A method for recovering porosity evolution of clastic reservoirs in a tectonic extrusion background

Abstract

The present application relates to a kind of methods for restoring porosity evolution of clastic reservoirs under tectonic extrusion, belonging to the technical field of oil and gas exploration and development.The method comprises the following steps: calculating the total compaction and pore loss of clastic rock samples, selecting samples with similar burial depth, similar rock structure and different maximum paleo-tectonic stress as selected samples, obtaining the lateral compaction and pore loss of the one with larger maximum paleo-tectonic stress by the difference of total compaction and pore loss corresponding to the two selected samples adjacent to the maximum paleo-tectonic stress, and establishing the functional relationship between lateral compaction and pore loss and maximum paleo-tectonic stress;calculating the lateral compaction and pore loss of each lateral extrusion in multiple lateral extrusions;calculating the vertical compaction and pore loss according to the total compaction and pore loss and lateral compaction and pore loss, and establishing the relationship chart between vertical compaction and pore loss and burial depth;using the inverse back stripping method, combining lateral compaction and pore loss and vertical compaction and pore loss, and drawing the porosity evolution curve of clastic reservoirs in geological history under tectonic extrusion.This method solves the problem of being unable to quantitatively calculate lateral and vertical compaction and pore loss in the process of restoring porosity evolution of foreland basin reservoirs.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil and gas exploration and development, and particularly relates to a method for restoring porosity evolution of clastic rock reservoirs under tectonic extrusion background. BACKGROUND

[0002] In recent years, with the gradual increase of the degree of shallow oil and gas exploration, oil and gas exploration gradually extends to deep layers-super deep layers. More than 60% of oil and gas resources in deep layers-super deep layers are distributed in clastic rocks, and the foreland basin is one of the most typical representatives of deep layer-super deep layer clastic rock exploration. The complex tectonic evolution, burial process and diagenetic modification of the foreland basin make the clastic rock reservoir have strong heterogeneity characteristics. Remodeling the reservoir porosity evolution process is the key to understanding the control factors of reservoir development and revealing the formation mechanism of high-quality reservoirs. The existing methods for restoring the porosity evolution of clastic rock reservoirs in the geological history period do not consider the compaction porosity reduction caused by lateral extrusion of the foreland basin, and cannot be applied to the restoration of reservoir porosity evolution under the background of tectonic extrusion. SUMMARY

[0003] In view of the problem that the existing method for restoring the porosity evolution of clastic rock reservoirs in the geological history period is not applicable to the restoration of reservoir porosity evolution under the background of tectonic extrusion of the foreland basin, the application provides a method for restoring the porosity evolution of clastic rock reservoirs under the background of tectonic extrusion, which determines the lateral compaction porosity reduction and the vertical compaction porosity reduction, corrects the reservoir porosity obtained by the inverse stripping method by using the lateral compaction porosity reduction and the vertical compaction porosity reduction, and thus obtains the real porosity evolution process of the clastic rock reservoir under the background of tectonic extrusion.

[0004] The application provides a method for restoring the porosity evolution of clastic rock reservoirs under the background of tectonic extrusion, which comprises the following steps:

[0005] (1) Select a plurality of samples from the study area, calculate the total compaction porosity reduction of each sample, obtain the maximum paleo-tectonic stress corresponding to the sample, select samples with similar burial depth, similar rock structure and different maximum paleo-tectonic stress as selected samples, sort the selected samples in the order of maximum paleo-tectonic stress from large to small, take the difference between the total compaction porosity reduction corresponding to the adjacent two selected samples as the lateral compaction porosity reduction of the sample with larger maximum paleo-tectonic stress, and establish a functional relationship between the lateral compaction porosity reduction and the maximum paleo-tectonic stress;

[0006] (2) Determine the number of lateral extrusions and the paleo-tectonic stress of each lateral extrusion during the diagenetic process of the study area, calculate the lateral compaction porosity reduction of each lateral extrusion in combination with the functional relationship between the lateral compaction porosity reduction and the maximum paleo-tectonic stress;

[0007] (3) The total compaction porosity reduction of the sample is subtracted from the lateral compaction porosity reduction to obtain the vertical compaction porosity reduction of the sample. Based on the vertical distribution characteristics of the vertical compaction porosity reduction of different samples, a chart of the relationship between vertical compaction porosity reduction and burial depth under different sediment parameter constraints is established.

[0008] (4) Determine the diagenetic stage of the study area, and use the inversion stripping method, combined with the lateral compaction porosity reduction of each lateral compression during the diagenetic process of the study area and the relationship between the vertical compaction porosity reduction and the burial depth, to draw the porosity evolution curve of the clastic reservoir during the geological history under the background of tectonic compression.

[0009] In some embodiments, the specific steps for calculating the total compaction reduction in pore volume in step (1) are as follows:

[0010] Based on the functional relationship between porosity and the sorting coefficient So, the original porosity φ of each sample is calculated. 原 ;

[0011] Obtain the current porosity φ of each sample 今 Total face rate φ 面 The porosity of various types of dissolution pores, the porosity of various types of cementitious materials, and the porosity of various types of microcracks; among which, the porosity of the i-th type of dissolution pore is denoted as φ. 面溶i Let i = 1, 2, ..., n, where n is the number of types of dissolution pores; the porosity of the j-th type of cement is denoted as φ. 面胶j j = 1, 2, ..., m, where m is the number of cement types; the porosity of the k-th type of microcrack is denoted as φ. 面缝k k = 1, 2, ..., p, where p is the number of types of microcracks;

[0012] Based on the current porosity φ of the sample 今 With total face rate φ 面 To establish the functional relationship between current porosity and total porosity;

[0013] Substituting the porosity of various types of dissolution pores, cement pores, and microcracks into the functional relationship between current porosity and total porosity, the contributions of various types of dissolution pores, cement pores, and microcracks are calculated. The contribution of the i-th type of dissolution pore is denoted as φ. 溶i The porosity contribution of the j-th type of cement is denoted as φ. 胶j The contribution of the kth type of microcrack porosity is denoted as φ. 缝k ;

[0014] Using formula Calculate the total compaction porosity reduction φ of the sample. 压 .

[0015] In some embodiments, in step (2), the lateral compaction reduction φ of the first lateral extrusion侧压l The calculation formula is:

[0016]

[0017] Where q represents the number of lateral compressions in the study area, and F l For the paleotectonic stress of the lth lateral compression, F l-1 Let F be the paleotectonic stress of the (l-1)th lateral compression, and F be the maximum paleotectonic stress. In the calculation, F0 is taken as 0 MPa, and F = F q ;φ 侧压 The lateral compaction porosity reduction is the amount of lateral compaction porosity reduction corresponding to the maximum paleotectonic stress, calculated based on the functional relationship between the lateral compaction porosity reduction and the maximum paleotectonic stress.

[0018] In some embodiments, when establishing the relationship between the vertical compaction porosity reduction and burial depth in step (3), samples with a cement content of less than 5% are selected, and the sediment parameters include sorting coefficient and sediment particle size.

[0019] In some embodiments, the specific steps for determining the diagenetic stage of the study area in step (4) are as follows: by analyzing cast thin sections, in-situ micro-element testing, fluid inclusion analysis, and U-Pb dating, the formation time and sequence of authigenic minerals, dissolution pores, and fractures in the study area are determined, and a diagenetic evolution sequence is established; by using inclusion homogenization temperature analysis, U-Pb dating analysis, combined with burial history and thermal history analysis, the occurrence time of each diagenetic event is determined, and the diagenetic stage is determined by combining the occurrence time of lateral compaction events.

[0020] In some embodiments, step (4) involves drawing the porosity evolution curve of clastic reservoirs during geological history under tectonic compression: using the projection of different diagenetic stages onto the burial history map, the paleoburial depth at the beginning and end of each diagenetic stage is obtained; constrained by the diagenetic evolution sequence, the microstructure of the reservoir at each diagenetic stage is restored by analyzing cast thin section images and using the inversion stripping method, combined with the lateral compaction porosity reduction and vertical compaction porosity reduction and burial depth relationship charts of each lateral compression during the diagenetic process in the study area, and the porosity and corresponding porosity of the reservoir at each diagenetic stage are obtained; according to the geological history time, the reservoir porosity evolution curve from the original porosity to the present porosity is drawn.

[0021] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0022] The application provides a method for restoring porosity evolution of a clastic rock reservoir under a tectonic extrusion background. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A function relationship diagram of present porosity and total surface porosity provided by the embodiment 1 of the application;

[0024] Figure 2 A function relationship diagram of lateral compaction porosity reduction and maximum paleo-tectonic stress provided by the embodiment 1 of the application;

[0025] Figure 3 A vertical compaction porosity reduction and burial depth relationship diagram provided by the embodiment 1 of the application;

[0026] Figure 4 A porosity evolution process diagram of a clastic rock reservoir in a tectonic extrusion background provided by the embodiment 1 of the application. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the application, but not all the embodiments of the application. Based on the embodiments in the application, all the other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0028] Embodiment 1

[0029] A method for restoring porosity evolution of a clastic rock reservoir under a tectonic extrusion background comprises the following steps:

[0030] (1) establishing a function relationship of lateral compaction porosity reduction and maximum paleo-tectonic stress

[0031] Selecting 139 sandstone samples in a certain research area, the sorting coefficient So of the samples is obtained by laser particle size analysis of sediments, and the original porosity φ of each sample is calculated according to the function relationship between porosity and sorting coefficient So, φ = 20.91 + 22.90 / So 原 .

[0032] The sample is prepared into a plunger sample with a diameter of 2.5 cm and a length of 3-5 cm, and the present porosity φ of each sample is obtained by plunger sample measurement 今 .

[0033] The sample is prepared into a casting sheet, and the total face porosity φ of each sample, the face porosity of each type of dissolution pore, the face porosity of each type of cement, and the face porosity of each type of microcrack are obtained by casting sheet image analysis under an optical microscope 面 ; wherein the face porosity of the i-th type of dissolution pore is denoted as φ 面溶i , i = 1, 2, …, n, n being the number of types of dissolution pores; the face porosity of the j-th type of cement is denoted as φ 面胶j , j = 1, 2, …, m, m being the number of types of cements; and the face porosity of the k-th type of microcrack is denoted as φ 面缝k , k = 1, 2, …, p, p being the number of types of microcracks.

[0034] As shown in Figure 1 , according to the present porosity φ 今 and the total face porosity φ 面 of the sample, a function relationship between the present porosity and the total face porosity is established as follows:

[0035] The face porosity of each type of dissolution pore, the face porosity of each type of cement, and the face porosity of each type of microcrack are respectively substituted into the function relationship between the present porosity and the total face porosity to obtain the contribution amount of each type of dissolution pore, the contribution amount of each type of cement, and the contribution amount of each type of microcrack, wherein the contribution amount of the i-th type of dissolution pore is denoted as φ 溶i , the contribution amount of the j-th type of cement is denoted as φ 胶j , and the contribution amount of the k-th type of microcrack is denoted as φ 缝k .

[0036] The total compaction and pore reduction amount φ 压 of the sample is calculated by using the formula .

[0037] The maximum paleo-tectonic stress corresponding to the sample is obtained through sample acoustic emission test and numerical simulation. In the sample, the medium sandstone samples with the burial depth in the range of 300 m, the sorting coefficient So in the range of 1.2-1.4, the cement content less than 5%, and distributed in different maximum paleo-tectonic stress regions are selected as selected samples, so as to minimize the influence of other factors on the compaction reduction of pore volume. The selected samples are sorted in the order of maximum paleo-tectonic stress from large to small, and the difference between the total compaction reduction of pore volume of the adjacent two selected samples is taken as the lateral compaction reduction of pore volume of the sample with larger maximum paleo-tectonic stress.

[0038] As shown in Figure 2 , the lateral compaction reduction of pore volume φ 侧压 and the maximum paleo-tectonic stress F are related as follows: φ 侧压 = 3.3952ln(F)-9.3104.

[0039] (2) Calculate the lateral compaction reduction of pore volume of each lateral extrusion in the multiple lateral extrusion process

[0040] There are four times of lateral extrusion in the diagenetic process of the research area. The maximum paleo-tectonic stresses corresponding to the four times of lateral extrusion are F1=35.2MPa, F2=59.9MPa, F3=74.8MPa, and F4=80.9MPa, respectively, which are obtained through sample acoustic emission test and numerical simulation.

[0041] The lateral compaction reduction of pore volume of each lateral extrusion is calculated by using the formula , wherein q is the number of lateral extrusion in the research area, F l is the paleo-tectonic stress of the lth lateral extrusion, F l-1 is the paleo-tectonic stress of the (l-1)th lateral extrusion, F is the maximum paleo-tectonic stress, and F0 is taken as 0MPa in calculation, F=F q ; φ 侧压 is the lateral compaction reduction of pore volume corresponding to the maximum paleo-tectonic stress, which is obtained according to the functional relationship between the lateral compaction reduction of pore volume and the maximum paleo-tectonic stress.

[0042] (3) Establish the relationship chart between the vertical compaction reduction of pore volume and the burial depth

[0043] The lateral compaction reduction of pore volume φ 侧压 of any sample is calculated by using the formula φ 侧压 = 3.3952ln(F)-9.3104, and the difference between the total compaction reduction of pore volume φ 压 and the lateral compaction reduction of pore volume φ 侧压 is obtained, so as to obtain the vertical compaction reduction of pore volume φ 垂压 of the sample.

[0044] Based on the comprehensive consideration of sorting coefficient, sediment grain size and other parameters, samples with cement content less than 5% were selected, and the relationship between the vertical compaction porosity reduction and burial depth under the constraint of different sediment parameters was established according to the vertical distribution characteristics of the vertical compaction porosity reduction of different samples, as shown in Figure 3 .

[0045] (4) Draw the porosity evolution curve of the clastic rock reservoir in the tectonic extrusion background

[0046] Through cast thin section analysis, in-situ major and trace element testing analysis, fluid inclusion analysis and U-Pb dating analysis, the formation time and sequence of authigenic minerals, dissolved pores and fractures in the study area were determined, and a diagenetic evolution sequence was established. The diagenetic evolution sequence of the study area is shown in Table 1, which is as follows: first stage of feldspar dissolution / authigenic albite, first stage of quartz cementation→first stage of calcite, dolomite and gypsum cementation, quartz dissolution→second stage of feldspar dissolution, authigenic quartz cementation→second stage of (iron-containing) calcite, dolomite and anhydrite cementation→late stage of a small amount of feldspar dissolution.

[0047] Using homogenization temperature analysis of fluid inclusions and U-Pb dating analysis, combined with burial history and thermal history analysis, the occurrence time of each diagenetic event was determined, and combined with the occurrence time of lateral compaction events, the diagenetic stage was determined, as shown in Table 1.

[0048] Using the projection of different diagenetic stage times on the burial history graph, the paleo-burial depth at the beginning and end of each diagenetic stage was obtained, as shown in Table 1.

[0049] Table 1 Diagenetic evolution sequence and paleo-burial depth and paleo-porosity recovery of different diagenetic stages

[0050]

[0051] Using cast thin section images and the functional relationship between present porosity and total face porosity The contribution of various chemical diagenetic events to reservoir porosity was quantitatively calculated, and the microcosmic features of the reservoir in each diagenetic stage were restored by inverse stripping method combined with the lateral compaction porosity reduction of each lateral extrusion in the diagenetic process and the relationship between vertical compaction porosity reduction and burial depth, and the face porosity and corresponding porosity of each diagenetic stage were obtained; according to the geological history time, the reservoir porosity evolution curve from original porosity to present porosity was drawn, and the clastic rock reservoir porosity evolution process graph in the tectonic extrusion background of the study area was obtained, as shown in Figure 4 .

Claims

1. A method for recovering the porosity evolution of clastic rock reservoirs under tectonic compression, characterized in that, Includes the following steps: (1) Select several samples from the study area and calculate the total compaction porosity reduction of each sample; obtain the maximum paleotectonic stress corresponding to the sample; select samples with similar burial depth, similar rock structure, and different maximum paleotectonic stresses as selected samples; sort the selected samples in descending order of maximum paleotectonic stress; take the difference between the total compaction porosity reduction of two adjacent selected samples as the lateral compaction porosity reduction of the sample with the larger maximum paleotectonic stress among the two selected samples; establish the functional relationship between lateral compaction porosity reduction and maximum paleotectonic stress. (2) Determine the number of lateral compressions during the diagenesis process in the study area and the paleotectonic stress of each lateral compression. Combine the functional relationship between the lateral compaction porosity reduction and the maximum paleotectonic stress to calculate the lateral compaction porosity reduction of each lateral compression. (3) The total compaction porosity reduction of the sample is subtracted from the lateral compaction porosity reduction to obtain the vertical compaction porosity reduction of the sample. Based on the vertical distribution characteristics of the vertical compaction porosity reduction of different samples, a chart of the relationship between vertical compaction porosity reduction and burial depth under different sediment parameter constraints is established. (4) Determine the diagenetic stage of the study area, and use the inversion stripping method, combined with the lateral compaction porosity reduction of each lateral compression during the diagenetic process of the study area and the relationship between the vertical compaction porosity reduction and the burial depth, to draw the porosity evolution curve of the clastic reservoir during the geological history under the background of tectonic compression.

2. The method for restoring porosity evolution in clastic reservoirs under tectonic compression as described in claim 1, characterized in that, In step (1), the specific steps for calculating the total compaction reduction are as follows: Based on the functional relationship between porosity and the sorting coefficient So, the original porosity φ of each sample is calculated. 原 ; Obtain the current porosity φ of each sample 今 Total face rate φ 面 The porosity of various types of dissolution pores, the porosity of various types of cementitious materials, and the porosity of various types of microcracks; among which, the porosity of the i-th type of dissolution pore is denoted as φ. 面溶i Let i = 1, 2, ..., n, where n is the number of types of dissolution pores; the porosity of the j-th type of cement is denoted as φ. 面胶j j = 1, 2, ..., m, where m is the number of cement types; the porosity of the k-th type of microcrack is denoted as φ. 面缝k k = 1, 2, ..., p, where p is the number of types of microcracks; Based on the current porosity φ of the sample 今 With total face rate φ 面 To establish the functional relationship between current porosity and total porosity; Substituting the porosity of various types of dissolution pores, cement pores, and microcracks into the functional relationship between current porosity and total porosity, the contributions of various types of dissolution pores, cement pores, and microcracks are calculated. The contribution of the i-th type of dissolution pore is denoted as φ. 溶i The porosity contribution of the j-th type of cement is denoted as φ. 胶j The contribution of the kth type of microcrack porosity is denoted as φ. 缝k ; Using formula Calculate the total compaction porosity φ of the sample 压 .

3. The method for restoring porosity evolution in clastic reservoirs under tectonic compression as described in claim 1, characterized in that, In step (2), the lateral compaction reduction φ of the lth lateral extrusion 侧压l The calculation formula is: Where q represents the number of lateral compressions in the study area, and F l For the paleotectonic stress of the lth lateral compression, F l-1 Let F be the paleotectonic stress of the (l-1)th lateral compression, and F be the maximum paleotectonic stress. In the calculation, F0 is taken as 0 MPa, and F = F q ;φ 侧压 The lateral compaction porosity reduction is the amount of lateral compaction porosity reduction corresponding to the maximum paleotectonic stress, calculated based on the functional relationship between the lateral compaction porosity reduction and the maximum paleotectonic stress.

4. The method for restoring porosity evolution in clastic reservoirs under tectonic compression as described in claim 1, characterized in that, In step (3), when establishing the relationship between the vertical compaction reduction and burial depth, samples with a cement content of less than 5% are selected. The sediment parameters include the sorting coefficient and the sediment particle size.

5. The method for restoring porosity evolution in clastic reservoirs under tectonic compression as described in claim 1, characterized in that, In step (4), the specific steps for determining the diagenetic stage of the study area are as follows: through cast thin section analysis, in-situ micro-element testing and analysis, fluid inclusion analysis and U-Pb dating analysis, the formation time and sequence of authigenic minerals, dissolution pores and fractures in the study area are determined, and a diagenetic evolution sequence is established; by using inclusion homogenization temperature analysis and U-Pb dating analysis, combined with burial history and thermal history analysis, the occurrence time of each diagenetic event is determined, and the diagenetic stage is determined by combining the occurrence time of lateral compaction events.

6. The method for restoring porosity evolution in clastic reservoirs under tectonic compression as described in claim 5, characterized in that, In step (4), the specific steps for drawing the porosity evolution curve of clastic reservoirs under tectonic compression are as follows: using the projection of different diagenetic stages onto the burial history map, the paleoburial depth at the beginning and end of each diagenetic stage is obtained; constrained by the diagenetic evolution sequence, through cast thin section image analysis and inversion stripping method, combined with the lateral compaction porosity reduction and vertical compaction porosity reduction and burial depth relationship map of each lateral compression during the diagenetic process in the study area, the reservoir micro-morphological features of each diagenetic stage are restored, and the porosity and corresponding porosity of the reservoir at each diagenetic stage are obtained; according to the geological history time, the reservoir porosity evolution curve from the original porosity to the present porosity is drawn.

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