Directional perforation hydraulic fracturing initiation pressure heat-fluid-solid coupling prediction method

Abstract

The invention discloses a directional perforation hydraulic fracturing initiation pressure heat-fluid-solid coupling prediction method. The method mainly comprises the steps that elastic mechanical parameters, rock physical property and heat-mechanical coupling parameters, tensile strength, ground stress and pore pressure of a casing pipe, a cement sheath and stratum rock are obtained; obtaining well body structure and well track data; a stress field analytical solution of rock around a directional well under the effect of casing-cement sheath-thermal coupling under the condition of non-uniform ground stress is used as a boundary condition for solving a heat-fluid-solid coupling control equation of porous rock, and a heat-fluid-solid coupling analytical solution of perforation hole channel surrounding rock field variables is deduced; a directional perforation fracturing initiation pressure heat-fluid-solid coupling prediction method is established and used for predicting the initiation angle and the dynamic initiation pressure of directional perforation hydraulic fracturing and optimizing the perforation depth, the phase angle and the construction displacement. Theoretical and technical guidance is provided for directional perforation hydrofracture design, and the evaluation result is high in credibility.

Description

Technical Field

[0001] The invention relates to a thermal-fluid-solid coupling prediction method for directional perforation hydraulic fracturing initiation pressure, belonging to the technical field of (ultra) deep oil and gas drilling and completion. Background Art

[0002] In the hydraulic fracturing operation of deep (super) shale oil, gas or tight sandstone oil, gas reservoirs, the hydraulic fracturing crack initiation pressure is extremely high and the reservoir transformation efficiency is low due to the large horizontal stress difference and high closing pressure in some areas. For the casing-cement sheath-formation combination formed by casing completion, the cement sheath-casing is not only affected by the in-situ stress field of the formation, but also reacts to the open hole formation rock formed by drilling, resulting in the redistribution of the stress field of the rock around the well. The core parameter for controlling the perforation fracturing initiation pressure, perforation phase angle, perforation depth and fracturing displacement during casing perforation hydraulic fracturing operation - the stress field around the perforation hole is closely related to the casing-cement sheath combination and thermal action (in the process of hydraulic fracturing injection of fracturing fluid, there is a temperature difference between the fracturing fluid and the casing, cement sheath and formation rock, inducing the generation of additional thermal stress), and the thermal fluid-solid coupling of the rock around the hole. However, the linear elastic solution of the surrounding rock of conventional open hole wells cannot reflect the effect of casing-cement sheath-heat coupling on the stress field of the surrounding rock of the well, and thus cannot accurately predict the fracture initiation pressure and related parameters of perforation hydraulic fracturing. Furthermore, when solving the in-plane (related to the r-θ plane) and out-of-plane (related to the rz and θ-z planes) stress and displacement solutions of the casing-cement sheath, the initial in-plane displacement caused by stratum deposition or tectonic movement should be removed. and and the out-of-plane shear initial displacement w 0 impact.

[0003] The thermal-fluid-solid coupling effect mentioned above is reflected in the fact that the perforation operation penetrates the casing and cement ring to form a perforation channel inside the formation. The original forces on the channel wall - pore pressure and radial stress are replaced by the fluid (fracturing fluid) pressure inside the channel, and the shear stress becomes zero. The stress difference (or pressure difference) before and after the formation of the perforation hole causes the rock solid phase to deform, inducing changes in rock permeability and porosity, which in turn affects the flow state of the fluid inside the pores of the formation rock. The pressure gradient reflecting the flow state of the fluid will react on the rock solid phase - resisting its deformation. Furthermore, when the rock pore fluid is heated (such as the fracturing fluid temperature is higher than the original formation temperature), the fluid bears part of the load on the solid phase skeleton due to expansion (note that the rock solid phase has lower expansion than the pore fluid), causing overpressure. Conversely, the cooling effect causes the pore fluid to shrink and cannot "fill" the pore space, causing low pore pressure, which in turn causes the load on the solid phase skeleton to increase. On the other hand, the solid phase skeleton not only generates thermal stress due to thermal expansion and contraction, but the thermal expansion and contraction process will also affect the degree of overpressure or underpressure formation and the seepage process of the porous fluid. In summary, the fracturing process of (ultra) deep high-temperature wells is affected by the pressure difference and temperature difference, resulting in changes in the stress field (displacement field), pressure field and temperature field around the well due to the thermal-fluid-solid coupling effect. Among them, the effective stress around the well (principal stress minus pore pressure) is the prerequisite for controlling the initiation of hydraulic fractures. In this way, it is necessary to introduce a thermal-fluid-solid coupling model to accurately predict the changing laws of the field variables around the well and clarify the multi-field coupling mechanism that affects the initiation of hydraulic fracturing fractures in high-temperature and high-pressure wells.

[0004] Therefore, it is particularly important to comprehensively consider the influence of the casing-cement sheath combination and thermal effects on the formation stress field and the field variable solution of the thermal-fluid-solid coupling effect of the rock around the perforation holes, and then establish a method for predicting the initiation pressure of directional perforating hydraulic fracturing and optimize the relevant perforating and fracturing parameters to improve the efficiency of reservoir transformation.

[0005] At present, there are methods to predict the formation fracturing pressure, such as the invention patent with the publication number CN 112177598 A owned by China Petrochemical Corporation, which discloses a method for predicting the formation fracturing pressure taking into account the compressibility of the fracturing fluid. It includes establishing a discretized wellbore model of the flow of wellbore fracturing fluid to obtain the law of the change of bottom hole pressure over time and the law of the change of wellhead pressure over time; establishing a three-dimensional thermal fluid-solid coupling mechanical numerical model of the wellbore-cement sheath-near wellbore wall formation under perforation conditions, obtaining the distribution law of the near wellbore wall stress field and the distribution law of the seepage field during the wellbore pressure holding process, and inverting the formation fracturing time and the wellhead fracturing pressure. This method improves the calculation method of the fracturing pressure and fracturing time of shale gas well hydraulic fracturing, and provides a theoretical basis and design basis for in-depth understanding of the fracturing mechanism of shale gas well hydraulic fracturing and fracturing design.

[0006] The invention patent with publication number CN113109162A belonging to Southwest Petroleum University discloses a method for calculating rock fracturing pressure based on thermal-fluid-solid coupling. It includes determining the basic parameters of the target formation based on well logging data, indoor triaxial compression tests and Brazilian splitting experiments; establishing a rock fracturing pressure calculation model in Laplace space based on thermal-fluid-solid coupling according to the thermal-fluid-solid coupling control equations of the formation rock (i.e., stress balance equation, constitutive equation, transmission equation, mass conservation equation, heat conservation equation), boundary conditions and maximum tensile stress failure criterion; the rock fracturing pressure can be determined by inputting the basic parameters of the target formation through the fracturing pressure calculation model and combining it with the Stehfest numerical inversion method. The advantage of this invention is that it takes into account the coupling relationship between fluid seepage, thermal diffusion and rock deformation in the wellbore; by calculating more accurate formation fracturing pressure, it provides high-precision parameters for fracturing construction design to meet the needs of reservoir evaluation and fracturing transformation guidance.

[0007] Although the above two patents and other existing technical solutions have achieved certain technical effects, they do not provide analytical solutions for the stress field of the surrounding rock of any well type (vertical well, directional well and horizontal well) under non-uniform ground stress conditions under the action of casing-cement sheath-heat coupling, and the analytical solutions for the field variables (stress field and pore pressure field) of the surrounding rock of the perforation channel under the action of thermal fluid-solid coupling. The existing numerical models have convergence problems and low calculation efficiency. Compared with analytical methods, they cannot quickly predict the initiation angle and dynamic initiation pressure of directional perforation hydraulic fracturing, optimize the perforation depth, phase angle and construction displacement. Therefore, it is urgent to establish a thermal fluid-solid coupling prediction method for directional perforation initiation pressure that integrates the coupling of casing-cement sheath-formation. Summary of the invention

[0008] The present invention mainly overcomes the deficiencies in the prior art and proposes a thermal-fluid-solid coupling prediction method for the initiation pressure of directional perforation hydraulic fracturing.

[0009] The technical solution provided by the present invention to solve the above technical problems is: a method for predicting the thermal-fluid-solid coupling of the fracturing initiation pressure of directional perforating hydraulic fracturing, comprising the following steps:

[0010] Step 1: Use a gas permeameter to measure the permeability and porosity of the core;

[0011] Step 2: Use a thermal expansion meter to test the thermal expansion coefficients of the casing, cement sheath and rock. Use a thermal expansion meter to test the thermal expansion coefficients of the casing, cement sheath and rock. Use a thermal conductivity meter and a differential scanning calorimeter to test the specific heat capacity and thermal conductivity of the rock. Use a high-temperature and high-pressure rock triaxial tester to measure the elastic mechanical parameters, porous medium mechanical parameters and strength parameters of cement stone and formation rock.

[0012] Step 3: Use acoustic emission experiments to measure ground stress data to determine horizontal structural strain and to collect statistics on field measured pore pressure data;

[0013] Step 4: Use the experimental measurement data to determine the fitting coefficients in the theoretical prediction formulas of rock elasticity, porous medium mechanics and strength parameters, and combine the logging data to obtain the elasticity, porous medium mechanics and strength parameters of the rock at the downhole research depth;

[0014] Step 5: Invert the well logging data to obtain the in-situ stress and original pore pressure at the depth of the study well;

[0015] Step 6: Count the wellbore structure, wellbore trajectory and casing mechanical parameters;

[0016] Step 7: Using the deformation control equation and harmonic equation of the "casing-cement sheath-formation combination", derive the analytical solution of the stress field of the surrounding rock of the directional well under the condition of non-uniform ground stress under the action of casing-cement sheath-heat coupling;

[0017] Step 8: Using the new solution of rock stress around the directional wellbore under the action of casing-cement sheath-heat coupling and the thermal-fluid-solid coupling control equation of porous rock around the perforation channel, the analytical solution of the field variables (stress field and pore pressure field) of the surrounding rock of the directional perforation channel under the action of thermal-fluid-solid coupling is derived;

[0018] Step 9: Integrate the thermal-fluid-solid coupling solution of the rock field variables around the directional perforation holes and the rock tensile cracking criterion to predict the cracking angle and dynamic cracking pressure of directional perforation hydraulic fracturing, and optimize the perforation depth, phase angle and construction displacement.

[0019] A further technical solution is that the elastic mechanical parameters of the cement stone and the formation rock in step 2 include elastic modulus and Poisson's ratio; the porous medium mechanical coupling parameters of the rock include Biot effective stress coefficient and Skempton pore pressure coefficient; and the strength parameter refers to the tensile strength of the rock.

[0020] A further technical solution is that the geostress data measured by the acoustic emission experiment in step three includes the horizontal maximum geostress and the horizontal minimum geostress; the tectonic strain includes the tectonic strain in the directions of the horizontal maximum geostress and the horizontal minimum geostress.

[0021] A further technical solution is to use the experimental measurement data in step 4 to determine the fitting coefficients in the theoretical prediction formulas of rock elasticity, porous medium mechanics and strength parameters. The measurement data include: elastic modulus, Poisson's ratio, uniaxial compressive strength, tensile strength and Biot effective stress coefficient.

[0022] A further technical solution is that the logging data in step 4 includes acoustic wave time difference, density, gamma value and porosity.

[0023] A further technical solution is that the geostress data in step five includes overlying rock pressure, horizontal maximum geostress and horizontal minimum geostress.

[0024] A further technical solution is that the wellbore structure data in step six include wellbore size, casing outer diameter, wall thickness and cement slurry return height; the wellbore trajectory data include well inclination and azimuth; and the casing mechanical parameters include the elastic modulus and Poisson's ratio of the casing.

[0025] A further technical solution is that the analytical solution of the stress field of the rock around the directional well in step 7 under the action of casing-cement sheath-heat coupling is:

[0026]

[0027] Where, T3 is the cement sheath-formation interface temperature, °C; r is the radial distance from the wellbore center to a certain position inside the formation, m; r3 is the wellbore radius, m; and They are the in-plane radial stress, tangential stress, and shear stress of the rock around the well, MPa; the out-of-plane shear stress includes and MPa; v3 is the Poisson's ratio of the formation rock, dimensionless; θ is the wellbore angle, the vector radius of the research location and the horizontal maximum ground stress σ H The angle of the azimuth, °; the average formation stress P0 and shear stress S0 are defined as and MPa; or is the stress component of the borehole coordinate system, MPa; the intermediate value of the conversion angle θ r Defined as °C 1，3 , C 2，3 , and M3 are unknown coefficients related to the internal stress of the stratum; B3 and D3 are unknown coefficients related to the external shear stress of the stratum; the Lame constant λ3 and shear modulus G3 of the rock are defined as The Biot effective stress coefficient α3 of the formation rock is defined as The dimensionless poroelastic stress coefficient η3 is defined as Dimensionless; coefficient related to thermal expansion stress MPa / ℃, where α s，3 is the volumetric thermal expansion coefficient of formation rock, 1 / °C.

[0028] A further technical solution is that the calculation formula for the field variables (stress field and pore pressure field) of the surrounding rock of the directional well perforation channel under the effect of thermal fluid-solid coupling in step eight is:

[0029] T p =T0+Tp(a)

[0030] p p =p p +p p(a) +p p(d)

[0031]

[0032]

[0033] Where: T0 is the original formation temperature, °C; p p is the original pore pressure of the formation, MPa; θ′ is the circumferential angle of the perforation channel, °; the stress field components around the perforation channel include radial stress Tangential stress Axial stress Shear stress in the θ′-z plane r-θ′ plane and the shear stress in the zr plane MPa. The intermediate quantities P′0 and S′0 are respectively and MPa. The intermediate value of the conversion angle θ′ with the perforation channel as the research object r definition °.

[0034] A further technical solution is that the tensile cracking criterion in step nine is:

[0035] σ′3=-S t

[0036] Where, the tensile strength of rock S t Defined as S t =σ c / ω, MPa; σ c is the uniaxial compressive strength, MPa; ω is the conversion coefficient ω. σ′3 is the minimum effective principal stress around the perforation channel, MPa.

[0037] A further technical solution is that the process of determining the dynamic fracturing pressure of the directional perforating well in step nine is as follows:

[0038] Definition of well inclination angle γ bi =i°(i=0:i:90), azimuth angle Ω bj =j°(j=0:j:360), wellbore angle (perforation phase angle)θ k = k°(k=0:k:360), circumferential angle of perforation channel θ′ m = m° (m = 0: m: 360), used to determine the fracture initiation pressure required for rock to undergo tensile fracture in, The binary method can be used to solve the problem. The specific steps are as follows: ① Under these conditions, the initial upper and lower limits p min , p max Substituting the tensile rupture criterion, we can obtain V min and V max (where p max can be set to be greater than the three principal in-situ stresses (σ H , σ h , σ v ) maximum value); ② Determine V min and V max Whether they are of different signs, take p1=(p min +p max ) / 2, update the upper and lower limits and Then, the stress around the perforation channel is introduced and combined with the tensile fracture criterion to obtain and Repeat step ② until a certain error is met and output; ③ Repeat operations ① and ② to obtain a three-dimensional matrix that meets the error ∈ (where i∈[0°,90°], j∈[0°,360°], θ′ m =m°(m=0:m:360)); ④ Further select the channel circumferential angle θ′ that meets the above conditions m =m°(m=0:m:360) Minimum value, given the well inclination and azimuth The directional perforation fracturing initiation pressure corresponding to the tensile fracture of the pore rock (* represents the specific value assigned to the parameter), the circumferential angle θ′ corresponding to the crack initiation value m is the crack initiation angle of the perforation channel.

[0039] A further technical solution is that the values ​​of the thermal-fluid-solid coupling field variables (stress field and pore pressure field) of the surrounding rock of the perforated channel in step nine have time correlation, and the boundary conditions for solving the field variables are affected by the wellhead injection displacement. Therefore, the fracture pressure value determined by this method changes dynamically with the fracturing construction time, and the wellhead injection displacement can be optimized by the fracture pressure value. Furthermore, the thermal-fluid-solid coupling field variable values ​​of the surrounding rock of the perforated channel depend on the perforation depth, and the perforation depth can be optimized by studying the fracture pressure value law of different perforation depths.

[0040] The present invention has the following beneficial effects: the thermal-fluid-solid coupling prediction method for the directional perforating hydraulic fracturing initiation pressure proposed in the present invention is simple and easy to understand, convenient to operate, and low in cost. It provides a scientific basis for the prediction of the directional perforating hydraulic fracturing initiation pressure in (ultra) deep high-temperature wells, and can effectively guide the directional perforating hydraulic fracturing design and optimize the on-site construction parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a flowchart of the present invention. DETAILED DESCRIPTION

[0042] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] like Figure 1 As shown, the present invention provides a method for thermal-fluid-solid coupling prediction of directional perforating hydraulic fracturing initiation pressure, comprising the following steps:

[0044] Step 1: Use a gas permeameter to measure the permeability and porosity of the core;

[0045] Step 2: Use a high temperature and high pressure rock triaxial tester to measure the elastic mechanical parameters of cement stone and formation rock, and the porous medium mechanical parameters and strength parameters of the rock;

[0046] Step 3: Use acoustic emission experiments to measure ground stress data to determine horizontal structural strain and to collect statistics on field measured pore pressure data;

[0047] Step 4: Use the experimental measurement data to determine the fitting coefficients in the theoretical prediction formulas of rock elasticity, porous medium mechanics and strength parameters, and combine the logging data to obtain the elasticity, porous medium mechanics and strength parameters of the rock at the downhole research depth;

[0048] The fitting coefficients include the dynamic and static conversion coefficients a1, b1, a2 and b2 involved in the elastic modulus and Poisson's ratio in rock mechanics parameters, the conversion coefficients c1, c2 and ω involved in the uniaxial compressive strength and tensile strength in strength parameters, and the coefficient d in the Biot effective stress coefficient in porous media mechanics.

[0049]

[0050] v3=a1+b1v d

[0051] E3=a2+b2E d

[0052]

[0053]

[0054] In the formula, Δt p and Δt sare the time differences of longitudinal and transverse waves, us / ft; ρ b is the rock mass density, g / cm 3 ;v s and v d are the dynamic and static Poisson's ratios of rock formations, dimensionless; E3, E d are the static and dynamic elastic moduli of the formation rock, GPa; V cl is the mud content, dimensionless; GR, GR max and GR min are the natural gamma values ​​of the actual strata, pure mudstone layers, and pure sandstone layers, respectively, dimensionless; the GCUR index is related to the new and old strata of underground sediments, and takes the values ​​of 3.7 (new strata) and 2.0 (old strata), dimensionless; I GR is the normalized natural gamma value, dimensionless; S t is the tensile strength of the rock S t , MPa; σ c is the uniaxial compressive strength, MPa; φ is the rock porosity, dimensionless; a1, b1, a2, b2, c1, c2, ω and d are fitting coefficients, dimensionless.

[0055] Step 5: Invert the well logging data to obtain the in-situ stress and original pore pressure at the depth of the study well;

[0056] The geostress calculation formula includes:

[0057] Overburden pressure

[0058] σ v =∫0 H ρ b gdz

[0059] Original pore pressure of formation

[0060] Δt p =Δt0e -cH

[0061]

[0062] Maximum and minimum horizontal ground stress

[0063]

[0064] In the above formula, σ v is the overburden pressure or vertical geostress, MPa; g is the gravitational acceleration, g, m / s 2 ; H is the vertical depth, m; Δt0 is the acoustic time difference corresponding to the normal compaction trend line, uf / ft; p p is the original pore pressure of the formation, MPa; p pnHydrostatic pressure, MPa; n is the Eaton index, dimensionless; c is the compaction coefficient, 1 / m; σ H and σ h are the maximum and minimum horizontal ground stress, MPa; ε H and ε h are the tectonic strains in the directions of maximum and minimum horizontal stress, respectively, and are dimensionless.

[0065] Step 6: Count the wellbore structure, wellbore trajectory and casing mechanical parameters;

[0066] Step 7: Using the deformation control equation and harmonic equation of the "casing-cement sheath-formation combination", derive the analytical solution of the stress field of the surrounding rock of the directional well under the condition of non-uniform ground stress under the action of casing-cement sheath-heat coupling;

[0067] The control equations include constitutive equations, geometric equations, stress balance equations, thermal balance equations, harmonic equations and related auxiliary equations.

[0068] Linear elastic thermo-solid coupling constitutive equation

[0069]

[0070] Geometric equations

[0071]

[0072] Linear elastic stress equilibrium equation

[0073]

[0074] Steady-state heat balance equation

[0075]

[0076] Harmonic equations

[0077]

[0078] Auxiliary equations (out-of-plane shear displacement)

[0079]

[0080] In the formula, the above control equations and related variables are applicable to describing the stress conditions of casing, cement sheath or formation (rock around the well). is the stress tensor, MPa; is the strain tensor, dimensionless; is the volume strain, dimensionless; is temperature, °C; is the displacement along different directions, m; is the out-of-plane shear displacement, m; r is the radius, m; θ is the wellbore angle, and the vector radius of the research location is related to the horizontal maximum ground stress σ H Angle of azimuth, °; is the coefficient related to thermal stress, MPa / ℃, where: is the volumetric thermal expansion coefficient, 1 / °C; the bulk modulus for non-drained conditions Defined as GPa; shear modulus GPa; among which, is the elastic modulus, GPa; is Poisson's ratio, dimensionless. and ψ are stress coordination functions. is the Laplace operator in the r-θ plane, Superscript / Subscript They represent casing, cement sheath and formation respectively.

[0081] The calculation formula for the rock stress field around the well considering the casing-cement sheath effect is:

[0082]

[0083] Where, T3 is the cement sheath-formation interface temperature, °C; r is the radial distance from the wellbore center to a certain position inside the formation, m; r3 is the wellbore radius, m; and They are the in-plane radial stress, tangential stress, and shear stress of the rock around the well, MPa; the out-of-plane shear stress includes and MPa; v3 is the Poisson's ratio of the formation rock, dimensionless; θ is the wellbore angle, the vector radius of the research location and the horizontal maximum ground stress σ H The angle of the azimuth, °; the average formation stress P0 and shear stress S0 are defined as and MPa; or is the stress component of the borehole coordinate system, MPa; the intermediate value of the conversion angle θ r Defined as °C 1，3 , C 2，3 , and M3 are unknown coefficients related to the internal stress of the stratum; B3 and D3 are unknown coefficients related to the external shear stress of the stratum; the Lame constant λ3 and shear modulus G3 of the rock are defined as The Biot effective stress coefficient α3 of the formation rock is defined as The dimensionless poroelastic stress coefficient η3 is defined as Dimensionless; coefficient related to thermal expansion stress MPa / ℃, where α s，3 is the volumetric thermal expansion coefficient of formation rock, 1 / °C.

[0084] The average formation stress P0 and shear stress S0 are denoted as

[0085]

[0086] Among them, the principal stress components of the wellbore coordinate system are and shear stress component Defined as

[0087]

[0088] In the formula, ω is defined as ω=ω b -ω i , where ω b is the borehole azimuth, °; ω i is the maximum horizontal in-situ stress σ H Azimuth, °; γ b is the well inclination angle, °.

[0089] The radial stress of the rock around the well and tangential stress The unknown coefficient (C 3，1 , C 3，2 , T3) is obtained by the following matrix AX=B.

[0090]

[0091] X=(C 1,1 C 1，2 C 2,1 C 2,2 C 3,1 C 3,2 T2 T3) T

[0092]

[0093] In the formula, the intermediate variable is defined as:

[0094]

[0095] B′ 3，3 =2A′ 3，3

[0096]

[0097] The unknown number (C 1，1 , C 1，2 , C 2，1 , C 2，2) and radial stress of casing and cement sheath and tangential stress, tangential stress and radial displacement p1 and T1 are the liquid column pressure (MPa) and temperature (℃) applied on the inner wall of the casing, respectively; T2 is the temperature at the interface between the casing and the cement ring, ℃; T0 is the original formation temperature, ℃; is the Lamé constant, GPa; is the shear modulus, GPa; is the thermal expansion coefficient, 1 / ℃; r1, r2 and r3 are the inner radius of the casing, r cas，i , casing outer radius r cas，o (Casing-cement sheath junction) or cement sheath inner radius r cem，i , and the outer radius of the cement ring r cem，o (cement sheath-stratum interface) or formation (wellbore) radius r w ,,m; They are casing, cement sheath and formation respectively.

[0098] The radial stress of the rock around the well Tangential stress and shear stress The relevant unknown coefficients (K3, M3) are obtained from the following matrix.

[0099]

[0100] The shear stress of the rock around the well and tangential stress The relevant coefficients (B3, D3) are calculated from the following matrix.

[0101]

[0102] It is noted that the stress field of the formation surrounding rock in the above study is not affected by the thermal-fluid-solid coupling effect, and is only within the scope of the linear elastic theory. Taking the pressure gradient required for the formation to seep, for example, there is no fluid force at the interface between the cement sheath and the formation, and the pressure gradient cannot be established with the original pore pressure of the formation to produce seepage, and thus no additional stress induced by seepage is generated.

[0103] Step 8. Using the new solution of rock stress around the directional wellbore under the action of casing-cement sheath-thermal coupling, the thermal-fluid-solid coupling control equations of the porous rock around the perforation channel include, deriving the analytical solutions of the field variables (stress field and pore pressure field) of the surrounding rock of the directional perforation channel under the action of thermal-fluid-solid coupling.

[0104] The thermal-fluid-solid coupling control equations of the porous rock around the perforation channel include a thermal-fluid-solid coupling constitutive equation, a stress balance equation and a mass conservation equation.

[0105] Thermal-fluid-solid coupling constitutive equation

[0106] σ ij =2Gε ij +(K-2G / 3)ε kk δ ij +αpδ ij +β s Tδ ij

[0107] p=M(ζ+αε kk +β fs T)

[0108] Stress balance equation

[0109]

[0110] Mass Conservation Equation

[0111]

[0112] Transient heat balance equation

[0113]

[0114] Among them, the poroelastic thermal fluid-solid coupling parameters in the above equations are defined as:

[0115]

[0116] β fs =αα s +φ(α f -α s )

[0117] The symbols in the above equations mean: the principal stress and shear stress components σ of the rock around the perforation hole ij or τ ij (i, j∈(r, θ, z)), MPa; p is the pore pressure around the hole, MPa; the increase (decrease) of the pore fluid content ζ, dimensionless; T is the rock temperature of the formation around the hole, °C; M is the Biot modulus, MPa; B is the Skempton pore pressure coefficient, dimensionless; the Biot effective stress coefficient α is defined as dimensionless, where K and K s are the bulk modulus of rock measured under undrained conditions and the bulk modulus of rock particles, GPa; K f is the bulk modulus of the formation pore fluid, GPa; t is time, s; displacement vector u, m; φ is the formation porosity, dimensionless; permeability coefficient κ is defined as the permeability k(m 2 ) to the fluid viscosity μ(mPa·s), m 2 / (mPa·s);δ ij is the Kronecker number, δ ij =1(i=j),δ ij =0, (i≠j); thermal diffusion coefficient of rock c T =k r / C r Defined as thermal conductivity k r (W / (m·K)) and specific heat capacity C r (J / (kg·K)) ratio, m 2 / s.

[0118] The calculation formula of the field variables (stress field and pore pressure field) of the surrounding rock of the directional well perforation channel under the action of thermal fluid-solid coupling is:

[0119] T p =T0+T p(a)

[0120] p p =p p +p p(a) +p p(d)

[0121]

[0122] Where: p p is the original pore pressure of the formation, MPa; is the dynamic fracturing fluid pressure applied to the perforation channel wall (determined by the fracturing fluid displacement q, ), MPa; θ′ is the circumferential angle of the perforation channel, °; the stress field components around the perforation channel include radial stress Tangential stress Axial stress Shear stress in the θ′-z plane r-θ′ plane and the shear stress in the zr plane MPa. The intermediate quantities P′0 and S′0 are respectively and MPa. The intermediate value of the conversion angle θ′ with the perforation channel as the research object r definition °. The superscripts (a) and (b) indicate that the field variables are related to axisymmetric and nonaxisymmetric loads.

[0123] The field variables (pore pressure field and stress field) of the rock around the perforation hole affected by thermal fluid-solid coupling in this step are expressed as follows:

[0124]

[0125]

[0126] Where q is the wellhead fracturing fluid injection rate, m 3 / min; a p is the wellbore radius, m; r p is the radial distance from the center of the perforation hole to a certain position inside the formation, m; c p is the seepage velocity of the fracturing fluid around the perforation channel, m 2 / s;T w is the temperature of the fracturing fluid applied to the wall of the perforation channel, ℃.

[0127] Step 9: Integrate the thermal-fluid-solid coupling solution of the rock field variables around the directional perforation holes and the rock tensile cracking criterion to predict the cracking angle and dynamic cracking pressure of directional perforation hydraulic fracturing, and optimize the perforation depth, phase angle and construction displacement.

[0128] The tensile cracking criterion in step nine is:

[0129] σ′3=-S t

[0130] Where, the tensile strength of rock S t Defined as S t =σ c / ω,MPa;σ′ c is the uniaxial compressive strength, MPa; ω is the conversion coefficient ω. The minimum effective principal stress σ′3 (MPa) around the perforation channel is defined as:

[0131]

[0132] A further technical solution is that the process of determining the dynamic fracturing pressure of the directional perforating well in step nine is as follows:

[0133] Definition of well inclination angle γ bi =i°(i=0:i:90), azimuth angle Ω bj =j°(j=0:j:360), wellbore angle (perforation phase angle)θ k = k°(k=0:k:360), circumferential angle of perforation channel θ′ m = m° (m = 0: m: 360), used to determine the fracture initiation pressure required for rock to undergo tensile fracture in, The binary method can be used to solve the problem. The specific steps are as follows: ① Under these conditions, the initial upper and lower limits p min , p max Substituting the tensile rupture criterion, we can obtain V min and V max (where p max can be set to be greater than the three principal in-situ stresses (σ H , σh , σ v ) maximum value); ② Determine V min and V max Whether they are of different signs, take p1=(p min +p max ) / 2, update the upper and lower limits and Then, the stress around the perforation channel is introduced and combined with the tensile fracture criterion to obtain and Repeat step ② until a certain error is met and output; ③ Repeat operations ① and ② to obtain a three-dimensional matrix that meets the error ∈ (where i∈[0°,90°], j∈[0°,360°], θ′ m =m°(m=0:m:360)); ④ Further select the channel circumferential angle θ′ that meets the above conditions m =m°(m=0:m:360) Minimum value, given the well inclination and azimuth The directional perforation fracturing initiation pressure corresponding to the tensile fracture of the pore rock (* represents the specific value assigned to the parameter), the circumferential angle θ′ corresponding to the crack initiation value m is the crack initiation angle of the perforation channel.

[0134] A further technical solution is that the values ​​of the thermal-fluid-solid coupling field variables (stress field and pore pressure field) of the surrounding rock of the perforated channel in step nine have time correlation, and the boundary conditions for solving the field variables are affected by the wellhead injection displacement. Therefore, the fracture pressure value determined by this method changes dynamically with the fracturing construction time, and the wellhead injection displacement can be optimized by the fracture pressure value. Furthermore, the thermal-fluid-solid coupling field variable values ​​of the surrounding rock of the perforated channel depend on the perforation depth, and the perforation depth can be optimized by studying the fracture pressure value law of different perforation depths.

[0135] Note that the smaller the positive real numbers i, j, k and m are, the higher the accuracy of the fracture initiation pressure determined by the above method is.

[0136] In addition, the present invention determines the mechanical parameters, strength parameters, and related geomechanical parameters of the cement sheath and formation rock required for model calculation through indoor tests and logging data. The deformation control equation and harmonic equation of the "casing-cement sheath-formation combination" are used to derive the analytical solution of the stress field of the rock around the directional well under the condition of non-uniform ground stress under the action of casing-cement sheath-thermal coupling, and the field variable analytical solution of the surrounding rock of the perforation channel is derived through the thermal-fluid-solid coupling control equation of porous rock. Combined with the rock tensile cracking criterion, the thermal-fluid-solid coupling prediction method of the directional perforation fracturing initiation pressure is determined. Drawing a chart of the initiation pressure affected by different perforation phase angles, perforation lengths, and hydraulic fracturing displacement can provide a scientific basis for on-site construction personnel to determine a reasonable directional perforation hydraulic fracturing design, and effectively optimize the perforation depth, phase angle, and fracturing construction displacement.

[0137] The above description is not intended to impose any form of limitation on the present invention. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for predicting the thermal-fluid-solid coupling of the fracturing pressure of oriented perforating hydraulic fracturing, characterized in that: The following steps are involved: Step 1: Use a gas permeameter to measure the permeability and porosity of the core; Step 2: Use a thermal expansion meter to test the thermal expansion coefficients of the casing, cement sheath and rock. Use a thermal expansion meter to test the thermal expansion coefficients of the casing, cement sheath and rock. Use a thermal conductivity meter and a differential scanning calorimeter to test the specific heat capacity and thermal conductivity of the rock. Use a high-temperature and high-pressure rock triaxial tester to measure the elastic mechanical parameters, porous medium mechanical parameters and strength parameters of cement stone and formation rock. Step 3: Use acoustic emission experiments to measure ground stress data to determine horizontal structural strain and to collect statistics on field measured pore pressure data; Step 4: Use the experimental measurement data to determine the fitting coefficients in the theoretical prediction formulas of rock elasticity, porous medium mechanics and strength parameters, and combine the logging data to obtain the elasticity, porous medium mechanics and strength parameters of the rock at the downhole research depth; Step 5: Invert the well logging data to obtain the in-situ stress and original pore pressure at the depth of the study well; Step 6: Count the wellbore structure, wellbore trajectory and casing mechanical parameters; Step 7: Using the deformation control equation and harmonic equation of "casing-cement sheath-formation combination", derive the analytical solution of the stress field of the surrounding rock of the directional well under the condition of non-uniform ground stress under the action of casing-cement sheath-heat coupling; Step 8: Using the new solution of rock stress around the directional wellbore under the action of casing-cement sheath-heat coupling and the thermal-fluid-solid coupling control equation of porous rock around the perforation channel, the analytical solution of the field variables (stress field and pore pressure field) of the surrounding rock of the directional perforation channel under the action of thermal-fluid-solid coupling is derived; Step 9: Integrate the thermal-fluid-solid coupling solution of the rock field variables around the directional perforation holes and the rock tensile cracking criterion to predict the cracking angle and dynamic cracking pressure of directional perforation hydraulic fracturing, and optimize the perforation depth, phase angle and construction displacement.

2. The method for predicting the thermal-fluid-solid coupling of the fracturing initiation pressure of oriented perforating hydraulic fracturing according to claim 1, characterized in that: The elastic mechanical parameters of the cement stone and the formation rock in step 2 include elastic modulus and Poisson's ratio; the porous medium mechanical coupling parameters of the rock include Biot effective stress coefficient and Skempton pore pressure coefficient; the strength parameter refers to the tensile strength of the rock.

3. The method for predicting the thermal-fluid-solid coupling of the oriented perforating hydraulic fracturing initiation pressure according to claim 1, characterized in that: The geostress data measured by the acoustic emission experiment in step three include the maximum horizontal geostress and the minimum horizontal geostress; the tectonic strain includes the tectonic strain in the directions of the maximum horizontal geostress and the minimum horizontal geostress.

4. The method for predicting the thermal-fluid-solid coupling of the fracturing initiation pressure of oriented perforating hydraulic fracturing according to claim 1, characterized in that: The logging data in step 4 include acoustic wave time difference, density, gamma value and porosity.

5. The method for predicting the thermal-fluid-solid coupling of the fracturing initiation pressure of oriented perforating hydraulic fracturing according to claim 1, characterized in that: The geostress data in step five include overburden stratum pressure, horizontal maximum geostress and horizontal minimum geostress.

6. The method for predicting the thermal-fluid-solid coupling of the fracturing initiation pressure of oriented perforating hydraulic fracturing according to claim 1, characterized in that: The wellbore structure data in step six include wellbore size, casing outer diameter, wall thickness and cement slurry return height; the wellbore trajectory data include well inclination angle and azimuth angle; and the casing mechanical parameters include the elastic modulus and Poisson's ratio of the casing.

7. The method for predicting the thermal-fluid-solid coupling of the fracturing initiation pressure of oriented perforating hydraulic fracturing according to claim 1, characterized in that: The analytical solution of the stress field of the rock around the directional well subjected to the casing-cement sheath-heat coupling in step 7 is: Where, T3 is the cement sheath-formation interface temperature, °C; r is the radial distance from the wellbore center to a certain position inside the formation, m; r3 is the wellbore radius, m; and They are the in-plane radial stress, tangential stress, and shear stress of the rock around the well, MPa; the out-of-plane shear stress includes and MPa; v3 is the Poisson's ratio of the formation rock, dimensionless; θ is the wellbore angle, the vector radius of the research location and the horizontal maximum ground stress σ H The angle of the azimuth, °; the average formation stress P0 and shear stress S0 are defined as and MPa; or is the stress component in the wellbore coordinate system, MPa; Conversion angle intermediate value θ r Defined as °C 1，3 , C 2，3 , and M3 are unknown coefficients related to the internal stress of the stratum; B3 and D3 are unknown coefficients related to the external shear stress of the stratum; the Lame constant λ3 and shear modulus G3 of the rock are defined as The Biot effective stress coefficient α3 of the formation rock is defined as The dimensionless poroelastic stress coefficient η3 is defined as Dimensionless; coefficient related to thermal stress MPa / ℃, where α s，3 is the volumetric thermal expansion coefficient of formation rock, 1 / °C.

8. The method for predicting the thermal-fluid-solid coupling of the fracturing initiation pressure of oriented perforating hydraulic fracturing according to claim 1, characterized in that: The calculation formula for the field variables (stress field and pore pressure field) of the surrounding rock of the directional well perforation channel under the effect of thermal fluid-solid coupling in step eight is: Where: T0 is the original formation temperature, °C; p p is the original pore pressure of the formation, MPa; θ′ is the circumferential angle of the perforation channel, °; the stress field components around the perforation channel include radial stress Tangential stress Axial stress Shear stress in the θ′-z plane r-θ′ plane and the shear stress in the zr plane MPa; the intermediate quantities P′0 and S′0 are respectively and MPa; The intermediate value of the conversion angle θ′ with the perforation channel as the research object r definition 9. The method for predicting the thermal-fluid-solid coupling of the fracturing initiation pressure of oriented perforating hydraulic fracturing according to claim 1, characterized in that: The tensile cracking criterion in step nine is: σ′3=-S t Where, the tensile strength of rock S t Defined as S t =σ c / ω, MPa; σ c is the uniaxial compressive strength, MPa; ω is the conversion coefficient ω; σ′3 is the minimum effective principal stress around the perforation channel, MPa; Further, the process of determining the dynamic fracturing pressure of the oriented perforating well in step nine is as follows: define the well inclination angle γ bi =i°(i=0:i:90), azimuth angle Ω bj =j°(j=0:j:360), wellbore angle (perforation phase angle)θ k = k°(k=0:k:360), circumferential angle of perforation channel θ′ m =m°(m=0:m:360) and pressure array To determine the final required fracture initiation pressure value; Set to be greater than the three principal in-situ stresses (σ H , σ h , σ v ) maximum value; given the matrix (γ bi ,Ω bj ) and phase angle θ k , pressure p ml With interval l from Decreases to 0, when the judgment condition σ′3+S is met t ≤m, the circumferential angle θ′ of the perforation channel can be obtained m The corresponding fracture initiation pressure matrix By filtering out the matrix The minimum value in As the given well inclination and azimuth (γ bi ,Ω bj ) along the phase angle θ k The fracture initiation pressure value during perforation and the circumferential angle θ′ corresponding to the fracture initiation value m is the crack initiation angle of the perforation channel.

10. The method for predicting the thermal-fluid-solid coupling of the oriented perforating hydraulic fracturing initiation pressure according to claim 1, characterized in that: The values ​​of the thermal-fluid-solid coupling field variables (stress field and pore pressure field) of the surrounding rock of the perforation channel in the step nine are time-correlated, and the boundary conditions for solving the field variables are affected by the wellhead injection displacement. Therefore, the fracturing pressure value determined by this method changes dynamically with the fracturing construction time, and the wellhead injection displacement can be optimized by the fracturing pressure value; furthermore, the values ​​of the thermal-fluid-solid coupling field variables of the surrounding rock of the perforation channel depend on the perforation depth, and the perforation depth can be optimized by studying the law of the fracturing pressure values ​​at different perforation depths.

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