A method for evaluating the sealing property of a gas storage boundary fault

Abstract

The present application belongs to the technical field of underground gas storage evaluation, and discloses a kind of evaluation method of gas storage boundary fault sealing property: according to gas storage dynamic and static data, boundary fault is determined, the lowest value of fault argillaceous content at reservoir unit is obtained, argillaceous content-depth-displacement pressure chart is established, the error of diagenetic time is eliminated, and the sealing capacity of gas storage fault is determined according to the sealing property evaluation data of each fault. The evaluation method is simple and feasible, and can quickly obtain relatively accurate fault sealing property parameters, which can provide certain reference for underground gas storage geological evaluation and reservoir capacity parameter design.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of underground gas storage evaluation, and relates to a method for evaluating the sealing property of boundary faults of a gas storage, in particular to a method for evaluating the sealing property of faults of a sandstone gas reservoir type gas storage. BACKGROUND

[0002] An underground gas storage is an artificial gas reservoir formed by re-injection of natural gas into an underground space, and has the characteristics of large storage capacity, wide peak-shaving range, economic rationality, and long service life. The underground gas storage is one of the important links in the natural gas industry chain, and has become a strategic infrastructure for ensuring safe and stable gas supply. With the increasing proportion of natural gas in energy consumption in China, in recent years, the underground gas storage has become a key link in the safe and stable supply of natural gas in China. The construction of the gas storage can promote the value of old oil and gas fields, increase operating profits, expand market share, and ensure seasonal peak shaving and emergency supply. There are a large number of sandstone gas reservoirs in the eastern part of China under a continental sedimentary environment, and they are relatively close to the natural gas consumption market and have relatively mature pipelines, which are the main positions for future reconstruction of gas storage. The construction of gas storage in China has experienced the initial exploration period at the beginning of this century, and is currently in a rapid development stage.

[0003] The sealing capacity of an underground reservoir is the most important in geological evaluation. The geological conditions of a large number of sandstone gas reservoirs in the eastern part of China are complex, and the faults are very developed. The sealing property evaluation of the faults is of great significance to the geological evaluation of the reconstruction of depleted gas reservoirs into gas storage. Scientific and effective evaluation of the sealing property of the faults of the gas storage is a prerequisite for the construction and safe operation of the gas storage.

[0004] There are mainly two methods for evaluating the sealing property of the faults of the gas storage 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 popularization and use, and the other is the analysis based on fault mudstone smearing, which is widely used due to its simplicity and convenience, but has the disadvantage that the diagenetic time of the fault rock is equated to the diagenetic time of the surrounding rock, resulting in a large error in the calculation result. Therefore, it is necessary to establish a more systematic, reliable, and operable method for evaluating the sealing capacity of the faults of the sandstone type gas storage. SUMMARY

[0005] In order to more master the sealing property parameters of the faults, obtain relatively accurate sealing property parameters of the faults in the fastest way, and provide a reference for the geological evaluation of the underground gas storage and the design of the storage capacity parameters, the present application provides a method for predicting the sealing property of the faults of the gas storage on the basis of lithofacies analysis and geophysical theory, mainly including:

[0006] Step one, determining the boundary faults according to the dynamic and static data of the gas storage

[0007] According to the fault distribution and the delivery order, the main fault of the gas storage is determined, and then according to the original oil and gas distribution and the production data such as test production and water injection, the boundary fault of the gas storage is further determined and clarified.

[0008] Step two, obtaining the minimum shale content of the fault mudstone in the reservoir unit

[0009] The structural model and lithofacies model of the gas storage are established by using the fault, seismic inversion and logging data.

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

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

[0012] Step three: Establishing the shale content-depth-displacement pressure chart

[0013] Because the fault rock sample is difficult to obtain, the shale content of the core sample in the gas storage range and its adjacent structural unit and the maximum displacement pressure value of the mercury injection test are used.

[0014] The shale content-depth-displacement pressure relationship chart of different lithology in this area is established.

[0015] Within a certain range of shale content, the displacement pressure and the rock burial depth show an exponential relationship, 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 the shale displacement pressure and the overlying strata pressure and time. Under the condition of certain time, the greater the overlying strata pressure, the higher the shale displacement pressure;

[0017] The smaller the overlying strata pressure, the lower the shale displacement pressure. Under the condition of certain pressure, the shale displacement pressure gradually increases with time; the longer the time, the higher the shale displacement pressure.

[0018] Step four, eliminating the error of diagenetic time.

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

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

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

[0022] The fault formation time is generally later than the formation time of the strata broken by the fault.

[0023] Under the same shale content, the fault rock displacement pressure is smaller than the surrounding rock displacement pressure.

[0024] Therefore, the corresponding correction formula (2) is established to eliminate the error caused by diagenetic time. The displacement pressure of the fault rock is obtained by interpolation according to the rock argillaceous content-burial depth-displacement pressure relationship chart in combination with the SGR value of the fault rock.

[0025] Z = K x S x (β / 90) x T (2)

[0026] Step five, according to the sealing evaluation data of each fault, the calculation formula given by (1) and (2) is applied to calculate the displacement pressure of each boundary fault of the gas storage, and the minimum value is the fault sealing capacity of the gas storage.

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

[0028] The application is simple and feasible, and can quickly obtain relatively accurate fault sealing parameters, and has certain reference effect for geological evaluation of underground gas storage and design of storage capacity parameters. BRIEF DESCRIPTION OF DRAWINGS

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

[0030] Figure 2 is a SGR profile of F1 fault of M gas storage;

[0031] Figure 3 is a relationship chart of mudstone burial depth-displacement pressure of M gas storage. DETAILED DESCRIPTION

[0032] The application will be described in detail below through specific examples, but the protection scope of the application is not limited. Unless otherwise specified, the experimental methods used in the application are conventional methods, and the experimental apparatus, materials and reagents used can be obtained from commercial channels.

[0033] Example 1

[0034] M gas storage is a depleted oil and gas reservoir of an underground gas storage in an eastern oil field. The research area of the gas storage is a faulted anticline structure sandwiched by two main faults, the structural high point is located near the middle of the fault block, and the structural high point is located near the middle of the fault block, and the structural high point is located near the middle of the fault block. Figure 1 The original formation pressure is 28.7 MPa.

[0035] The sealing capacity of the boundary fault is evaluated by using the method described in the application.

[0036] First step:

[0037] From the analysis of the M gas reservoir structure, it is known that the gas reservoir is controlled by F1 and F2 faults in the north-south direction, and by F3 and F4 faults in the east-west direction, and the secondary faulted blocks develop inside the gas reservoir, and the gas reservoir has no sealing ability, so the boundary faults of the gas reservoir are F1, F2, F3 and F4 faults.

[0038] Second step:

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

[0040] According to the sandstone and shale distribution and fault throw of the strata on both sides of the fault, a three-dimensional SGR model of the fault plane is established.

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

[0042] The SGR model of the F1 fault plane is shown in Figure 2 At this time, the shale content distribution of the whole plane can be obtained.

[0043] Third step:

[0044] Because the drilling process generally avoids drilling through the fault, the wells passing through the fault in the oilfield range are relatively few, and at the same time, the fault rock thickness is thin and difficult to coring in the drilling process.

[0045] Therefore, the data of the rock samples and their displacement pressure without the above-mentioned faults in the gas reservoir and the surrounding oilfield range must be obtained, and this data is the data of the fault wall rock.

[0046] Because the mudstone displacement pressure is generally used as the data for distinguishing the cap rock in the process of oil and gas reservoir development, the number of coring is small. Therefore, the shale content and the maximum displacement pressure value of the mercury injection test of the coring sample in the M gas reservoir range and its adjacent structural units are collected to establish the mudstone burial depth-displacement pressure relationship chart at different depths in this region.

[0047] In this example, the displacement pressure and the rock burial depth show an exponential relationship. The fitting relationship is:

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

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

[0050] Fourth step:

[0051] In the third step, the mudstone data used is actually the data of the fault wall rock.

[0052] The fault rock and its surrounding rock are not consistent in diagenetic time. The fault formation time is generally later than the formation time of the broken strata, and the displacement pressure of the fault rock with the same argillaceous content is less than that of the surrounding rock.

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

[0054] Z = K x S x (β / 90) x T (2)

[0055] The influence of diagenesis on the displacement pressure of the fault rock is eliminated by using this formula.

[0056] Step 5:

[0057] According to the sealing evaluation data of each fault, combined with the SGR value of the fault rock, the displacement pressure of each boundary fault of the gas storage is calculated by using the calculation formula given by (1) and (2):

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

[0059] From the above data, the sealing capacity of the boundary fault of the M gas storage is F1>F2>F4>F3, and the sealing capacity of F3 is the weakest. The sealing pressure of this fault is 32.1 MPa, which is the sealing capacity of the M gas storage.

[0060] The original stratum pressure of the M gas storage is 28.7 MPa, so the gas storage has a potential pressure of 3.4 MPa.

[0061] The above-described embodiments are only preferred embodiments of the present application, and not all the embodiments that can be implemented by the present application. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present application should be considered to be included in the protection scope of the claims of the present application.

Claims

1. A method for evaluating the tightness of a fault in the boundary of a gas storage, characterized in that, The method comprises the following steps: Step one, determining the boundary fault according to the static and dynamic data of the gas storage, judging the main fault of the gas storage according to the fault distribution and the order of intersection, and further judging and determining the boundary fault of the gas storage according to the original oil and gas distribution and the production data of the test production and water injection; Step two, obtaining the minimum value of the shale content in the fault of the reservoir unit, establishing the structure model and the lithofacies model of the gas storage by using the fault, seismic inversion and logging data, establishing the three-dimensional SGR model of the fault plane according to the sand-shale distribution and the fault throw of the strata on both sides of the fault, and obtaining the minimum value of the shale content in the fault section; Step three, establishing the relationship chart of the shale content of the rock, the burial depth and the displacement pressure; Step four, eliminating the error of the diagenetic time, fitting the formula by the test results of the rock samples with different shale contents of the geological body of the gas storage, simultaneously establishing the corresponding correction formula to eliminate the error caused by the diagenetic time, combining the SGR value of the fault rock, and obtaining the displacement pressure of the fault rock by interpolation according to the relationship chart of the shale content of the rock, the burial depth and the displacement pressure; Step five, calculating the displacement pressure of each boundary fault of the gas storage according to the evaluation data of the sealing property of each fault, applying the fitted formula and the correction formula, and taking the minimum value as the sealing capacity of the fault of the gas storage. The correction formula is: Z = K × S × (β / 90) × T, and Z is the burial depth.

2. The method for evaluating the fault seal of a gas reservoir boundary according to claim 1, characterized in that, Step three is specifically: according to the shale content of the coring sample in the range of the gas storage and the adjacent structure unit and the maximum displacement pressure value of the mercury injection test, the relationship chart of the shale content of the rock, the burial depth and the displacement pressure in the region is established.

3. The method for evaluating the fault seal of a gas reservoir boundary according to claim 1, characterized in that, The relationship of the shale content, the burial depth and the displacement pressure includes: In a specific shale content range, the displacement pressure and the burial depth of the rock have an exponential relationship, and at the same depth, the higher the shale content of the rock, the greater the displacement pressure; There is a certain relationship between the displacement pressure of the shale and the overburden pressure and the time, in the case of a certain time, the greater the overburden pressure, the higher the displacement pressure of the shale; The smaller the overburden pressure, the lower the displacement pressure of the shale, in the case of a certain pressure, the displacement pressure of the shale gradually increases with the passage of time, and the longer the time, the higher the displacement pressure of the shale.

4. The method for evaluating the fault seal of a gas reservoir boundary according to claim 1, characterized in that, The formula obtained by fitting is: Pd = 4.06Z 2 - 0.0077Z + 4.3997, Pd is the mudstone displacement pressure.

Images