Methods and apparatus for borehole measurement of formation stress
First Claim
1. A system for obtaining measurements in a borehole (102) from which in-situ stress of an underground formation can be estimated, wherein the system comprises a sonde (100) and an electric wireline cable (104) connected to the sonde for conveying the sonde in the borehole, and wherein the sonde comprises:
- a. an accumulator module (130) having a reservoir (210) for storing hydraulic energy, a flow line (202), and a controllable valve (218) coupled to the reservoir and to the flow line for controlling transfer of hydraulic energy between the reservoir and the flow line;
b. a stress/rheology module (120) coupled to the accumulator module and having;
i. force applying means (312) coupled to the flow line for receiving hydraulic energy from the flow line and applying to the formation at a controlled rate a force opposing in-situ stress in the formation;
ii. pressure sensing means (344) for monitoring a pressure related to the force applied to the formation by the force applying means; and
iii. an acoustic sensor (342) for detecting acoustic emissions in the borehole as the force is applied to the formation;
c. force reducing means (314) coupled to the force applying means for controllably reducing the force applied to the formation; and
d. a flow control means (122,
324) in hydraulic communication with the borehole for withdrawing formation fluid from the formation at a controlled rate for pressure draw-down pre-test.
1 Assignment
0 Petitions
Accused Products
Abstract
A modular sonde may be configured in various ways for measurements in open or cased boreholes. The sonde is conveyed on an electric wireline with or without a coiled tubing for conveying hydraulic energy from the surface. Modules common to the configurations include telemetry electronics, orientation, hydraulic energy accumulator, fluid chambers, hydraulic power, pumpout, and flow control. Each configuration has a stress/rheology module suited to the borehole situation. An open-hole sonde configuration has a stress/rheology module with an instrumented, inflatable packer module, an orienting module, and a probe module. A second open-hole sonde configuration has a stress/rheology module with an instrumented straddlepacker assembly. A cased-hole sonde configuration has a gunblock assembly, a gunblock orienting module hydraulics for formation pre-test and hydraulics for stressing the formation to obtain data related to formation stress characteristics. A second cased-hole sonde configuration has a straddle-packer assembly, a casing perforation device in the straddle interval, and hydraulics for stressing the formation to obtain data related to formation stress characteristics.
152 Citations
37 Claims
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1. A system for obtaining measurements in a borehole (102) from which in-situ stress of an underground formation can be estimated, wherein the system comprises a sonde (100) and an electric wireline cable (104) connected to the sonde for conveying the sonde in the borehole, and wherein the sonde comprises:
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a. an accumulator module (130) having a reservoir (210) for storing hydraulic energy, a flow line (202), and a controllable valve (218) coupled to the reservoir and to the flow line for controlling transfer of hydraulic energy between the reservoir and the flow line; b. a stress/rheology module (120) coupled to the accumulator module and having; i. force applying means (312) coupled to the flow line for receiving hydraulic energy from the flow line and applying to the formation at a controlled rate a force opposing in-situ stress in the formation; ii. pressure sensing means (344) for monitoring a pressure related to the force applied to the formation by the force applying means; and iii. an acoustic sensor (342) for detecting acoustic emissions in the borehole as the force is applied to the formation; c. force reducing means (314) coupled to the force applying means for controllably reducing the force applied to the formation; and d. a flow control means (122,
324) in hydraulic communication with the borehole for withdrawing formation fluid from the formation at a controlled rate for pressure draw-down pre-test. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method of determining stress in a bed of an underground formation having multiple lithological beds traversed by a borehole, comprising the steps of:
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a. positioning an inflatable packer in a location of the borehole passing through a predetermined bed; b. controllably pressurizing the packer in a sequence of pressurization steps while monitoring a plurality of parameters, wherein the parameters include packer inflation pressure (P), radial displacement (U) of the borehole wall at multiple locations about an axis passing through the packer, packer inflation volume (V), and acoustic emissions (AE) in the vicinity of the packer, and wherein the sequence of pressurization steps includes; i. inflating the packer until the packer contacts the formation surrounding the borehole as indicated by at least one of the monitored parameters; ii. inflating and deflating the packer a plurality of times in a series of cycles in which the packer inflation pressure is progressively increased and is maintained below the formation breakdown pressure (1 Pb), to thereby apply a series of load-unload cycles useful in determining elasticity of the formation bed; iii. increasing packer inflation pressure (P) until formation fracture is indicted by a decrease in the rate (dP/dt) of increase of packer inflation pressure and an increase in the rate (dV/dt) of packer inflation volume as packer inflation pressure (P) approaches a first formation breakdown pressure (1 Pb); iv. maintaining packer inflation pressure (P) at the first formation breakdown pressure (1 Pb) for a time interval (t3-t4); v. reducing packer inflation pressure (P) below the first formation breakdown pressure (1 Pb) to allow the formation fracture to close; vi. increasing packer inflation pressure (P) until fracture re-opening is indicated by radial displacement (U) of the borehole wall and by packer inflation volume (V) as packer inflation pressure (P) approaches a fracture re-opening pressure (1 Pro); and vii. increasing packer inflation pressure (P) beyond the fracture re-opening pressure (1 Pro) to extend the first fracture, extension of the fracture being indicated by an increase of acoustic emissions (AE) and increase of packer inflation volume (V); and c. determining magnitude of least principal stress (Sh) of the formation from the monitored parameters. - View Dependent Claims (18, 19, 20, 21, 22, 23)
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24. A method of determining stress in a bed of an underground formation having multiple lithological beds traversed by a borehole, comprising the steps of:
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a. positioning an inflatable first packer of a straddle-packer pair in a location of the borehole passing through a predetermined bed; b. increasing inflation pressure (P) of the first packer to induce a formation fracture while monitoring a plurality of parameters including inflation pressure (P) of the first packer, radial displacement (U) of the borehole wall at multiple locations about an axis passing through the packer, inflation volume (V) of the first packer, and acoustic emissions (AE) in the vicinity of the first packer, the formation fracture being indicated by the monitored parameters as inflation pressure (P) of the first packer approaches a formation breakdown pressure (1 Pb); c. deflating the first packer to allow the straddle-packer pair to be displaced in the borehole; d. displacing the straddle-packer pair in the borehole to position a straddle interval of the straddle-packer pair over the predetermined bed; e. inflating the first packer and an inflatable second packer of the straddle-packer pair to isolate the predetermined bed; f. controllably pressurizing the straddle interval in a sequence of pressurization steps while monitoring a plurality of parameters including radial displacement (U) of the borehole wall in the vicinity of the straddle interval, fluid pressure (P2) within the straddle interval, volume of fluid injected into the straddle interval, and acoustic emissions in the vicinity of the straddle interval, wherein the sequence of pressurization steps includes; i. injecting a controlled quantity of fluid into the straddle interval at a controlled rate to propagate the fracture induced in step b., the quantity and injection rate of the fluid being controlled so as to limit the diameter of the fracture to approximately the thickness of the predetermined bed, and ii. reducing fluid pressure in the straddle interval to allow the fracture to re-close; and g. determining magnitude of least principal stress (Sh) of the formation from the monitored parameters. - View Dependent Claims (25, 26, 27, 28, 29, 30)
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31. A method of determining stress in a bed of an underground formation having multiple lithological beds traversed by a borehole lined with cemented casing, comprising the steps of:
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a. selecting a bed of interest based on available information about lithology and bed thickness; b. estimating an azimuth about the borehole axis of the maximum principal stress of the bed of interest; c. placing a casing perforating device in a location of the borehole passing through the bed of interest; d. orienting the perforating device within the borehole in alignment with the estimated azimuth of maximum principal stress; e. applying the perforating device to the inner wall of the casing; f. activating the perforating device to produce a single perforation through the casing and cement to establish pressure communication with the bed of interest; g. injecting a controlled first volume of fluid through the perforation into the bed of interest at a controlled rate to create a fracture in the bed of interest of a diameter not exceeding approximately the thickness of the bed of interest, while monitoring parameters including pressure in the perforation and acoustic emissions; h. terminating fluid injection and allowing pressure in the perforation to decline, while monitoring pressure in the perforation after fluid injection is terminated, and determining a fracture closure stress from a change in rate of decline of pressure in the perforation; and i. after determining fracture closure stress, pumping from the bed of interest via the perforation a quantity of fluid approximately equal to the quantity of fluid injected in step g. j. injecting a controlled second volume of fluid through the perforation into the bed of interest at a controlled rate to extend the fracture in the bed of interest to a diameter not exceeding approximately the thickness of the bed of interest, while monitoring parameters including pressure in the perforation and acoustic emissions; k. terminating fluid injection and allowing pressure in the perforation to decline, while monitoring pressure in the perforation after fluid injection is terminated, and determining a fracture closure stress from a change in rate of decline of pressure in the perforation; and l. after determining fracture closure stress in step k, pumping from the bed of interest via the perforation a quantity of fluid approximately equal to the quantity of fluid injected in step j.; and m. determining formation stress from the monitored parameters. - View Dependent Claims (32, 33, 34)
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35. A method of determining stress in at least one bed of an underground formation having multiple lithological beds traversed by a borehole lined with cemented casing, comprising the steps of:
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a. selecting a bed of interest based on available information about lithology and bed thickness; b. placing a tool having a straddle-packer pair defining a straddle interval and having a perforating gun with helical perforation capability about the borehole axis in a location of the borehole passing through the bed of interest; c. setting the straddle packers in the casing to isolate a region of the borehole lying in the bed of interest; d. pumping substantially all fluid out of the straddle interval; e. selectively firing the perforating device to create multiple perforations through the casing and cement over 360 degrees of azimuth about the borehole axis, to thereby establish fluid communication between the straddle interval and the bed of interest; f. injecting a controlled first volume of fluid into the bed of interest via the perforations at a controlled rate to create a fracture in the bed of interest no larger than approximately the bed thickness, while monitoring parameters including pressure in the straddle interval and acoustic emissions; g. terminating fluid injection, and determining fracture closure stress from pressure vs. time by monitoring pressure leak-off after fluid injection has terminated; h. after determining fracture closure stress, pumping from the bed of interest via the perforations a quantity of fluid approximately equal to the first volume of fluid; i. injecting a controlled second volume of fluid though the perforations into the bed of interest at a controlled rate, while monitoring parameters including pressure in the straddle interval and acoustic emissions; j. pumping back from the bed of interest via the perforations a quantity of fluid approximately equal to the quantity of fluid injected, at a controlled rate; k. during pump-back, monitoring parameters including pressure in the straddle interval; and l. determining fracture closure pressure and formation stress from the monitored parameters. - View Dependent Claims (36, 37)
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Specification