CN108710762B - Coal bed liquid CO2Method for judging cracking dominant direction of phase change oriented perforation - Google Patents
Coal bed liquid CO2Method for judging cracking dominant direction of phase change oriented perforation Download PDFInfo
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Abstract
The invention discloses liquid CO in a coal bed2The method for judging the cracking dominant direction of the phase change oriented perforation comprises the following steps: the theoretical corresponding relation between the hole wall fracture pressure P and the borehole azimuth angle alpha, the inclination angle beta and the perforation angle theta is calculated; (II) testing the three-dimensional ground stress parameters of the application; thirdly, testing the Poisson's ratio of the rock and the tensile strength parameter of the hole wall; fourthly, calculating the fracture pressure values of the hole wall under the conditions of different drilling azimuth angles, different drilling inclination angles and different drilling angle; fifthly, determining the minimum hole wall fracture pressure under the conditions of different drilling azimuth angles and inclination angles; sixthly, drawing a minimum hole wall fracture pressure distribution cloud picture and a relation curve chart under different drilling azimuth angles and inclination angles; (VII) analysis and determination of liquid CO2And (4) orienting the perforation and cracking dominant direction by phase change. The invention can be liquid CO2Permeability increasing by phase change crackingIn the technical application process, the optimization of the drilling arrangement mode provides theoretical support, and the liquid CO in the coal bed is effectively increased2The phase change directional perforation cracks to influence the radius, reduces the drilling work amount and improves the construction efficiency.
Description
Technical Field
The invention belongs to the technical field of coal mine drilling and fracturing construction, and particularly relates to liquid CO in a coal bed2Provided is a phase change oriented perforation cracking dominant direction judging method.
Background
Mine gas is a main factor influencing the safe production of coal mines in China, and the proportion of gas accidents is high among dead people caused by coal mine accidents in China, and the gas accidents are particularly prominent. Meanwhile, the coal bed gas is a potential clean energy, and under the situation of energy shortage, the development and utilization of the coal bed gas are accelerated, so that the method has important practical significance for improving the energy structure and the full utilization of energy in China, reducing environmental pollution and the like. The research shows that: more than 50% of coal seams in China are high gas coal seams, the geological resource amount of shallow coal bed gas is about 36.81 trillions per cubic meter when the burial depth is 2000m, the coal seams are third in the world, and the gas reserves are relatively rich, so that the effective exploitation and utilization of coal seam gas have important significance for guaranteeing energy safety and safe production of coal enterprises in China.
Because the occurrence conditions of coal bed gas in China are complexThe permeability of the coal seam is generally (0.1-0.001) x 10-3μm2In the range, the gas content is 2 to 3 orders of magnitude lower than that of the United states, so that the gas content of the coal bed in China is high, and the safety production situation of coal mines is severe. Because the geological conditions of the coal bed in China are poor, the permeability of the coal bed is low, the gas extraction rate of a mine is low, and the gas extraction efficiency is low, the coal bed needs to be artificially enhanced and permeability increased, and related scholars propose that measures such as hydraulic fracturing and deep hole presplitting permeability increase are adopted to obtain certain effects, but various defects exist in the application process.
Through laboratory tests and field researches, the inventor provides a liquid carbon dioxide directional blasting and cracking device (ZL 201610634343.2)' CO 201610634343.22After later practices, people find that the gas extraction method (ZL201610632790.4) with coupling permeability increase of directional blasting cracking and hydraulic fracturing has different cracking pressures due to the influence of ground stress and drill holes with different azimuth angles and inclination angles in the practical application process, and the cracking pressure has an important influence on crack development in the carbon dioxide phase change cracking process. Therefore, how to obtain coal rock mass liquid CO under three-dimensional ground stress2The advantage of the phase change oriented perforation cracking is the cracking direction to guide the site drilling construction, which is a technical problem to be solved urgently.
Disclosure of Invention
In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide liquid CO in coal seam2Method for judging cracking dominant direction of phase change oriented perforation to obtain liquid CO of coal bed2The advantage direction of the phase change oriented perforation cracking is reduced, the construction amount of drilling is reduced, and the perforation cracking efficiency is improved.
The technical scheme of the invention is as follows:
coal bed liquid CO2The method for judging the cracking dominant direction of the phase change oriented perforation comprises the following main steps:
the theoretical corresponding relation between the hole wall fracture pressure P and the borehole azimuth angle alpha, the inclination angle beta and the perforation angle theta is calculated,
specifically, a calculation model of perforation induced cracking hole wall cracking pressure under the action of ground stress is established by adopting an elastic mechanics theory, three-dimensional ground stress is converted into a drilling hole Cartesian coordinate system by adopting a formula (1),
in the formula: sigmaH、σh、σvRespectively the stress components of the drill hole in the directions of X, Y and Z in a Cartesian coordinate system, and the unit is MPa; tau isxy、τxz、τyzIs the shear stress component in MPa; sigma1、σ2、σ3Maximum, intermediate and minimum principal stresses, respectively, in units of MPa; alpha and beta are respectively the azimuth angle and the inclination angle of the drill hole, and the unit is DEG,
and (3) obtaining the stress distribution at the surrounding rock r of the hole wall of the drill hole by considering the superposition of the ground stress and the perforation stress as follows:
in the formula: r, r for borehole diameter and polar radius, m, respectively; pwfThe perforation pressure in the hole is MPa; sigmar、σθ、σzz、σrθ、σθz、σzrAre respectively at a distance r from the axis of the drilled hole and at a distance σHThe radial, tangential and axial normal stress and shear stress components at the angle theta, MPa, can obtain the stress distribution at the hole wall of the drill hole (R ═ R) by the formula (2) as follows:
the main stress of any point on the wall of the hole is satisfied,
therefore, the main stress of any point on the wall of the drilled hole can be obtained by the combination formula (3):
in the formula: sigma1′、σ2′、σ3' maximum, middle and minimum principal stress of any point on the hole wall of the drill hole, MPa,
according to the theory of elasticity and mechanics combined formula (4), the maximum tensile stress of the hole wall of the drilled hole can be obtained as follows:
in the perforation and fracturing process, the condition of the fracture of the hole wall of the drilled hole is the maximum tensile stress sigma of the hole wallmax(theta) greater than the maximum tensile strength sigma of the wall rocktAnd the critical conditions for the perforation to cause the cracking of the hole wall are as follows:
the relation between the hole wall fracture pressure and the ground stress, the hole wall tensile strength, the rock Poisson's ratio, the drilling azimuth angle, the inclination angle and the perforation angle can be obtained by driving the formula (3) into the formula (6):
(II) testing the three-dimensional ground stress parameters of the application site;
thirdly, testing the Poisson's ratio of the rock and the tensile strength parameter of the hole wall;
fourthly, calculating the fracture pressure values of the hole wall under the conditions of different drilling azimuth angles, different drilling inclination angles and different drilling angle;
fifthly, determining the minimum hole wall fracture pressure under the conditions of different drilling azimuth angles and inclination angles;
sixthly, drawing a minimum hole wall fracture pressure distribution cloud picture and a relation curve chart under different drilling azimuth angles and inclination angles;
(VII) dividing according to the minimum pore wall fracture pressure distribution cloud chart and the relation curve chartAnalysis and determination of liquid CO2And (4) orienting the perforation and cracking dominant direction by phase change.
Preferably, the step (II) adopts an acoustic emission method three-dimensional ground stress testing method to test ground stress parameters, specifically, a rock test piece is drilled and extracted on a working surface to be subjected to coal bed gas extraction on site, the test piece is processed into a cylindrical test piece, the diameter-height ratio is 1: 2-1: 3, in order to determine the three-dimensional stress state of a measuring point, the test piece is prepared in six different directions in a rock sample of the point, a local coordinate system is set as oxyz, three directions are coordinate axis directions, the other three directions are axial angle bisector directions in an oxy, oyz and ozx plane, 15-25 samples are taken in each direction, the rock test piece is taken back to a laboratory to perform acoustic emission testing under the condition of uniaxial loading, a stress-cumulative acoustic emission ringing count-time curve is drawn according to an experimental result, Kaiser effect points are judged according to the curve, and the time of the Kaiser effect points of the rock test piece in each direction and the stress corresponding to the Kaiser effect points are obtained, i.e. sigmax、σy、σz、σxθy、σxγz、σyψzAnd recording, then adopting the following formula (8) to calculate the three-dimensional stress state of the ground stress measuring point,
in the formula sigma1、σ2、σ3The maximum principal stress, the middle principal stress and the minimum principal stress of the three-dimensional ground stress are respectively expressed in MPa; w, p and Q are calculation parameters, w is an inverse cosine function calculation result and has no unit; p is in MPa2(ii) a Q unit is MPa3W, p, and Q are calculated using the following formulas (9) and (10):
in the formula I1、I2、I3The first, second and third invariants of the stress tensor are respectively in the following units: MPa, MPa2，MPa3To calculate the parameters;
σx、σy、σzis the stress value corresponding to the Kaiser point of the rock test piece in the sampling directions of x, y and z on site, and the unit is MPa,
τxy、τxz、τyzrespectively are the shear stress on the planes xy, xz and yz in the space of the measuring point O, the unit is MPa, and the shear stress is calculated by the following formula (11),
lambda, gamma and psi are respectively xy, xz and yz in-plane sampling angles, and the unit is degree;
σxλy、σxγz、σyψz、σx、σy、σzthe unit of the stress value corresponding to each rock test piece Kaiser point in the field sampling direction is MPa, and the three-dimensional main stress direction of the test point is calculated according to the following formula (12):
the cosine of the direction of the principal stress vector relative to the y-axis and the z-axis is:
wherein:
principal stress sigmaiThe inclination angle and azimuth angle of (c) are calculated by equation (14):
in the formula
Is the angle between the principal stress and the xoy plane, i.e., the dip angle, in degrees,
in the form of an elevation angle,
is a depression angle; xiiIs the included angle between the projection of the main stress on the xoy surface and the x axis, and the unit is degree and xiiWhen more than 0 is anticlockwise rotation angle, xiiAnd if the rotation angle is less than 0, the rotation angle is anticlockwise rotation angle, and the rotation angle is converted into the azimuth angle of the main stress according to the x-axis azimuth angle measured on the sampling site after calculation.
Preferably, the rock poisson ratio parameter test in the step (three) adopts a rock elasticity mechanical parameter in-situ tester for testing, and the test method mainly utilizes longitudinal and transverse wave time difference data of the ultrasound in the rock mass to obtain the dynamic poisson ratio of the coal rock mass according to the following formula (15) by theoretical calculation:
in the formula: t iscThe time difference of longitudinal waves of the sound waves is us/m; t issThe method is used for the acoustic transverse wave time difference us/m and the rock elastic mechanical parameter in-situ test, and can adopt the following steps: a longitudinal and transverse wave direct test method, a longitudinal and transverse wave single hole test method or a longitudinal and transverse wave cross hole test method.
Preferably, the mechanical parameter test of the tensile strength of the pore wall in the step (three) adopts the Brazilian splitting method, and the following formula (16) is adopted to calculate after the test is finished,
in the formula sigmatTensile strength of rock, MPa; p is the failure load of the test, N; d is the diameter of the test piece, mm; h is the thickness of the test piece, mm, and three effective digits are calculated.
Preferably, the step (IV) is specifically,
(41) the ground stress parameter sigma obtained by the test1、σ2、σ3Obtaining the pore wall stress component (sigma) under the ground stress condition with the formula (1)H、σh、σv、τxy、τxz、τyz) Mechanical relation between the relative azimuth angle and inclination angle of the borehole, where1、σ2、σ3Alpha is a known parameter and belongs to 0-360 degrees, beta belongs to 0-90 degrees;
(42) stress component (sigma) of hole wallH、σh、σv、τxy、τxz、τyz) And the dynamic Poisson ratio v is put into the formula (3) to obtain the hole wall sigmar、σθ、σz、σθz、σrθAnd the mechanical relation among the azimuth angle, the inclination angle and the perforation angle of the borehole, wherein: v is the dynamic poisson's ratio; sigmaH、σh、σv、τxy、τxz、τyzIs an equation relating to alpha, beta; theta is a perforation angle and takes the value of 0-360 degrees;
(43) will sigmaθ、σz、σθzAnd testing the obtained rock tensile strength sigmatAnd (6) driving in, finally obtaining the mechanical relation between the hole wall fracture pressure P in the formula (7) and the drilling azimuth angle, the inclination angle and the perforation angle, and then inputting the azimuth angle, the inclination angle and the perforation angle of any drilling hole to obtain the fracture pressure of the drilling hole at the perforation angle.
Preferably, the step (v) is to sequentially perform the drilling azimuth angle α after obtaining the mechanical relationship between the hole wall fracture pressure P and the drilling azimuth angle α, the inclination angle β and the perforation angle θi(i ═ 1,2,3, … 360) (where α isi(i 1,2,3, … 360) sequentially takes 1 °,2 °,3 °, 360 °, and inclination βij(i ═ 1,2,3 … 360, j ═ 1,2,3 … 90) (where β isi(j1,2,3 … 360; j-1, 2,3 … 90) sequentially takes the values 1 °,2 °,3 °.90 °), and the perforation angle θijkCyclic calculation of (i 1,2,3 … 360; j 1,2,3 … 90; k 1,2,3 … 360) (1 °,2 °,3 °.360 ° in this order), and storage and comparison thereofCalculating the result, and keeping the smaller value of the rupture pressure until the minimum rupture pressure p is obtainedmin。
Preferably, the matlab mathematical calculation software is adopted in the step (six) for analysis and calculation, the data of the fracture pressure of the hole wall under different drilling azimuth angles, inclination angles and perforation angles are obtained, according to the calculated data sets of the fracture pressure of the hole wall, the inclination angles, the perforation angles and the inclination angles of the hole wall under the polar coordinate condition, the azimuth angle of the fracture pressure of the hole wall while drilling and the inclination angle change cloud chart under the rectangular coordinate system condition are drawn, and the azimuth angle of the fracture pressure of the hole wall while drilling and the inclination angle change curve under the rectangular coordinate system condition are drawn.
Has the advantages that: the invention adopts an acoustic emission three-dimensional ground stress test method to test and obtain the size and the direction of the three-dimensional ground stress of the coal bed, obtains a mechanical equation between the fracture pressure of the hole wall and the azimuth angle and the inclination angle of the drill hole under the condition of the three-dimensional ground stress, obtains a cloud picture of the change of the fracture pressure of the hole wall along with the azimuth angle and the inclination angle under the condition of polar coordinates, obtains a cloud picture of the change of the fracture pressure of the hole wall along with the azimuth angle and the inclination angle under the condition of a rectangular coordinate system, obtains the curve of the change of the fracture pressure of the hole wall along with the azimuth angle and the inclination angle under the condition of the rectangular coordinate system, and obtains the liquid CO of the coal bed through analysis according to the result2The direction of the phase change directional perforation cracking is the liquid CO2The drilling arrangement mode in the application process of the phase change fracturing permeability-increasing technology provides data support for increasing liquid CO2The phase change perforation cracking crack expanding size plays an important role, the technology can effectively increase the cracking hole influence radius, reduce the drilling engineering amount, improve the construction efficiency and achieve higher safety and reliability.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a cloud view of fracture at different azimuth and inclination angles in polar coordinates according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating the fracture variation law under the conditions of a fixed azimuth and different borehole inclination angles according to an embodiment of the present invention.
Detailed Description
The invention is further illustrated by the following examples in conjunction with the accompanying drawings:
coal seam liquid CO as shown in figure 12The method for judging the cracking dominant direction of the phase change oriented perforation specifically comprises the following steps: the theoretical corresponding relation between the hole wall fracture pressure P and the borehole azimuth angle alpha, the inclination angle beta and the perforation angle theta is calculated,
specifically, a calculation model of perforation induced cracking hole wall cracking pressure under the action of ground stress is established by adopting an elastic mechanics theory, three-dimensional ground stress is converted into a drilling hole Cartesian coordinate system by adopting a formula (1),
in the formula: sigmaH、σh、σvRespectively the stress components of the drill hole in the directions of X, Y and Z in a Cartesian coordinate system, and the unit is MPa; tau isxy、τxz、τyzIs the shear stress component in MPa; sigma1、σ2、σ3Maximum, intermediate and minimum principal stresses, respectively, in units of MPa; alpha and beta are respectively the azimuth angle and the inclination angle of the drill hole, and the unit is DEG,
and (3) obtaining the stress distribution at the surrounding rock r of the hole wall of the drill hole by considering the superposition of the ground stress and the perforation stress as follows:
in the formula: r, r for borehole diameter and polar radius, m, respectively; pwfThe perforation pressure in the hole is MPa; sigmar、σθ、σzz、σrθ、σθz、σzrAre respectively at a distance r from the axis of the drilled hole and at a distance σHThe radial, tangential and axial normal stress and shear stress components at the angle theta, MPa, can obtain the stress distribution at the hole wall of the drill hole (R ═ R) by the formula (2) as follows:
the main stress of any point on the wall of the hole is satisfied,
therefore, the main stress of any point on the wall of the drilled hole can be obtained by the combination formula (3):
in the formula: sigma1′、σ2′、σ3' maximum, middle and minimum principal stress of any point on the hole wall of the drill hole, MPa,
according to the theory of elasticity and mechanics combined formula (4), the maximum tensile stress of the hole wall of the drilled hole can be obtained as follows:
in the perforation and fracturing process, the condition of the fracture of the hole wall of the drilled hole is the maximum tensile stress sigma of the hole wallmax(theta) greater than the maximum tensile strength sigma of the wall rocktAnd the critical conditions for the perforation to cause the cracking of the hole wall are as follows:
the relation between the hole wall fracture pressure and the ground stress, the hole wall tensile strength, the rock Poisson's ratio, the drilling azimuth angle, the inclination angle and the perforation angle can be obtained by driving the formula (3) into the formula (6):
the relations of the hole wall rupture pressure, the ground stress, the hole wall tensile strength, the Poisson's ratio, the drilling azimuth angle, the inclination angle and the like can be seen from the formulas (1) and (7); determining that the hole wall fracture pressure of a site is controlled by an azimuth angle and an inclination angle, and in the hole with a specific azimuth and an inclination angle, different fracture initiation stresses of a perforation angle have certain difference;
(II) testing the three-dimensional ground stress parameters of an application site, performing the ground stress parameter test by adopting a three-dimensional ground stress test method of an acoustic emission method, drilling a hole on a working surface to be subjected to coal bed gas extraction on site to extract a rock test piece, processing the test piece into a cylindrical test piece with the diameter-height ratio of 1: 2-1: 3, preparing the test piece in the rock sample of the point along six different directions in order to determine the three-dimensional stress state of a measuring point, setting a local coordinate system as oxyz, taking coordinate axis directions from three directions, taking axial angle bisector directions in an oxy, oyz and ozx plane from the other three directions, sampling 15-25 blocks in each direction, returning the rock test piece to a laboratory to perform acoustic emission test under the condition of uniaxial loading, drawing a stress-cumulative ringing count-time curve according to the experimental result, judging the Kaiser effect points according to the curve to obtain the time of the Kaiser effect points of the rock test piece in each direction and the stress corresponding to the Kaiser effect points, i.e. sigmax、σy、σz、σxθy、σxγz、σyψzAnd recording; then, the three-dimensional stress state of the ground stress measuring point is calculated by adopting the following formula (8),
in the formula: sigma1、σ2、σ3The maximum principal stress, the middle principal stress and the minimum principal stress of the three-dimensional ground stress are respectively expressed in MPa;
w, p and Q are calculation parameters, w is an inverse cosine function calculation result and has no unit; p is in MPa2(ii) a Q unit is MPa3W, p, Q are calculated by the following formulas (9) and (10),
in the formula:
I1、I2、I3the first, second and third invariants of the stress tensor are respectively in the following units: MPa, MPa2，MPa3To calculate the parameters;
τxy、τxz、τyzthe shear stress on the planes xy, xz and yz in the space where the measuring point O is located is calculated by the following formula (11) in a unit of MPa.
σx、σy、σzIs the stress value corresponding to the Kaiser point of the rock test piece in the sampling directions of x, y and z on site, and the unit is MPa,
lambda, gamma and psi are respectively xy, xz and yz in-plane sampling angles, and the unit is degree;
σxλy、σxγz、σyψz、σx、σy、σzthe stress value corresponding to each rock test piece Kaiser point in the field sampling direction is expressed in MPa
The three-dimensional principal stress direction of the measuring point is calculated by the following formula (12):
the cosine of the direction of the principal stress vector relative to the y-axis and the z-axis is:
wherein:
principal stress sigmaiThe inclination angle and azimuth angle of (c) are calculated by equation (14):
in the formula:
is the angle between the principal stress and the xoy plane, i.e., the dip angle, in degrees,
in the form of an elevation angle,
is a depression angle; xiiIs the included angle between the projection of the main stress on the xoy surface and the x axis, and the unit is degree and xiiWhen more than 0 is anticlockwise rotation angle, xiiIf the rotation angle is less than 0, the rotation angle is anticlockwise rotation angle, and the rotation angle is converted into the azimuth angle of the main stress according to the x-axis azimuth angle measured on the sampling site after calculation;
(III) testing dynamic Poisson's ratio and tensile strength parameters of rock
1. Rock dynamic poisson ratio parameter test
The method mainly utilizes longitudinal and transverse wave time difference data of ultrasonic waves in a rock mass and obtains the dynamic Poisson's ratio of the coal rock mass according to the following formula (15) by theoretical calculation:
in the formula: t iscThe time difference of longitudinal waves of the sound waves is us/m; t issThe time difference of the transverse wave of the sound wave is us/m. The rock elastic mechanical parameter in-situ test can adopt the following steps: a longitudinal and transverse wave direct test method, a longitudinal and transverse wave single-hole test method and a longitudinal and transverse wave cross-hole test method;
2. mechanical parameter test for rock tensile strength
The rock reaches the biggest tensile stress that can bear when destroying under the uniaxial tension condition, be called the uniaxial tensile strength of rock, generally be referred to as tensile strength for short, can adopt direct tension method to the test of rock tensile strength, brazilian splitting method, point load method etc, because direct tension method test piece preparation difficulty, the test technique is complicated, point load method discreteness is very big, brazilian splitting method test piece is easily processed, consuming time and expense are few, can satisfy the engineering needs, consequently, this embodiment adopts brazilian splitting method to go on, brazilian splitting principle is that exert linear load on phi 50X 25 mm's disc test piece diameter direction, make the test piece produce the tensile stress destruction along radial, according to the elastomechanics principle: the maximum stress that the rock test piece can bear on a unit area is called uniaxial tensile strength of the rock, namely the ratio of the maximum load in the breaking process of the rock test piece to the sectional area perpendicular to the loading direction, and the test steps are as follows:
numbering test pieces, respectively measuring the diameter D and the height H of the test piece to be tested by using a vernier caliper, and measuring the same test piece for three times, taking an average value and making a record;
placing the splitting method test fixture in the center of a bearing plate of the testing machine, vertically placing a piece to be tested into the splitting method test fixture along the diameter, adjusting a press machine to load a pressure head, enabling the pressure head to be in contact with the fixture, and enabling the rock test piece to be uniformly stressed by adjusting a Brazilian splitting method spherical seat;
thirdly, through a computer control program, in a stress loading mode, adopting a stress loading rate of 0.1MPa per second until the test piece is damaged;
observing the damage development process of the test piece in the loading process, and recording the damage load of the test piece and the form after damage;
and (3) after the test results are collated, calculating the uniaxial tensile strength of the rock by adopting the following formula:
in the formula: sigmatUniaxial tensile strength, MPa, of the rock; p is the failure load of the test, N; d is the diameter of the test piece, mm; h is the thickness of the test piece, mm, and three effective digits are calculated;
(IV) calculating the fracture pressure values of the hole wall under the conditions of different drilling azimuth angles, different drilling inclination angles and different drilling angles
Specifically, the method comprises (41) testing the geostress parameter sigma obtained in the step (II)1、σ2、σ3Bringing into formula (1)Component of pore wall stress (σ) under geostress conditionsH、σh、σv、τxy、τxz、τyz) The mechanical relation between the relative azimuth angle and the inclination angle of the drilling hole,
in the formula: sigma1、σ2、σ3Alpha is a known parameter and belongs to 0-360 degrees, beta belongs to 0-90 degrees;
(42) then the stress component (sigma) of the hole wall is measuredH、σh、σv、τxy、τxz、τyz) And the dynamic Poisson ratio v is brought into the formula (3) to obtain the radial force, the circumferential force, the tangential force, the axial force and the like (sigma)r、σθ、σz、σθz、σrθ) The mechanical relation among the relative azimuth angle, the inclination angle and the perforation angle of the drilling hole,
in the formula: v is the dynamic poisson's ratio; sigmaH、σh、σv、τxy、τxz、τyzIs an equation relating to alpha, beta; theta is a perforation angle and ranges from 0 degree to 360 degrees,
(43) then will sigmaθ、σz、σθzAnd testing the uniaxial tensile strength sigma of the obtained rocktThe formula (6) is carried in, so that the mechanical relationship between the hole wall rupture pressure p of the formula (7) and the relative azimuth angle, inclination angle and perforation angle of the drill hole can be obtained,
wherein: sigmaH、σh、σv、τxy、τxz、τyzIs an equation for α, β, θ; v, sigmatIn order for the parameters to be known,
therefore, the fracture pressure of the borehole at the perforation angle can be obtained by inputting the relative azimuth angle, the inclination angle and the perforation angle of any borehole.
(V) determining the minimum hole wall fracture pressure under different drilling azimuth angles and inclination angles
To determine liquid CO in coal seams2The dominant direction of the phase change oriented perforation cracking is obtained by sequentially carrying out the mechanical relationship between the hole wall fracture pressure p and the relative azimuth angle alpha, the inclination angle beta and the perforation angle theta of the drill holei(i ═ 1,2,3, … 360) (where α isi(i 1,2,3, … 360) sequentially takes 1 °,2 °,3 °, 360 °, and inclination βi(j1,2,3 … 360; j ═ 1,2,3 … 90) (where β isi(j1,2,3 … 360; j-1, 2,3 … 90) sequentially takes the values 1 °,2 °,3 °.90 °), and the perforation angle θij(k1,2,3 … 360; j ═ 1,2,3 … 90; and (3) carrying out cyclic calculation on k-1, 2 and 3 … 360) (sequentially taking values of 1 degree, 2 degrees and 3 degreesmin。
Examples are: taking the relative azimuth angle as alpha1＝1°，β11Calculate θ sequentially as 1 °11k(k 1,2,3.. 360) is 1-360 degrees, and the calculation results are stored and compared to obtain the relative azimuth angle alpha1＝1°，β11The perforation angle and the minimum burst pressure at which the wall burst pressure is the minimum at 1 ° are given. Similarly, another alpha11 deg. and circulating sequentially1jAnd theta1jkAnd when the relative azimuth angle is 1 degree, calculating the fracture pressure of the drill holes with different inclination angles at different perforation angles, and comparing to obtain the corresponding drill hole inclination angle when the minimum fracture pressure is obtained. Finally, calculate αiWhen the values of (i ═ 1,2,3 and … 360) are 1 °,2 ° and 3 ° -360 °, the fracture pressure values at different inclination angles and different perforation angles are compared to obtain the minimum fracture pressure.
(VI) drawing the minimum hole wall fracture pressure distribution cloud chart and the relation curve chart under the conditions of different drilling azimuth angles and inclination angles
In the actual calculation process, matlab mathematical calculation software is adopted for analysis and calculation, hole wall fracture pressure data under different hole drilling azimuth angles, inclination angles and perforation angles are obtained according to calculated arrays of different hole drilling azimuth angles, inclination angles, perforation angles and hole wall fracture pressure, hole wall fracture pressure while drilling azimuth angles and inclination angle change cloud charts under the polar coordinate condition are drawn, and hole wall fracture pressure while drilling azimuth angles and inclination angle change curves under the rectangular coordinate system condition are drawn.
(VII) analyzing and determining the liquid CO according to the minimum pore wall fracture pressure distribution cloud chart and the relation curve chart2And (4) orienting the perforation and cracking dominant direction by phase change.
The process of the invention is illustrated below in a specific example.
In this embodiment, taking a white gelatin coal mine application place as an example, the three-dimensional ground stress testing method in step (two) is adopted to obtain ground stress parameters of the application place, as shown in the following table:
TABLE 1 mineral ground stress parameter of white gelatin (Unit: MPa)
And (3) testing to obtain an application site with the coal-rock Poisson ratio of 0.25 and the tensile strength of pore wall coal-rock of 5MPa by adopting the method of the step (three).
Adopting the step (IV), obtaining different drilling azimuth angles, inclination angles, perforation angles and hole wall fracture pressure arrays by applying a matlab calculation method, and drawing a hole wall fracture pressure while drilling azimuth angle and inclination angle change cloud chart under the polar coordinate condition, wherein a hole wall fracture pressure while drilling azimuth angle and inclination angle change curve under the rectangular coordinate system condition is shown in fig. 2 and fig. 3 specifically;
as can be seen from fig. 2: minimum burst pressure P of the hole wallminThe difference between the orientation angle alpha and the inclination angle beta of the hole is large while drilling, and when (alpha, beta) is (271, 56), P isminP is 26.7MPa, and (α, β) is (180,30)minThe former is 4.45 times of the latter under 6 MPa. And the relative orientation of the drilled holes can be seen in figure 2Angle alpha is [0,30 ]]、[150,210]、[330,360]When is, PminIs relatively low. It can be seen from FIG. 3 that the inclination angle is [0,45 ] under the condition of a certain azimuth angle α]And [135,180]Burst pressure PminThe value is relatively small, and P is measured when the inclination angle is 30 to 150minTaking the minimum value, P at the inclination angles of 54 and 125minThe maximum value is taken.
The analysis shows that in the process of drilling, fracturing and permeability increasing, the fracture stress of the hole wall changes along with the change of the azimuth angle and the inclination angle of the hole, so that the liquid CO is used for the drilling2In the process of determining the dominant direction of the phase change oriented perforation, optimal arrangement is carried out by combining the position relation of the site roadway and the coal seam. And the hole wall cracks firstly from the relative azimuth angle alpha of 0,30]、[150,210]、[330,360]A block section, i.e. the direction in which the maximum principal stresses are approximately parallel; obtaining liquid CO from test area of white gelatin coal mine2The optimal direction interval of the phase change oriented perforation is alpha epsilon [0,30]∪[150,210]∪[330,360]If the relative azimuth angle of the drill hole is influenced by the position relation between the roadway and the coal seam on the application site or other special factors, the relative azimuth angle needs to be arranged in alpha E [30,150 ]]∪[210,330]When the borehole inclination angle beta should be set to [25,45 ]]Within the interval. The result can be white gelatin coal mine liquid CO2The phase change fracturing permeability enhancement process drilling arrangement provides data support.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.
Claims (7)
1. Coal bed liquid CO2The method for judging the dominant direction of the phase change oriented perforation cracking is characterized by comprising the following main steps of:
the theoretical corresponding relation between the hole wall fracture pressure P and the borehole azimuth angle alpha, the inclination angle beta and the perforation angle theta is calculated,
specifically, a calculation model of perforation induced cracking hole wall cracking pressure under the action of ground stress is established by adopting an elastic mechanics theory, three-dimensional ground stress is converted into a drilling hole Cartesian coordinate system by adopting a formula (1),
in the formula: sigmaH、σh、σvRespectively the stress components of the drill hole in the directions of X, Y and Z in a Cartesian coordinate system, and the unit is MPa; tau isxy、τxz、τyzIs the shear stress component in MPa; sigma1、σ2、σ3The maximum principal stress, the middle principal stress and the minimum principal stress of the three-dimensional ground stress are respectively expressed in MPa; alpha and beta are respectively the azimuth angle and the inclination angle of the drill hole, and the unit is DEG,
and (3) obtaining the stress distribution at the surrounding rock r of the hole wall of the drill hole by considering the superposition of the ground stress and the perforation stress as follows:
in the formula: r, r for borehole diameter and polar radius, m, respectively; pwfThe perforation pressure in the hole is MPa; sigmar、σθ、σzzAre respectively at a distance r from the axis of the drilled hole and at a distance σHComponent of positive radial, tangential, axial stress at angle theta, sigmarθ、σθz、σzrIs a distance r from the axis of the drilled hole and is equal to sigmaHThe radial, tangential and axial shear stress components at the theta angle are shown, MPa and v are dynamic Poisson's ratio, and the stress distribution at the position where the hole wall R is R can be obtained by the formula (2):
the principal stress sigma of any point on the borehole wall is satisfied,
therefore, the main stress of any point on the wall of the drilled hole can be obtained by the combination formula (3):
in the formula: sigma'1、σ′2、σ′3Respectively the maximum principal stress, the middle principal stress and the minimum principal stress of any point on the hole wall of the drill hole, sigmazIs the stress component in the Z direction under the rectangular coordinate system, the unit is MPa,
according to the theory of elasticity and mechanics combined formula (4), the maximum tensile stress of the hole wall of the drilled hole can be obtained as follows:
in the perforation and fracturing process, the condition of the fracture of the hole wall of the drilled hole is the maximum tensile stress sigma of the hole wallmax(theta) greater than the maximum tensile strength sigma of the wall rocktAnd the critical conditions for the perforation to cause the cracking of the hole wall are as follows:
the relation between the hole wall fracture pressure and the ground stress, the hole wall tensile strength, the rock Poisson's ratio, the drilling azimuth angle, the inclination angle and the perforation angle can be obtained by driving the formula (3) into the formula (6):
(II) testing the three-dimensional ground stress parameters of the application site;
thirdly, testing the Poisson's ratio of the rock and the tensile strength parameter of the hole wall;
fourthly, calculating the fracture pressure values of the hole wall under the conditions of different drilling azimuth angles, different drilling inclination angles and different drilling angle;
fifthly, determining the minimum hole wall fracture pressure under the conditions of different drilling azimuth angles and inclination angles;
sixthly, drawing a minimum hole wall fracture pressure distribution cloud picture and a relation curve chart under different drilling azimuth angles and inclination angles;
(VII) analyzing and determining the liquid CO according to the minimum pore wall fracture pressure distribution cloud chart and the relation curve chart2And (4) orienting the perforation and cracking dominant direction by phase change.
2. Coal seam liquid CO according to claim 12The method for judging the cracking dominant direction of the phase change oriented perforation is characterized by comprising the following steps: step (two), a three-dimensional ground stress testing method of an acoustic emission method is adopted to test ground stress parameters, specifically, a rock test piece is extracted by drilling holes on a working surface to be subjected to coal bed gas extraction on site, the test piece is processed into a cylindrical test piece, the diameter-height ratio is 1: 2-1: 3, in order to determine the three-dimensional stress state of a measuring point, the test piece is prepared in six different directions in a rock sample of the point, a local coordinate system is set as oxyz, coordinate axis directions are taken in three directions, axial angle bisector directions in the planes of oxyy, oyz and ozx are taken in the other three directions, 15-25 blocks are sampled in each direction, the rock test piece is taken back to a laboratory to carry out acoustic emission testing under the condition of uniaxial loading, a stress-acoustic emission cumulative ringing count-time curve is drawn according to the experimental result, Kaiser effect points are judged according to the curve, and stress values corresponding to each test piece rock Kaiser point in the field sampling direction are obtained, i.e. sigmax、σy、σz、σxλy、σxγz、σyψzAnd recording, then adopting the following formula (8) to calculate the three-dimensional stress state of the ground stress measuring point,
in the formula sigma1、σ2、σ3The maximum principal stress, the middle principal stress and the minimum principal stress of the three-dimensional ground stress are respectively expressed in MPa; w, p and Q are calculation parameters, w is an inverse cosine function calculation result and has no unit; p is in MPa2(ii) a Q unit is MPa3W, p, and Q are calculated using the following formulas (9) and (10):
in the formula I1、I2、I3The first, second and third invariants of the stress tensor are respectively in the following units: MPa, MPa2，MPa3To calculate the parameters;
τxy、τxz、τyzrespectively are the shear stress components on the xy, xz and yz planes in the space of the measuring point O, the unit is MPa, and the shear stress components are calculated by the following formula (11),
lambda, gamma and psi are respectively xy, xz and yz in-plane sampling angles, and the unit is degree;
σxλy、σxγz、σyψz、σx、σy、σzand the unit is MPa, the stress value corresponding to each rock test piece Kaiser point in the field sampling direction is obtained by calculating the following formula (12) in the three-dimensional main stress direction of the test point:
the cosine of the direction of the principal stress vector relative to the y-axis and the z-axis is:
wherein m isiIs a complementary rotation in the y-axis direction, niIs the residual rotation in the direction of the z axis,
wherein:
principal stress sigmaiThe inclination angle and azimuth angle of (c) are calculated by equation (14):
in the formula
Is the angle between the principal stress and the xoy plane, i.e., the dip angle, in degrees,
in the form of an elevation angle,
is a depression angle; xiiIs the included angle between the projection of the main stress on the xoy surface and the x axis, and the unit is degree and xiiWhen more than 0 is anticlockwise rotation angle, xiiAnd if the rotation angle is less than 0, the rotation angle is anticlockwise rotation angle, and the rotation angle is converted into the azimuth angle of the main stress according to the x-axis azimuth angle measured on the sampling site after calculation.
3. Coal seam liquid CO according to claim 22The method for judging the cracking dominant direction of the phase change oriented perforation is characterized by comprising the following steps: and (3) testing the Poisson ratio parameter of the rock in the step (III) by adopting a rock elasticity mechanical parameter in-situ tester, wherein the testing method utilizes the longitudinal and transverse wave time difference data of the ultrasound in the rock mass to obtain the dynamic Poisson ratio of the coal rock mass according to the following formula (15) by theoretical calculation:
in the formula: t iscThe time difference of longitudinal waves of the sound waves is us/m; t issThe method is used for the in-situ test of the acoustic transverse wave time difference us/m and the rock elastic mechanical parameters, and miningThe following steps are used: a longitudinal and transverse wave direct test method, a longitudinal and transverse wave single hole test method or a longitudinal and transverse wave cross hole test method.
4. Coal seam liquid CO according to claim 32The method for judging the cracking dominant direction of the phase change oriented perforation is characterized by comprising the following steps: in the step (III), the Brazilian splitting method is adopted for testing the mechanical parameters of the tensile strength of the pore wall, the following formula (16) is adopted for calculation after the test is finished,
wherein P is the experimental hole wall rupture pressure, N; d is the diameter of the test piece, mm; h is the thickness of the test piece, mm, and three effective digits are calculated.
5. Coal seam liquid CO according to claim 42The method for judging the cracking dominant direction of the phase change oriented perforation is characterized by comprising the following steps: the step (four) is specifically that,
(41) the maximum principal stress, the middle principal stress and the minimum principal stress, sigma, of the three-dimensional ground stress obtained by the test1、σ2、σ3Obtaining stress components sigma of a drill hole in the X, Y and Z directions by the following formula (1)H、σh、σvAnd a shear stress component τxy、τxz、τyzMechanical relation between the relative azimuth angle and inclination angle of the borehole, where1、σ2、σ3Alpha is a known parameter and belongs to 0-360 degrees, beta belongs to 0-90 degrees;
(42) will sigmaH、σh、σv、τxy、τxz、τyzAnd the dynamic Poisson ratio v is substituted into the formula (3) to obtain the stress sigma at the position of the hole wall R-Rr、σθ、σz、σθz、σrAnd the mechanical relation between theta and the azimuth angle, the inclination angle and the perforation angle of the borehole is as follows: v is the dynamic poisson's ratio; sigmaH、σh、σv、τxy、τxz、τyzIs an equation related to alpha and betaFormula (I); theta is a perforation angle and takes the value of 0-360 degrees;
(43) will sigmaθ、σz、σθzAnd sigma obtained by testingtAnd (6) carrying in, finally obtaining the mechanical relation between the formula (7) P and the azimuth angle, the inclination angle and the perforation angle of the drilling hole, and then inputting the azimuth angle, the inclination angle and the perforation angle of any drilling hole to obtain the fracture pressure of the drilling hole at the perforation angle.
6. Coal seam liquid CO according to claim 52The method for judging the cracking dominant direction of the phase change oriented perforation is characterized by comprising the following steps: the step (V) is to carry out the drilling azimuth angle alpha after the mechanical relation among the hole wall fracture pressure P, the drilling azimuth angle alpha, the inclination angle beta and the perforation angle theta is obtainediThe values 1 °,2 °,3 °.360 ° in this order, i ═ 1,2,3, … 360, and the angle of inclination βijThe values are 1 °,2 °,3 °.90 ° in sequence, where i is 1,2,3 … 360; j is 1,2,3 … 90, and perforation angle thetaijkThe values are 1 °,2 °,3 °.360 ° in sequence, where i is 1,2,3 … 360; j ═ 1,2,3 … 90; the calculation of k is 1,2,3 … 360, and the calculation results are stored and compared, and the smaller value of the rupture pressure is kept until the minimum rupture pressure p is obtainedmin。
7. Coal seam liquid CO according to claim 62The method for judging the cracking dominant direction of the phase change oriented perforation is characterized by comprising the following steps: and step six, analyzing and calculating by using matlab mathematical calculation software to obtain hole wall fracture pressure data under different drilling azimuth angles, inclination angles and perforation angles, drawing a hole wall fracture pressure while drilling azimuth angle and inclination angle change cloud chart under the polar coordinate condition, drawing a hole wall fracture pressure while drilling azimuth angle and inclination angle change cloud chart under the rectangular coordinate system condition, and drawing a hole wall fracture pressure while drilling azimuth angle and inclination angle change cloud chart under the rectangular coordinate system condition according to the calculated different drilling azimuth angles, inclination angles, perforation angles and hole wall fracture pressure arrays.
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