Method for determining the sealing capacity of a carbonate gas reservoir barrier

Abstract

The present application relates to a kind of determination methods of carbonate gas reservoir interlayer sealing capacity, belong to oil and gas reservoir exploration and development technical field.The method includes the following steps: first, the porosity, permeability, breakthrough pressure and length of interlayer rock sample are obtained, and the rock sample is divided;Then, the breakthrough pressure gradient of each rock sample is calculated, and the lower limit of the breakthrough pressure gradient of non-fracture interlayer and fracture interlayer is determined;The critical breakthrough pressure and critical differential pressure of target interlayer are calculated;Finally, whether the interlayer has sealing capacity is determined by comparing the size of critical breakthrough pressure and critical differential pressure of target interlayer in single well.The method can realize quantitative, accurately determine whether target interlayer has the ability to connect the upper and lower two gas reservoirs of target interlayer.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for determining the sealing capacity of a carbonate gas reservoir barrier, and belongs to the technical field of oil and gas reservoir exploration and development. BACKGROUND

[0002] In carbonate oil and gas reservoir formations, sedimentation, diagenesis and tectonism jointly result in strong heterogeneity of the formations. In the profile of carbonate formations, a non-permeable formation composed of one or more dense layers of argillaceous or pure rock with a certain thickness, which can prevent the flow of oil, gas and water, is a barrier. These barriers play an important control role in the distribution of oil, gas and water during the development of oil and gas fields. Therefore, the fine study of barriers is a prerequisite for the fine description and fine development of oil and gas fields, and the evaluation of the sealing capacity of barriers is crucial.

[0003] In the Sichuan Basin of China, there are a large number of carbonate gas reservoirs, and barriers between different layers of these carbonate oil and gas reservoirs are also very common. Since the barriers in these carbonate formations are mainly limestone or dolomite barriers with relatively small argillaceous content, there must be certain micro-pores in them, and the development of local fractures in the barriers due to tectonic action is an influencing factor that breaks through the sealing effect of the barriers.

[0004] With the development of oil and gas reservoirs, the pressure difference between the present formation pressure and the original formation pressure is constantly expanding. In this case, if the barrier is to play a sealing role, it must reach a certain thickness to prevent the negative effects caused by this pressure difference, thereby leading to the fact that even if there is a barrier between two sets of gas reservoirs on the plane, due to the differences in barrier thickness and fracture development degree, part of the area may be connected between the two sets of gas reservoirs, and part of the area may not be connected between the two sets of gas reservoirs. Therefore, the accurate determination of the sealing capacity of the barrier will directly affect the fine development of the stratigraphic layer of the gas reservoir.

[0005] In the prior art, the analysis means for the lithology and physical property logging identification of the interlayer, the fracture development characteristics and the lateral distribution law are relatively mature, and some researches have been conducted on the interlayer sealing capacity of the carbonate rock, such as Yi Shuo et al. proposed that according to the lithology, physical property, scale and sedimentary characteristics of the interlayer, the interlayer in the research area is divided into five types, the cross-plot and the gray correlation theory are used to determine the comprehensive index for dividing the interlayer of each type, and the lower limit standard of the effective interlayer of the interlayer type is summarized by comprehensively analyzing the production dynamic data (Journal of Xi'an University of Science and Technology, 2021). Wang Hongqiang et al. proposed that based on the core, slice, logging and analysis test and other data, the interlayer type and characteristics in the research area are comprehensively analyzed, three types of interlayer, namely mudstone, hard gypsum and mud-microcrystalline carbonate rock, are identified, it is found that the mud-microcrystalline carbonate belongs to fine-grained carbonate rock deposition, the porosity is low, but the fracture is generally developed, and the fracture can damage the sealing capacity of the interlayer, so that the interlayer cannot play an effective sealing role (Application of Petroleum and Chemical Industry, 2021).

[0006] Although these interlayer effectiveness evaluation methods have certain effects in actual production, there are problems that the real formation characteristics of the dynamic change of the interlayer sealing capacity under the dynamic change of the gas reservoir pressure in the development process cannot be reflected, and the influencing factors such as the fracture development position and density in the interlayer are not considered, and then the sealing capacity of the interlayer is misjudged.

[0007] Therefore, in the process of determining the interlayer sealing capacity of the carbonate rock gas reservoir by using the prior art method, there are defects that the quantitative characterization is not comprehensive, there are many uncertain factors and it is easy to misjudge, and then the accurate determination of the interlayer sealing capacity of the carbonate rock gas reservoir is affected, which brings obstacles to the reasonable and efficient development of the reservoir of the carbonate rock gas reservoir. SUMMARY

[0008] The purpose of the present application is to provide a method for determining the interlayer sealing capacity of a carbonate rock gas reservoir, which solves the problem of incomplete quantitative characterization and easy misjudgment in the prior art.

[0009] In order to achieve the above purpose, the technical scheme adopted by the method for determining the interlayer sealing capacity of the carbonate rock gas reservoir of the present application is as follows:

[0010] A method for determining the interlayer sealing capacity of a carbonate rock gas reservoir, comprising the following steps:

[0011] (1) Obtain the porosity, permeability, breakthrough pressure and length of the interlayer rock sample, and divide the rock sample into non-fracture rock sample and fracture rock sample according to the high and low permeability of each rock sample;

[0012] (2) The ratio of the breakthrough pressure and the length of each rock sample is defined as the breakthrough pressure gradient of each rock sample, and the breakthrough pressure gradient lower limit of the non-fracture interlayer and the fracture interlayer is determined according to the cross-plot relationship of the porosity and the breakthrough pressure gradient of the non-fracture interlayer and the fracture interlayer;

[0013] (3) obtaining the vertical thickness of the target barrier, the vertical total thickness of the fracture cluster in the target barrier section, the original formation pressure and the present formation pressure of the upper and lower gas reservoirs on the target barrier of a single well;

[0014] (4) constructing a barrier critical breakthrough pressure calculation model according to the lower limit of the breakthrough pressure gradient of the non-fractured barrier and the fractured barrier, the vertical thickness of the barrier, the vertical total thickness of the fracture cluster in the barrier section and the original formation pressure of the upper and lower gas reservoirs on the target barrier of a single well, and calculating the critical breakthrough pressure of the target barrier;

[0015] (5) determining the critical pressure difference according to the original formation pressure and the present formation pressure of the upper and lower gas reservoirs on the target barrier of a single well;

[0016] (6) comparing the critical breakthrough pressure of the target barrier and the critical pressure difference in a single well to determine whether the barrier has a sealing capacity: when the critical breakthrough pressure of the target barrier is greater than or equal to the critical pressure difference, the target barrier does not have a sealing capacity; when the critical breakthrough pressure of the target barrier is less than the critical pressure difference, the target barrier has a sealing capacity.

[0017] The method for determining the sealing capacity of a carbonate gas reservoir barrier provided by the application first divides the rock sample into two types of non-fractured rock sample and fractured rock sample, then obtains the lower limit of the breakthrough pressure gradient of the non-fractured barrier and the fractured barrier, calculates the critical breakthrough pressure of the target barrier by using the lower limit, the vertical thickness of the barrier, the vertical total thickness of the fracture cluster in the barrier section and the original formation pressure of the upper and lower gas reservoirs on the barrier, and finally compares the critical breakthrough pressure of the target barrier with the critical pressure difference to determine the sealing capacity of the barrier.

[0018] The rock sample is divided according to the fact that when there is no fracture in the barrier, the permeability of the rock sample is less than or equal to a fixed value in the same study area, and when there is a fracture in the rock sample, the permeability of the rock sample is greater than the fixed value.

[0019] For the judgment of the sealing capacity of the target barrier: when the calculated critical breakthrough pressure of the target barrier is greater than or equal to the critical pressure difference, it indicates that the target barrier needs a thicker barrier to block the flow breakthrough of the upper and lower gas reservoirs, the target barrier does not have a sealing capacity, and the upper and lower gas reservoirs of the target barrier are connected; when the critical breakthrough pressure of the target barrier is less than the critical pressure difference, it indicates that the thickness of the target barrier can block the flow breakthrough of the upper and lower gas reservoirs, the target barrier has a sealing capacity, and the upper and lower gas reservoirs of the target barrier are not connected.

[0020] The method of this invention can quantitatively and accurately determine whether a target interlayer has the ability to connect the upper and lower gas reservoirs. Experiments have shown that it is more consistent with the gas reservoir distribution confirmed by actual drilling, thus providing a basis and guidance for the stratified and refined development of gas reservoirs and laying the foundation for the rational and efficient exploration and development of carbonate oil and gas reservoirs.

[0021] Preferably, the calculation model for the critical breakthrough pressure of the interlayer in step (4) is: P B =P A -((LL f P1+L f P f );

[0022] Among them, P B The critical breakthrough pressure of the interlayer is MPa; P A L represents the maximum original formation pressure of the gas reservoirs above and below the interlayer, in MPa; L represents the target interlayer thickness, in meters. f P1 is the total thickness of the crack cluster in the target interlayer, in meters; P2 is the lower limit of the pressure gradient at which the non-cracked interlayer breaks through, in MPa / m; P f The pressure gradient limit for the fracture interlayer is exceeded, MPa / m.

[0023] Preferably, the lower limit of the pressure gradient breakthrough mentioned in step (2) is determined by analyzing the intersection of porosity and pressure gradient breakthrough of non-fractured and fractured rock samples, and taking the minimum pressure gradient breakthrough value that conforms to the correlation as the lower limit of the pressure gradient breakthrough. The intersection of porosity and pressure gradient breakthrough is an approximately power function-like negative correlation.

[0024] Preferably, the vertical thickness of the target interlayer in step (4) is obtained based on the well logging interpretation results, and the total vertical thickness of the fracture cluster in the target interlayer section is obtained by adding the vertical thicknesses of the single fracture clusters in the target interlayer section based on the analysis of the relationship between each fracture interpreted by electrical imaging in the interlayer.

[0025] In the interpretation of interlayer electrical imaging, if the cracks intersect, the vertical thickness between the top of the uppermost crack and the bottom of the lowermost crack is taken as the vertical thickness of a single crack cluster; if the crack is isolated, the vertical thickness between the top and bottom of the crack is taken as the vertical thickness of a single crack cluster. The vertical thicknesses of the single crack clusters in the target interlayer segment are added together to obtain the total vertical thickness of the crack cluster.

[0026] Preferably, the critical pressure difference in step (5) is the difference between the maximum original formation pressure of the upper and lower gas reservoirs of the target layer in a single well and the minimum current formation pressure. Attached Figure Description

[0027] Figure 1A flow chart of a method for determining the sealing capacity of a carbonate gas reservoir barrier is shown in Figure 1.

[0028] Figure 2 A crossplot of porosity and permeability of the barrier rock sample in Example 1 is shown in Figure 2.

[0029] Figure 3 A crossplot of porosity and calculated breakthrough pressure gradient of the barrier rock sample in Example 1 is shown in Figure 3.

[0030] Figure 4 A combined well logging straightening result map of Well P10 in Example 1 is shown in Figure 4.

[0031] Figure 5 A combined well logging straightening result map of Well P203 in Example 2 is shown in Figure 5. DETAILED DESCRIPTION

[0032] A method for determining the sealing capacity of a carbonate gas reservoir barrier is shown in Figure 1. Figure 1 The method specifically includes the following steps:

[0033] (1) Take a batch of barrier rock samples in the study area to conduct physical property analysis experiments and breakthrough pressure tests, respectively, to obtain the porosity and permeability of each rock sample, the breakthrough pressure of each rock sample, and the length of each rock sample;

[0034] (2) Draw a crossplot of the porosity and permeability of each rock sample, and divide the rock samples into two categories, i.e., non-fractured rock samples and fractured rock samples, according to the positions of the rock samples in the crossplot;

[0035] (3) Divide the breakthrough pressure of each rock sample by the length of each rock sample to obtain the breakthrough pressure gradient of each rock sample, and determine the lower limit of the breakthrough pressure gradient of non-fractured barriers and fractured barriers according to the crossplot of the porosity and breakthrough pressure gradient of the non-fractured rock samples and the fractured rock samples;

[0036] (4) Obtain the vertical thickness of the target barrier in a single well according to the well logging interpretation results, and obtain the vertical total thickness of the fracture cluster in the target barrier section in combination with the electrical imaging logging interpretation results;

[0037] (5) Construct a critical breakthrough pressure calculation model of the barrier using the lower limit of the breakthrough pressure gradient of the non-fractured barriers and the fractured barriers, the vertical thickness of the barrier, and the vertical total thickness of the fracture cluster in the barrier section, and calculate the critical breakthrough pressure of the target barrier in the single well;

[0038] (6) Obtain the original formation pressure and the present formation pressure of the upper and lower gas reservoirs of the target barrier in the single well, respectively, and define the critical pressure difference as the difference between the maximum value of the original formation pressure and the minimum value of the present formation pressure of the upper and lower gas reservoirs of the target barrier in the single well;

[0039] (7)Compare the critical breakthrough pressure and the critical differential pressure of the target interval in a single well to determine whether the interval has the ability to seal.

[0040] When the critical breakthrough pressure of the target interval is greater than or equal to the critical differential pressure, the target interval does not have the ability to seal; when the critical breakthrough pressure of the target interval is less than the critical differential pressure, the target interval has the ability to seal.

[0041] The intersection relationship between the porosity and the breakthrough pressure gradient of the non-fractured rock sample and the fractured rock sample in step (3) is a negative power function relationship, if a rock sample significantly deviates from the intersection relationship between the corresponding porosity and the breakthrough pressure gradient, the rock sample should be deleted, and then the minimum value of the breakthrough pressure gradient of the non-fractured rock sample and the fractured rock sample is taken as the lower limit of the corresponding breakthrough pressure gradient.

[0042] The technical solutions of the present application will be further described in combination with specific embodiments.

[0043] The specific implementation of the method for determining the sealing ability of the carbonate rock gas reservoir interval of the present application is as follows:

[0044] Embodiment 1

[0045] This embodiment takes P10 well of a certain gas field as an example to introduce the method for determining the sealing ability of the carbonate rock gas reservoir interval, and the following steps are adopted:

[0046] (1) In the core drilling wells of a certain gas field, 33 interval rock samples between the T3f3 and T3f12 intervals of 6 wells are taken to conduct physical property analysis experiments and breakthrough pressure tests.

[0047] The physical property analysis experiment, since the lower limit of the porosity of the reef flat facies reservoir of the Feixianguan Formation in a certain gas field is 2%, it is required that the porosity of the taken interval sample is less than 2%, and in addition, the rock sample is taken as a cylinder with a uniform diameter of 2.452 cm, and the length of the rock sample has certain differences. The porosity and permeability values of each rock sample are obtained through the physical property analysis experiment, and the results are shown in Table 1.

[0048] The specific operation steps of the breakthrough pressure experiment are as follows: first, saturate each rock sample with water, and fix the side surface of the rock sample cylinder according to the actual overburden pressure value of the formation. Since the overburden pressure of the Feixianguan Formation reservoir is about 80 MPa, a fixed overburden pressure of 80.066 MPa is adopted in this experiment to press each rock sample, and then a continuously increasing pressure is applied from one end of the rock sample cylinder to make the air drive the water in the rock sample cylinder to the other end of the rock sample cylinder. When the applied pressure reaches a certain value, continuous bubbles are emitted from the other end of the rock sample cylinder, at which time the applied pressure is recorded as the breakthrough pressure of the rock sample. The results are shown in Table 1.

[0049] Table 1: Physical property experiment, breakthrough pressure test and other achievement data of 33 interval rock samples

[0050]

[0051] (2) Through the porosity and permeability cross-plot of 33 rock samples, as shown in Figure 2

[0052] The porosity and permeability analysis of all rock samples in the core analysis of Feixianguan Formation in a gas field shows that, when in the reservoir, i.e. porosity is greater than or equal to 2%, there is a certain positive correlation between porosity and permeability; in the non-reservoir and non-fracture sample points, the permeability sample points are between 0.001 and 0.1 mD, and there is no positive correlation between porosity and permeability; and in the non-reservoir and fracture sample points, the permeability is obviously greater than 0.1 mD.

[0053] According to the above characteristics, the 33 barrier rock samples are divided into non-fracture rock samples and fracture rock samples, and the results are shown in Table 1, in which the permeability of 10 rock samples is less than 0.1 mD, which is a non-fracture barrier rock sample, and the permeability of 23 rock samples is greater than 0.1 mD, which is a fracture barrier rock sample.

[0054] (3) The breakthrough pressure gradient value of each rock sample is obtained by using the test breakthrough pressure of 33 rock samples divided by the length of the rock sample, and the unit is MPa / m, and the results are shown in Table 1. Further, the porosity and breakthrough pressure gradient cross-plot of non-fracture rock samples and fracture rock samples is made, as shown in Figure 3

[0055] In the non-fracture barrier rock sample, although the porosity of the reservoir is very small, the porosity and breakthrough pressure gradient still show a negative power function correlation, i.e. with the increase of porosity, the breakthrough pressure gradient of the rock sample shows a decreasing characteristic, and when the porosity is greater than a certain value, the corresponding breakthrough pressure gradient changes little, which has certain similarity with the power function characteristic; in the fracture barrier rock sample, due to the effect of the fracture, the fracture development segment in the cylindrical rock sample will soon break through, resulting in the further reduction of the overall breakthrough pressure gradient value with the increase of porosity, but the porosity and breakthrough pressure gradient of the fracture barrier rock sample still maintain a certain negative power function correlation.

[0056] Through the porosity and breakthrough pressure gradient cross-plot analysis of the fracture rock sample and the fracture rock sample in Figure 3 , there is no rock sample significantly deviating from the corresponding porosity and breakthrough pressure gradient cross-plot, so there is no need to remove part of the sample points. The minimum value of the breakthrough pressure gradient of the non-fracture rock sample is taken as the lower limit of the breakthrough pressure gradient of the non-fracture barrier, and the lower limit of the breakthrough pressure gradient of the non-fracture barrier is 1.9 MPa / m. The minimum value of the breakthrough pressure gradient of the fracture rock sample is taken as the lower limit of the breakthrough pressure gradient of the fracture barrier, and the lower limit of the breakthrough pressure gradient of the fracture barrier is 0.9 MPa / m. ​​

[0057] (4) The total vertical thickness of the crack cluster in the target interlayer is determined by analyzing the relationship between the cracks in the interlayer as interpreted by electrical imaging. If the cracks intersect, the vertical thickness between the top of the uppermost crack and the bottom of the lowermost crack is taken as the vertical thickness of a single crack cluster. If the crack is isolated, the vertical thickness between the top and bottom of the crack is taken as the vertical thickness of a single crack cluster. The vertical thicknesses of the single crack clusters in the target interlayer are added together to obtain the total vertical thickness of the crack cluster.

[0058] Well P10 is a development and evaluation well for a certain gas field. Figure 4 The P10 well logging alignment results show that, based on stratigraphic correlation and reservoir property interpretation, the vertical depth range of the interlayer between the Fei-3 and Fei-1-2 sections is 6150.8m to 6161.0m. The vertical thickness of this target interlayer is 10.2m. Electron imaging shows that there are two fractures in this target interlayer, and the two fractures intersect to some extent. Therefore, the vertical thickness between the top of the uppermost fracture and the bottom of the lowermost fracture is selected as the vertical thickness of a single fracture cluster. Thus, the vertical thickness of a single fracture cluster is 1.1m. Since there is only this one single fracture cluster in this target interlayer, the total vertical thickness of the fracture cluster is determined to be 1.1m.

[0059] (5) Due to the difference in the lower limit of the breakthrough pressure gradient between fractured and non-fractured interlayers, the critical breakthrough pressure calculation model for interlayers based on thickness-weighted theory is as follows: P B =P A -((LL f P1+L f P f Formula 1;

[0060] Among them, P B The critical breakthrough pressure of the interlayer is MPa; P A L represents the maximum original formation pressure of the gas reservoirs above and below the interlayer, in MPa; L represents the target interlayer thickness, in meters. f P1 is the total thickness of the crack cluster in the target interlayer, in meters; P2 is the lower limit of the pressure gradient at which the non-cracked interlayer breaks through, in MPa / m; P f The pressure gradient limit for the fracture interlayer is exceeded, MPa / m.

[0061] The original formation pressures of the Fei-3 and Fei-1 / 2 sections of well P10 were determined based on the pressure gradient method during the initial development of the surrounding gas reservoir. The original formation pressure of the Fei-3 section was 55.4 MPa, and the original formation pressure of the Fei-1 / 2 section was 56 MPa. Therefore, the maximum original formation pressure of the upper and lower gas reservoirs of the target interlayer is 56 MPa. In other embodiments, P A It can also be determined through actual measurement or well testing.

[0062] The vertical thickness of the target interval of the P10 well is 10.2 m, the total vertical thickness of the fracture cluster is 1.1 m, the lower limit of the breakthrough pressure gradient of the non-fractured interval is 1.9 MPa / m, the lower limit of the breakthrough pressure gradient of the fractured interval is 0.9 MPa / m, and the maximum value of the original pressure of the gas reservoir above and below the target interval is 56 MPa. The critical breakthrough pressure P of the target interval is determined by substituting the above values into formula 1. B is 36.2 MPa.

[0063] (6) The present formation pressure of the E3f3 interval of the P10 well is determined by the pressure buildup test method to be 28 MPa, and the present formation pressure of the E3f12 interval of the P10 well is determined by the numerical simulation method to be 27 MPa. In other embodiments, the present formation pressure of the gas reservoir can also be determined by the actual measurement method.

[0064] Since the beginning of the development of the gas reservoir to the present, with the continuous exploitation of the gas reservoir, the formation pressure of the gas reservoir is continuously reduced, and a certain pressure difference is inevitably generated between the original formation pressure of the gas reservoir. This pressure difference is the source of the breakthrough of the interval of the gas reservoir, and a parameter is needed to reflect the maximum value of the pressure difference, that is, the breakthrough pressure difference of the interval. Therefore, the critical pressure difference is defined as the difference between the maximum value of the original formation pressure of the gas reservoir above and below the target interval of a single well and the minimum value of the present formation pressure.

[0065] According to the maximum value of the original formation pressure of the E3f3 and E3f12 gas reservoirs above and below the target interval of the P10 well being 56 MPa, and the minimum value of the present formation pressure of the E3f3 and E3f12 gas reservoirs above and below the target interval of the P10 well being 27 MPa, the critical pressure difference of the target interval is determined to be 29 MPa.

[0066] (7) The size of the critical breakthrough pressure and the critical pressure difference of the target interval in a single well is compared to determine whether the interval has the sealing capacity: the critical pressure difference of the target interval between the E3f3 and E3f12 intervals of the P10 well is 29 MPa, and the critical breakthrough pressure is 36.2 MPa. The critical breakthrough pressure is significantly greater than the critical pressure difference, indicating that the interval does not have the sealing capacity, and the E3f3 gas reservoir and the E3f12 gas reservoir are connected in the well area.

[0067] In order to verify the reliability of the present application, the E3f3 reservoir with a vertical depth of 6108-6151 m in the P10 well is perforated for testing. According to the logging interpretation standard of the region, the E3f3 reservoir is a gas layer, and the bottom of the target interval below the vertical depth of 6161 m is a gas-water layer according to the logging interpretation standard of the region. The perforation test result of the E3f3 reservoir with a vertical depth of 6108-6151 m is 112,000 cubic meters of gas per day and 9.7 cubic meters of water per day, indicating that the target interval of the P10 well connects the upper and lower gas reservoirs, resulting in water breakthrough above the target interval. This confirms the determination of the present embodiment that the target interval of the P10 well does not have the sealing capacity, proving that the method for determining the sealing capacity of the carbonate gas reservoir interval provided by the present application is reliable.

[0068] Example 2

[0069] The method for determining the sealing capacity of carbonate gas reservoirs in this embodiment adopts the following steps:

[0070] Taking well P203 in a gas field as an example, the isolation capacity of the isolation layer was determined. Compared with Example 1, the difference is as follows:

[0071] (4) Well P203 is a development evaluation well in the Puguang Gas Field. Figure 5 This is a diagram showing the results of the combined logging and alignment of well P203.

[0072] Based on stratigraphic correlation and reservoir property interpretation, the vertical depth range of the interlayer between the Fei-3 and Fei-1-2 members was determined to be 5965m to 5984.1m. The vertical thickness of this target interlayer is 19.1m. Electron imaging shows that there are four single fracture clusters with vertical thicknesses of 0.35m, 0.35m, 0.5m and 2.7m respectively in this target interlayer. The total vertical thickness of the fracture clusters is determined to be 3.9m.

[0073] (5) Due to the difference in the lower limit of the breakthrough pressure gradient between fractured and non-fractured interlayers, the critical breakthrough pressure calculation model for interlayers based on thickness-weighted theory is as follows: P B =P A -((LL f P1+L f P f Formula 1;

[0074] Among them, P B The critical breakthrough pressure of the interlayer is MPa; P A L represents the maximum original formation pressure of the gas reservoirs above and below the interlayer, in MPa; L represents the target interlayer thickness, in meters. f P1 is the total thickness of the crack cluster in the target interlayer, in meters; P2 is the lower limit of the pressure gradient at which the non-cracked interlayer breaks through, in MPa / m; P f The pressure gradient limit for the fracture interlayer is exceeded, MPa / m.

[0075] The original formation pressures of the Fei-3 section and Fei-1 and Fei-2 sections of well P203 were determined based on the pressure gradient method during the early stage of gas reservoir development in surrounding wells. The original formation pressure of the Fei-3 section was determined to be 55.4 MPa, and the original formation pressure of Fei-1 and Fei-2 sections was determined to be 56 MPa. Therefore, the maximum original formation pressure of the upper and lower gas reservoirs of the target interlayer is 56 MPa.

[0076] The vertical thickness of the target interval of the P203 well is 19.1 m, the total vertical thickness of the fracture cluster is 3.9 m, the lower limit of the breakthrough pressure gradient of the non-fractured interval is 1.9 MPa / m, the lower limit of the breakthrough pressure gradient of the fractured interval is 0.9 MPa / m, and the maximum value of the original pressure of the gas reservoir above and below the target interval is 56 MPa. The critical breakthrough pressure P of the target interval is determined by substituting the above values into formula 1. B The critical breakthrough pressure P is 23.61 MPa.

[0077] (6) The current formation pressure of the E3t3 interval of the P203 well is determined by the pressure buildup test to be 30 MPa, and the current formation pressure of the E31-2 interval of the P203 well is determined by numerical simulation to be 26.5 MPa.

[0078] According to the maximum value of the original formation pressure of the gas reservoir above and below the target interval of the P203 well being 56 MPa and the minimum value of the current formation pressure of the gas reservoir above and below the target interval of the P203 well being 26.5 MPa, the critical pressure difference of the target interval is determined to be 29.5 MPa.

[0079] (7) The critical breakthrough pressure and the critical pressure difference of the target interval are compared in a single well to determine whether the interval has sealing capacity: the critical pressure difference of the target interval between the E3t3 interval and the E31-2 interval of the P203 well is 29.5 MPa, and the critical breakthrough pressure is 23.61 MPa. The critical breakthrough pressure is significantly smaller than the critical pressure difference, indicating that the interval has sealing capacity, and the gas reservoir of the E3t3 interval and the gas reservoir of the E31-2 interval are not connected in this well area.

[0080] In order to verify the reliability of the present application, the E3t3 reservoir with a vertical depth of 5920.5-5965 m of the P203 well is tested by perforation, and the reservoir of this section is gas according to the logging interpretation standard of this region. The bottom of the target interval below the vertical depth of 5984.1 m is a gas-water layer according to the logging interpretation standard of this region. The perforation test result of the E3t3 reservoir with a vertical depth of 5920.5-5965 m is 176,000 cubic meters of gas per day, and no water is seen, indicating that the water of the gas reservoir below the target interval of the P203 well has not broken through the target interval into the gas reservoir above the target interval, and the target interval has sealed the upper and lower gas reservoirs, which confirms the determination of the sealing capacity of the target interval of the P203 well in this embodiment, and further proves that the method for determining the sealing capacity of a carbonate gas reservoir interval provided by the present application is reliable.

Claims

1. A method for determining the sealing capacity of a carbonate gas reservoir's interlayer, characterized in that, Includes the following steps: (1) Obtain the porosity, permeability, breakthrough pressure and length of the interlayer rock samples, and classify the rock samples into non-fractured rock samples and fractured rock samples according to the permeability of each rock sample; (2) Define the ratio of breakthrough pressure to length of each rock sample as the breakthrough pressure gradient of each rock sample. Based on the intersection of porosity and breakthrough pressure gradient of non-fractured rock samples and fractured rock samples, determine the lower limit of breakthrough pressure gradient of non-fractured strata and fractured strata. (3) Obtain the vertical thickness of the target interlayer, the total vertical thickness of the fracture cluster in the target interlayer section, and the original formation pressure and current formation pressure of the two gas reservoirs above and below the target interlayer in a single well; (4) Based on the lower limit of the breakthrough pressure gradient of non-fractured and fractured interlayers, the vertical thickness of the interlayer, the total vertical thickness of the fracture cluster in the interlayer section, and the original formation pressure of the two gas reservoirs above and below the target interlayer in a single well, construct a calculation model for the critical breakthrough pressure of the interlayer and calculate the critical breakthrough pressure of the target interlayer. (5) Determine the critical pressure difference based on the original formation pressure and current formation pressure of the two gas reservoirs above and below the target layer of a single well; (6) In a single well, the critical breakthrough pressure and critical pressure difference of the target interlayer are compared to determine whether the interlayer has sealing capability: when the critical breakthrough pressure of the target interlayer is greater than or equal to the critical pressure difference, the target interlayer does not have sealing capability; when the critical breakthrough pressure of the target interlayer is less than the critical pressure difference, the target interlayer has sealing capability.

2. The method for determining the sealing capacity of a carbonate gas reservoir according to claim 1, characterized in that, The calculation model for the critical breakthrough pressure of the interlayer in step (4) is: P B =P A -((LL f P1+L f P f ); Among them, P B The critical breakthrough pressure of the interlayer is MPa; P A L represents the maximum original formation pressure of the gas reservoirs above and below the interlayer, in MPa; L represents the target interlayer thickness, in meters. f P1 is the total thickness of the crack cluster in the target interlayer, in meters; P2 is the lower limit of the pressure gradient at which the non-cracked interlayer breaks through, in MPa / m; P f The pressure gradient limit for the fracture interlayer is exceeded, MPa / m.

3. The method for determining the sealing capacity of a carbonate gas reservoir according to claim 1, characterized in that, The lower limit of the breakthrough pressure gradient mentioned in step (2) is determined by the intersection of the porosity of non-fractured rock samples and fractured rock samples with the breakthrough pressure gradient. The minimum breakthrough pressure gradient that conforms to the correlation is taken as the lower limit of the breakthrough pressure gradient.

4. The method for determining the sealing capacity of a carbonate gas reservoir according to claim 2, characterized in that, The vertical thickness of the target interlayer in step (4) is obtained based on the well logging interpretation results. The total vertical thickness of the fracture cluster in the target interlayer section is obtained by adding the vertical thicknesses of the single fracture clusters in the target interlayer section based on the analysis of the relationship between the fractures interpreted by electrical imaging in the interlayer.

5. The method for determining the sealing capacity of a carbonate gas reservoir according to any one of claims 1-4, characterized in that, The critical pressure difference mentioned in step (5) is the difference between the maximum original formation pressure of the upper and lower gas reservoirs in the target layer of a single well and the minimum current formation pressure.

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