CN113255123A - Evaluation method for geological conditions of staged multi-cluster fracturing applicability of horizontal well of coal seam roof - Google Patents

Evaluation method for geological conditions of staged multi-cluster fracturing applicability of horizontal well of coal seam roof Download PDF

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CN113255123A
CN113255123A CN202110531317.8A CN202110531317A CN113255123A CN 113255123 A CN113255123 A CN 113255123A CN 202110531317 A CN202110531317 A CN 202110531317A CN 113255123 A CN113255123 A CN 113255123A
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曹金豪
郭天魁
曲占庆
陈铭
刘晓强
王云鹏
牛保伦
吕明锟
徐建春
王森
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China University of Petroleum East China
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Abstract

The embodiment of the invention relates to a method for evaluating geological conditions of staged multi-cluster fracturing applicability of a horizontal well of a coal seam roof, which comprises the following steps: step S10, obtaining parameters of a fracturing well shaft, geological parameters of an oil reservoir, fracturing well completion information and fracturing construction parameters, and establishing a physical model of fracture expansion; step S20, establishing a three-dimensional fracture expansion efficient calculation model of the inhomogeneous reservoir with inhomogeneous expansion of fracture height; step S30, aiming at improving the effective area in the coal seam, establishing a coal seam roof fracturing applicability evaluation index, and determining the coal seam roof horizontal well subsection multi-cluster fracturing transformation effect under different geological conditions; and step S40, determining the seam height extension condition by combining construction pressure analysis and distributed optical fiber strain monitoring, correcting model calculation, and simulating and analyzing the roof fracturing transformation effect.

Description

Evaluation method for geological conditions of staged multi-cluster fracturing applicability of horizontal well of coal seam roof
Technical Field
The embodiment of the invention relates to the technical field of oil and gas field development, in particular to a modeling method for integrating staged multi-cluster fracturing fracture expansion and proppant migration of a horizontal well.
Background
The method has the advantages that the broken soft coal beds are widely distributed in partial areas of China, the coal bed gas resources are rich, however, the coal beds are poor in physical property, the porosity is less than 2%, the permeability is less than 0.1mD, the development difficulty is high, drilling and fracturing are carried out in the coal beds due to the characteristics of low coal bed strength and easiness in breaking, drilling liquid pollutes the coal beds and coal bed drilling well wall collapse accidents are caused, and follow-up fracturing transformation is not facilitated.
The top plate fracturing coal bed provides a new idea for soft coal bed gas development, fracturing is carried out on the coal bed top plate by utilizing the technology, and fracturing reformation of a soft coal gas reservoir is realized through vertical cross-layer expansion of cracks. By using the shale gas large-scale fracturing transformation idea for reference, the coal seam roof fracturing also develops the research and application of the horizontal well subsection multi-cluster fracturing theory. However, research on favorable geological conditions suitable for fracturing of a roof horizontal well is rarely reported at present, and the accurate design of the distance between the horizontal well and the top surface of a coal seam, the cluster spacing and the like lacks theoretical basis. Aiming at the problem, the invention provides an evaluation method for geological conditions of subsection multi-cluster fracturing applicability of a horizontal well of a coal seam roof.
Disclosure of Invention
The embodiment of the invention aims to provide an evaluation method for geological conditions of staged multi-cluster fracturing applicability of a horizontal well of a coal seam roof, aiming at solving the problem of how to evaluate and optimize proper geological conditions for fracturing the coal seam roof and designing a certain guiding significance for a fracturing construction scheme of the horizontal well of the coal seam roof.
In order to solve the technical problem, the embodiment of the invention provides a method for evaluating geological conditions of staged multi-cluster fracturing applicability of a horizontal well of a coal seam roof, which comprises the following steps:
step S10, obtaining parameters of a fracturing well shaft, geological parameters of an oil reservoir, fracturing well completion information and fracturing construction parameters, and establishing a physical model of fracture expansion;
step S20, establishing a three-dimensional fracture expansion efficient calculation model of the inhomogeneous reservoir with inhomogeneous expansion of fracture height;
step S30, aiming at improving the effective area in the coal seam, establishing a coal seam roof fracturing applicability evaluation index, and determining the coal seam roof horizontal well subsection multi-cluster fracturing transformation effect under different geological conditions;
and step S40, determining the seam height extension condition by combining construction pressure analysis and distributed optical fiber strain monitoring, correcting model calculation, and simulating and analyzing the roof fracturing transformation effect.
Preferably, the step S10 includes:
acquiring parameters of a fracturing well shaft, geological parameters of an oil reservoir, fracturing well completion information and fracturing construction parameters;
and establishing a physical model of fracture propagation according to geological and engineering parameters, wherein the physical model of fracture propagation comprises a computational domain geometric model, a reservoir geological model and a shaft geometric model.
Preferably, the parameters of the fractured well shaft comprise the inner diameter of a casing, the roughness of the inner wall of the casing, the length of a straight well section and the length of a fractured section;
the oil reservoir geological parameters are obtained by a logging technology and comprise longitudinal distribution of minimum horizontal principal stress, Young modulus of rock, Poisson's ratio, fracture toughness and fluid loss coefficient;
the fracturing well completion information comprises cluster spacing, cluster number and perforation parameters;
the fracturing construction parameters comprise construction discharge capacity and liquid viscosity.
Preferably, the step S20 includes:
establishing a solid equation;
building a shaft flow model;
establishing an in-seam flow model;
and establishing a fluid-solid coupling equation in the gap.
Preferably, the establishing process of the solid equation comprises:
and calculating rock deformation by adopting a three-dimensional displacement discontinuous model, wherein the pressure in the crack and the crack width can be expressed as follows:
pf(x，y，z，t)-σ0(x，y，z)＝∫A(t)G(x-x′，y-y′，z-z′)w(x′，y′，z′)dA； (1)
based on the stress equivalent idea, a homogenization method is adopted to calculate the upscaling of the mechanical change of the thin rock and the change of the ground stress, an equivalent depicting method of the mechanical property and the stress distribution of the heterogeneous rock of the reservoir under a coarse grid is established, the efficient solving of the three-dimensional fracture stress interference of the heterogeneous reservoir is realized, and the upscaling equivalent calculation formula of the thin interbed mechanical parameters is as follows:
Figure BDA0003068003910000021
wherein the content of the first and second substances,
pf(x, y, z, t) is the fluid pressure, MPa;
σ0(x, y, z) is far field ground stress, MPa;
(x, y, z) are field points;
t is time, s;
g (x ', y', z ') is a non-uniform reservoir Green function, and is obtained by superposing the uniform reservoir Green functions through a mirror image method, wherein (x', y ', z') is a source point;
a (t) is the area of the opened crack at time t, m2；
w (x ', y ', z ') is a fracture width function, m;
< q > is the equivalent value of the thin interbed mechanical parameter upscaling;
qiis the value of the ith layer mechanical parameter q;
hiis the thickness of the ith layer.
Preferably, the process of establishing the wellbore flow model comprises:
Figure BDA0003068003910000031
pw＝pp,k+pc,k+pin,k； (4)
Figure BDA0003068003910000033
Figure BDA0003068003910000032
wherein Q istTotal flow rate for diversion of wellbore to clusters of fractures, m3/s；
QiThe flow rate of the ith crack, m3/s；
NfThe number of fractures opened for a fracturing stage;
pwbottom hole pressure;
k＝1，2，......，Nf；
pp,kthe perforation friction resistance of k cracks is MPa;
pc,kthe flow friction resistance of a shaft from a well mouth to a k crack is MPa;
pin,kthe inlet pressure of the k crack, MPa;
Qkinlet flow of k cracks, m3/s；
nkThe number of perforations is k perforation clusters;
dkthe perforation diameter of the k perforation cluster is mm;
k is a perforation abrasion correction coefficient and has no dimension;
fc(Re, epsilon) is the on-way friction coefficient of the flowing fracturing fluid in a shaft, and has no dimension;
Dwis the inner diameter of the fracturing string, m;
lkthe length of the pipe column from the well head to the k crack is m;
epsilon is the roughness of the inner wall of the fracturing string, m;
Vwthe flow velocity of the liquid in the shaft, m/s;
re is Reynolds number, Re ═ DwρVw/μ；
μ is the liquid viscosity, mPas;
rho is the liquid density, kg/m3。
Preferably, the establishing of the intra-slit flow model comprises:
establishing a constitutive equation of fluid flow in the gap as follows:
Figure BDA0003068003910000041
wherein the component form of formula (7) is:
Figure BDA0003068003910000042
the continuity equation for fluid flow within the slot is:
Figure BDA0003068003910000043
substituting formula (7) for formula (9) yields:
Figure BDA0003068003910000044
wherein the content of the first and second substances,
q is the volume flow, m3/s；
μ is the fluid viscosity, Pa & s;
Qkinlet flow of k cracks, m3/s；
ClIs the fluid loss coefficient, m/min0.5；
t0Min, the moment when fluid loss begins;
Nfthe number of cracks;
(xin,k，yin,k，zin,k) Is the position of the feed point of the k crack;
(x, y, z) are field points;
w is the crack width, m;
t is time, s;
pffluid pressure, MPa;
δ () is the dirac function, m-2。
Preferably, the establishing of the fluid-solid coupling equation in the gap comprises:
the inlet flow of each crack satisfies:
Figure BDA0003068003910000051
the flow at the fracture boundary is zero, i.e.:
Figure BDA0003068003910000052
when the stress intensity factor of the crack tip meets the fracture toughness of the rock, the crack is expanded
Ktip＝KIc； (13)
The tip stress intensity factor is calculated by the formula
Figure BDA0003068003910000053
The crack tip satisfies:
Figure BDA0003068003910000054
all opening units and tip units are sequentially labeled as I, and the number of units at the current time is Ne, I is 1, 2. Adopting a constant unit displacement discontinuous method discrete equation:
Figure BDA0003068003910000055
the matrix form of equation (16) is:
p＝Cw+σ0； (17)
wherein the content of the first and second substances,
Q|inan inlet flow rate for the fracture;
Figure BDA0003068003910000056
flow at the fracture boundary;
wtipis the slit tip unit width, m;
in the formula (14), d is a unit length, m;
KIcis the fracture toughness of rock type I, MPa.m0.5；
w is the crack width, m;
μ is the fluid viscosity, Pa & s;
d in formula (15)1/2To the power of 1/2, m, of the distance from the tip;
K′＝4(2/π)0.5KIc，MPa·m0.5；
e 'is the plane strain Young's modulus, E ═ E/(1-v)2)，MPa。
v-rock poisson's ratio, dimensionless;
Ktipis the tip stress intensity factor;
n is the direction of fluid flow;
ne is the number of cells;
σ0at least horizontal principal stress，MPa；
p is the fluid pressure in the fracture, MPa;
CIJderived from the Green function, and is a component in a stiffness matrix of the displacement discontinuous boundary element;
wjis the width of the j cell, m;
and solving by adopting a Newton-Raphson method, and iteratively calculating the flow of each cluster with a fluid-solid coupling equation in the gap.
Preferably, the step S30 includes:
step S310, calculating fracture areas of the fractures at different positions according to the three-dimensional fracture expansion efficient calculation model of the heterogeneous reservoir established in the step S20, and smoothing data;
step S320, drawing a crack form cloud picture according to the smoothed crack area;
step S330, according to the crack form cloud picture, the coal seam crack area R is improvedA1And the specific gravity R of the coal seam crack area in the total fracturing reconstruction area is improvedA2Selecting the fracturing dominant geological conditions of the coal seam roof for evaluating indexes,
wherein the content of the first and second substances,
RA1the area of a coal seam crack is shown;
RA2the area ratio of the cracks expanded into the coal seam, namely the effective area ratio;
Acis the area of the crack in the coal seam, i.e. the effective area, m2；
AtIs the total area of the crack, m2。
Preferably, the step S40 includes:
step S410, determining the seam height extension condition by combining construction pressure analysis and distributed optical fiber strain monitoring, correcting model calculation, and simulating and analyzing the roof fracturing transformation effect;
and step S420, carrying out sensitivity analysis on geological conditions based on the Morris method, and evaluating and determining key geological parameters which have obvious influences on the fracture area of the coal seam and the fracture area.
Drawings
One or more embodiments are illustrated by way of example in the accompanying drawings, which correspond to the figures in which like reference numerals refer to similar elements and which are not to scale unless otherwise specified.
FIG. 1 is a schematic diagram of a physical fracture model of a horizontal coal bed well;
FIG. 2 is an exemplary illustration of fracture morphology when three clusters of fracture roofs are fractured;
FIG. 3 is an exemplary graph showing the change of fracture areas of different layers along with the injection time of fracturing fluid when three clusters of fracture roof are fractured;
FIG. 4 is an exemplary plot of coal seam fracture area ratio as a function of fracturing fluid injection time.
The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that, if directional indications (such as up, down, left, right, front, and back … …) are involved in the embodiment of the present invention, the directional indications are only used to explain the relative positional relationship between the components, the movement situation, and the like in a specific posture (as shown in the drawing), and if the specific posture is changed, the directional indications are changed accordingly.
In addition, if there is a description of "first", "second", etc. in an embodiment of the present invention, the description of "first", "second", etc. is for descriptive purposes only and is not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention.
The invention provides an evaluation method of geological conditions of subsection multi-cluster fracturing applicability of a horizontal well of a coal seam roof, which comprises the following steps:
step S10: acquiring parameters of a fracturing well shaft, geological parameters of an oil reservoir, fracturing well completion information and fracturing construction parameters, and establishing a physical model of crack expansion;
specifically, the step S10 includes:
step S11: acquiring parameters of a fracturing well shaft, geological parameters of an oil reservoir, fracturing well completion information and fracturing construction parameters;
the parameters of the fracturing well shaft comprise the inner diameter of a casing, the roughness of the inner wall of the casing, the length of a straight well section and the length of a fracturing section;
the oil reservoir geological parameters are obtained by a logging technology and comprise longitudinal distribution of minimum horizontal principal stress, Young modulus of rock, Poisson's ratio, fracture toughness and fluid loss coefficient;
the fracturing well completion information comprises cluster spacing, cluster number and perforation parameters (the number of perforation holes in each cluster, perforation diameter and the like);
the fracturing construction parameters comprise construction discharge capacity and liquid viscosity.
Step S12: and establishing a physical model of fracture propagation according to geological and engineering parameters, wherein the physical model of fracture propagation comprises a computational domain geometric model, a reservoir geological model and a shaft geometric model.
The present invention is further described with reference to numerical simulations and the accompanying drawings.
Taking an X coal-bed gas well as an example, specific reservoir geology, engineering parameters and wellbore parameters are shown in Table 1.
Table 1 example geological and engineering parameter table of X coal bed gas well
Figure BDA0003068003910000081
In this example, a physical model of 3 fractures of a horizontal well staged multi-cluster fracture of an X coalbed methane roof was established based on the geological and engineering parameters in table 1.
Step S20: establishing a three-dimensional fracture expansion efficient calculation model of the nonuniform reservoir with seam height and nonuniform expansion;
specifically, the three-dimensional crack propagation high-efficiency calculation model for the non-uniform propagation of the crack height mainly comprises four parts, namely a solid equation, a shaft flow model, an intra-crack flow model and an intra-crack fluid-solid coupling equation;
the step S20 includes:
step S21: establishing a solid equation;
specifically, the establishment process of the solid equation comprises the following steps:
and calculating rock deformation by adopting a three-dimensional displacement discontinuous model, wherein the pressure in the crack and the crack width can be expressed as follows:
pf(x，y，z，t)-σ0(x，y，z)＝∫A(t)G(x-x′，y-y′，z-z′)w(x′，y′，z′)dA； (1)
in order to realize the efficient calculation of the thin interbed condition, based on the stress equivalent thought, a homogenization method is adopted to calculate the upscaling of the mechanical change of the thin rock and the change of the ground stress, an equivalent depicting method of the mechanical property and the stress distribution of the heterogeneous rock of the reservoir under a coarse grid is established, the efficient solution of the three-dimensional crack stress interference of the heterogeneous reservoir is realized, and the upscaling equivalent calculation formula of the mechanical parameters of the thin interbed is as follows:
Figure BDA0003068003910000091
wherein the content of the first and second substances,
pf(x, y, z, t) is the fluid pressure, MPa;
σ0(x，y, z) is far field ground stress, MPa;
(x, y, z) are field points;
t is time, s;
(x ', y ', z ') as a source point;
g is a non-uniform reservoir Green function, and is obtained by superposing the Green functions of uniform reservoirs through a mirror image method;
a (t) is the area of the opened crack at time t, m2；
w is the crack width, m;
< q > is the equivalent value of the thin interbed mechanical parameter upscaling;
qiis the value of the ith layer mechanical parameter q;
hiis the thickness of the ith layer.
Step S22: building a shaft flow model;
specifically, the process of establishing the wellbore flow model comprises the following steps:
the flow distribution from the shaft to each cluster of cracks meets the conditions of mass conservation and pressure continuity, and the two conditions form a shaft flow model. For a section of open Nf slits, the total injection flow is equal to the sum of the branch flows, i.e.
Figure BDA0003068003910000101
The branch circuits formed by each crack have the same pressure drop, so
pw＝pp,k+pc,k+pin,k； (4)
Figure BDA0003068003910000102
Figure BDA0003068003910000103
Wherein Q istTotal flow for diversion of wellbore to clusters of fractures，m3/s；
QiThe flow rate of the ith crack, m3/s；
NfThe number of fractures opened for a fracturing stage;
pwbottom hole pressure;
k＝1，2，......，Nf；
pp,kthe perforation friction resistance of k cracks is MPa;
pc,kthe flow friction resistance of a shaft from a well mouth to a k crack is MPa;
pin,kthe inlet pressure of the k crack, MPa;
nkthe number of perforations is k perforation clusters;
dkthe perforation diameter of the k perforation cluster is mm;
k is a perforation abrasion correction coefficient and has no dimension;
Qkinlet flow of k cracks, m3/s；
fc(Re, epsilon) is the on-way friction coefficient of the flowing fracturing fluid in a shaft, and has no dimension;
Dwis the inner diameter of the fracturing string, m;
lkthe length of the pipe column from the well head to the k crack is m;
epsilon is the roughness of the inner wall of the fracturing string, m;
Vwthe flow velocity of the liquid in the shaft, m/s;
re is Reynolds number, Re ═ DwρVw/μ；
μ is the liquid viscosity, mPas;
rho is the liquid density, kg/m3。
Step S23: establishing an in-seam flow model;
specifically, the establishment of the intra-slit flow model includes:
the flow of the fracturing fluid in the hydraulic fracture is mainly laminar flow and accords with the Poiseup equation, so the constitutive equation of the flow of the fluid in the fracture is as follows:
Figure BDA0003068003910000111
wherein the component form of formula (7) is:
Figure BDA0003068003910000112
the continuity equation for fluid flow within the slot is:
Figure BDA0003068003910000113
substituting formula (7) for formula (9) yields:
Figure BDA0003068003910000114
wherein the content of the first and second substances,
q is the volume flow, m3/s；
μ is the fluid viscosity, Pa & s;
Qkinlet flow of k cracks, m3/s；
ClIs the fluid loss coefficient, m/min0.5；
t0Min, the moment when fluid loss begins;
Nfthe number of cracks;
(xin,k，yin,k，zin,k) Is the position of the feed point of the k crack;
(x, y, z) are field points;
w is the crack width, m;
t is time, s;
pffluid pressure, MPa;
δ () is the dirac function, m-2。
Step S24: and establishing a fluid-solid coupling equation in the gap.
Specifically, the establishment of the fluid-solid coupling equation in the gap comprises the following steps:
the inlet flow of each crack satisfies:
Figure BDA0003068003910000121
the flow at the fracture boundary is zero, i.e.:
Figure BDA0003068003910000122
when the stress intensity factor of the crack tip meets the fracture toughness of the rock, the crack is expanded
ktip＝KIc； (13)
The tip stress intensity factor is calculated by the formula
Figure BDA0003068003910000123
And calculating the crack propagation process by adopting a fixed grid, wherein the fixed grid is a rectangular unit structured grid. The unit is labeled as (i, j, k), and the corresponding position is (x)i,yj,zk). The cell types include 4 types: a channel unit, a tip unit, a unit to be activated and a unit not to be activated. Whether the tip cell reaches the expansion condition is judged each time, so that the cell type of the grid is updated. The cell center point is the solution point of the unknown quantity (width and pressure), and the cell boundary is the flow solution position.
The crack tip satisfies:
Figure BDA0003068003910000124
all opening units and tip units are sequentially labeled as I, and the number of units at the current time is Ne, I is 1, 2. Adopting a constant unit displacement discontinuous method discrete equation:
Figure BDA0003068003910000125
the matrix form of equation (16) is:
p＝Cw+σ0； (17)
wherein the content of the first and second substances,
Q|inan inlet flow rate for the fracture;
Figure BDA0003068003910000126
flow at the fracture boundary;
wtipis the slit tip unit width, m;
in the formula (14), d is a unit length, m;
KIcis the fracture toughness of rock type I, MPa.m0.5；
w is the crack width, m;
μ is the fluid viscosity, Pa & s;
d in formula (15)1/2To the power of 1/2, m, of the distance from the tip;
K′＝4(2/π)0.5KIc，MPa·m0.5；
e 'is the plane strain Young's modulus, E ═ E/(1-v)2)，MPa。
v-rock poisson's ratio, dimensionless;
Ktipis the tip stress intensity factor;
n is the direction of fluid flow;
ne is the number of cells;
σ0minimum horizontal principal stress, MPa;
CIJderived from the Green function, and is a component in a stiffness matrix of the displacement discontinuous boundary element;
wjis the width of the j cell, m;
p is the fluid pressure in the fracture, MPa;
and solving by adopting a Newton-Raphson method, and iteratively calculating the flow of each cluster with a fluid-solid coupling equation in the gap.
In this example, a 3-cluster fracture propagation model was established. Designing the grid size to be 2m multiplied by 2m, obtaining the flow of each cluster of cracks through a shaft model, further solving a fluid-solid coupling equation of flow and solid deformation in the cracks, solving the equation through an explicit method, comparing bottom hole pressure after obtaining unit width and pressure, if the bottom hole pressure of the equation is not converged with the bottom hole pressure of the shaft model, updating the bottom hole pressure, and returning to the shaft model until the bottom hole pressure is converged; and after a convergence result is obtained, updating the unit according to an expansion condition formula until the injection ending time.
Step S30: aiming at improving the effective area in the coal seam, establishing a coal seam roof fracturing applicability evaluation index, and determining the modification effect of the coal seam roof horizontal well staged multi-cluster fracturing under different geological conditions;
specifically, the step S30 includes:
step S310, calculating fracture areas of the fractures at different positions according to the three-dimensional fracture expansion efficient calculation model of the heterogeneous reservoir established in the step S20, and smoothing data;
step S320, drawing a crack form cloud picture according to the smoothed crack area;
step S330, according to the crack form cloud picture, the coal seam crack area R is improvedA1And the specific gravity R of the coal seam crack area in the total fracturing reconstruction area is improvedA2Selecting the fracturing dominant geological conditions of the coal seam roof for evaluating indexes,
wherein the content of the first and second substances,
RA1the area of a coal seam crack is shown;
RA2the area ratio of the cracks expanded into the coal seam, namely the effective area ratio;
Acis the area of the crack in the coal seam, i.e. the effective area, m2；
AtIs the total area of the crack, m2。
And based on the step S30, calculating the fracture areas of the fractures at different positions, smoothing the data by adopting a Gaussian filtering method, and drawing a fracture form cloud picture. Example results are shown in figures 2, 3, and 4. FIG. 2 is a fracture morphology chart of three-cluster fracture roof fracturing, and FIG. 3 is a chart of the changes of the fracture areas of different layers along with the injection time during the three-cluster fracture coal seam roof fracturingAnd 4, a chart of the coal seam fracture area ratio changing along with time. According to the figures 2, 3 and 4, geological conditions are changed, and changes of the fracture morphology, the coal seam fracture area and the coal seam fracture area ratio are analyzed to improve the coal seam fracture area RA1And the specific gravity R of the coal seam crack area in the total fracturing reconstruction area is improvedA2And selecting the fracturing dominant geological conditions of the coal seam roof for evaluation indexes.
Step S40: and determining the seam height extension condition by combining construction pressure analysis and distributed optical fiber strain monitoring, correcting model calculation, and simulating and analyzing the roof fracturing transformation effect.
Specifically, the step S40 includes:
step S410, determining the seam height extension condition by combining construction pressure analysis and distributed optical fiber strain monitoring, correcting and perfecting model calculation to enable the calculation to be more practical, and further simulating and analyzing the roof fracturing transformation effect;
and step S420, carrying out sensitivity analysis on geological conditions based on the Morris method, and evaluating and determining key geological parameters which have obvious influences on the fracture area of the coal seam and the fracture area.
Based on the step S40, the crack height extension condition is determined by combining construction pressure analysis and optical fiber strain monitoring, model calculation is corrected and perfected, calculation is more practical, and meanwhile, the roof fracturing transformation effect is further simulated and analyzed. And (4) carrying out sensitivity analysis on geological conditions based on a Morris method, and screening out geological condition parameters which have large influences on the coal seam crack area and the crack area ratio.
The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims (10)

1. The method for evaluating the geological conditions of the staged multi-cluster fracturing applicability of the horizontal well of the coal seam roof is characterized by comprising the following steps of:
step S10, obtaining parameters of a fracturing well shaft, geological parameters of an oil reservoir, fracturing well completion information and fracturing construction parameters, and establishing a physical model of fracture expansion;
step S20, establishing a three-dimensional fracture expansion efficient calculation model of the inhomogeneous reservoir with inhomogeneous expansion of fracture height;
step S30, aiming at improving the effective area in the coal seam, establishing a coal seam roof fracturing applicability evaluation index, and determining the coal seam roof horizontal well subsection multi-cluster fracturing transformation effect under different geological conditions;
and step S40, determining the seam height extension condition by combining construction pressure analysis and distributed optical fiber strain monitoring, correcting model calculation, and simulating and analyzing the roof fracturing transformation effect.
2. The method for evaluating geological conditions of the staged multi-cluster fracturing suitability of horizontal wells of the coal seam roof as claimed in claim 1, wherein the step S10 comprises:
acquiring parameters of a fracturing well shaft, geological parameters of an oil reservoir, fracturing well completion information and fracturing construction parameters;
and establishing a physical model of fracture propagation according to geological and engineering parameters, wherein the physical model of fracture propagation comprises a computational domain geometric model, a reservoir geological model and a shaft geometric model.
3. The method for evaluating geological conditions of the staged multi-cluster fracturing applicability of the horizontal well with the coal seam roof as claimed in claim 2, wherein the wellbore parameters of the fracturing well comprise the inner diameter of a casing, the roughness of the inner wall of the casing, the length of a straight well section and the length of a fracturing section;
the oil reservoir geological parameters are obtained by a logging technology and comprise longitudinal distribution of minimum horizontal principal stress, Young modulus of rock, Poisson's ratio, fracture toughness and fluid loss coefficient;
the fracturing well completion information comprises cluster spacing, cluster number and perforation parameters;
the fracturing construction parameters comprise construction discharge capacity and liquid viscosity.
4. The method for evaluating geological conditions of the staged multi-cluster fracturing suitability of horizontal wells of the coal seam roof as claimed in claim 1, wherein the step S20 comprises:
establishing a solid equation;
building a shaft flow model;
establishing an in-seam flow model;
and establishing a fluid-solid coupling equation in the gap.
5. The method for evaluating geological conditions of the staged multi-cluster fracturing applicability of horizontal wells of the coal seam roof as claimed in claim 4, wherein the establishing process of the solid equation comprises:
and calculating rock deformation by adopting a three-dimensional displacement discontinuous model, wherein the pressure in the crack and the crack width can be expressed as follows:
pf(x，y，z，t)-σ0(x，y，z)＝∫A(t)G(x-x′，y-y′，z-z′)w(x′，y′，z′)dA； (1)
based on the stress equivalent idea, a homogenization method is adopted to calculate the upscaling of the mechanical change of the thin rock and the change of the ground stress, an equivalent depicting method of the mechanical property and the stress distribution of the heterogeneous rock of the reservoir under a coarse grid is established, the efficient solving of the three-dimensional fracture stress interference of the heterogeneous reservoir is realized, and the upscaling equivalent calculation formula of the thin interbed mechanical parameters is as follows:
Figure FDA0003068003900000021
wherein the content of the first and second substances,
pf(x, y, z, t) is the fluid pressure, MPa;
σ0(x, y, z) is far field ground stress, MPa;
(x, y, z) are field points;
t is time, s;
g (x ', y', z ') is a non-uniform reservoir Green function, and is obtained by superposing the uniform reservoir Green functions through a mirror image method, wherein (x', y ', z') is a source point;
a (t) is the area of the opened crack at time t, m2；
w (x ', y ', z ') is a fracture width function, m;
< q > is the equivalent value of the thin interbed mechanical parameter upscaling;
qiis the value of the ith layer mechanical parameter q;
hiis the thickness of the ith layer.
6. The method for evaluating geological conditions of the staged multi-cluster fracturing applicability of horizontal wells of the coal seam roof as claimed in claim 4, wherein the process of establishing the wellbore flow model comprises:
Figure FDA0003068003900000022
pw＝pp，k+pc，k+pin，k； (4)
Figure FDA0003068003900000023
Figure FDA0003068003900000024
wherein Q istTotal flow rate for diversion of wellbore to clusters of fractures, m3/s；
QiThe flow rate of the ith crack, m3/s；
NfThe number of fractures opened for a fracturing stage;
pwbottom hole pressure;
k＝1，2，......，Nf；
pp，kthe perforation friction resistance of k cracks is MPa;
Qkinlet flow of k cracks, m3/s；
pc，kThe flow friction resistance of a shaft from a well mouth to a k crack is MPa;
pin，kthe inlet pressure of the k crack, MPa;
nkthe number of perforations is k perforation clusters;
dkthe perforation diameter of the k perforation cluster is mm;
k is a perforation abrasion correction coefficient and has no dimension;
fc(Re, epsilon) is the on-way friction coefficient of the flowing fracturing fluid in a shaft, and has no dimension;
Dwis the inner diameter of the fracturing string, m;
lkthe length of the pipe column from the well head to the k crack is m;
epsilon is the roughness of the inner wall of the fracturing string, m;
Vwthe flow velocity of the liquid in the shaft, m/s;
re is Reynolds number, Re ═ DwρVw/μ；
μ is the liquid viscosity, mPas;
rho is the liquid density, kg/m3。
7. The method for evaluating geological conditions of staged multi-cluster fracturing applicability of horizontal wells of coal seam roof according to claim 4, wherein the establishment of the intra-seam flow model comprises:
establishing a constitutive equation of fluid flow in the gap as follows:
Figure FDA0003068003900000031
wherein the component form of formula (7) is:
Figure FDA0003068003900000032
the continuity equation for fluid flow within the slot is:
Figure FDA0003068003900000041
substituting formula (7) for formula (9) yields:
Figure FDA0003068003900000042
wherein the content of the first and second substances,
q is the volume flow, m3/s；
μ is the fluid viscosity, Pa & s;
Qkinlet flow of k cracks, m3/s；
ClIs the fluid loss coefficient, m/min0.5；
t0Min, the moment when fluid loss begins;
Nfthe number of cracks;
(xin，k，yin，k，zin，k) Is the position of the feed point of the k crack;
(x, y, z) are field points;
w is the crack width, m;
t is time, s;
pffluid pressure, MPa;
δ () is the dirac function, m-2。
8. The method for evaluating geological conditions of the staged multi-cluster fracturing applicability of the horizontal well of the coal seam roof as claimed in claim 4, wherein the establishment of the fluid-solid coupling equation in the seam comprises:
the inlet flow of each crack satisfies:
Figure FDA0003068003900000043
the flow at the fracture boundary is zero, i.e.:
Figure FDA0003068003900000044
when the stress intensity factor of the crack tip meets the fracture toughness of the rock, the crack is expanded
Ktip＝KIc； (13)
The tip stress intensity factor is calculated by the formula
Figure FDA0003068003900000051
The crack tip satisfies:
Figure FDA0003068003900000052
all opening units and tip units are sequentially labeled as I, and the number of units at the current time is Ne, I is 1, 2. Adopting a constant unit displacement discontinuous method discrete equation:
Figure FDA0003068003900000053
the matrix form of equation (16) is:
p＝Cw+σ0： (17)
wherein the content of the first and second substances,
Q|inan inlet flow rate for the fracture;
Figure FDA0003068003900000054
flow at the fracture boundary;
wtipis the slit tip unit width, m;
in the formula (14), d is a unit length, m;
KIcis the fracture toughness of rock type I, MPa.m0.5；
w is the crack width, m;
μ is the fluid viscosity, pas;
d in formula (15)1/2To the power of 1/2 of the distance from the tip;
K′＝4(2/π)0.5KIc，MPa·m0.5；
e 'is the plane strain Young's modulus, E ═ E/(1-v)2)，MPa。
v-rock poisson's ratio, dimensionless;
Ktipis the tip stress intensity factor;
σ0minimum horizontal principal stress, MPa;
n is the direction of fluid flow;
ne is the number of cells;
p is the fluid pressure in the fracture, MPa;
CIJderived from the Green function, and is a component in a stiffness matrix of the displacement discontinuous boundary element;
wjis the width of the j cell, m; and solving by adopting a Newton-Raphson method, and iteratively calculating the flow of each cluster with a fluid-solid coupling equation in the gap.
9. The method for evaluating geological conditions of the staged multi-cluster fracturing suitability of horizontal wells of the coal seam roof as claimed in claim 1, wherein the step S30 comprises:
step S310, calculating fracture areas of the fractures at different positions according to the three-dimensional fracture expansion efficient calculation model of the heterogeneous reservoir established in the step S20, and smoothing data;
step S320, drawing a crack form cloud picture according to the smoothed crack area;
step S330, according to the crack form cloud picture, the coal seam crack area R is improvedA1And the specific gravity R of the coal seam crack area in the total fracturing reconstruction area is improvedA2Selecting the fracturing dominant geological conditions of the coal seam roof for evaluating indexes,
wherein the content of the first and second substances,
RA1the area of a coal seam crack is shown;
RA2the area ratio of the cracks expanded into the coal seam, namely the effective area ratio;
Acis the area of the crack in the coal seam, i.e. the effective area, m2；
AtIs the total area of the crack, m2。
10. The method for evaluating geological conditions of the staged multi-cluster fracturing suitability of horizontal wells of the coal seam roof as claimed in claim 1, wherein the step S40 comprises:
step S410, determining the seam height extension condition by combining construction pressure analysis and distributed optical fiber strain monitoring, correcting model calculation, and simulating and analyzing the roof fracturing transformation effect;
and step S420, carrying out sensitivity analysis on geological conditions based on the Morris method, and evaluating and determining key geological parameters which have obvious influences on the fracture area of the coal seam and the fracture area.
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