Ultra-deep gas well heat-fluid-solid coupling borehole wall stability evaluation method and system

Abstract

The invention discloses an ultra-deep gas well thermal-fluid-solid coupling borehole wall stability evaluation method and system, and belongs to the technical field of oil-gas field development, and the method comprises the following steps: 1, building a well periphery stress model considering the coupling effect of a transient temperature field, a seepage field and a stress field; step 2, evaluating the stability of the well wall by adopting an extended Mogi-Coulomb nonlinear rock strength failure criterion; 3, introducing a limit collapse angle theta b as a stability criterion, and establishing a collapse angle and drilling fluid density calculation expression; and step 4, outputting drilling parameters through an optimization design module. The system comprises a data acquisition module, a stress calculation module, a stability evaluation module and an optimization design module, and all the modules cooperatively work through standardized interfaces. The problem that a traditional method is insufficient in precision when applied to the ultra-deep gas well is solved, and reliable technical support is provided for safe and efficient well drilling.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development engineering. Specifically, it relates to a method and system for evaluating the thermo-fluid-solid coupling wellbore stability of ultra-deep gas wells, which is particularly suitable for the drilling design and safe construction of ultra-deep high-pressure gas wells. Background Art

[0002] With the continuous growth of global energy demand, oil and gas exploration and development have been continuously expanding into deep (4500 - 6000m) and ultra-deep (>6000m) fields. According to statistics, more than 60% of the newly added reserves in key exploration areas such as the Tarim Basin and Sichuan Basin in China come from deep reservoirs. However, with the increase in well depth, the wellbore stability problem presents new and diverse characteristics.

[0003] The multi-physical field coupling effect is significantly enhanced: The downhole temperature of ultra-deep wells can reach 180 - 220°C. The high temperature causes the deterioration of rock mechanical properties (the elastic modulus decreases by 15 - 30%), the failure of drilling fluid performance (such as high-temperature thickening and a sharp increase in filtration loss), and significant thermal stress (up to 20 - 40MPa).

[0004] The nonlinear failure characteristics of rocks are prominent: Deep rocks show obvious strength anisotropy and nonlinear failure characteristics under triaxial stress. The conventional Mohr-Coulomb criterion underestimates the effect of the intermediate principal stress, with an error of up to 20 - 35%. The traditional linear D-P criterion overestimates the rock strength by 15 - 25% in the high-stress area. The existing wellbore stability analysis methods recommended by API standards are based on elastic theory and cannot effectively characterize the strain-softening effect of crack propagation and the creep failure behavior of rocks.

[0005] Lack of engineering adaptability: Existing commercial software such as Wellplan and StressCheck has limitations, ignoring transient heat transfer during the drilling process; the seepage model only considers Darcy flow and is not applicable to ultra-low permeability reservoirs <0.01mD; it lacks the function of dynamically calibrating geomechanical parameters with depth.

[0006] Deep drilling practice shows that when the well depth exceeds 7000m, the non-productive time (NPT) caused by wellbore instability accounts for as high as 35 - 50%, and the accident loss of a single well can reach 20 million - 50 million yuan. Therefore, there is an urgent need to develop a method and system for evaluating the thermo-fluid-solid coupling wellbore stability of ultra-deep gas wells, which can accurately characterize the mechanism of thermo-fluid-solid coupling, truly reflect the nonlinear strength failure characteristics of ultra-deep well rocks, and realize an intelligent analysis system from data collection to decision support. Summary of the Invention

[0007] Aiming at the existing problems in evaluating the wellbore stability of ultra-deep gas wells, the present invention proposes a method and system for evaluating the thermo-fluid-solid coupling wellbore stability of ultra-deep gas wells.

[0008] To solve the above technical problems, the present invention adopts the following technical solutions:

[0009] A method and system for evaluating the thermal-fluid-solid coupling wellbore stability of ultra-deep gas wells, comprising the following steps:

[0010] Step 1: Establish a wellbore stress distribution model considering the thermal-fluid-solid coupling effect, and the stress component expression is:

[0011]

[0012] In the formula: σ r , σ θ , σ z are the radial, tangential and axial stresses respectively, in MPa; P w is the wellbore pressure, in MPa; P p is the pore pressure, in MPa; α is the Biot coefficient, dimensionless; E is the elastic modulus, in GPa; α T is the coefficient of thermal expansion, 1 / °C; ΔT is the temperature difference, in °C; v is the Poisson's ratio, dimensionless; r w is the wellbore radius, in m; r is the radial distance, in m.

[0013] Step 2: Conduct stability evaluation based on the extended Mogi-Coulomb nonlinear failure criterion, and its expression is:

[0014]

[0015] In the formula: τ oct is the octahedral shear stress, in MPa; σ m,2 is the effective mean stress, in MPa; a, b, c are material parameters determined by triaxial experiments.

[0016] Step 3: Introduce the limit collapse angle θ b as the stability criterion. When θ b ≤90°, it is determined to be in a stable state, and its calculation formula is:

[0017] θ b = 90° - 1 / 2 arcsin(2τ max / σ θ -σ r )

[0018] In the formula: θ b is the limit collapse angle in degrees; τ max is the rock shear strength, in MPa.

[0019] Step 4: Determine the safe drilling fluid density window through numerical simulation, and the calculation formula for its lower limit density ρ min is:

[0020] ρ min = P collapse / 0.00981D

[0021] Where: P collapse is the critical collapse pressure, MPa; D is the well depth, m; ρ min is the density of drilling fluid, g / cm 3 .

[0022] Step 5: Construct a thermal-fluid-solid coupling wellbore stability evaluation system for ultra-deep gas wells. The system includes four major modules: data acquisition, stress calculation, stability evaluation, and optimization design. Each module works together through a standardized interface.

[0023] Furthermore, in the said Step 1, the calculation of thermal stress considers the transient temperature field distribution:

[0024]

[0025] Where: T w is the wellbore temperature, °C; T0 is the original formation temperature, °C; κ is the thermal diffusivity, m 2 / s; t is the time, s; erf is the error function.

[0026] Furthermore, in the said Step 2, the material parameters are determined by fitting the triaxial experimental data:

[0027]

[0028] Where: c—cohesion, MPa; —internal friction angle, °.

[0029] Furthermore, in the said Step 4, the critical collapse pressure P collapse is determined by solving the following equations:

[0030]

[0031] Where: f is the critical collapse pressure function.

[0032] Furthermore, in the said Step 5, the data acquisition module is mainly used to obtain core experimental data, logging data, and on-site test data, providing the basic parameters for stress calculation in Claims 1-4.

[0033] Furthermore, in the said Step 5, the stress calculation module includes a formation stress conversion unit, a seepage stress calculation unit, and a thermal stress calculation unit, mainly used to implement the stress calculation methods described in Claims 1-4.

[0034] Further, in step 5, the stability evaluation module mainly conducts wellbore stability analysis based on the extended Mogi-Coulomb criterion in step 2.

[0035] Further, in step 5, the optimization design module includes a collapse pressure calculation unit and a wellbore trajectory optimization unit for different in-situ stress modes, and is mainly used to determine the safe drilling fluid density window and optimize the wellbore trajectory.

[0036] The beneficial effects of the present invention are as follows:

[0037] (1) Innovatively combining the transient thermal-fluid-solid coupling theory with the extended Mogi-Coulomb criterion, the calculation accuracy is increased by 25%;

[0038] (2) The system modular design realizes the full-process automatic processing from data acquisition to scheme optimization;

[0039] (3) Verified by on-site application, it can reduce the risk of wellbore instability and improve the drilling efficiency by about 15%-20%. Description of the Drawings

[0040] Figure 1 It is a schematic diagram of an embodiment of the thermal-fluid-solid coupling wellbore stability evaluation method and system for ultra-deep gas wells of the present invention.

[0041] Figure 2 It is a mechanism diagram of the thermal-fluid-solid coupling for ultra-deep gas wells of the present invention.

[0042] Figure 3 It is a fitting curve diagram of the extended Mogi-Coulomb criterion of the present invention.

[0043] Figure 4 It is a cloud map of the drilling fluid density window of an embodiment of the present invention.

[0044] Figure 5 It is a calculation result diagram of the collapse pressure under different in-situ stress modes of an embodiment of the present invention. Detailed Embodiments

[0045] To better understand the purpose and technical solutions of the present invention, the thermal-fluid-solid coupling wellbore stability evaluation method and system for ultra-deep gas wells of the present invention will be further described in detail below with reference to the drawings and specific embodiments. Embodiment 1

[0046] As Figure 1 shown, the thermal-fluid-solid coupling wellbore stability evaluation method and system for ultra-deep gas wells of the present invention include the following steps:

[0047] Step 1: Establish a wellbore peripheral stress distribution model considering thermal-fluid-solid coupling, and the stress component expression is:

[0048]

[0049] Where: σ r , σ θ , σ z are the radial, tangential and axial stresses respectively, in MPa; P w is the wellbore pressure, in MPa; P p is the pore pressure, in MPa; α is the Biot coefficient, dimensionless; E is the elastic modulus, in GPa; α T is the coefficient of thermal expansion, 1 / °C; ΔT is the temperature difference, in °C; v is the Poisson's ratio, dimensionless; r w is the wellbore radius, in m; r is the radial distance, in m.

[0050] Step 2: Conduct stability evaluation based on the extended Mogi-Coulomb nonlinear failure criterion, and its expression is:

[0051]

[0052] Where: τ oct is the octahedral shear stress, in MPa; σ m,2 is the effective mean stress, in MPa; a, b, c are material parameters determined by triaxial experiments.

[0053] Step 3: Introduce the limit collapse angle θ b as the stability criterion. When θ b ≤90°, it is judged as a stable state, and its calculation formula is:

[0054] θ b = 90° - 1 / 2 arcsin(2τ max / σ θ -σ r )

[0055] Where: θ b is the limit collapse angle in degrees; τ max is the shear strength of the rock, in MPa.

[0056] Step 4: Determine the safe drilling fluid density window through numerical simulation. The lower limit density ρ min The calculation formula is:

[0057] ρ min = P collapse / 0.00981D

[0058] Where: P collapse is the critical collapse pressure, in MPa; D is the well depth, in m; ρ min is the drilling fluid density, in g / cm 3 .

[0059] Step 5: Construct a thermo-fluid-solid coupling wellbore stability evaluation system for ultra-deep gas wells. The system includes four major modules: data acquisition, stress calculation, stability evaluation, and optimization design. The modules work together through standardized interfaces. Example 2

[0060] As Figure 1 shown, the thermo-fluid-solid coupling wellbore stability evaluation method and system of the present invention include the following steps:

[0061] Step 1: Establish a wellbore stress distribution model considering thermo-fluid-solid coupling. The stress component expressions are as follows:

[0062]

[0063] In the formula: σ r , σ θ , σ z are the radial, tangential, and axial stresses, respectively, in MPa; P w is the wellbore pressure, in MPa; P p is the pore pressure, in MPa; α is the Biot coefficient, dimensionless; E is the elastic modulus, in GPa; α T is the thermal expansion coefficient, in 1 / °C; ΔT is the temperature difference, in °C; v is the Poisson's ratio, dimensionless; r w is the wellbore radius, in m; r is the radial distance, in m.

[0064] Step 2: Conduct stability evaluation based on the extended Mogi-Coulomb nonlinear failure criterion. The expression is as follows:

[0065]

[0066] In the formula: τ oct is the octahedral shear stress, in MPa; σ m,2 is the effective mean stress, in MPa; a, b, c are material parameters determined through triaxial experiments.

[0067] Step 3: Introduce the ultimate collapse angle θ b as the stability criterion. When θ b ≤90°, it is determined to be in a stable state. The calculation formula is as follows:

[0068] θ b = 90° - 1 / 2 arcsin(2τ max / σ θ -σ r )

[0069] In the formula: θ b is the ultimate collapse angle in degrees; τ max is the rock shear strength, in MPa.

[0070] Step 4: Determine the safe drilling fluid density window through numerical simulation. The lower limit density ρ min The calculation formula is:

[0071] ρ min = P collapse / 0.00981D

[0072] In the formula: P collapse is the critical collapse pressure, MPa; D is the well depth, m; ρ min is the drilling fluid density, g / cm 3 .

[0073] Step 5: Construct a thermal-fluid-solid coupling wellbore stability evaluation system for ultra-deep gas wells. The system includes four major modules: data acquisition, stress calculation, stability evaluation, and optimization design. The modules work together through standardized interfaces.

[0074] The difference between this embodiment and Embodiment 1 is that:

[0075] In Step 1, the thermal stress calculation considers the transient temperature field distribution:

[0076]

[0077] In the formula: T w is the wellbore temperature, °C; T0 is the original formation temperature, °C; κ is the thermal diffusivity, m 2 / s; t is the time, s; erf is the error function.

[0078] In Step 2, the material parameters are determined by fitting the triaxial experimental data:

[0079]

[0080] In the formula: c—cohesion, MPa; —internal friction angle, °.

[0081] In Step 4, the critical collapse pressure P collapse is determined by solving the following system of equations:

[0082]

[0083] In the formula: f is the critical collapse pressure function.

[0084] In Step 5, the data acquisition module is mainly used to obtain core experimental data, logging data, and on-site test data, providing the basic parameters for stress calculation in Claims 1-4.

[0085] In step 5, the stress calculation module includes a in-situ stress conversion unit, a seepage stress calculation unit, and a thermal stress calculation unit, which are mainly used to implement the stress calculation method described in claims 1-4.

[0086] In step 5, the stability evaluation module mainly conducts wellbore stability analysis based on the extended Mogi-Coulomb criterion in step 2.

[0087] In step 5, the optimization design module includes a collapse pressure calculation unit and a wellbore trajectory optimization unit for different in-situ stress modes, which are mainly used to determine the safe drilling fluid density window and optimize the wellbore trajectory. Example 3

[0088] Taking Well X1 in the Tarim Basin as an example, combined with Figures 1-5 , the thermo-hydro-mechanical coupling wellbore stability evaluation method and system of the present invention will be described in detail, specifically including the following steps:

[0089] Step 1: Taking Well X1 in the Tarim Basin (total depth of 8150 m) as the target well, drilling, logging, and core data are collected. The target interval is the Ordovician carbonate reservoir, with a formation pressure coefficient of 1.88 and a bottom-hole temperature of 208 °C. Representative rock samples are obtained through field coring and prepared into experimental samples with standard dimensions (Φ25 mm × 50 mm).

[0090] Step 2: Uniaxial and triaxial rock mechanics parameter tests are carried out to obtain static rock mechanics parameters such as uniaxial compressive strength, triaxial compressive strength, Poisson's ratio, Young's modulus, and Biot coefficient under different confining pressures and formation pressures. The static rock mechanics parameters obtained in this example are shown in Table 1:

[0091] Table 1. Static rock mechanics parameters under different confining pressure conditions

[0092] Step 3: A wellbore stress distribution model considering thermo-hydro-mechanical coupling is established. Considering the coupling effect of transient temperature field and seepage field, a stress component equation is established:

[0093]

[0094] where ΔT = T w - T0 = 88 °C, and the maximum calculated thermal stress is 49.7 MPa.

[0095] Step 4: Wellbore stability evaluation is carried out based on the extended Mogi-Coulomb criterion.

[0096] Based on the quasi-triaxial experimental data, a non-linear strength failure curve of the extended Mogi-Coulomb criterion is fitted, as shown in Figure 3As shown, the expression of the non-linear failure criterion obtained by fitting:

[0097]

[0098] Calculation of the ultimate collapse angle, introducing the collapse angle criterion θ b ≤90°, calculate the critical collapse pressure:

[0099] θ b = 90° - 1 / 2 arcsin(2τ max / σ θ -σ r ), where τ max = 58.3 MPa, and the calculation results are shown in Table 2.

[0100] Table 2. Pressure calculation results at different collapse angles

[0101] Step 5: Determine the safe drilling fluid density window by numerically solving the system of equations:

[0102]

[0103] In the formula: f is the critical collapse pressure function.

[0104] Combined with the well depth D = 8150 m, the safe drilling fluid density window is determined to be 1.60 g / cm 3 ~1.65 g / cm 3 , as Figure 4 shown.

[0105] Step 6: Carry out drilling optimization design according to the system integration module, and the on-site application effect is shown in Table 3.

[0106] Table 3. On-site application effect

[0107] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method and system for evaluating the thermo-fluid-solid coupling wellbore stability of ultra-deep gas wells, characterized in that, It includes the following steps: Step 1: Establish a wellbore stress distribution model considering the thermo-fluid-solid coupling effect, and the stress component expression is as follows: where: σ r , σ θ , σ z are the radial, tangential and axial stresses, respectively, in MPa; P w is the wellbore pressure, in MPa; P p is the pore pressure, in MPa; α is the Biot coefficient, dimensionless; E is the elastic modulus, GPa; α T is the coefficient of thermal expansion, 1 / °C; ΔT is the temperature difference, °C; v is the Poisson's ratio, dimensionless; r w is the wellbore radius, m; r is the radial distance, m; Step 2: Conduct stability evaluation based on the extended Mogi-Coulomb nonlinear failure criterion, and the expression is as follows: Where: τ oct is the octahedral shear stress, MPa; σ m,2 is the effective mean stress, MPa; a, b, c are material parameters determined by triaxial tests; Step 3: Introduce the limit collapse angle θ b As a stability criterion, when θ b ≤ 90°, it is determined to be in a stable state, and its calculation formula is: θ b = 90° - 1 / 2 arcsin(2τ max / σ θ - σ r ) Where: θ b is the angle of the ultimate collapse angle, °; τ max is the shear strength of the rock, MPa; Step 4: Determine the safe drilling fluid density window through numerical simulation, and its lower limit density ρ min The calculation formula is as follows: ρ min = P collapse / 0.00981D Where: P collapse is the critical collapse pressure, MPa; D is the well depth, m; ρ min is the density of drilling fluid, g / cm 3 ; Step 5: Construct a thermo-fluid-solid coupling wellbore stability evaluation system for ultra-deep gas wells. The system includes four major modules: data acquisition, stress calculation, stability evaluation, and optimization design. The modules work together through standardized interfaces.

2. The thermal-fluid-solid coupling wellbore stability evaluation method for ultra-deep gas wells according to claim 1, characterized in that In Step 1, the calculation of thermal stress considers the transient temperature field distribution: where: T w is the wellbore temperature, °C; T0 is the original formation temperature, °C; κ is the thermal diffusivity, m 2 / s; t is the time, s; erf is the error function.

3. The thermo-hydro-mechanical coupled wellbore stability evaluation method for ultra-deep gas wells according to claim 1, characterized in that In Step 2, the material parameters are determined by fitting the triaxial experimental data: Where: c—cohesion, MPa; —angle of internal friction, °.

4. The method according to claim 1, characterized in that, In step 4, the critical collapse pressure P collapse is determined by solving the following system of equations: In the formula: f is the critical collapse pressure function.

5. The method according to claim 1, characterized in that, In Step 5, the data acquisition module is mainly used to obtain core experimental data, logging data, and on-site test data, providing the basic parameters for stress calculation in Claims 1-4.

6. The method according to claim 1, wherein In Step 5, the stress calculation module is mainly used to implement the stress calculation method described in Claims 1-4.

7. The method according to claim 1, wherein In Step 5, the stability evaluation module mainly conducts wellbore stability analysis based on the extended Mogi-Coulomb criterion in Step 2.

8. The method according to claim 1, wherein In Step 5, the optimization design module is mainly used to determine the safe drilling fluid density window and optimize the wellbore trajectory.

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