CN116877060A - Current ground stress inversion method based on well wall strain monitoring - Google Patents
Current ground stress inversion method based on well wall strain monitoring Download PDFInfo
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- CN116877060A CN116877060A CN202310993881.0A CN202310993881A CN116877060A CN 116877060 A CN116877060 A CN 116877060A CN 202310993881 A CN202310993881 A CN 202310993881A CN 116877060 A CN116877060 A CN 116877060A
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- 238000000034 method Methods 0.000 title claims abstract description 32
- 238000012544 monitoring process Methods 0.000 title claims abstract description 15
- 238000011065 in-situ storage Methods 0.000 claims abstract description 19
- 238000005553 drilling Methods 0.000 claims abstract description 14
- 238000005259 measurement Methods 0.000 claims abstract description 13
- 239000007788 liquid Substances 0.000 claims abstract description 5
- 239000002002 slurry Substances 0.000 claims abstract description 4
- 238000009933 burial Methods 0.000 claims description 6
- 230000008569 process Effects 0.000 abstract description 5
- 238000012360 testing method Methods 0.000 abstract description 4
- 238000010276 construction Methods 0.000 abstract description 2
- 239000000463 material Substances 0.000 abstract description 2
- 238000012935 Averaging Methods 0.000 abstract 1
- 239000011435 rock Substances 0.000 description 6
- 238000011161 development Methods 0.000 description 5
- 238000000691 measurement method Methods 0.000 description 4
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 230000007547 defect Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 239000003208 petroleum Substances 0.000 description 2
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 229920001971 elastomer Polymers 0.000 description 1
- 239000000806 elastomer Substances 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000009662 stress testing Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
Classifications
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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
- E21B47/00—Survey of boreholes or wells
- E21B47/06—Measuring temperature or pressure
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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
- E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
- E21B49/006—Measuring wall stresses in the borehole
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- Life Sciences & Earth Sciences (AREA)
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- Geology (AREA)
- Mining & Mineral Resources (AREA)
- Physics & Mathematics (AREA)
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- Fluid Mechanics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Geophysics (AREA)
- Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)
Abstract
The invention discloses a current ground stress inversion method based on borehole wall strain monitoring, which comprises the steps of placing three groups of right-angle strain gauges at the same horizontal position in a local borehole wall surface far away from an orifice and outside an influence area of a hole bottom in a ground stress measurement borehole; applying slurry liquid column pressure to the well wall, and simultaneously recording strain values on the strain gauge, and respectively determining circumferential strain and axial strain at 3 positions on the well wall; according to the elasticity theory, determining the maximum and minimum horizontal stress of the in-situ stress field at 3 positions on the well wall by utilizing the relation between the strain of the wall of the measuring point hole at different positions and the global ground stress field; and (3) averaging according to the maximum and minimum horizontal stresses of the in-situ stress fields at 3 positions, and determining the maximum and minimum horizontal stresses of the actual in-situ stress fields. Compared with the traditional stress test, the invention does not need to drill the core on the well wall, avoids complex construction process and saves manpower and material resources required by drilling the core.
Description
Technical Field
The invention relates to a current ground stress inversion method based on borehole wall strain monitoring, and belongs to the technical field of petroleum exploration and development.
Background
In oil exploration and development, an assessment of the initial ground stress state is indispensable. Ground stress refers to natural stresses present in the crust that are not disturbed by engineering, and is not only the primary controlling factor affecting the mechanical behavior of the rock mass, but also one of the primary sources of force that cause deformation and destruction of the rock mass. Accurate measurement of the ground stress field can significantly improve the safety of underground engineering: in the drilling process, knowing the ground stress field can help constructors design reasonable drilling schemes, such as drilling fluid density required by borehole stability and casing design required by borehole wall support, ensure the safety and stability of the borehole, and reduce underground accidents and drilling cost. During the production and development process, the deformation and crack development conditions of the reservoir can be known through the ground stress measurement data, the productivity and permeability of the reservoir are evaluated, and the oil and gas exploitation scheme is optimized. Therefore, in the petroleum exploration and development process, the accurate measurement of the ground stress field plays an important role.
The method is based on the principle that a core is drilled from surrounding rock, and the change of strain or displacement of the core before and after stress relief is detected by using a measuring sensor, so that the magnitude and the direction of a stress value are calculated. In general, the stress relief method can be divided into an aperture deformation measurement method, an aperture wall stress relief method and an aperture bottom strain measurement method according to different measurement positions and measurement parameters, wherein the aperture deformation measurement method is to put a sensor into a drill hole, and the in-situ stress state is determined by utilizing aperture changes before and after stress relief, but the length of a drill core is required to exceed 300mm and is kept complete; the hole wall stress relief method is to install a sensor at the hole wall of a drill hole, and obtain an in-situ stress state by utilizing the strain difference value on the hole wall before and after stress relief, but the method also requires that the length of a drilled core exceeds 300mm and remains complete; in the hole bottom strain measurement method, a measuring device is placed at the bottom of a processed drilling hole, and the ground stress state is determined by using the strain difference value of the end parts of the drilling hole before and after stress relief, but the ground stress test precision of the method is affected by the concentration of the hole bottom stress.
Therefore, it is easy to see that in practical application, the stress relief method still has room for improvement due to the difficulty in drilling the complete core and the limitation of the measuring device, and therefore, the present ground stress inversion method based on the well wall strain monitoring is provided.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a current ground stress inversion method based on borehole wall strain monitoring, which assumes that the rock mass of the measured borehole wall area is a homogeneous, continuous and isotropic linear elastomer, derives the main stress of the stress field of the area by the stress information of the measuring point on the local wall surface, and has the advantage that compared with the existing drilling local wall surface stress full-relief technical method, the method does not need to drill cores on the borehole wall.
The technical scheme provided by the invention for solving the technical problems is as follows: a method for inversion of the present ground stress based on the well wall strain monitoring comprises the following steps:
s10, placing three groups of right-angle strain flowers at the same horizontal position in a local well wall surface outside an influence area of a hole opening and a hole bottom in a ground stress measurement drilling hole;
step S20, applying slurry liquid column pressure to the well wall, simultaneously recording strain values on the strain gauge, and respectively determining circumferential strain and axial strain at 3 positions on the well wall according to the strain values of the strain gauge at 3 positions;
s30, determining maximum and minimum horizontal stress of in-situ stress fields at 3 positions on a well wall by utilizing the relation between the strain of the wall of the measuring point hole at different positions and the global ground stress field according to an elasticity theory;
and S40, calculating an average value according to the maximum and minimum horizontal stresses of the in-situ stress fields at 3 positions, and determining the maximum and minimum horizontal stresses of the actual in-situ stress fields.
The further technical scheme is that in the step 10, the interval between two adjacent right-angle strain gauges is 120 degrees.
The further technical scheme is that the calculation formula in the step S20 is as follows:
wherein:is the included angle between the attached strain gauge and the circumferential direction; />Is formed by the circumferential included angleIs a strain of (2); epsilon θ 、ε z Is the circumferential and axial strain on the borehole wall.
The further technical scheme is that the specific steps of the step S30 are as follows:
step S31, determining the principal stress sigma in the vertical direction according to the relation between the vertical ground stress and the burial depth z ；
Step S32, according to the principal stress sigma in the vertical direction z And determining the maximum and minimum horizontal stress of the in-situ stress field by circumferential strain and axial strain on the well wall.
The further technical scheme is that the calculation formula in the step S31 is as follows:
σ z ＝γh
wherein: gamma is the volume weight; h is the depth of burial; sigma (sigma) z Is the principal stress in the vertical direction.
The further technical scheme is that the calculation formula in the step S32 is as follows:
wherein:and->For the horizontal stress found at the measurement point; θ is the position of the strain gauge on the borehole wall; v is poisson's ratio; e is the elastic modulus; epsilon θj And epsilon zj To measure the circumferential and axial strain occurring in the borehole wall at the point.
The invention has the following beneficial effects: the novel ground stress testing method can make up for the defects of the traditional stress test, and compared with the traditional stress test, the method does not need to drill cores on the well wall, avoids complex construction process, and saves manpower and material resources required by drilling the cores; the relation between the stress state of the measuring point on the local wall surface and the global ground stress field is utilized to deduce the main stress of the in-situ stress field, so that a new scheme is provided for identifying the ground stress of the underground geotechnical engineering.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a diagram showing the arrangement of the strain gauge by the full relief of the stress on the local wall of the borehole;
fig. 3 is a representation of strain at any point on the borehole wall.
Description of the embodiments
The following description of the embodiments of the present invention will be made apparent and fully in view of the accompanying drawings, in which some, but not all embodiments of the invention are shown. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
As shown in fig. 1, the present ground stress inversion method based on borehole wall strain monitoring of the present invention comprises the following steps:
s10, placing three groups of right-angle strain flowers at the same horizontal position in a local well wall surface outside an influence area of a hole opening and a hole bottom in a ground stress measurement drilling hole; the interval between two adjacent right-angle strain flowers is 120 degrees;
step S20, applying slurry liquid column pressure to the well wall, simultaneously recording strain values on the strain gauge, and respectively determining circumferential strain and axial strain at 3 positions on the well wall according to the strain values of the strain gauge at 3 positions;
in a vertical well, the relation between the strain on the strain gauge and the axial and circumferential strain of the well wall:
the circumferential and axial strain on the borehole wall can thus be solved according to the least squares method:
wherein:is the included angle between the attached strain gauge and the circumferential direction; />Is formed by the circumferential included angleIs a strain of (2); epsilon θ 、ε z Is the circumferential and axial strain on the borehole wall;
s30, determining maximum and minimum horizontal stress of in-situ stress fields at 3 positions on a well wall by utilizing the relation between the strain of the wall of the measuring point hole at different positions and the global ground stress field according to an elasticity theory;
step S31, in the vertical well, sigma z ＝σ v So the principal stress sigma in the vertical direction can be determined according to the relation between the vertical ground stress and the burial depth z ；
σ z ＝γh
Wherein: gamma is the volumeWeighing; h is the depth of burial; sigma (sigma) z Is the principal stress in the vertical direction;
step S32, according to the principal stress sigma in the vertical direction z And determining the maximum and minimum horizontal stress of the in-situ stress field by circumferential strain and axial strain on the well wall;
wherein:and->The horizontal stress calculated at the measuring point at 3; θ is the position of the strain gauge on the borehole wall; v is poisson's ratio; e is the elastic modulus; epsilon θj And epsilon zj Circumferential strain and axial strain occurring at the well wall at 3 measurement points;
and S40, calculating an average value according to the maximum and minimum horizontal stresses of the in-situ stress fields at 3 positions, and determining the maximum and minimum horizontal stresses of the actual in-situ stress fields.
Examples
The elastic modulus and poisson ratio in the mechanical properties of the rock mass are 14000MPa and 0.324 respectively.
1. The ground stress measurement drilling is regarded as a vertical round hole on an infinite rock mass, a local wall surface far away from an orifice and outside an influence area of a hole bottom is taken as a research object, strain gauges are mounted on the same horizontal position of the surface of a measured object through an adhesive, a group of 3-piece type right-angle strain gauges are placed at intervals of 120 degrees, and an included angle between the strain gauges is 45 degrees, as shown in figure 2. The principal stress sigma in the vertical direction can be known according to the principal stress calculation formula in the vertical direction z ＝20MPa。
2. Applying a column pressure P of mud liquid to the well wall i The strain values on the strain rosettes were recorded at 40MPa, strain rosettes at 0 ° with strain at-0.0033, -0.0015,0.0003468, respectively, -0.0012, -0.0003627,0.00034667, respectively, at 120 ° with strain at 2 °The strain relief at the 40 ° position becomes-0.00119, -0.0003619,0.0003501.
3. And obtaining axial and circumferential strain values of the well wall at the measuring point according to the relation between the strain at the measuring point and the strain of the well wall, wherein the circumferential strain and the axial strain of the well wall at the 0-degree position are respectively-0.0033,0.000339, the circumferential strain and the axial strain of the well wall at the 120-degree position are respectively-0.00119,0.000339, and the circumferential strain and the axial strain of the well wall at the 240-degree position are respectively-0.0012,0.00036945.
4. According to the horizontal main stress of the ground stress field calculated by the wall strain of the well at different measuring points, the main stress in the horizontal direction calculated at the position of 0 degrees is 25.4606MPa and 11.8269MPa, the main stress in the horizontal direction calculated at the position of 120 degrees is 24.1273MPa and 12.1602MPa, and the main stress in the horizontal direction calculated at the position of 240 degrees is 24.2006MPa and 11.9451MPa.
5. Determining the horizontal principal stress sigma of the in-situ stress field according to the average value of the horizontal principal stresses at three measuring points H 、σ h 24.5961MPa and 11.9774MPa, respectively.
It is clear that the horizontal stress error calculated by different measuring points is less than 5% as a whole, which indicates that the present ground stress inversion method based on the well wall strain monitoring is reliable.
The present invention is not limited to the above-mentioned embodiments, but is not limited to the above-mentioned embodiments, and any person skilled in the art can make some changes or modifications to the equivalent embodiments without departing from the scope of the technical solution of the present invention, but any simple modification, equivalent changes and modifications to the above-mentioned embodiments according to the technical substance of the present invention are still within the scope of the technical solution of the present invention.
Claims (6)
1. The present ground stress inversion method based on the well wall strain monitoring is characterized by comprising the following steps:
s10, placing three groups of right-angle strain flowers at the same horizontal position in a local well wall surface outside an influence area of a hole opening and a hole bottom in a ground stress measurement drilling hole;
step S20, applying slurry liquid column pressure to the well wall, simultaneously recording strain values on the strain gauge, and respectively determining circumferential strain and axial strain at 3 positions on the well wall according to the strain values of the strain gauge at 3 positions;
s30, determining maximum and minimum horizontal stress of in-situ stress fields at 3 positions on a well wall by utilizing the relation between the strain of the wall of the measuring point hole at different positions and the global ground stress field according to an elasticity theory;
and S40, calculating an average value according to the maximum and minimum horizontal stresses of the in-situ stress fields at 3 positions, and determining the maximum and minimum horizontal stresses of the actual in-situ stress fields.
2. A method of inversion of present day earth stress based on well wall strain monitoring according to claim 1, wherein the interval between two adjacent right angle strain relief patterns in step 10 is 120 °.
3. The method for inversion of present ground stress based on well wall strain monitoring according to claim 1, wherein the calculation formula in step S20 is:
wherein:is the included angle between the attached strain gauge and the circumferential direction; />Is formed by the circumferential included angleIs a strain of (2); epsilon θ 、ε z Is the circumferential strain and axial stress on the well wallAnd (3) changing.
4. The method for inversion of present ground stress based on well wall strain monitoring according to claim 1, wherein the specific steps of step S30 are as follows:
step S31, determining the principal stress sigma in the vertical direction according to the relation between the vertical ground stress and the burial depth z ；
Step S32, according to the principal stress sigma in the vertical direction z And determining the maximum and minimum horizontal stress of the in-situ stress field by circumferential strain and axial strain on the well wall.
5. The method for inversion of present ground stress based on well wall strain monitoring according to claim 4, wherein the calculation formula in step S31 is:
σ z ＝γh
wherein: gamma is the volume weight; h is the depth of burial; sigma (sigma) z Is the principal stress in the vertical direction.
6. The method for inversion of present ground stress based on well wall strain monitoring according to claim 4, wherein the calculation formula in step S32 is:
wherein:and->For the horizontal stress found at the measurement point; θ is the position of the strain gauge on the borehole wall; v is poisson's ratio; e is the elastic modulus; epsilon θj And epsilon zj To measure the circumferential and axial strain occurring in the borehole wall at the point.
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| CN202310993881.0A CN116877060A (en) | 2023-08-08 | 2023-08-08 | Current ground stress inversion method based on well wall strain monitoring |
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| CN202310993881.0A CN116877060A (en) | 2023-08-08 | 2023-08-08 | Current ground stress inversion method based on well wall strain monitoring |
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