Alternatively, thebridge plug 90 may be replaced by a packer that is part of thestring 60. Therefore, many different seal arrangements may be used to form theisolated zone 90 in the various embodiments of the invention. - Thus, in some embodiments of the invention, the
upper packer 64 is set to establish theisolated interval 80 after the formation of thepreliminary perforations 72. After theisolated interval 80 is created, fluid may then be pumped from the surface of the well through the central passageway of thestring 60. The pumped fluid exits the central passageway of thestring 60 through radial ports 70 (for example) into theisolated interval 80. Thus, by pumping fluid from the surface of the well, the region of the well inside theisolated interval 80 is pressurized. The resultant fluid pressure is communicated into theformation 51 to increase the nearby pore fluid pressure. This increase in nearby pore fluid pressure, in turn, reduces the effective stress on theformation 51 near thewellbore 54, i.e., the portion of theformation 51 in which perforating is to occur. - After the increase in fluid pressure, shaped charges of a perforating gun 84 (of the string 60) are fired to create corresponding
extended depth perforations 86 into theformation 51. Depending on the particular embodiment of the invention, the perforatinggun 84 may be fired by any of a number of different mechanisms, such as tubing conveyed pressure, an inductive coil, an electrical wire, etc. As depicted inFIG. 5 , theextended depth perforations 86, due to the reduced effective stress, extend deeper into theformation 51 than thepreliminary perforations 72. - As set forth above, the firing of the shaped charges of the perforating
gun 84 occurs during the time interval in which the nearby pore fluid pressure is elevated (near or exceeding the mean total stress, for example). - The nearby pore fluid pressure may be increased using other techniques, in accordance with other embodiments of the invention. For example,
FIG. 6 depicts asystem 100 to increase the nearby fluid pore pressure in aformation 104 in accordance with an embodiment of the invention. Unlike thesystem 50 that is depicted inFIG. 5 , thesystem 100 does not use an increased or high wellbore pressure inside a wellbore 112 (a lateral wellbore in this example) in which extendeddepth perforations 170 are formed. Instead of pressurizing thewellbore 112, an adjacent wellbore, such as an adjacentlateral wellbore 110, is used as an injector to pressure up the reservoir and increase the local pore fluid pressure near thewellbore 112. - More specifically, in accordance with some embodiments of the invention, the
wellbores vertical wellbore 102. However, it is noted that the arrangement that is depicted inFIG. 6 is for purposes of example only. Thus, in other embodiments of the invention, thewellbores - Referring to the specific arrangement that is depicted in
FIG. 6 , astring 120 may be inserted into thewellbore 110 for purposes of pressurizing the reservoir and increasing the pore fluid pressure near thewellbore 112. Thestring 120 may include, for example, a sealing element, such as apacker 122, for purposes of forming one end of anisolated interval 114. Another end of theisolated interval 114 may be formed by anotherseal 124. As examples, theseal 122 may be a packer that is set to form an annular seal between thestring 120 and the wall of thewellbore 110; and theseal 124 may be a bridge plug. Furthermore, in some embodiments of the invention, the bridge plug may be run in separately from thestring 120; or alternatively, the bridge plug may be run and set by thestring 120. Thus, many variations are possible and are within the scope of the appended claims. - After the
seals isolated interval 114,radial ports 130 of thestring 120, which are located inside theinterval 114, may be used to communicate pumped well fluid from the well surface for purposes of pressurizing theisolation interval 114 and thus, pressurizing the formation near thewellbore 112. Prior to this fluid pressurization of theinterval 114, one or morepreliminary perforations 129 may be formed in theinterval 114 to enhance fluid communication between the reservoir and theisolated interval 114. - The pressurization of the fluid inside the
interval 114 increases the nearby pore fluid pressure of thewellbore 112. During this time interval of elevated pore fluid pressure, shaped charges of a perforating gun 160 (located in the wellbore 112) may be fired to form extendeddepth perforations 170 that extend into theformation 104 from thewellbore 112 prior to the pressurization of theinterval 114. As an example, the perforatinggun 160 may be part of anotherstring 150 that is lowered downhole inside thewellbore 102 and inside thelateral wellbore 112. In some embodiments of the invention, a sealingelement 154, such as a packer, may form a seal between thestring 150 and the interior wall of thewellbore 112. - To summarize the technique used to form the
extended depth perforations 170, thestrings preliminary perforations 129 may be subsequently formed in thewellbore 110; or, alternatively, thepreliminary perforations 129 may be formed prior to the running of thestring 120 into the well. Thestring 120 is then used to form the sealedinterval 114 so that fluid pressure may be increased inside theinterval 114 to increase the pore fluid pressure near thewellbore 112. While the pore fluid pressure near thewellbore 112 is elevated (near or exceeding the mean total stress, for example), the perforatinggun 160 fires its shaped charges to create theextended depth perforations 170. - Referring to
FIG. 7 , to generalize, in accordance with an embodiment of the invention, atechnique 180 includes creating preliminary perforations inside an interval of a first wellbore to establish communication between a reservoir and the first wellbore, as depicted inblock 184. Next, the interval is sealed off, as depicted inblock 186. Pressure is then applied to the first wellbore inside the interval to increase the pore fluid pressure near another second wellbore, as depicted inblock 188. Subsequently, the formation is perforated from the second wellbore while the pore fluid pressure remains elevated, as depicted inblock 190. - It is noted that an annular seal (to form the above-described isolated interval) may not be formed in other embodiments of the invention. For example, in accordance with some embodiments of the invention, the wellbore may be pressurized using a heavier fluid so that the hydrostatic head of the fluid may be relied on rather than an annular seal to isolate the region of the well in which the perforating occurs.
- Other techniques may be used to reduce the effective stress on the formation, in other embodiments of the invention. For example, referring to
FIG. 8 , in accordance with some embodiments of the invention, awellbore system 200 includes astring 210 that, in turn, includes one ormore heating elements 220 for purposes of altering a pressure balance between the formation rock matrix and the nearby pore fluid. More specifically, thestring 210 includes a perforatinggun 214 that is lowered downhole inside a wellbore 202 (lined by acasing string 104 in this example) to a position in which extendeddepth perforations 230 are to be formed. Theheating elements 220 may be integrated among the perforating charges of the perforatinggun 214, above the perforatinggun 214 or below the perforatinggun 214, depending on the particular embodiment of the invention. Furthermore, thestring 210 may include a sealing element, such as apacker 212, to form a seal between the outside of thestring 210 and thecasing 204. - Therefore, when the
extended depth perforations 230 are to be formed, the perforatinggun 214 is lowered downhole on thestring 210 until the perforatinggun 214 reaches the proper position. Afterwards, thepacker 212 is set and theheater elements 220 is activated to heat up the formation to alter the pressure balance between the rock matrix and the pore fluid. After the pressure balance has been significantly altered, the shaped charges of the perforatinggun 214 may then be fired to form theextended depth perforations 230. - Referring to
FIG. 9 , thus, in accordance with some embodiments of the invention, atechnique 250 includes applying (block 252) thermal energy inside an interval of a wellbore to alter the pressure balance between a formation rock matrix and pore fluid due to differences in thermal expansion coefficients. Next, the formation is perforated (block 256) in the interval while the pressure balance remains altered. - The above-described application of thermal energy assumes that the thermal expansion coefficient of the fluid is greater than the thermal expansion coefficient of the formation. By knowing these thermal expansion coefficients, the temperature needed to be achieved may be determined. Furthermore, knowledge of the relevant heat capacities and heat transfer rates enables determination of the energy and power requirements, respectively.
- The thermal energy may be applied using other arrangements, in other embodiments of the invention. For example, the
string 210, instead of containing theheater elements 220, may instead communicate a heated fluid from the surface into an isolated zone to be perforated. Alternatively, a chemical reaction may be used to generate the thermal energy. Thus, many variations are possible and are within the scope of the appended claims. - Other techniques and systems to reduce the effective stress on the formation during perforating to extend perforation depth are possible and are within the scope of the appended claims.
- While the present invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.
Claims (24)
1. A method usable with a subterranean well, comprising:
reducing a stress on a formation in the well; and
while the stress is reduced, perforating the formation.
2. The method of claim 1 , wherein the stress comprises an effective stress on the formation.
3. The method of claim 1 , wherein the stress is caused by a difference between a mean total stress of the formation and a pore fluid pressure of the formation.
4. The method of claim 1 , wherein the act of reducing comprises increasing a pore fluid pressure.
5. The method of claim 4 , wherein the act of reducing further comprises temporarily increasing the pore fluid pressure during a time interval, wherein the act of perforating occurs during the time interval.
6. The method of claim 5 , wherein the time interval is a function of a permeability of the formation.
7. The method of claim 1 , wherein the act of reducing comprises:
sealing off an interval of the well containing perforations; and
pressurizing the interval.
8. The method of claim 7 , further comprising:
perforating the formation to form the perforations.
9. The method of claim 1 , further comprising:
forming perforations in the formation prior to the act of perforating.
10. The method of claim 1 , wherein the act of reducing comprises:
pressuring the well with a heavy fluid to form a hydrostatic head to isolate a region of the well.
11. The method of claim 1 , wherein the perforating occurs in a first wellbore and the act of reducing is performed at least partially in another second wellbore.
12. The method of claim 11 , wherein the act of reducing further comprises pressurizing the second wellbore to reduce the stress of the formation near the first wellbore.
13. The method of claim 1 , wherein the act of reducing comprises applying thermal energy to the formation.
14. The method of claim 13 , wherein the act of applying thermal energy alters a pressure between the formation and the pore fluid.
15. A system usable with a subterranean well, comprising:
a first tool to reduce a stress on a formation; and
a perforating tool to, while the stress is reduced, perforate the formation.
16. The system of claim 15 , wherein the stress comprises an effective stress on the formation.
17. The system of claim 15 , wherein the stress is caused by a difference between a mean total stress of the formation and a pore fluid pressure of the formation.
18. The system of claim 15 , wherein the first tool is used to increase a pore fluid pressure on the formation.
19. The system of claim 18 , wherein the first tool is used temporarily increase the pore fluid pressure during a time interval so that the perforating tool may form the perforations in the formation during the time interval.
20. The system of claim 19 , wherein the time interval is a function of a permeability of the formation.
21. The system of claim 15 , wherein the first tool and the perforating tool are part of a string, the string further comprising a sealing device to seal off an interval of the well containing the perforations so that the interval may be pressurized.
22. The system of claim 21 , wherein the perforating tool is adapted to form the perforations during the existence of the seal.
23. The system of claim 15 , wherein the first tool comprises a heater element.
24. The system of claim 15 , wherein the first tool and the perforating tool are part of a string.
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/162,185 US20070044969A1 (en) | 2005-08-31 | 2005-08-31 | Perforating a Well Formation |
CA2541407A CA2541407C (en) | 2005-08-31 | 2006-03-30 | Perforating a well formation |
RU2006113450/03A RU2416022C2 (en) | 2005-08-31 | 2006-04-20 | Procedures and system for perforating reservoir in underground well |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/162,185 US20070044969A1 (en) | 2005-08-31 | 2005-08-31 | Perforating a Well Formation |
Publications (1)
Publication Number | Publication Date |
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US20070044969A1 true US20070044969A1 (en) | 2007-03-01 |
Family
ID=37802433
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/162,185 Abandoned US20070044969A1 (en) | 2005-08-31 | 2005-08-31 | Perforating a Well Formation |
Country Status (3)
Country | Link |
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US (1) | US20070044969A1 (en) |
CA (1) | CA2541407C (en) |
RU (1) | RU2416022C2 (en) |
Cited By (2)
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WO2020180350A3 (en) * | 2019-03-04 | 2020-10-15 | Halliburton Energy Services, Inc. | Wellbore perforation analysis and design system |
US11466541B2 (en) * | 2019-01-29 | 2022-10-11 | Aarbakke Innovation As | Heat transfer prevention method for wellbore heating system |
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Also Published As
Publication number | Publication date |
---|---|
CA2541407C (en) | 2011-07-12 |
RU2416022C2 (en) | 2011-04-10 |
RU2006113450A (en) | 2007-10-27 |
CA2541407A1 (en) | 2007-02-28 |
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Owner name: SCHLUMBERGER TECHNOLOGY CORPORATION, TEXAS Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:GROVE, BRENDEN M.;REEL/FRAME:016497/0938 Effective date: 20050831 |
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