Method and system for evaluating seepage capacity of tight oil reservoir

Abstract

The invention provides a method and a system for evaluating the seepage capacity of a tight oil reservoir. The method comprises the following steps: evaluating the first seepage capacity according to rock content data; extracting an internal pore image according to the scanned image of the rock core, establishing a pore-based three-dimensional network model, obtaining pore distribution, judging the number of throats, and performing second seepage capacity evaluation according to the number of throats; performing third seepage capacity evaluation according to the movable fluid saturation data of the rock; and finally, combining the first seepage capacity evaluation, the second seepage capacity evaluation and the third seepage capacity evaluation to obtain final seepage capacity evaluation according to a preset rule. The seepage capacity is comprehensively evaluated according to the three indexes, and the obtained evaluation result is more comprehensive and more accurate.

Description

Technical Field

[0001] The present invention specifically relates to a method and system for evaluating the seepage capacity of a tight oil reservoir. Background Art

[0002] Tight oil refers to crude oil in tight reservoirs, where the reservoir matrix permeability is less than or equal to 0.2×10 -3 um 2 (Air permeability is less than 2×10 -3 um 2 ), reservoir types include tight sandstone and tight carbonate. With the gradual depletion of conventional oil and gas resources, unconventional oil and gas represented by tight oil has become a new hotspot for global exploration and development. However, the accumulation mechanism, reservoir characteristics and seepage law of tight oil are very different from those of conventional oil reservoirs. Related research has just started in China, and the lack of understanding has seriously restricted the effective development of tight oil.

[0003] The property of rock that allows liquid and gas to pass through when there is a pressure difference is called rock permeability. Permeability is a quantitative expression of rock permeability. It characterizes the ability of oil and gas to flow through formation rocks to the bottom of the well. It is one of the important reference standards for developing oil layers. Due to the diverse pore types, multi-scale pore throats, and unclear seepage laws in tight oil reservoirs, the pore structure and seepage laws of the reservoir are core issues related to reserve evaluation and efficient development. Summary of the invention

[0004] The inventors found that the existing technology mainly evaluates the seepage capacity of tight oil reservoirs through the contribution of feldspar minerals to the storage and seepage capacity of tight oil reservoirs and their priority in reservoir evaluation. The inventors conducted a large number of experiments using this method and found that the evaluation results were not accurate enough and there were certain differences from the actual situation. Therefore, it is particularly urgent to develop a method and system for evaluating the seepage capacity of tight oil reservoirs.

[0005] The method for evaluating the seepage capacity of a tight oil reservoir of the present invention comprises the following steps:

[0006] Analyze rock structure, obtain rock content data, and perform a first seepage capacity evaluation based on the rock content data, wherein the rock content data includes quartz content, feldspar content, and clay mineral content;

[0007] Get the scanned image of the core, extract the internal pore image based on the scanned image, establish a pore-based three-dimensional network model, obtain the pore distribution, determine the number of throats, and perform a second seepage capacity evaluation based on the number of roars;

[0008] The T2 spectra of rocks in saturated state and under different centrifugal forces are tested respectively to obtain movable fluid saturation data, and the third seepage capacity is evaluated based on the movable fluid saturation data;

[0009] The first seepage capacity evaluation, the second seepage capacity evaluation and the third seepage capacity evaluation are combined according to preset rules to obtain a final seepage capacity evaluation.

[0010] Further, the rock structure is analyzed to obtain rock content data, including:

[0011] Use electron probe to take backscattered grayscale images;

[0012] Reconstruct the grayscale image of the first layer using X-ray micro-CT scanning;

[0013] Compare the backscattered grayscale image and the first layer grayscale image. If the grayscale value ranges of quartz, feldspar and clay minerals shown in the two are the same, the composition of the first layer image is determined.

[0014] The rock content data is obtained based on the composition of the first layer image.

[0015] Furthermore, a scanned image of the core is obtained, and the internal pore image is extracted according to the scanned image, and a 3D network model based on the pores is established to obtain the pore distribution and determine the number of throats, including:

[0016] Scan the core using CT to obtain a scanned image of the core;

[0017] Extract the internal pore image based on the scanned image and establish a pore-based three-dimensional network model;

[0018] Observe the pore distribution and size of the core in the three-dimensional network model, and determine at least one connected pore with the largest volume that is interconnected in pore space based on the pore distribution analysis of the core to form a backbone network;

[0019] The number of peripheral throats is calculated based on the backbone network.

[0020] Furthermore, the T2 spectra of rocks in saturated state and under different centrifugal forces were tested to obtain movable fluid saturation data, including:

[0021] Cutting, grinding and drying the rocks to obtain dried rock columns;

[0022] Pour the prepared simulated formation water into the dried rock column, pressurize and saturate it under vacuum, and test the T2 spectrum of the saturated state;

[0023] Drive away the rock column containing simulated formation water and test the T2 spectrum under different centrifugal forces;

[0024] The movable fluid saturation under the condition of saturated formation water in the rock column is determined according to the T2 spectrum in the saturated state and the T2 spectrum under different centrifugal forces.

[0025] Further, the rock is cut, ground and dried to obtain a dried rock column, including:

[0026] The rock is cut and ground to obtain a rock column, and the rock column is washed with oil and salt. The rock column after oil and salt washing is placed in a constant temperature oven for drying until the rock column reaches a constant weight.

[0027] Furthermore, the rock column containing simulated formation water was driven out and the T2 spectra under different centrifugal forces were tested, including:

[0028] A high-speed centrifuge was used to drive the simulated formation water in the rock column with gradually increasing centrifugal force, and a high-temperature and high-pressure nuclear magnetic resonance core analysis device was used to test the T2 spectra under different centrifugal forces.

[0029] Furthermore, the movable fluid saturation under the condition of saturated formation water in the rock column is determined according to the T2 spectrum in the saturated state and the T2 spectrum under different centrifugal forces, including:

[0030] From the T2 spectrum in the saturated state to the T2 spectrum under different centrifugal forces, the T2 spectrum shows that the movable space gradually decreases, thereby determining the movable fluid saturation under the condition of saturated formation water in the rock column.

[0031] Furthermore, the first seepage capacity evaluation is performed based on the rock content data, including:

[0032] If the content of feldspar>quartz content>clay minerals, the internal content of feldspar is considered. If the total content of potassium feldspar and sodium feldspar in the feldspar is higher than that of other feldspars, the reservoir seepage capacity in this area is high, otherwise it is judged that the reservoir seepage capacity in this area is low;

[0033] If the clay mineral content is less than the feldspar content and less than the quartz content, the internal content of the quartz is considered. If the proportion of the secondary quartz content is less than the preset first threshold, the reservoir seepage capacity in the area is judged to be high; otherwise, the reservoir seepage capacity in the area is judged to be low.

[0034] Furthermore, the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation are combined according to preset rules to obtain a final seepage capacity evaluation, including:

[0035] When the results of the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation are all high, it is judged that the reservoir seepage capacity in the area is high;

[0036] When the results of the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation are all low, it is judged that the reservoir seepage capacity in the area is low;

[0037] When any two of the results of the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation are high and the other is low, it is judged that the reservoir seepage capacity of the region is high;

[0038] When any two of the results of the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation are low and the other one is high, it is judged that the reservoir seepage capacity of the area is low.

[0039] On the other hand, the present invention also provides a system for evaluating the permeability of a tight oil reservoir, comprising: a first permeability evaluation unit, a second permeability evaluation unit, a third permeability evaluation unit, and an evaluation report unit, wherein:

[0040] A first seepage capacity evaluation unit, used to analyze rock structure, obtain rock content data, and perform a first seepage capacity evaluation based on the rock content data, wherein the rock content data includes quartz content, feldspar content, and clay mineral content;

[0041] The second seepage capacity evaluation unit is used to obtain a scanned image of the core, extract an internal pore image based on the scanned image, establish a pore-based three-dimensional network model, obtain pore distribution, determine the number of throats, and perform a second seepage capacity evaluation based on the number of roars;

[0042] The third seepage capacity evaluation unit is used to test the T2 spectrum of the rock in the saturated state and under different centrifugal forces, obtain movable fluid saturation data, and perform the third seepage capacity evaluation according to the movable fluid saturation data;

[0043] The evaluation report unit is used to combine the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation to obtain a final seepage capacity evaluation according to preset rules.

[0044] Compared with the prior art, the present invention has the following beneficial effects: the present invention uses the rock content data to perform the first seepage capacity evaluation; extracts the internal pore image based on the scanned image of the core, establishes a pore-based three-dimensional network model, obtains the pore distribution, determines the number of throats, and performs the second seepage capacity evaluation based on the number of roars; performs the third seepage capacity evaluation based on the movable fluid saturation data of the rock; and finally combines the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation to obtain the final seepage capacity evaluation according to the preset rules. The present invention performs a comprehensive evaluation of the seepage capacity based on the three indicators, and the evaluation results obtained are more comprehensive and accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0046] Figure 1 This is a flow chart of a method for evaluating the seepage capacity of a tight oil reservoir in Embodiment 1 of the present invention;

[0047] Figure 2 This is a flowchart of step S110 in the first embodiment of the present invention;

[0048] Figure 3 This is a flowchart of step S130 in the first embodiment of the present invention;

[0049] Figure 4 Schematic diagram of the preset rules in step S140 in the first embodiment of the present invention;

[0050] Figure 5 This is a schematic diagram of implementation details of a method for evaluating the seepage capacity of a tight oil reservoir in Embodiment 1 of the present invention;

[0051] Figure 6 This is a schematic diagram of the structure of a system for evaluating the seepage capacity of a tight oil reservoir in Embodiment 2 of the present invention. DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] Embodiment 1

[0054] This embodiment provides a method for evaluating the seepage capacity of a tight oil reservoir. Figure 1 As shown, it specifically includes steps S110-S140:

[0055] Step S110, analyzing the rock structure, obtaining rock content data, and performing a first seepage capacity evaluation based on the rock content data, wherein the rock content data includes quartz content, feldspar content, and clay mineral content.

[0056] This step at least includes sub-steps S111-S114, such as Figure 2 As shown:

[0057] Step S111: using an electron probe to capture a backscattered grayscale image.

[0058] In practical applications, the rock samples of the tight oil reservoir need to be cut and ground to obtain a rock column, and then the backscattered grayscale image of the rock column is taken using an electron probe.

[0059] Step S112, reconstructing the first layer grayscale image by using X-ray micro-CT scanning.

[0060] Step S113, compare the backscattered grayscale image and the first layer grayscale image. If the grayscale value ranges of quartz, feldspar and clay minerals shown in the two are the same, the composition of the first layer image is determined.

[0061] Step S114, obtaining rock content data according to the components of the first layer image, and performing a first seepage capacity evaluation according to the rock content data.

[0062] In some embodiments, the mineral composition of dense sandstone in a certain area is mainly quartz (average 40%), feldspar (average 31%) and clay minerals (average 19%). The quartz is composed of quartz in the original debris and secondary quartz. The inventors found that the higher the content of secondary quartz, the lower the porosity, and thus the lower the seepage capacity.

[0063] Clay minerals include but are not limited to illite, chlorite and kaolinite, among which illite is filamentous or honeycomb-shaped. As the illite content increases, the porosity of the sample decreases and the seepage capacity decreases; chlorite is a needle-shaped coating or rose-shaped spherule. The chlorite coating can effectively inhibit the precipitation of siliceous and carbonate rocks, and can inhibit the growth of secondary quartz. As the chlorite content increases, the porosity increases and the seepage capacity is enhanced; kaolinite has a variety of shapes such as needle-shaped, flaky, granular, plate-shaped, and spherical. As the kaolinite content increases, the porosity increases and the seepage capacity is enhanced.

[0064] Feldspar is composed of potassium feldspar, sodium feldspar, calcium feldspar and barium feldspar. The contents of potassium feldspar, sodium feldspar, calcium feldspar and barium feldspar are collected respectively, among which the contribution of calcium feldspar to seepage capacity is greater than the contribution of potassium feldspar to seepage capacity> the contribution of sodium feldspar to seepage capacity> the contribution of barium feldspar to seepage capacity.

[0065] Based on the above analysis experience, the inventors have studied a scheme for evaluating the first seepage capacity according to rock content data, including:

[0066] If the feldspar content > quartz content > clay minerals, the internal content of the feldspar is considered. If the total content of potassium feldspar and sodium feldspar in the feldspar is higher than that of other feldspars, the reservoir seepage capacity in this area is high, otherwise it is judged that the reservoir seepage capacity in this area is low.

[0067] If the clay mineral content is less than the feldspar content and less than the quartz content, the internal content of the quartz is considered. If the proportion of the secondary quartz content is less than the preset first threshold (for example, 5%), the reservoir seepage capacity in the area is judged to be high; otherwise, the reservoir seepage capacity in the area is judged to be low.

[0068] Step S120, obtain a scanned image of the core, extract an internal pore image based on the scanned image, establish a pore-based three-dimensional network model, obtain pore distribution, determine the number of throats, and perform a second seepage capacity evaluation based on the number of roars.

[0069] Specifically, a micrometer CT is used to scan the core sample to obtain a scanned image of the core, and the internal pore image is extracted based on the scanned image. A pore-based three-dimensional network model is established, and the pore distribution and size of the core in the three-dimensional network model are observed. Based on the pore distribution analysis of the core, it is determined that the pore spaces are interconnected and at least one connected pore with the largest volume is determined to form a trunk network. The number of surrounding throats is calculated based on the trunk network. The more obvious the trunk network is, the more throats there are, and the stronger the rock seepage capacity is.

[0070] In practical applications, the throat threshold can be set for the number of throats based on historical experience. When the number of throats is greater than the throat threshold, the seepage capacity of the area is judged to be high; otherwise, the seepage capacity is judged to be poor.

[0071] In some embodiments, the inventors have found in practice that the throat threshold can be set to about 1500.

[0072] Step S130, respectively testing the T2 spectra of the rock in the saturated state and under different centrifugal forces to obtain movable fluid saturation data, and performing a third seepage capacity evaluation based on the movable fluid saturation data.

[0073] This step at least includes sub-steps S131-S134, such as Figure 3 As shown:

[0074] Step S131, cutting, grinding and drying the rock to obtain a dried rock column.

[0075] Generally, the rock raw material needs to be cut and ground according to the effective size of the instrument to obtain a rock column. Preferably, the rock column is washed with oil and salt, and the washed rock column is placed in a constant temperature oven for drying until the rock column reaches a constant weight.

[0076] Step S132, pouring the prepared simulated formation water into the dried rock column, pressurizing and saturating it under vacuum, and testing the T2 spectrum of the saturated state.

[0077] It is necessary to prepare simulated formation water, pour the simulated formation water into the rock column, pressurize and saturate it using a pressurized saturation device under vacuum, and use a high-temperature and high-pressure nuclear magnetic resonance core analysis device to test the T2 spectrum of the saturated state.

[0078] Step S133, driving away the rock column containing simulated formation water, and testing the T2 spectra under different centrifugal forces.

[0079] After the saturated sample measurement is completed, a high-speed centrifuge is used to drive away the movable water in the core with gradually increasing centrifugal force, and a high-temperature and high-pressure nuclear magnetic resonance core analysis device is used to test the T2 spectrum under different centrifugal forces.

[0080] Step S134, determining the movable fluid saturation under the condition of saturated formation water in the rock column according to the T2 spectrum in the saturated state and the T2 spectrum under different centrifugal forces.

[0081] T2 spectrum is the time constant that describes the recovery process of the transverse component of nuclear magnetization intensity, so it is called transverse relaxation time. The transverse relaxation process is caused by the internal exchange of energy in the nuclear spin system, so it is also called spin-spin relaxation time. Due to the complexity of rock pore structure and the diversity of pore fluids and their occurrence states, the relaxation process will be the result of contributions from multiple components with different relaxation times. It can be expressed by a multi-exponential function: when the formation is saturated with water and the echo interval is relatively small, the T2 spectrum has a good correspondence with the distribution of rock pore size.

[0082] Starting from the saturated state, as the centrifugal force increases, the simulated formation water in the rock column is gradually discharged. The T2 spectrum shows that the movable space is gradually reduced, and the reduction amplitude decreases with the increase of centrifugal force, thereby determining the movable fluid saturation under the condition of the sample being saturated with formation water.

[0083] In practical applications, a movable fluid saturation threshold can be set for the movable fluid saturation based on historical experience. When the movable fluid saturation is greater than the movable fluid saturation, the seepage capacity of the area is determined to be high, otherwise, the seepage capacity is determined to be poor.

[0084] In some embodiments, the inventors have found in practice that the movable fluid saturation threshold is set to about 40%.

[0085] Step S140, combining the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation to obtain a final seepage capacity evaluation according to a preset rule.

[0086] Specific, combined Figure 4 As shown, when the rock structure has high permeability, many throats, and high saturation of the mobile fluid, it is determined that the tight oil reservoir in the area has high permeability.

[0087] When the rock structure has high permeability, a large number of throats, and low saturation of the mobile fluid, it is determined that the tight oil reservoir in the area has high permeability.

[0088] When the rock structure has high permeability, few throats, and high saturation of the mobile fluid, it is determined that the tight oil reservoir in the area has high permeability.

[0089] When the rock structure has high permeability, few throats, and low saturation of the mobile fluid, it is judged that the tight oil reservoir in the area has low permeability.

[0090] When the rock structure has low permeability, a large number of throats, and high saturation of the mobile fluid, it is determined that the tight oil reservoir in the area has high permeability.

[0091] When the rock structure has low permeability, many throats, and low saturation of the mobile fluid, it is determined that the tight oil reservoir in the area has low permeability.

[0092] When the rock structure has low permeability, few throats, and high saturation of the mobile fluid, it is determined that the tight oil reservoir in the area has low permeability.

[0093] When the rock structure has low seepage capacity, few throats, and low saturation of the mobile fluid, it is determined that the tight oil reservoir in the area has low seepage capacity.

[0094] For ease of understanding, Figure 5 The implementation details of the evaluation of the seepage capacity of the tight oil reservoir of the present invention are also illustrated, wherein the seepage capacity analysis one corresponds to the first seepage capacity evaluation, the seepage capacity analysis two corresponds to the second seepage capacity evaluation, and the seepage capacity analysis three corresponds to the third seepage capacity evaluation.

[0095] The present invention uses the rock content data to perform the first seepage capacity evaluation; extracts the internal pore image based on the scanned image of the core, establishes a pore-based three-dimensional network model, obtains the pore distribution, determines the number of throats, and performs the second seepage capacity evaluation based on the number of roars; performs the third seepage capacity evaluation based on the movable fluid saturation data of the rock; and finally combines the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation to obtain the final seepage capacity evaluation according to the preset rules. The present invention performs a comprehensive evaluation of the seepage capacity based on the three indicators, and the evaluation results obtained are more comprehensive and accurate.

[0096] Embodiment 2

[0097] The embodiment of the present invention further provides a system for evaluating the permeability of a tight oil reservoir, comprising a first permeability evaluation unit 10, a second permeability evaluation unit 20, a third permeability evaluation unit 30, and an evaluation report unit 40, wherein:

[0098] The first seepage capacity evaluation unit 10 is used to analyze the rock structure, obtain rock content data, and perform a first seepage capacity evaluation based on the rock content data, wherein the rock content data includes quartz content, feldspar content, and clay mineral content.

[0099] Specifically, this module is used to cut and grind a small piece of reservoir rock sample to obtain a rock column. Then take the rock column, and use the electron probe to take the backscattered grayscale image and use the X-ray micro-CT scan to reconstruct the first layer grayscale image; compare the two grayscale images, and the grayscale value range of quartz, feldspar and other minerals shown in the two is the same, so the composition of the first layer image in the X-ray micro-CT data can be determined. According to the composition of the first layer image, the composition of the internal image can be judged, that is, the quartz content, feldspar content and clay mineral content information in the rock layer can be obtained.

[0100] The mineral composition of dense sandstone is mainly quartz, feldspar and clay minerals. Quartz is composed of quartz in the original debris and secondary quartz. The inventors found that the higher the content of secondary quartz, the lower the porosity, and thus the lower the seepage capacity.

[0101] Clay minerals include but are not limited to illite, chlorite and kaolinite, among which illite is filamentous or honeycomb-shaped. As the illite content increases, the porosity of the sample decreases and the seepage capacity decreases; chlorite is a needle-shaped coating or rose-shaped spherule. The chlorite coating can effectively inhibit the precipitation of siliceous and carbonate rocks, and can inhibit the growth of secondary quartz. As the chlorite content increases, the porosity increases and the seepage capacity is enhanced; kaolinite has a variety of shapes such as needle-shaped, flaky, granular, plate-shaped, and spherical. As the kaolinite content increases, the porosity increases and the seepage capacity is enhanced.

[0102] Feldspar is composed of potassium feldspar, sodium feldspar, calcium feldspar and barium feldspar. The contents of potassium feldspar, sodium feldspar, calcium feldspar and barium feldspar are collected respectively, among which the contribution of calcium feldspar to seepage capacity is greater than the contribution of potassium feldspar to seepage capacity> the contribution of sodium feldspar to seepage capacity> the contribution of barium feldspar to seepage capacity.

[0103] Based on the above analysis experience, the inventors have studied a scheme for evaluating the first seepage capacity according to rock content data, including:

[0104] If the feldspar content > quartz content > clay minerals, the internal content of the feldspar is considered. If the total content of potassium feldspar and sodium feldspar in the feldspar is higher than that of other feldspars, the reservoir seepage capacity in this area is high, otherwise it is judged that the reservoir seepage capacity in this area is low.

[0105] If the clay mineral content is less than the feldspar content and less than the quartz content, the internal content of the quartz is considered. If the proportion of the secondary quartz content is less than the preset first threshold (for example, 5%), the reservoir seepage capacity in the area is judged to be high; otherwise, the reservoir seepage capacity in the area is judged to be low.

[0106] The second seepage capacity evaluation unit 20 is used to obtain a scanned image of the core, extract an internal pore image based on the scanned image, establish a pore-based three-dimensional network model, obtain pore distribution, determine the number of throats, and perform a second seepage capacity evaluation based on the number of roars.

[0107] Specifically, the module is used to scan core samples using micron CT to obtain scanned images of core samples, extract internal pore images based on the scanned images, establish a pore-based three-dimensional network model, observe the pore distribution and size of the core in the three-dimensional network model, and determine the interconnected pore spaces and at least one connected pore with the largest volume based on the pore distribution analysis of the core to form a trunk network. The number of surrounding throats is calculated based on the trunk network, where the more obvious the trunk network is, the more throats there are, and the stronger the rock seepage capacity is.

[0108] In practical applications, the throat threshold can be set for the number of throats based on historical experience. When the number of throats is greater than the throat threshold, the seepage capacity of the area is judged to be high; otherwise, the seepage capacity is judged to be poor.

[0109] The third seepage capacity evaluation unit 30 is used to test the T2 spectrum of the rock in the saturated state and under different centrifugal forces, obtain movable fluid saturation data, and perform the third seepage capacity evaluation according to the movable fluid saturation data.

[0110] Specifically, the module is used to cut and grind the rock raw materials according to the effective size of the instrument to obtain rock columns, wash the rock columns with oil and salt, and put the washed rock columns into a constant temperature oven for drying until the rock columns are of constant weight. The prepared simulated formation water is also poured into the dried rock columns, and the pressurized saturation device is used to pressurize and saturate them under vacuum, and the saturated state T2 spectrum is tested using a high-temperature and high-pressure nuclear magnetic resonance core analysis device. After the saturated sample measurement is completed, a high-speed centrifuge is used to drive away the movable water in the core with gradually increasing centrifugal force, and the high-temperature and high-pressure nuclear magnetic resonance core analysis device is used to test the T2 spectrum under different centrifugal forces. Starting from the saturated state, as the centrifugal force increases, the simulated formation water in the sample is gradually discharged, and the T2 spectrum shows that the movable space is gradually reduced, and the reduction amplitude decreases with the increase of centrifugal force, thereby determining the movable fluid saturation under the condition of the sample saturated with formation water.

[0111] In practical applications, a movable fluid saturation threshold can be set for the movable fluid saturation based on historical experience. When the movable fluid saturation is greater than the movable fluid saturation, the seepage capacity of the area is determined to be high, otherwise, the seepage capacity is determined to be poor.

[0112] The evaluation report unit 40 is used to combine the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation to obtain a final seepage capacity evaluation according to a preset rule.

[0113] Specifically: when the results of the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation are all high, it is judged that the reservoir seepage capacity in the region is high;

[0114] When the results of the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation are all low, it is judged that the reservoir seepage capacity in the area is low;

[0115] When any two of the results of the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation are high and the other is low, it is judged that the reservoir seepage capacity of the region is high;

[0116] When any two of the results of the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation are low and the other one is high, it is judged that the reservoir seepage capacity of the area is low.

[0117] The present invention uses the rock content data to perform the first seepage capacity evaluation; extracts the internal pore image based on the scanned image of the core, establishes a pore-based three-dimensional network model, obtains the pore distribution, determines the number of throats, and performs the second seepage capacity evaluation based on the number of roars; performs the third seepage capacity evaluation based on the movable fluid saturation data of the rock; and finally combines the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation to obtain the final seepage capacity evaluation according to the preset rules. The present invention performs a comprehensive evaluation of the seepage capacity based on the three indicators, and the evaluation results obtained are more comprehensive and accurate.

[0118] The more detailed theoretical basis and implementation process of the evaluation system for the seepage capacity of tight oil reservoirs of the present invention can be found in Example 1, which will not be described in detail here.

[0119] In the above detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that the embodiments of the claimed subject matter require more features than are clearly stated in each claim. On the contrary, as reflected in the appended claims, the invention is in a state of having less than all the features of the disclosed individual embodiments. Therefore, the appended claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0120] The above description includes examples of one or more embodiments. Of course, it is not possible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it should be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is encompassed in a manner similar to the term "including", as explained by "including," used as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or".

Claims

1. A method for evaluating the seepage capacity of a tight oil reservoir, characterized in that: The following steps are involved: Analyze rock structure, obtain rock content data, and perform a first seepage capacity evaluation based on the rock content data, wherein the rock content data includes quartz content, feldspar content, and clay mineral content; Get the scanned image of the core, extract the internal pore image based on the scanned image, establish a pore-based three-dimensional network model, obtain the pore distribution, determine the number of throats, and perform a second seepage capacity evaluation based on the number of roars; The T2 spectra of rocks in saturated state and under different centrifugal forces are tested respectively to obtain movable fluid saturation data, and the third seepage capacity is evaluated based on the movable fluid saturation data; The first seepage capacity evaluation, the second seepage capacity evaluation and the third seepage capacity evaluation are combined according to preset rules to obtain a final seepage capacity evaluation.

2. The evaluation method according to claim 1, characterized in that: The rock structure analysis and rock content data acquisition include: Use electron probe to take backscattered grayscale images; Reconstruct the grayscale image of the first layer using X-ray micro-CT scanning; Compare the backscattered grayscale image and the first layer grayscale image. If the grayscale value ranges of quartz, feldspar and clay minerals shown in the two are the same, the composition of the first layer image is determined. The rock content data is obtained based on the composition of the first layer image.

3. The evaluation method according to claim 1, wherein: The method of obtaining a scanned image of the core, extracting an internal pore image according to the scanned image, establishing a pore-based three-dimensional network model, obtaining pore distribution, and determining the number of throats includes: Scan the core using CT to obtain a scanned image of the core; Extract the internal pore image based on the scanned image and establish a pore-based three-dimensional network model; Observe the pore distribution and size of the core in the three-dimensional network model, and determine at least one connected pore with the largest volume that is interconnected in pore space based on the pore distribution analysis of the core to form a backbone network; The number of peripheral throats is calculated based on the backbone network.

4. The evaluation method according to claim 1, wherein: The T2 spectra of the rock in the saturated state and under different centrifugal forces are tested respectively to obtain movable fluid saturation data, including: Cutting, grinding and drying the rocks to obtain dried rock columns; Pour the prepared simulated formation water into the dried rock column, pressurize and saturate it under vacuum, and test the T2 spectrum of the saturated state; Drive away the rock column containing simulated formation water and test the T2 spectrum under different centrifugal forces; The movable fluid saturation under the condition of saturated formation water in the rock column is determined according to the T2 spectrum in the saturated state and the T2 spectrum under different centrifugal forces.

5. The evaluation method according to claim 4, characterized in that: The method of cutting, grinding and drying the rock to obtain a dried rock column comprises: The rock is cut and ground to obtain a rock column, and the rock column is washed with oil and salt. The rock column after oil and salt washing is placed in a constant temperature oven for drying until the rock column reaches a constant weight.

6. The evaluation method according to claim 4, characterized in that: The method of driving away a rock column containing simulated formation water and testing T2 spectra under different centrifugal forces includes: A high-speed centrifuge was used to drive the simulated formation water in the rock column with gradually increasing centrifugal force, and a high-temperature and high-pressure nuclear magnetic resonance core analysis device was used to test the T2 spectra under different centrifugal forces.

7. The evaluation method according to claim 4, characterized in that: The method of determining the movable fluid saturation under the condition of saturated formation water state of the rock column according to the T2 spectrum of the saturated state and the T2 spectrum under different centrifugal forces includes: From the T2 spectrum of the saturated state to the T2 spectrum under different centrifugal forces, the T2 spectrum shows that the movable space gradually decreases, thereby determining the movable fluid saturation under the condition of saturated formation water in the rock column.

8. The evaluation method according to claim 1, wherein: The first seepage capacity evaluation is carried out based on the rock content data, including: If the content of feldspar>quartz content>clay minerals, the internal content of feldspar is considered. If the total content of potassium feldspar and sodium feldspar in the feldspar is higher than that of other feldspars, the reservoir seepage capacity in this area is high, otherwise it is judged that the reservoir seepage capacity in this area is low; If the clay mineral content is less than the feldspar content and less than the quartz content, the internal content of the quartz is considered. If the proportion of the secondary quartz content is less than the preset first threshold, the reservoir seepage capacity in the area is judged to be high; otherwise, the reservoir seepage capacity in the area is judged to be low.

9. The evaluation method according to claim 1, wherein: The final seepage capacity evaluation is obtained by combining the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation according to preset rules, including: When the results of the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation are all high, it is judged that the reservoir seepage capacity in the area is high; When the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation are all low, it is judged that the reservoir seepage capacity in this area is low; When any two of the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation are high and the other is low, it is judged that the reservoir seepage capacity of the region is high; When any two of the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation are low and the other one is high, it is judged that the reservoir seepage capacity in the area is low.

10. A system for evaluating the seepage capacity of a tight oil reservoir, characterized in that: It includes a first seepage capacity evaluation unit, a second seepage capacity evaluation unit, a third seepage capacity evaluation unit, and an evaluation report unit, wherein: A first seepage capacity evaluation unit, used to analyze rock structure, obtain rock content data, and perform a first seepage capacity evaluation based on the rock content data, wherein the rock content data includes quartz content, feldspar content, and clay mineral content; The second seepage capacity evaluation unit is used to obtain a scanned image of the core, extract an internal pore image based on the scanned image, establish a pore-based three-dimensional network model, obtain pore distribution, determine the number of throats, and perform a second seepage capacity evaluation based on the number of roars; The third seepage capacity evaluation unit is used to test the T2 spectrum of the rock in the saturated state and under different centrifugal forces, obtain movable fluid saturation data, and perform the third seepage capacity evaluation according to the movable fluid saturation data; The evaluation report unit is used to combine the first seepage capacity evaluation, the second seepage capacity evaluation, and the third seepage capacity evaluation to obtain a final seepage capacity evaluation according to preset rules.

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