A method for evaluating the dynamic stability of faults in underground gas storage reservoirs of the oil and gas reservoir type under alternating loads

Abstract

The present invention relates to the technical field of safety assessment engineering, and particularly relates to a method for evaluating the dynamic stability of faults in gas storage reservoirs of the oil and gas reservoir type under alternating loads. The method includes establishing a relationship model between the operation period of the gas storage reservoir and the cohesive force within the rock and a relationship model between the operation period of the gas storage reservoir and the friction angle within the rock based on the dynamic mechanical strength parameters of the formation rock of the gas storage reservoir; establishing a limit operating pressure calculation model based on the above two relationship models; establishing a gas storage reservoir limit operating pressure calculation model based on the friction coefficient of the fault gouge of the target gas storage reservoir; using the above two calculation models to calculate the bearing limit pressure of shear rupture failure of the gas storage reservoir fault and the bearing limit pressure of frictional sliding failure at different dip angles at different operation periods according to the maximum principal stress and the minimum principal stress, and evaluating the dynamic stability of the target gas storage reservoir, thereby solving the problem that the existing evaluation method has poor accuracy in evaluating the dynamic stability of faults in gas storage reservoirs of the oil and gas reservoir type.

Description

Technical Field

[0001] The present invention relates to the technical field of safety assessment engineering, and particularly to a method for evaluating the dynamic stability of faults in oil and gas reservoir type gas storage caverns under alternating loads. Background Art

[0002] Constructing underground gas storage caverns is one of the most effective means to alleviate the seasonal imbalance of natural gas consumption. With the rapid development of the construction project of underground gas storage caverns in China, 29 underground gas storage caverns have been built so far. Among them, the oil and gas reservoir type underground gas storage caverns account for more than 85%, which is the main type of gas storage caverns in China. The geological conditions of the oil and gas reservoir type underground gas storage caverns in China are complex, and faults are generally developed in the gas storage geological bodies. The long-term cyclic injection and production work of the gas storage caverns cause the fault rocks to be affected by alternating loads, thereby increasing the instability risk of the faults in the gas storage caverns. The instability of the faults may lead to accidents such as deformation and fracture of the injection and production well strings in the gas storage caverns and gas leakage, and further cause greater economic losses and social impacts. Therefore, accurately evaluating the dynamic stability of the faults in the gas storage caverns under alternating loads is of great significance for the safe operation of the gas storage caverns.

[0003] The existing evaluation methods have three defects: ① The existing evaluation methods for the dynamic stability of faults are all established based on a single instability theory. However, due to the differences in parameters such as in-situ stress and dip angle between gas storage caverns in different regions or even different faults in the same region, the instability failure forms that may occur in different faults are also different, and a reasonable fault instability theory needs to be selected according to the specific parameters of the faults; ② In the existing evaluation methods based on the rock strength criterion, the rock strength parameters are fixed. However, for the fault rocks in the gas storage caverns, the alternating loads may cause changes in their strength parameters, thereby affecting the reliability of the evaluation results of the dynamic stability of the faults; ③ In the existing evaluation methods based on the rock friction law, the friction coefficients of the faults in the research target gas storage caverns are not determined according to the specific conditions of the faults, and the friction coefficients of the faults in different regions may vary greatly. This may result in an incorrect estimation of the ultimate operating pressure of the gas storage cavern, and further lead to a reduction in the effective gas storage volume of the gas storage cavern or an increase in the instability risk of the faults.

[0004] In view of this, there is an urgent need to establish an evaluation method that comprehensively considers various fault instability theories, simultaneously considers the dynamic changes in rock strength and the differences in friction coefficients of different faults, so as to more accurately evaluate the dynamic stability of the faults in the oil and gas reservoir type gas storage caverns, and further determine a more reasonable and reliable operating pressure range for the gas storage caverns, while ensuring the safe operation of the gas storage caverns and maximizing their gas storage capacity. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for evaluating the dynamic stability of faults in oil and gas reservoir type gas storage caverns under alternating loads, aiming to solve the problem that the existing evaluation methods have poor accuracy in evaluating the dynamic stability of faults in oil and gas reservoir type gas storage caverns.

[0006] To achieve the above object, the present invention provides a method for evaluating the dynamic stability of faults in a gas storage reservoir under alternating loads, comprising the following steps:

[0007] Testing the dynamic mechanical strength parameters of the rock in the reservoir formation;

[0008] Based on the dynamic mechanical strength parameters of the rock in the reservoir formation, establishing a relationship model between the operation period of the gas storage reservoir and the cohesion within the rock and a relationship model between the operation period of the gas storage reservoir and the internal friction angle within the rock;

[0009] Based on the relationship model between the operation period of the gas storage reservoir and the cohesion within the rock and the relationship model between the operation period of the gas storage reservoir and the internal friction angle within the rock, establishing a calculation model for the ultimate operating pressure of the target gas storage reservoir based on the rock shear failure criterion;

[0010] Determining the friction coefficient of the fault gouge in the target gas storage reservoir;

[0011] Based on the friction coefficient of the fault gouge in the target gas storage reservoir, establishing a calculation model for the ultimate operating pressure of the gas storage reservoir based on the rock friction sliding law for the target gas storage reservoir;

[0012] Using the calculation model for the ultimate operating pressure of the target gas storage reservoir based on the rock shear failure criterion, according to the maximum principal stress and minimum principal stress of the target gas storage reservoir formation, calculating the bearing limit pressure of the shear failure of the gas storage reservoir fault at different operation periods to obtain a first calculation result;

[0013] Using the calculation model for the ultimate operating pressure of the gas storage reservoir based on the rock friction sliding law for the target gas storage reservoir, according to the maximum principal stress and minimum principal stress of the target gas storage reservoir formation, calculating the bearing limit pressure of the friction sliding failure of the gas storage reservoir fault at different dip angles to obtain a second calculation result;

[0014] Evaluating the dynamic stability of the target gas storage reservoir according to the first calculation result and the second calculation result, and determining the highest upper limit pressure for ensuring the stability of the gas storage reservoir fault.

[0015] Wherein, the dynamic mechanical strength parameters of the rock in the reservoir formation include the dynamic elastic modulus of the rock, the static compressive strength, the cohesion and the internal friction angle.

[0016] Wherein, the testing of the dynamic mechanical strength parameters of the rock in the reservoir formation includes:

[0017] Using the rock sampled from the target gas storage reservoir formation to prepare core samples, setting multiple confining pressures with different numerical values within the range of 0 to the maximum horizontal principal stress of the target gas storage reservoir, conducting single-cycle triaxial compression rock mechanics experiments and acoustic time difference rock mechanics experiments, and obtaining the dynamic elastic modulus and static compressive strength of the rock under different confining pressures;

[0018] According to the maximum axial stress values and radial stress values of the rock in the triaxial compression experiment under different confining pressures, respectively, and the maximum axial stress value of the rock in the state without confining pressure, Mohr stress circles are plotted pairwise on the τ-σ plane, and the intersection point of the common tangent of the two Mohr stress circles with the τ-axis and the included angle with the σ-axis are read to obtain the internal cohesion and internal friction angle of the rock under different stress states;

[0019] Select the fault rock of the target gas storage reservoir, and carry out an alternating load mechanical experiment under the effective stress of the rock corresponding to the upper and lower limit operating pressures designed for the target gas storage reservoir, and use the acoustic time difference method to measure the change of the elastic modulus of the fault rock under the alternating load.

[0020] Among them, the establishment of the relationship model between the operation period of the gas storage reservoir and the internal cohesion of the rock and the relationship model between the operation period of the gas storage reservoir and the internal friction angle of the rock based on the dynamic mechanical strength parameters of the rock formation of the gas storage reservoir includes:

[0021] According to the dynamic elastic modulus of the rock and the static compressive strength, a relationship equation between the static compressive strength of the rock and the dynamic elastic modulus is established by means of mathematical regression analysis to obtain the first equation model;

[0022] According to the internal cohesion, the internal friction angle and the static compressive strength of the rock, a relationship equation between the internal cohesion, the static compressive strength of the rock, the internal friction angle and the internal cohesion is established by means of mathematical regression analysis to obtain the second equation model and the third equation model;

[0023] According to the change of the elastic modulus of the rock under the alternating load, the first equation model is used to calculate the change of the static compressive strength of the fault rock under the alternating load;

[0024] According to the change of the static compressive strength of the fault rock under the alternating load, the second equation model is used to obtain the change of the internal cohesion of the fault rock under the alternating load, and a relationship model between the operation period of the gas storage reservoir and the internal cohesion of the rock is established;

[0025] According to the change of the static compressive strength of the fault rock under the alternating load, the third equation model is used to obtain the change of the internal friction angle of the fault rock under the alternating load, and a relationship model between the operation period of the gas storage reservoir and the internal friction angle of the rock is established.

[0026] Among them, the establishment of the ultimate operating pressure calculation model based on the rock shear failure criterion for the target gas storage reservoir based on the relationship model between the operation period of the gas storage reservoir and the internal cohesion of the rock and the relationship model between the operation period of the gas storage reservoir and the internal friction angle of the rock includes:

[0027] According to the rock shear strength criterion and combined with the effective stress theory, a calculation model for the ultimate bearing pressure of the gas storage reservoir fault based on the rock shear strength criterion in the form of principal stress is established;

[0028] Substitute the relationship model between the operation period of the gas storage reservoir and the cohesive force in the rock and the relationship model between the operation period of the gas storage reservoir and the friction angle in the rock into the calculation model for the ultimate bearing pressure of the gas storage reservoir fault based on the rock shear strength criterion in the form of principal stress, and establish a calculation model for the ultimate operating pressure based on the rock shear fracture criterion for the target gas storage reservoir.

[0029] Among them, the determination of the friction coefficient of the fault gouge of the target gas storage reservoir includes:

[0030] Obtain a fault gouge sample of the target gas storage reservoir, conduct a fault gouge friction experiment, and obtain the friction coefficient of the fault gouge of the target gas storage reservoir.

[0031] Among them, the determination of the friction coefficient of the fault gouge of the target gas storage reservoir includes:

[0032] According to the logging analysis data and well logging analysis data, based on the analysis results of the composition of the fault gouge of the target gas storage reservoir, configure a fault gouge sample, conduct a fault gouge friction experiment, and obtain the friction coefficient of the fault gouge of the target gas storage reservoir.

[0033] Among them, the establishment of a calculation model for the ultimate operating pressure of the gas storage reservoir based on the rock friction sliding law for the target gas storage reservoir includes:

[0034] According to the rock sliding friction law and combined with the effective stress theory, establish a calculation model for the ultimate bearing pressure of the gas storage reservoir fault based on the rock friction law in the form of principal stress;

[0035] Substitute the friction coefficient of the fault gouge of the target gas storage reservoir into the calculation model for the ultimate bearing pressure of the gas storage reservoir fault based on the rock friction law in the form of principal stress, and establish a calculation model for the ultimate operating pressure of the gas storage reservoir based on the rock friction sliding law for the target gas storage reservoir.

[0036] A method for evaluating the dynamic stability of faults in an oil and gas reservoir type gas storage reservoir under alternating loads includes testing the dynamic mechanical strength parameters of the reservoir formation rock; based on the dynamic mechanical strength parameters of the reservoir formation rock, establishing a relationship model between the operation period of the gas storage reservoir and the cohesive force in the rock and a relationship model between the operation period of the gas storage reservoir and the friction angle in the rock; based on the relationship model between the operation period of the gas storage reservoir and the cohesive force in the rock and the relationship model between the operation period of the gas storage reservoir and the friction angle in the rock, establishing a limit operating pressure calculation model for the target gas storage reservoir based on the rock shear failure criterion; determining the friction coefficient of the fault gouge in the target gas storage reservoir; based on the friction coefficient of the fault gouge in the target gas storage reservoir, establishing a gas storage reservoir limit operating pressure calculation model for the target gas storage reservoir based on the rock friction sliding law; using the limit operating pressure calculation model for the target gas storage reservoir based on the rock shear failure criterion, according to the maximum principal stress and minimum principal stress of the target gas storage reservoir formation, calculating the bearing limit pressure of the fault shear failure of the gas storage reservoir at different operation periods to obtain a first calculation result; using the gas storage reservoir limit operating pressure calculation model for the target gas storage reservoir based on the rock friction sliding law, according to the maximum principal stress and minimum principal stress of the target gas storage reservoir formation, calculating the bearing limit pressure of the friction sliding failure of the gas storage reservoir fault at different dip angles to obtain a second calculation result; evaluating the dynamic stability of the target gas storage reservoir according to the first calculation result and the second calculation result, and determining the highest upper limit pressure to ensure the stability of the gas storage reservoir fault. First, the present invention comprehensively considers two instability forms of fault shear rupture and friction sliding, and comprehensively adopts two instability theories, which is applicable to evaluating the stability of faults with any parameters; second, the present invention considers the dynamic change of fault rock strength with the operation of the gas storage reservoir, which is closer to the actual operation of the gas storage reservoir than the existing static methods; the present invention considers the differences in the friction coefficients of different gas storage reservoir faults, and specific gas storage reservoirs use specific friction coefficients for evaluation, making the evaluation method more targeted, rather than using the same friction coefficient for all gas storage reservoir faults, so as to solve the problem that the accuracy of the existing evaluation method for evaluating the dynamic stability of faults in oil and gas reservoir type gas storage reservoirs is poor. Brief Description of the Drawings

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0038] Figure 1 It is a schematic diagram for obtaining the internal cohesive force and internal friction angle through the Mohr stress circle.

[0039] Figure 2It is a flowchart of a method for evaluating the dynamic stability of faults in an oil and gas reservoir type gas storage under alternating loads provided by the present invention.

[0040] Figure 3 It is a schematic diagram of the relationship curve between the dynamic elastic modulus and the axial load.

[0041] Figure 4 It is a graph of the relationship between the static compressive strength of rock and the dynamic elastic modulus.

[0042] Figure 5 It is a graph of the relationship between the internal cohesion and the static compressive strength of rock.

[0043] Figure 6 It is a graph of the relationship between the internal friction angle and the internal cohesion.

[0044] Figure 7 It is a schematic diagram of the friction coefficient of fault gouge with different clay contents in Gas Storage W.

[0045] Figure 8 It is a schematic diagram of the operating pressure limit based on the shear failure criterion.

[0046] Figure 9 It is a schematic diagram of the operating pressure limit based on the friction law. Detailed implementation manners

[0047] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0048] Please refer to Figures 1 to 9 , the present invention provides a method for evaluating the dynamic stability of faults in an oil and gas reservoir type gas storage under alternating loads, including the following steps:

[0049] S1 Test the dynamic mechanical strength parameters of the rock in the gas storage formation;

[0050] Specifically, the dynamic mechanical strength parameters of the rock in the gas storage formation include the dynamic elastic modulus of the rock, the static compressive strength, the internal cohesion, and the internal friction angle.

[0051] Core samples are prepared from the rock sampled from the target gas storage formation. According to the magnitude of the horizontal principal stress of the target gas storage, multiple confining pressures with different numerical values are set within the range of 0 to the maximum horizontal principal stress of the gas storage formation, and single-cycle triaxial compression rock mechanics experiments and acoustic time difference rock mechanics experiments are carried out to obtain the dynamic elastic modulus E d of the rock and the static compressive strength σ s ;

[0052] As shown Figure 1 in the figure, according to the maximum axial stress values and radial stress values of the rock in the triaxial compression experiment under different confining pressures, respectively, and the maximum axial stress value of the rock in the state without confining pressure, Mohr stress circles are plotted pairwise on the τ-σ plane, and the intersection point of the common tangent of the two Mohr stress circles with the τ-axis and the included angle with the σ-axis are read to obtain the internal cohesion C and internal friction angle φ of the rock under different stress states;

[0053] Select the fault rock of the target gas storage reservoir, and carry out an alternating load mechanical experiment under the effective stress of the rock corresponding to the upper and lower limit operating pressures designed for the target gas storage reservoir, and use the acoustic time difference method to measure the change of the elastic modulus E of the fault rock under the alternating load d .

[0054] S2 Based on the dynamic mechanical strength parameters of the formation rock of the gas storage reservoir, establish a relationship model between the operation cycle of the gas storage reservoir and the internal cohesion of the rock and a relationship model between the operation cycle of the gas storage reservoir and the internal friction angle of the rock;

[0055] Specifically, according to the obtained dynamic elastic modulus E of the rock d and the static compressive strength σ s , a relationship equation σ s = aE d (the first equation model) is established by the mathematical regression analysis method;

[0056] According to the obtained internal cohesion C and internal friction angle φ of the rock under different stress states of the rock, combined with the obtained static compressive strength σ of the rock s , a relationship equation C = bσ s , and between φ and C, C = bσ s + c (the second equation model, where the lowercase c in the equation is the fitting parameter and the uppercase C is the internal cohesion), (the third equation model);

[0057] According to the change of the elastic modulus of the fault rock under the alternating load, using the established σ s = aE d model, calculate the change of the static compressive strength σ of the fault rock under the alternating load s ;

[0058] According to the change of the static compressive strength of the fault rock under the alternating load, using the established C = bσ s + c model, obtain the change of the internal cohesion of the fault rock under the alternating load, and establish a relationship model C = fT between the operation cycle T of the gas storage reservoir and the internal cohesion C of the rock g ;

[0059] Based on the change of the static compressive strength of fault rocks under alternating loads, using the above-established model, obtain the change of the internal friction angle of fault rocks under alternating loads, and establish the relationship model between the operation cycle T of the gas storage reservoir and the internal friction angle of the rock ;

[0060] S3 Based on the relationship model between the operation cycle of the gas storage reservoir and the internal cohesion of the rock and the relationship model between the operation cycle of the gas storage reservoir and the internal friction angle of the rock, establish a limit operation pressure calculation model based on the rock shear failure criterion for the target gas storage reservoir;

[0061] Specifically, according to the rock shear strength criterion and combining with Terzaghi's effective stress theory, establish a gas storage reservoir fault limit bearing pressure calculation model based on the rock shear strength criterion in the form of principal stress

[0062]

[0063] Substitute the established relationship model C = f(T) between the operation cycle T of the gas storage reservoir and the internal cohesion C of the rock g , and the relationship model between the operation cycle T of the gas storage reservoir and the internal cohesion C of the rock into the gas storage reservoir limit operation pressure calculation model based on the rock shear strength criterion in the form of principal stress, and establish a limit operation pressure calculation model based on the rock shear failure criterion for the target gas storage reservoir

[0064]

[0065] S4 Determine the friction coefficient of the fault gouge of the target gas storage reservoir;

[0066] Specifically, obtain the fault gouge sample of the target gas storage reservoir and conduct a fault gouge friction experiment. Since it is relatively difficult to obtain the fault gouge sample, if there is no condition to obtain the sample, then based on the analysis data of logging, well logging, etc., and based on the analysis results of the fault gouge composition of the target gas storage reservoir, configure an artificial fault gouge sample with a similar rock mineral composition to the fault gouge of the target gas storage reservoir, conduct a fault gouge friction experiment, and obtain the friction coefficient μ of the fault gouge of the target gas storage reservoir s .

[0067] S5 Based on the friction coefficient of the fault gouge of the target gas storage reservoir, establish a gas storage reservoir limit operation pressure calculation model based on the rock friction sliding law for the target gas storage reservoir;

[0068] Specifically, according to the rock sliding friction law and combining with Terzaghi's effective stress theory, establish a gas storage reservoir fault limit bearing pressure calculation model based on the rock friction law in the form of principal stress

[0069]

[0070] Substitute the obtained friction coefficient μ of the fault gouge in the target gas storage reservoir s into the calculation model of the ultimate operating pressure of the gas storage reservoir based on the rock friction law in the form of principal stresses, and establish a calculation model of the ultimate operating pressure of the gas storage reservoir based on the rock friction sliding law applicable to the target gas storage reservoir

[0071]

[0072] S6 Use the calculation model of the ultimate operating pressure based on the rock shear fracture criterion for the target gas storage reservoir, and calculate the bearing limit pressure of the fault shear fracture in the gas storage reservoir under different operating cycles according to the maximum principal stress and the minimum principal stress of the target gas storage reservoir formation, so as to obtain the first calculation result;

[0073] S7 Use the calculation model of the ultimate operating pressure of the gas storage reservoir based on the rock friction sliding law for the target gas storage reservoir, and calculate the bearing limit pressure of the friction sliding failure of the gas storage reservoir fault at different dip angles according to the maximum principal stress and the minimum principal stress of the target gas storage reservoir formation, so as to obtain the second calculation result;

[0074] S8 Evaluate the dynamic stability of the target gas storage reservoir according to the first calculation result and the second calculation result, and determine the highest upper limit pressure to ensure the stability of the gas storage reservoir fault.

[0075] The advantage of the present invention is that it can more accurately evaluate the dynamic stability of the fault during the gas injection and production process of the gas storage reservoir. This advantage is mainly reflected in three aspects: First, the present invention comprehensively considers two instability forms of fault shear fracture and friction sliding, and comprehensively adopts two instability theories, which is applicable to evaluating the stability of faults with any parameters; Second, the present invention considers the dynamic change of the fault rock strength with the operation of the gas storage reservoir, which is closer to the actual operation of the gas storage reservoir than the existing static methods; The present invention considers the differences in the friction coefficients of different gas storage reservoir faults, and specific gas storage reservoirs use specific friction coefficients for evaluation, making the evaluation method more targeted, rather than using the same friction coefficient for all gas storage reservoir faults.

[0076] Embodiment

[0077] W Gas Storage Reservoir belongs to a gas reservoir type gas storage reservoir, and the designed upper and lower limit pressures for operation are 38.62 MPa and 15.0 MPa respectively. The maximum principal stress σ1 of the W Gas Storage Reservoir formation is 66.32 MPa, and the minimum principal stress σ3 is 44.02 MPa. The dip angles θ of each fault in the gas storage reservoir are shown in Table 1;

[0078] Table 1 Parameters of the boundary faults of the W Gas Storage Reservoir

[0079]

[0080] 1. Test the dynamic mechanical strength parameters of the formation rocks in the gas storage reservoir

[0081] (1-1) Core samples were prepared from the formation samples taken from the W gas storage reservoir. According to the magnitudes of the horizontal principal stresses in the W gas storage reservoir, multiple confining pressures with different numerical values were set within the range of 0 to the maximum horizontal principal stress of the gas storage reservoir formation, and single-cycle triaxial compression rock mechanics experiments and acoustic time difference rock mechanics experiments were carried out to obtain the dynamic elastic modulus Ed and static compressive strength σs of the rock under different confining pressures (Table 2);

[0082] Table 2 Test results of single-cycle triaxial compression rock mechanics experiments and acoustic time difference rock mechanics experiments

[0083]

[0084]

[0085] (1-2) As Figure 1 shown, according to the maximum axial stress values and radial stress values of the rocks in the triaxial compression experiments under different confining pressures, and respectively with the maximum axial stress values of the rocks in the unconfined state, Mohr stress circles were plotted pairwise on the τ-σ plane, and the intersection point of the common tangent of the two Mohr stress circles with the τ-axis and the included angle with the σ-axis were read to obtain the internal cohesion C and internal friction angle φ of the rocks under different stress states (Table 3);

[0086] Table 3 Calculation results of the internal cohesion and internal friction angle of the rock

[0087]

[0088] (1-3) Select the fault rocks of the W gas storage reservoir, and carry out alternating load mechanics experiments under the effective stresses of the rocks corresponding to the upper and lower limit operating pressures designed for the target gas storage reservoir, and use the acoustic time difference method to measure the change of the dynamic elastic modulus of the fault rocks under the alternating load( Figure 3 ).

[0089] 2. Obtain the calculation model of the rock dynamic mechanical strength parameters

[0090] (2-1) According to the obtained dynamic elastic modulus Ed and static compressive strength σs of the rock, a relationship equation between the static compressive strength and the dynamic elastic modulus of the rock was established by means of mathematical regression analysis method σ s =2.7373E d ( Figure 4 );

[0091] (2-2) According to the obtained internal cohesion C and internal friction angle φ of the rock under different stress states, combined with the previously obtained static compressive strength σs of the rock, relationship equations between C and σs, and between φ and C were established by means of mathematical regression analysis method C = 0.0381σs +8.7767, ( Figure 5 , Figure 6 );

[0092] (2 - 3) According to the change of elastic modulus of fault rock under alternating load, use the established σ s = 2.7373E d model to calculate the change of static compressive strength of fault rock under alternating load;

[0093] (2 - 4) According to the change of static compressive strength of fault rock under alternating load, use the established C = 0.0381σ s + 8.7767 model to obtain the change of internal cohesion of fault rock under alternating load, and establish the relationship model C = 10.790T between the operation cycle T of the gas storage reservoir and the internal cohesion C of the rock -0.003 ;

[0094] (2 - 5) According to the change of static compressive strength of fault rock under alternating load, use the established model to obtain the change of internal friction angle of fault rock under alternating load, and establish the relationship model between the operation cycle T of the W gas storage reservoir and the internal friction angle φ of the rock

[0095] 3. Obtain the calculation model of the ultimate bearing pressure of the fault based on the shear failure criterion

[0096] According to the rock shear strength criterion and combined with Terzaghi's effective stress theory, establish the calculation model of the ultimate bearing pressure of the gas storage reservoir fault based on the rock shear strength criterion in the form of principal stress. Substitute the established relationship model C = 10.790T between the operation cycle T of the gas storage reservoir and the internal cohesion C of the rock -0.003 , and the relationship model between the operation cycle T of the gas storage reservoir and the internal cohesion C of the rock into the calculation model of the ultimate operating pressure of the gas storage reservoir based on the rock shear strength criterion in the form of principal stress to establish the calculation model of the ultimate operating pressure applicable to the W gas storage reservoir

[0097]

[0098] 4. Determine the fault friction coefficient of the target gas storage reservoir

[0099] First, according to the composition of the fault gouge in the W gas storage reservoir, configure the fault gouge containing different types and different contents of clay minerals, conduct the fault gouge friction experiment, and obtain the relationship model between the fault gouge friction coefficient and the clay mineral content( Figure 7 ); then, according to the average clay content of the W gas storage reservoir formation, determine the fault gouge friction coefficient μ s = 0.71.

[0100] 5. Obtain the calculation model for the ultimate bearing pressure of the fault based on the friction-sliding failure criterion

[0101] According to the rock sliding friction law and combined with Terzaghi's effective stress theory, establish a calculation model for the ultimate bearing pressure of the gas storage reservoir fault based on the rock friction law in the form of principal stresses. Substitute the obtained friction coefficient μ s = 0.71 of the fault gouge in the W gas storage reservoir into the calculation model for the ultimate operating pressure of the gas storage reservoir based on the rock friction law in the form of principal stresses, and establish a calculation model for the ultimate operating pressure of the gas storage reservoir applicable to the W gas storage reservoir

[0102]

[0103] 6. Calculate the ultimate bearing pressure for the shear rupture failure of the fault

[0104] According to the obtained maximum principal stress σ1 and minimum principal stress σ3 of the W gas storage reservoir formation, use the calculation model for the ultimate bearing pressure of the fault based on the shear rupture failure criterion applicable to the W gas storage reservoir to calculate the ultimate operating pressure within T operating cycles of the W gas storage reservoir, and study its variation ([[]] Figure 8 ), the shear rupture instability pressure limit of the main fault in the main block of the W gas storage reservoir is between 51.26 MPa and 52.28 MPa, which is higher than the upper limit operating pressure of 38.62 MPa designed for the gas storage reservoir

[0105] 7. Calculate the ultimate bearing pressure for the friction-sliding failure of the fault

[0106] According to the obtained maximum principal stress σ1, minimum principal stress σ3 and fault dip angle θ of the W gas storage reservoir formation, use the calculation model for the ultimate bearing pressure of the fault based on the friction-sliding failure criterion applicable to the W gas storage reservoir to calculate the ultimate operating pressure at different dip angles of each fault in the gas storage reservoir ([[]] Figure 9 ), the friction-sliding instability pressure limit of the main fault in the main block of the W gas storage reservoir at the part with the minimum dip angle is between 39.46 MPa and 63.43 MPa, all of which are higher than the upper limit operating pressure of 38.62 MPa designed for the gas storage reservoir, and the limit of the F1 fault exceeds 60 MPa; ② the friction-sliding instability pressure limit of the main fault in the main block of the W gas storage reservoir at the part with the maximum dip angle is between 36.53 MPa and 37.66 MPa, and all 4 main faults are slightly lower than the upper limit operating pressure of 38.62 MPa designed for the gas storage reservoir. There is a certain risk of friction-sliding instability in the main block of the W gas storage reservoir after reaching the capacity

[0107] 8. Evaluate the dynamic stability of the faults in the target gas storage reservoir

[0108] Evaluate the dynamic stability of the faults in the target gas storage reservoir. The results show that: the risk of shear rupture instability of the 4 main faults in the W gas storage reservoir is relatively small, and the risk of frictional sliding instability of the 4 faults at the part with the smallest dip angle is relatively small, but there is a relatively large risk of frictional sliding instability at the part with the largest dip angle. During operation, attention should be paid to the pressure change at the part with a large dip angle of the fault to prevent local overpressure from causing frictional sliding of the fault and further leading to natural gas leakage. At the same time, attention should also be paid to monitoring the deformation of the pipe string at the part where the gas well encounters the fault, and timely prevent and control the possible deformation and rupture of the pipe string. At the same time, to ensure the safe operation of the main block of the W gas storage reservoir, it is recommended to reduce the upper limit operating pressure to 36.53 MPa.

[0109] The above-disclosed is only a preferred embodiment of a method for evaluating the dynamic stability of faults in an oil and gas reservoir type gas storage reservoir under alternating loads. Of course, the scope of the rights of the present invention cannot be limited by this. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A method for evaluating the dynamic stability of faults in gas storage reservoirs of oil and gas reservoir type under alternating loads, characterized in that, It includes the following steps: Testing the dynamic mechanical strength parameters of the formation rock in the gas storage reservoir; Based on the dynamic mechanical strength parameters of the formation rock in the gas storage reservoir, establishing a relationship model between the operation cycle of the gas storage reservoir and the cohesive force in the rock and a relationship model between the operation cycle of the gas storage reservoir and the friction angle in the rock; Based on the relationship model between the operation cycle of the gas storage reservoir and the cohesive force in the rock and the relationship model between the operation cycle of the gas storage reservoir and the friction angle in the rock, establishing a limit operation pressure calculation model for the target gas storage reservoir based on the rock shear fracture criterion; Determining the friction coefficient of the fault gouge in the target gas storage reservoir; Based on the friction coefficient of the fault gouge in the target gas storage reservoir, establishing a limit operation pressure calculation model for the target gas storage reservoir based on the rock friction sliding law; Using the limit operation pressure calculation model for the target gas storage reservoir based on the rock shear fracture criterion, according to the maximum principal stress and minimum principal stress of the formation in the target gas storage reservoir, calculating the bearing limit pressure of the fault shear fracture in the gas storage reservoir under different operation cycles to obtain the first calculation result; Using the limit operation pressure calculation model for the target gas storage reservoir based on the rock friction sliding law, according to the maximum principal stress and minimum principal stress of the formation in the target gas storage reservoir, calculating the bearing limit pressure of the friction sliding of the fault in the gas storage reservoir at different dip angles to obtain the second calculation result; Evaluating the dynamic stability of the target gas storage reservoir according to the first calculation result and the second calculation result, and determining the highest upper limit pressure to ensure the stability of the fault in the gas storage reservoir.

2. The method for evaluating the dynamic stability of the fault in the oil and gas reservoir type gas storage reservoir under alternating loads according to claim 1, characterized in that The dynamic mechanical strength parameters of the formation rock in the gas storage reservoir include the dynamic elastic modulus of the rock, the static compressive strength, the cohesive force in the rock, and the friction angle in the rock.

3. The method for evaluating the dynamic stability of the fault in the oil and gas reservoir type gas storage reservoir under alternating loads according to claim 2, characterized in that The testing of the dynamic mechanical strength parameters of the formation rock in the gas storage reservoir includes: Using the rock sampled from the formation of the target gas storage reservoir to prepare core samples, setting multiple confining pressures with different numerical values within the range of 0 to the maximum horizontal principal stress of the formation of the target gas storage reservoir according to the magnitude of the horizontal principal stress of the target gas storage reservoir, and conducting single-cycle triaxial compression rock mechanics experiments and acoustic wave travel time rock mechanics experiments to obtain the dynamic elastic modulus and static compressive strength of the rock under different confining pressures; According to the maximum axial stress value and radial stress value of the rock in the triaxial compression experiment under different confining pressures, respectively, and the maximum axial stress value of the rock in the state without confining pressure, plotting Mohr stress circles pairwise on the τ-σ plane, and reading the intersection point of the common tangent of the two Mohr stress circles and the τ axis and the included angle with the σ axis to obtain the cohesive force in the rock and the friction angle in the rock under different stress states; Selecting the rock of the fault in the target gas storage reservoir, conducting alternating load mechanics experiments under the effective stress of the rock corresponding to the upper and lower limit operation pressures designed for the target gas storage reservoir, and using the acoustic wave travel time method to measure the change in the elastic modulus of the fault rock under alternating loads.

4. The method for evaluating the dynamic stability of the fault in the oil and gas reservoir type gas storage reservoir under alternating loads according to claim 3, characterized in that Based on the dynamic mechanical strength parameters of the formation rock of the gas storage reservoir, establishing a relationship model between the operation cycle of the gas storage reservoir and the cohesion within the rock and a relationship model between the operation cycle of the gas storage reservoir and the internal friction angle of the rock, including: According to the dynamic elastic modulus of the rock and the static compressive strength, establishing a relationship equation between the static compressive strength of the rock and the dynamic elastic modulus through mathematical regression analysis to obtain a first equation model; According to the cohesion, the internal friction angle and the static compressive strength of the rock, establishing a relationship equation between the cohesion, the static compressive strength of the rock, the internal friction angle and the cohesion through mathematical regression analysis to obtain a second equation model and a third equation model; According to the change of the elastic modulus of the rock under alternating loads, using the first equation model to calculate the change of the static compressive strength of the fault rock under alternating loads; According to the change of the static compressive strength of the fault rock under alternating loads, using the second equation model to obtain the change of the cohesion of the fault rock under alternating loads and establish a relationship model between the operation cycle of the gas storage reservoir and the cohesion within the rock; According to the change of the static compressive strength of the fault rock under alternating loads, using the third equation model to obtain the change of the internal friction angle of the fault rock under alternating loads and establish a relationship model between the operation cycle of the gas storage reservoir and the internal friction angle of the rock.

5. The method for evaluating the dynamic stability of a fault in an oil and gas reservoir type gas storage reservoir under alternating loads according to claim 4, wherein Based on the relationship model between the operation cycle of the gas storage reservoir and the cohesion within the rock and the relationship model between the operation cycle of the gas storage reservoir and the internal friction angle of the rock, establishing a limit operating pressure calculation model based on the rock shear failure criterion for the target gas storage reservoir, including: According to the rock shear strength criterion and combined with the effective stress theory, establishing a limit bearing pressure calculation model for the gas storage reservoir fault based on the rock shear strength criterion in the form of principal stresses; Substituting the relationship model between the operation cycle of the gas storage reservoir and the cohesion within the rock and the relationship model between the operation cycle of the gas storage reservoir and the internal friction angle of the rock into the limit bearing pressure calculation model for the gas storage reservoir fault based on the rock shear strength criterion in the form of principal stresses to establish a limit operating pressure calculation model based on the rock shear failure criterion for the target gas storage reservoir.

6. The method for evaluating the dynamic stability of a fault in an oil and gas reservoir type gas storage reservoir under alternating loads according to claim 1, wherein Determining the friction coefficient of the fault gouge of the target gas storage reservoir includes: Obtaining a fault gouge sample of the target gas storage reservoir, conducting a fault gouge friction experiment, and obtaining the friction coefficient of the fault gouge of the target gas storage reservoir.

7. The method for evaluating the dynamic stability of a fault in an oil and gas reservoir type gas storage reservoir under alternating loads according to claim 1, wherein Determining the friction coefficient of the fault gouge of the target gas storage reservoir includes: According to the logging analysis data and the well logging analysis data, based on the analysis results of the composition of the fault gouge of the target gas storage reservoir, configuring a fault gouge sample, conducting a fault gouge friction experiment, and obtaining the friction coefficient of the fault gouge of the target gas storage reservoir.

8. The method for evaluating the dynamic stability of a fault in an oil and gas reservoir type gas storage reservoir under alternating loads according to claim 1, wherein The calculation model for the ultimate operating pressure of the gas storage reservoir based on the rock friction sliding law for the target gas storage reservoir established based on the friction coefficient of the fault gouge of the target gas storage reservoir includes: According to the rock sliding friction law and combined with the effective stress theory, establish a calculation model for the ultimate bearing pressure of the gas storage reservoir fault based on the rock friction law in the form of principal stresses; Substitute the friction coefficient of the fault gouge of the target gas storage reservoir into the calculation model for the ultimate bearing pressure of the gas storage reservoir fault based on the rock friction law in the form of principal stresses, and establish a calculation model for the ultimate operating pressure of the gas storage reservoir based on the rock friction sliding law for the target gas storage reservoir.

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