Method for evaluating sealing performance of boundary fault of gas storage

Abstract

The invention belongs to the technical field of underground gas storage evaluation, and discloses a gas storage boundary fault sealing performance evaluation method which comprises the following steps: determining a boundary fault according to dynamic and static data of a gas storage, obtaining a minimum value of shale content of fault rock at a storage unit, establishing a shale content-burial depth-displacement pressure chart, eliminating errors of diagenetic time, and evaluating the sealing performance of the boundary fault. And determining the gas storage fault sealing capability according to the sealing evaluation data of each fault. The evaluation method provided by the invention is simple and feasible, can quickly obtain relatively accurate fault sealing parameters, and plays a certain reference role in geological evaluation, reservoir capacity parameter design and the like of the underground gas storage.

Description

Technical Field

[0001] The invention belongs to the technical field of underground gas storage evaluation, and relates to a method for evaluating the sealing performance of a gas storage boundary fault, and specifically to a method for evaluating the sealing performance of a sandstone gas reservoir type gas storage fault. Background Art

[0002] Underground gas storage is an artificial gas reservoir formed by re-injecting natural gas into underground space. It has the characteristics of large storage capacity, wide peak-shaving range, economic rationality, and durability. Underground gas storage is one of the important links in the natural gas industry chain and has become a strategic infrastructure to ensure safe and stable gas supply. As the proportion of natural gas in my country's energy consumption increases year by year, underground gas storage has become a key link in my country's natural gas security supply in recent years. The construction of gas storage can promote the revitalization of the value of old oil and gas fields, increase operating profits, expand market share, and ensure seasonal peak-shaving and emergency supply. There are many sandstone gas reservoirs in the continental sedimentary environment in eastern my country, which are close to the natural gas consumption market and have relatively mature pipeline networks. They are the main positions for the reconstruction of gas storage in the future. The construction of gas storage in my country has gone through the initial exploration period at the beginning of this century and is currently in a rapid development stage.

[0003] The sealing capacity of underground reservoirs is the top priority of geological evaluation. A large number of sandstone gas reservoirs in eastern my country have complex geological conditions and well-developed faults. The evaluation of the sealing of faults is of great significance for the geological evaluation of such depleted gas reservoirs for reconstruction into gas storage facilities. Scientific and effective evaluation of the sealing of gas storage faults is a prerequisite for the construction and safe operation of gas storage facilities.

[0004] There are two main methods for evaluating the sealing performance of gas storage faults in China. One is the structural stress analysis method, which has high accuracy but is time-consuming and has many uncertain factors in the analysis process, which is not conducive to rapid promotion and use. The other is based on fault mudstone smear analysis. This method is simple and fast and widely used, but its disadvantage is that the diagenesis time of fault rock is equal to the diagenesis time of surrounding rock, resulting in large errors in the calculation results. Therefore, it is necessary to establish a more systematic, reliable, and operational method for evaluating the sealing performance of sandstone-type gas storage faults. Summary of the invention

[0005] In order to better understand the fault sealing parameters and obtain relatively accurate fault sealing parameters as quickly as possible, so as to provide a certain reference for geological evaluation and storage capacity parameter design of underground gas storage, the present invention provides a method for predicting fault sealing of gas storage based on lithofacies analysis and geophysical theory, which mainly includes:

[0006] Step 1: Determine boundary faults based on dynamic and static data of gas storage

[0007] The main faults of the gas storage reservoir are determined based on the fault distribution and delivery order, and the boundary faults of the gas storage reservoir are further determined and clarified based on the original oil and gas distribution conditions and production data such as test production and water injection.

[0008] Step 2: Obtain the minimum value of the shale content of the fault rock at the reservoir unit

[0009] Establish gas storage reservoir structural model and lithofacies model using fault, seismic inversion and well logging data;

[0010] According to the distribution of sandstone and mudstone in the two sides of the fault and the fault throw, a three-dimensional SGR model of the fault plane was established.

[0011] The mud content distribution of the entire section can be obtained, and the minimum mud content value in the fault section can also be obtained.

[0012] Step 3: Create a chart of mud content, burial depth and displacement pressure

[0013] Since fault rock samples are difficult to obtain, the maximum displacement pressure values ​​of the mercury injection test were determined based on the mud content of core samples taken within the gas storage area and its adjacent structural units.

[0014] Establish a relationship chart between mud content, burial depth and displacement pressure of different lithologies in this area.

[0015] Within a specific range of shale content, the displacement pressure is exponentially related to the rock burial depth, and at the same depth, the higher the shale content of the rock, the greater the displacement pressure.

[0016] There is a certain relationship between mudstone displacement pressure, overlying formation pressure and time. Under the condition of a certain time, the greater the overlying formation pressure, the higher the mudstone displacement pressure;

[0017] The lower the overburden pressure, the lower the mudstone displacement pressure. Under constant pressure, the mudstone displacement pressure gradually increases with time; the longer the time, the higher the mudstone displacement pressure.

[0018] Step 4: Eliminate the error in diagenesis time.

[0019] Pd=4.06Z 2 -0.0077Z+4.3997. (1)

[0020] Pd is the displacement pressure of mudstone, and Z is the vertical depth of the rock;

[0021] Formula (1) is obtained by fitting the test results of rock samples with different shale contents in the gas storage geological body.

[0022] The formation time of faults is generally later than the formation time of disconnected strata.

[0023] Under the same mud content, the displacement pressure of fault rock is less than that of surrounding rock.

[0024] Therefore, it is necessary to establish the corresponding correction formula (2) to eliminate the error caused by diagenesis time. Combined with the SGR value of fault rock, the displacement pressure of fault rock is interpolated from the rock shale content-burial depth-displacement pressure relationship chart.

[0025] Z=K×S×(β / 90)×T (2)

[0026] Step 5: Based on the evaluation data of the sealing property of each fault, the calculation formulas given in (1) and (2) are applied to calculate the displacement pressure of each boundary fault of the gas storage reservoir. The minimum value is the fault sealing capacity of the gas storage reservoir.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] The invention is simple and feasible to use, and can quickly obtain relatively accurate fault sealing parameters, which can serve as a reference for geological evaluation of underground gas storage and storage capacity parameter design. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the fault distribution map of M gas storage;

[0030] Figure 2 This is the SGR cross section of F1 fault of M gas storage;

[0031] Figure 3 This is the relationship diagram between mudstone burial depth and displacement pressure of M gas storage. DETAILED DESCRIPTION

[0032] The present invention is described in detail below by specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0033] Example 1

[0034] The M gas storage is an underground gas storage rebuilt from a depleted oil and gas reservoir in the eastern oil field. The research area of ​​the gas storage is generally a fault anticline structure sandwiched by two main faults. The structural high point is located near the middle of the fault block, dipping to the surroundings and oriented northeastward. The gas layer gas is mainly distributed in the high part of the fault block structure ( Figure 1 ), the original formation pressure is 28.7MPa.

[0035] The sealing ability of the boundary fault is evaluated using the method of the present invention.

[0036] first step:

[0037] From the structural analysis of the M gas storage, it can be seen that the gas storage is controlled by faults F1 and F2 in the north-south direction and by faults F3 and F4 in the east-west direction. Secondary block faults are developed inside and have no sealing ability. Therefore, the boundary faults of the gas storage are faults F1, F2, F3, and F4.

[0038] Step 2:

[0039] The structural model and lithofacies model of the gas storage reservoir are established using fault, seismic inversion and well logging data.

[0040] According to the distribution of sandstone and mudstone in the two sides of the fault and the fault throw, a three-dimensional SGR model of the fault plane was established.

[0041] In this case, only the F1 fault is taken as an example, and the other three boundary faults are processed in the same way.

[0042] The established F1 fault section SGR model is as follows: Figure 2 As shown, the mud content distribution of the entire section can be obtained at this time.

[0043] Step 3:

[0044] Since drilling generally needs to avoid faults, there are relatively few wells that pass through faults within the oil field. At the same time, during the drilling process, the thickness of the fault rock is relatively thin and it is difficult to coring in time.

[0045] Therefore, it is necessary to analyze the fault rock samples and displacement pressure data that are not available within the gas storage and surrounding oil fields. These data are the fault surrounding rock data.

[0046] During the development of oil and gas reservoirs, mudstone displacement pressure is generally used as caprock identification data, and the number of cores is relatively small. Therefore, the mud content and the maximum displacement pressure values ​​of the core samples taken within the M gas storage area and its adjacent structural units were collected, and a map of the relationship between mudstone burial depth and displacement pressure at different depths in this area was established.

[0047] In this case, the displacement pressure is exponentially related to the rock burial depth. The fitting relationship is:

[0048] Pd=4.06Z 2 -0.0077Z+4.3997. (1)

[0049] Pd is the displacement pressure of mudstone, and Z is the vertical depth of the rock;

[0050] Step 4:

[0051] In the third step, the mudstone data used are actually fault surrounding rock data.

[0052] The diagenesis time of fault rock and its surrounding rock is not consistent. The formation time of fault is generally later than that of disconnected strata. Under the same mud content, the displacement pressure of fault rock is less than that of surrounding rock.

[0053] Therefore, the corresponding correction formula needs to be established using the following relationship to eliminate the error caused by diagenesis time.

[0054] Z=K×S×(β / 90)×T (2)

[0055] This formula is used to eliminate the effect of diagenesis on the displacement pressure of fault rocks.

[0056] Step 5:

[0057] Based on the evaluation data of the sealing performance of each fault and the SGR value of the fault rock, the displacement pressure of each boundary fault of the gas storage reservoir is calculated by applying the calculation formulas given in (1) and (2):

[0058] The displacement pressure of F1 is 36.3MPa, the displacement pressure of F2 is 33.2MPa, the displacement pressure of F3 is 32.1MPa, and the displacement pressure of F4 is 32.6MPa.

[0059] From the above data, we can see that the sealing capacity of the boundary faults of the M gas storage reservoir is: F1>F2>F4>F3. The sealing capacity of the F3 fault is the weakest, and the closing pressure of the fault is 32.1MPa, which is the sealing capacity of the M gas storage reservoir fault.

[0060] The original formation pressure of the M gas storage is 28.7MPa, so the gas storage still has a potential for increasing pressure by 3.4MPa.

[0061] The above-described embodiments are only preferred embodiments of the present invention, but not all feasible embodiments of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A method for evaluating the sealing performance of a gas storage reservoir boundary fault, characterized in that: The following steps are involved: Step 1: Determine the boundary fault based on the dynamic and static data of the gas storage reservoir; Step 2, obtaining the minimum value of the shale content of the fault rock at the reservoir unit; Step 3: Establish a mud content-burial depth-displacement pressure chart; Step 4: Eliminate the error of diagenesis time. The test results of rock samples with different shale contents in the gas storage geological body are fitted to obtain a formula. At the same time, a corresponding correction formula is established to eliminate the error caused by diagenesis time. Combined with the SGR value of the fault rock, the displacement pressure of the fault rock is interpolated from the rock shale content-burial depth-displacement pressure relationship chart; Step 5: Based on the sealing evaluation data of each fault, the displacement pressure of each boundary fault of the gas storage reservoir is calculated using the fitting formula and the correction formula, and the minimum value is the fault sealing capacity of the gas storage reservoir.

2. The method for evaluating the sealing performance of a gas storage reservoir boundary fault according to claim 1, characterized in that: Step one is as follows: determine the main fault of the gas storage reservoir based on fault distribution and delivery order, and then further determine and clarify the boundary fault of the gas storage reservoir based on the original oil and gas distribution conditions and production data of test production and water injection.

3. The method for evaluating the sealing performance of a gas storage reservoir boundary fault according to claim 1, characterized in that: Step 2 is as follows: using fault, seismic inversion and logging data to establish a gas storage reservoir structural model and lithofacies model; according to the distribution and fault distance of sandstone and mudstone in the two sides of the fault, a three-dimensional SGR model of the fault surface is established to obtain the minimum mud content in the fault section.

4. The method for evaluating the sealing performance of a gas storage reservoir boundary fault according to claim 1, characterized in that: Step 2 is as follows: Based on the mud content of core samples taken within the gas storage area and its adjacent structural units and the maximum displacement pressure values ​​of mercury injection testing, a relationship chart between mud content, burial depth and displacement pressure of different lithologies in the area is established.

5. The method for evaluating the sealing performance of a gas storage reservoir boundary fault according to claim 4, characterized in that: The relationship between mud content, burial depth and displacement pressure includes: Within a specific range of shale content, displacement pressure is exponentially related to rock burial depth, and at the same depth, the higher the shale content of the rock, the greater the displacement pressure; There is a certain relationship between mudstone displacement pressure, overlying formation pressure and time. Under the condition of a certain time, the greater the overlying formation pressure, the higher the mudstone displacement pressure. The smaller the overlying stratum pressure is, the lower the mudstone displacement pressure is. Under constant pressure, the mudstone displacement pressure gradually increases with the passage of time; the longer the time is, the higher the mudstone displacement pressure is.

6. The method for evaluating the sealing performance of a gas storage reservoir boundary fault according to claim 1, characterized in that: The fitting formula is: Pd = 4.06Z 2 -0.0077Z+4.3997, Pd is the mudstone displacement pressure, and Z is the vertical depth of the rock.

7. The method for evaluating the sealing performance of a gas storage reservoir boundary fault according to claim 1, characterized in that: The correction formula is: Z = K × S × (β / 90) × T.

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