CN113107363B - Horizontal well construction method for promoting fracture dislocation and improving self-supporting capacity - Google Patents
Horizontal well construction method for promoting fracture dislocation and improving self-supporting capacity Download PDFInfo
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- CN113107363B CN113107363B CN202110598977.8A CN202110598977A CN113107363B CN 113107363 B CN113107363 B CN 113107363B CN 202110598977 A CN202110598977 A CN 202110598977A CN 113107363 B CN113107363 B CN 113107363B
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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
- E21B7/00—Special methods or apparatus for drilling
- E21B7/04—Directional drilling
- E21B7/046—Directional drilling horizontal drilling
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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
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/11—Perforators; Permeators
- E21B43/116—Gun or shaped-charge perforators
- E21B43/117—Shaped-charge perforators
-
- 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
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
- E21B43/267—Methods for stimulating production by forming crevices or fractures reinforcing fractures by propping
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- 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
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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
- E21B7/00—Special methods or apparatus for drilling
- E21B7/04—Directional drilling
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/10—Geothermal energy
Abstract
The invention discloses a horizontal well construction method for promoting fracture dislocation and improving self-supporting capacity, which is suitable for underground coal mines. Firstly, detecting reservoir parameters, and acquiring rock mechanical parameters and ground stress parameters of a reservoir target mining interval; constructing a vertical shaft, wherein the axial direction of the vertical shaft is perpendicular to a plane in which the directions of the maximum and minimum horizontal main stresses are located; constructing a steering horizontal well, wherein the axial direction of the steering horizontal well is in the direction of the maximum horizontal main stressAn included angle; perforating and expanding joints in a horizontal well, wherein the perforating generates alternate longitudinal double-wing cracks, and after the joint expansion, a crack surface which is horizontal to the axis of the horizontal well and is perpendicular to the plane in which the maximum and minimum horizontal main stresses are located is formed between the cracks; the fracture dislocation self-supporting is realized, the dislocation sliding of the upper and lower sections of the fracture is promoted by utilizing an artificial fracturing means, and a three-dimensional self-supporting fracture network is constructed.
Description
Technical Field
The invention relates to a horizontal well construction method, in particular to a horizontal well construction method for promoting fracture dislocation and improving self-supporting capacity.
Background
Exploration and development of unconventional gas reservoirs such as coal-bed gas reservoirs, tight sandstone gas reservoirs and shale gas reservoirs have become hot spots. Unconventional oil and gas reservoirs have the characteristics of deep burial, large closure pressure, low permeability and the like, and the establishment of a fracture network which is communicated with each other is key for fully excavating the potential of the reservoirs. However, the artificially created slit may be re-closed under the closing pressure. Therefore, students at home and abroad research the self-supporting fracturing yield-increasing theory, the self-supporting fracturing construction does not use or uses a small amount of propping agent, cracks are directly generated, the fracture surface is subjected to dislocation sliding under the action of shearing stress, and as the fracture section often presents an irregular concave-convex shape, the micro-convex points of the upper and lower fracture sections of the dislocated fracture can play the effect of mutual supporting, and the flow guiding capability of the fracture is effectively improved.
The staged fracturing of the horizontal well has become an important mode for developing a tight gas reservoir, and compared with the traditional drilling process, the horizontal well drilling cost has obvious advantages and has wide application space in China. The horizontal well is a general term of a straight Duan Jing well with a well inclination angle in a region of about 90 degrees, the well depth of the horizontal well is drilled to a gas reservoir in the horizontal direction, and exploitation is realized through cooperation of an underground pump set and ground equipment. In general, the well body degree of the horizontal well has a certain deviation from 90 degrees, and the angle is generally adjusted according to the actual condition of the oil and gas reservoir.
The crack self-supporting characteristics of the underground rock mass are studied, and three main ground stresses in the underground rock mass, namely a maximum horizontal main stress, a minimum horizontal main stress and a vertical main stress, are considered, wherein the three main ground stresses are mutually perpendicular in the direction. Studies indicate that the propagation path of a fracture created by manual fracturing measures is affected by the earth stress field of the reservoir primary rock.
In order to improve the self-supporting capacity of the fracture network, from the aspect of promoting fracture dislocation, stress analysis is carried out on the fracture based on the original rock stress field to obtain the angle relation between the fracture surface and the three main ground stresses, and the steering direction selection of the horizontal well is optimized accordingly, so that the dislocation slippage of the fracture is guaranteed under the action of the original rock ground stress field, and the number of self-supporting fractures is increased.
Disclosure of Invention
Aiming at the defects of the prior art, the horizontal well construction method for promoting fracture dislocation and improving the self-supporting capacity is provided, and from the perspective of promoting fracture dislocation, the angle relation between a fracture surface and three major ground stresses during artificial joint making needs to be researched so as to ensure the dislocation slippage of the fracture under the action of an original rock ground stress field, and further improve the self-supporting capacity of a fracture network.
In order to achieve the above purpose, the horizontal well construction method for promoting crack dislocation and improving self-supporting capacity is characterized by comprising the following steps:
firstly, acquiring rock mechanical parameters and ground stress parameters of a reservoir target mining interval, wherein the rock mechanical parameters comprise elastic modulus, poisson ratio, internal friction angle and cohesive force, and the ground stress parameters comprise the magnitudes and directions of vertical main stress, maximum horizontal main stress and minimum horizontal main stress;
b, a vertical shaft is arranged on the ground to a target mining layer section of the reservoir, and the axial direction of the vertical shaft section is perpendicular to the plane in which the directions of the maximum and minimum horizontal main stresses are located;
c, steering the end part of the vertical shaft to construct a horizontal well, wherein the axial direction of the horizontal well is in the direction of the maximum horizontal main stressAn included angle;
d, arranging two rows of shaped perforating guns vertically on the upper and lower sides of the horizontal well by using the perforating guns, wherein the perforating direction is perpendicular to the axis of the horizontal well and parallel to the vertical main stress direction, and generating symmetrical longitudinal double-wing crack clusters on the upper and lower sides of the horizontal well by using the shaped perforating guns to form a seam; perforation aperture is 5-7cm, and crack clusters with perforation interval of 20cm are generated;
recovering perforating guns and sealing holes of the horizontal well, injecting fracturing fluid into the horizontal well section by utilizing a hydraulic fracturing technology to further expand and fracture crack clusters formed by perforating and fracture, so that adjacent perforating cracks are communicated with each other to form a plane which is horizontal well axis and is perpendicular to the plane where the maximum and minimum horizontal main stresses are located, wherein the plane is a longitudinal crack plane, namely the crack length direction is parallel to the horizontal well axis direction;
f crack dislocation self-supporting: and (3) promoting the shearing, dislocation and sliding of the cracks by using a high-energy gas blasting and fracturing technology to construct a three-dimensional self-supporting crack network.
The selection process of the axial angle of the horizontal well in the step of steering construction of the horizontal well and the selection process of the perforation direction in the step of perforation and seam expansion are as follows:
the crack opening degree is:
in e 0 The ratio of the crack length to the crack short axis under the action of the artificial fracturing measure; e, taking 0 when the ratio of the length and the short axis of the crack compressed under the action of the ground stress of the original rock is completely closed after the artificial fracturing measure is removed; v is poisson's ratio; e is the elastic modulus; sigma (sigma) ep Effective compressive stress for the fracture;
from formula (1), e 0 The larger e means that the crack is at sigma ep Is easier to close under the action of the (2), and in the original rock ground stress field, the effective compressive stress of the crack is as follows:
middle sigma H Is the maximum horizontal principal stress; sigma (sigma) h Is the minimum horizontal principal stress; sigma (sigma) v Is the vertical principal stress; alpha is the included angle between the crack surface and the maximum horizontal main stress, alpha is 0 DEG, 90 DEG]The method comprises the steps of carrying out a first treatment on the surface of the Beta is the included angle between the normal direction of the crack surface and the vertical main stress, and beta is 0 DEG, 90 DEG]；
It is known that f (α) =cos 2α monotonically decreases over the interval [0 °,90 ° ], and the interval left and right end point values are substituted into formula (1) to obtain
Due to sigma H ﹥σ h Therefore there is (e) 0 -e) 90° ﹥(e 0 -e) 0° ，
So α=0°, the crack opens to the greatest extent, i.e. is least prone to closure along the direction of maximum horizontal principal stress; in this case, the formula (2) is simplified as:
σ ep ＝σ h sin 2 β+σ v cos 2 β (4)
at sigma Hv Sigma (sigma) v In the stress field of the original rock, sigma is present v ﹥σ h So when β=90°, σ ep Taking the minimum value, the value is equal to the minimum horizontal main stress.
From the above, it can be seen from the formulas (1) and (2) that the crack opens and the effective stress sigma ep There is a linear negative correlation and the effective stress sigma ep And is also related to principal stress and fracture face angle;
under the action of shear stress, the surfaces of the cracks mutually slide to generate shear cracks, the dislocation of crack surfaces under the action of the shear stress is researched by adopting a mole-coulomb damage criterion, and when the shear stress tau on one surface exceeds the limit shear stress tau which can be born by the surface f The rock is sheared and damaged, i.e. the damage criteria are:
τ≥τ f (5)
ultimate shear stress τ f Concerning the effective compressive stress sigma ep Is given by:
τ in f Is the limit shear stress;is the internal friction angle of the rock; c is the cohesive force of the rock;
according toLine elasticity theory, under plane stress state, rock is subjected to maximum horizontal principal stress sigma H And a minimum horizontal principal stress sigma h Effective compressive stress sigma acting on fracture surface ep And shear stress τ are:
in sigma ep Normal stress generated on the fracture plane as the maximum and minimum horizontal main stress, namely effective stress when beta=90°;
τ is the shear stress generated by the maximum and minimum horizontal principal stresses in the fracture plane.
Combined type (5) (6) (7) (8), then:
let δ=τ - τ f It is understood that a larger δ indicates that shear failure is more likely to occur, and that the amount of slip in the fracture surface is larger;
due to the maximum horizontal principal stress sigma H Minimum horizontal principal stress sigma h Internal friction angle of rockThe rock cohesion c is a measurable parameter, so the functional relation delta (alpha) defining the amount of slip delta with respect to the angle alpha is:
wherein the constant isConstant->Alpha represents the included angle between the axial direction of the horizontal well and the direction of the maximum horizontal main stress,
as can be derived from the auxiliary angle formula,
wherein the constant is
By the nature of a sine function whenWhen k is E Z, the function delta (alpha) takes the maximum value;
because alpha is [0 DEG, 90 DEG ], when the included angle alpha between the axial direction of the horizontal well and the direction of the maximum horizontal main stress is as follows:
in this case, the degree of dislocation of the fracture surface is the greatest.
The high-energy gas in the step f is methane gas.
The beneficial effects are that: according to the invention, the horizontal well is constructed by selecting a proper angle, the selected construction steering can fully utilize the shearing action of the original rock ground stress field on the crack on the premise of keeping the crack to a certain extent, the longitudinal crack surface parallel to the axial direction of the horizontal well is formed by matching the shaped perforation for crack making and hydraulic fracturing for crack expanding in the early stage, the crack surface is enabled to slide in a staggered manner to the greatest extent by using the technical means mainly for methane high-energy gas explosion and fracturing in the later stage, a better self-supporting effect is realized, the number of the unclosed cracks is increased, the diversion capacity of the artificial cracks is further improved, and the gas extraction efficiency of a reservoir is improved.
Drawings
FIG. 1 is a step diagram of a horizontal well construction method of the present invention for promoting fracture dislocation to enhance self-supporting capacity;
FIG. 2 (a) is a schematic illustration of a horizontal well construction in which the ability of fracture dislocation to promote self-support is facilitated in accordance with the present invention;
FIG. 2 (b) is a schematic illustration of perforating construction in a horizontal well to facilitate fracture dislocation to promote self-supporting capability in accordance with the present invention;
FIG. 2 (c) is a schematic illustration of a longitudinal fracture surface generated in a horizontal well that promotes fracture dislocation lifting self-supporting capabilities in accordance with the present invention;
FIG. 3 (a) is a perspective view of a horizontal well construction method of the present invention for promoting fracture dislocation to enhance self-supporting capacity;
FIG. 3 (b) is a plan view of a horizontal well construction method of the present invention that promotes fracture dislocation to promote self-supporting capability.
Detailed Description
The preferred embodiments of the present invention will be described below with reference to the accompanying drawings, it being understood that the preferred embodiments described herein are for illustration and explanation of the present invention only, and are not intended to limit the present invention.
As shown in fig. 1, the horizontal well construction method for promoting crack dislocation and improving self-supporting capacity is characterized by comprising the following steps:
firstly, acquiring rock mechanical parameters and ground stress parameters of a reservoir target mining interval, wherein the rock mechanical parameters comprise elastic modulus, poisson ratio, internal friction angle and cohesive force, and the ground stress parameters comprise the magnitudes and directions of vertical main stress, maximum horizontal main stress and minimum horizontal main stress;
b, a vertical shaft is arranged on the ground to a target mining layer section of the reservoir, and the axial direction of the vertical shaft section is perpendicular to the plane in which the directions of the maximum and minimum horizontal main stresses are located;
c, steering the end part of the vertical shaft to construct a horizontal well, wherein the axial direction of the horizontal well is in the direction of the maximum horizontal main stressAn included angle;
d, arranging two rows of shaped perforating guns vertically on the upper and lower sides of the horizontal well by using the perforating guns, wherein the perforating direction is perpendicular to the axis of the horizontal well and parallel to the vertical main stress direction, and generating symmetrical longitudinal double-wing crack clusters on the upper and lower sides of the horizontal well by using the shaped perforating guns to form a seam; perforation aperture is 5-7cm, and crack clusters with perforation interval of 20cm are generated;
recovering perforating guns and sealing holes of the horizontal well, injecting fracturing fluid into the horizontal well section by utilizing a hydraulic fracturing technology to further expand and fracture crack clusters formed by perforating and fracture, so that adjacent perforating cracks are communicated with each other to form a plane which is horizontal well axis and is perpendicular to the plane where the maximum and minimum horizontal main stresses are located, wherein the plane is a longitudinal crack plane, namely the crack length direction is parallel to the horizontal well axis direction;
f crack dislocation self-supporting: and (3) promoting the shearing dislocation sliding of the cracks by using a methane gas blasting fracturing technology to construct a three-dimensional self-supporting crack network.
The selection process of the axial angle of the horizontal well in the step of steering construction of the horizontal well and the selection process of the perforation direction in the step of perforation and seam expansion are as follows:
the crack opening degree is:
in e 0 The ratio of the crack length to the crack short axis under the action of the artificial fracturing measure; e, taking 0 when the ratio of the length and the short axis of the crack compressed under the action of the ground stress of the original rock is completely closed after the artificial fracturing measure is removed; v is poisson's ratio; e is the elastic modulus; sigma (sigma) ep Effective compressive stress for the fracture;
from formula (1), e 0 The larger e means that the crack is at sigma ep Is easier to close under the action of the stress field, and in the original rock ground stress field, the effective compressive stress is as follows:
middle sigma H Is the maximum horizontal principal stress; sigma (sigma) h Is the minimum level principalForce; sigma (sigma) v Is the vertical principal stress; alpha is the included angle between the crack surface and the maximum horizontal main stress, alpha is 0 DEG, 90 DEG]The method comprises the steps of carrying out a first treatment on the surface of the Beta is the included angle between the normal direction of the crack surface and the vertical main stress, and beta is 0 DEG, 90 DEG]；
It is known that f (α) =cos 2α monotonically decreases over the interval [0 °,90 ° ], and the interval left and right end point values are substituted into formula (1) to obtain
Due to sigma H ﹥σ h Therefore there is (e) 0 -e) 90° ﹥(e 0 -e) 0° ，
So α=0°, the crack opens to the greatest extent, i.e. is least prone to closure along the direction of maximum horizontal principal stress; in this case, the formula (2) is simplified as:
σ ep ＝σ h sin 2 β+σ v cos 2 β (4)
at sigma Hv Sigma (sigma) v In the stress field of the original rock, sigma is present v ﹥σ h So when β=90°, σ ep Taking the minimum value, the value is equal to the minimum horizontal main stress.
From the above, it can be seen from the formulas (1) and (2) that the crack opens and the effective stress sigma ep There is a linear negative correlation and the effective stress sigma ep And is also related to principal stress and fracture face angle;
under the action of shear stress, the surfaces of the cracks mutually slide to generate shear cracks, the dislocation of crack surfaces under the action of the shear stress is researched by adopting a mole-coulomb damage criterion, and when the shear stress tau on one surface exceeds the limit shear stress tau which can be born by the surface f The rock is sheared and damaged, i.e. the damage criteria are:
τ≥τ f (5)
ultimate shear stress τ f Concerning the effective compressive stress sigma ep Is given by:
τ in f Is the limit shear stress;is the internal friction angle of the rock; c is the cohesive force of the rock;
according to the linear elastic theory, under the plane stress state, the rock is subjected to the maximum horizontal main stress sigma H And a minimum horizontal principal stress sigma h Effective compressive stress sigma acting on fracture surface ep And shear stress τ are:
in sigma ep Normal stress generated on the fracture plane for maximum and minimum horizontal principal stress, i.e. effective compressive stress at β=90°; τ is the shear stress generated by the maximum and minimum horizontal principal stresses in the fracture plane.
Combined type (5) (6) (7) (8), then:
let δ=τ - τ f It is understood that a larger δ indicates that shear failure is more likely to occur, and that the amount of slip in the fracture surface is larger;
due to the maximum horizontal principal stress sigma H Minimum horizontal principal stress sigma h Internal friction angle of rockThe rock cohesion c is a measurable parameter, so a functional relation δ (α) of the amount of slip δ with respect to the angle α is defined:
wherein the constant isConstant->Alpha represents the included angle between the axial direction of the horizontal well and the direction of the maximum horizontal main stress,
as can be derived from the auxiliary angle formula,
wherein the constant is
By the nature of a sine function whenWhen k is E Z, the function delta (alpha) takes the maximum value;
because alpha is [0 DEG, 90 DEG ], when the included angle alpha between the axial direction of the horizontal well and the direction of the maximum horizontal main stress is as follows:
in this case, the degree of dislocation of the fracture surface is the greatest.
Embodiment 1,
Taking a shale reservoir as an example, the horizontal well construction method for promoting fracture dislocation and improving self-supporting capacity provided by the invention is shown in fig. 1, and mainly comprises the following steps:
(A) And (5) detecting reservoir parameters. Various parameters of shale reservoir rock mechanics and ground stress in the examples are shown in table 1:
table 1 reservoir parameters
(B) Constructing a vertical shaft;
(C) Perforating and expanding. As shown in fig. 2 and 3, in order to explore the relation between the angle of the fracture generated by the perforation and the dislocation slip amount of the fracture under the action of the stress field of the original rock, the opening degree and the dislocation degree of the fracture surface are analyzed, wherein the stress analysis comprises vertical main stress, maximum horizontal main stress, minimum horizontal main stress, effective compressive stress, shearing stress and the like.
Calculating the crack angle as according to (12)
Calculating the effective compressive stress as shown in formula (7) and formula (8)
The crack opening degree is calculated according to the formula (1)
The shear stress is calculated according to the formula (8)
Calculating the value of the slip function as the value of the slip according to (10)
(D) - (E) abbreviation.
Claims (2)
1. A horizontal well construction method for promoting crack dislocation and improving self-supporting capacity is characterized by comprising the following steps:
firstly, acquiring rock mechanical parameters and ground stress parameters of a reservoir target mining interval, wherein the rock mechanical parameters comprise elastic modulus, poisson ratio, internal friction angle and cohesive force, and the ground stress parameters comprise the magnitudes and directions of vertical main stress, maximum horizontal main stress and minimum horizontal main stress;
b, a vertical shaft is arranged on the ground to a target mining layer section of the reservoir, and the axial direction of the vertical shaft section is perpendicular to the plane in which the directions of the maximum and minimum horizontal main stresses are located;
c, steering the end part of the vertical shaft to construct a horizontal well, wherein the axial direction of the horizontal well is in the direction of the maximum horizontal main stressAn included angle;
d, arranging two rows of shaped perforating guns vertically on the upper and lower sides of the horizontal well by using the perforating guns, wherein the perforating direction is perpendicular to the axis of the horizontal well and parallel to the vertical main stress direction, and generating symmetrical longitudinal double-wing crack clusters on the upper and lower sides of the horizontal well by using the shaped perforating guns to form a seam;
recovering perforating guns and sealing holes of the horizontal well, injecting fracturing fluid into the horizontal well section by utilizing a hydraulic fracturing technology to further expand and fracture crack clusters formed by perforating and fracture, so that adjacent perforating cracks are communicated with each other to form a plane which is horizontal well axis and is perpendicular to the plane where the maximum and minimum horizontal main stresses are located, wherein the plane is a longitudinal crack plane, namely the crack length direction is parallel to the horizontal well axis direction;
f crack dislocation self-supporting: the high-energy gas explosion fracturing technology is used for promoting the shearing, dislocation and sliding of the cracks, and a three-dimensional self-supporting crack network is constructed;
perforation aperture is 5-7cm, and crack clusters with perforation interval of 20cm are generated;
the selection process of the axial angle of the horizontal well in the step of steering construction of the horizontal well and the selection process of the perforation direction in the step of perforation and seam expansion are as follows:
the crack opening degree is:
in e 0 The ratio of the crack length to the crack short axis under the action of the artificial fracturing measure; e, taking 0 when the ratio of the length and the short axis of the crack compressed under the action of the ground stress of the original rock is completely closed after the artificial fracturing measure is removed; v is poisson's ratio; e is the elastic modulus; sigma (sigma) ep Effective compressive stress for the fracture;
from formula (1), e 0 The larger e means that the crack is at sigma ep Is easier to close under the action of the stress field, and in the original rock ground stress field, the effective compressive stress is as follows:
middle sigma H Is the maximum horizontal principal stress; sigma (sigma) h Is the minimum horizontal principal stress; sigma (sigma) v Is the vertical principal stress; alpha is the included angle between the crack surface and the maximum horizontal main stress, alpha is 0 DEG, 90 DEG]The method comprises the steps of carrying out a first treatment on the surface of the Beta is the included angle between the normal direction of the crack surface and the vertical main stress, and beta is 0 DEG, 90 DEG]；
It is known that f (α) =cos 2α monotonically decreases over the interval [0 °,90 ° ], and the interval left and right end point values are substituted into formula (1) to obtain
Due to sigma H ﹥σ h Therefore there is (e) 0 -e) 90° ﹥(e 0 -e) 0° ，
So α=0°, the crack opens to the greatest extent, i.e. is least prone to closure along the direction of maximum horizontal principal stress; in this case, the formula (2) is simplified as:
σ ep ＝σ h sin 2 β+σ v cos 2 β (4)
at sigma Hv Sigma (sigma) v In the stress field of the original rock, sigma is present v ﹥σ h So when β=90°, σ ep Taking a minimum value which is equal to the minimum horizontal main stress in value;
from the above, it can be seen from the formulas (1) and (2) that the crack opens and the effective stress sigma ep There is a linear negative correlation and the effective stress sigma ep And is also related to principal stress and fracture face angle;
under the action of shear stress, the surfaces of the cracks mutually slide to generate shear cracks, the dislocation of crack surfaces under the action of the shear stress is researched by adopting a mole-coulomb damage criterion, and when the shear stress tau on one surface exceeds the limit shear stress tau which can be born by the surface f The rock is sheared and damaged, i.e. the damage criteria are:
τ≥τ f (5)
ultimate shear stress τ f Concerning the effective compressive stress sigma ep Is given by:
τ in f Is the limit shear stress;is the internal friction angle of the rock; c is the cohesive force of the rock;
according to the linear elastic theory, under the plane stress state, the rock is subjected to the maximum horizontal main stress sigma H And a minimum horizontal principal stress sigma h Effective compressive stress sigma acting on fracture surface ep And shear stress τ are:
in sigma ep Normal stress generated on the fracture plane for maximum and minimum horizontal principal stress, i.e. effective compressive stress at β=90°; τ is the shear stress generated by the maximum and minimum horizontal principal stresses on the fracture plane;
combined type (5) (6) (7) (8), then:
let δ=τ - τ f It is understood that a larger δ indicates that shear failure is more likely to occur, and that the amount of slip in the fracture surface is larger;
due to the maximum horizontal principal stress sigma H Minimum horizontal principal stress sigma h Internal friction angle of rockThe rock cohesion c is a measurable parameter, so a functional relation δ (α) of the amount of slip δ with respect to the angle α is defined:
wherein the constant isConstant->Alpha represents the included angle between the axial direction of the horizontal well and the direction of the maximum horizontal main stress,
as can be derived from the auxiliary angle formula,
wherein the constant is
By the nature of a sine function whenWhen k is E Z, the function delta (alpha) takes the maximum value;
because alpha is [0 DEG, 90 DEG ], when the included angle alpha between the axial direction of the horizontal well and the direction of the maximum horizontal main stress is as follows:
in this case, the degree of dislocation of the fracture surface is the greatest.
2. The method for horizontal well construction to promote fracture dislocation and self supporting as recited in claim 1, wherein the high energy gas in step f is methane gas.
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