Method for testing relationship between breakthrough pressure of soluble salts and cap natural gas

Abstract

The invention discloses a method for testing a relationship between breakthrough pressure of soluble salts and natural gas in a cover layer. Comprising the following steps: selecting compact carbonate rocks as a test sample of a cover layer; carrying out saturation treatment on the test sample by using distilled water and simulated formation water containing different soluble salts to obtain a test rock sample; measuring the natural gas breakthrough pressure of the test rock sample based on a free hydrocarbon concentration method; and determining the influence of the simulated formation water containing different soluble salts on the natural gas breakthrough pressure of the test sample based on the natural gas breakthrough pressure of the distilled water and the simulated formation water corresponding to the test rock sample. And data support can be provided for cap breakthrough pressure research, cap sealing performance evaluation and oil and gas reservoir storage condition determination under the condition of salinized formation water.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration technology, and in particular to a test method for the relationship between easily soluble salts and the breakthrough pressure of caprock natural gas. Background Technology

[0002] Source rocks, reservoirs, and caprocks are crucial conditions for oil and gas storage, playing a vital role in the enrichment of oil and gas. The caprock, located above the reservoir, is an impermeable or low-permeability layer that prevents oil and gas from escaping upwards. The ability of any caprock in nature to isolate gaseous or liquid hydrocarbons is relative; an absolutely impermeable caprock does not exist.

[0003] There are numerous studies and experimental analyses on the formation mechanisms of source rocks and reservoirs in saline environments. Existing research indicates that the main factors affecting the breakthrough pressure of caprocks are temperature, pressure, lithology, physical properties, and the development of pores and fractures. However, changes in the properties of the pore medium fluid can also affect the breakthrough pressure of caprock natural gas. Currently, the influence of salts on the breakthrough pressure of caprock natural gas has not been quantitatively evaluated. Therefore, determining the influence of easily soluble salts on the breakthrough pressure of caprock natural gas is of great significance. Summary of the Invention

[0004] To address the aforementioned problems, the inventors developed this invention, which, through specific embodiments, provides a test method for the relationship between easily soluble salts and the breakthrough pressure of caprock natural gas.

[0005] This invention provides a method for testing the relationship between easily soluble salts and the breakthrough pressure of caprock natural gas, comprising:

[0006] Dense carbonate rocks were selected as test samples for the caprock.

[0007] Test rock samples were obtained by saturating the test samples with distilled water and simulated formation water containing different soluble salts.

[0008] The natural gas breakthrough pressure of the test rock sample was determined based on the free hydrocarbon concentration method.

[0009] Based on the natural gas breakthrough pressures of the test rock samples corresponding to distilled water and simulated formation water, the influence of simulated formation water containing different soluble salts on the natural gas breakthrough pressures of the test samples was determined.

[0010] Furthermore, the selection of dense carbonate rocks from the caprock as test samples includes the following steps:

[0011] Test samples were drilled perpendicular to the bedding plane of the cap layer, and the test samples were plunger samples.

[0012] Furthermore, after the step of selecting dense carbonate rocks as test samples for the caprock, the following steps are included:

[0013] Water sensitivity test and salt sensitivity test are performed on the test sample. If the water sensitivity of the test sample is higher than the water sensitivity threshold or the salt sensitivity of the test sample is higher than the salt sensitivity threshold, the test sample is reselected.

[0014] If the water sensitivity of the test sample is lower than the water sensitivity threshold and the salt sensitivity of the test sample is lower than the salt sensitivity threshold, the test sample is determined as the target test sample.

[0015] The process of saturating test samples with simulated formation water containing different soluble salts to obtain test rock samples includes the following steps:

[0016] The target test sample was saturated with simulated formation water containing different soluble salts to obtain the test rock sample.

[0017] Furthermore, the step of saturating the test sample with distilled water and simulated formation water containing different soluble salts to obtain the test rock sample includes the following steps:

[0018] The same test sample was saturated with distilled water and simulated formation water to obtain the test rock sample;

[0019] After the natural gas breakthrough pressure of the test rock sample is measured, the test rock sample is cleaned and dried to obtain a clean test sample.

[0020] Furthermore, the step of saturating the test sample with distilled water and simulated formation water containing different soluble salts to obtain the test rock sample includes the following steps:

[0021] Test rock samples were obtained by saturating distilled water and simulated formation water containing different soluble salts with the corresponding test samples.

[0022] Furthermore, the simulated formation water consists of seven types, namely NaHCO3 type, CaCl2 type, Na2SO4 type, MgCl2 type, NaCl type, KCl type and standard saline type.

[0023] Furthermore, the determination of the natural gas breakthrough pressure of the test rock sample based on the free hydrocarbon concentration method includes the following steps:

[0024] Based on caprock parameters, the experimental parameters of the rock gas breakthrough pressure measurement experimental device were adjusted.

[0025] Gradually increase the inlet pressure of the rock gas breakthrough pressure measuring experimental device, and when the gas in the test rock sample breaks out, obtain the outlet pressure of the rock gas breakthrough pressure measuring experimental device.

[0026] The natural gas breakthrough pressure is determined based on the inlet and outlet pressures.

[0027] Furthermore, the determination of the impact of simulated formation water containing different soluble salts on the natural gas breakthrough pressure of the test sample based on the natural gas breakthrough pressure of the test rock sample corresponding to distilled water and simulated formation water includes the following steps:

[0028] The influence of readily soluble salts on the natural gas breakthrough pressure of the test samples is determined based on the difference between the first breakthrough pressure and the second breakthrough pressure. The first breakthrough pressure is the natural gas breakthrough pressure of the test rock sample saturated with distilled water, and the second breakthrough pressure is the natural gas breakthrough pressure of the test rock sample saturated with simulated formation water. The larger the difference between the first breakthrough pressure and the second breakthrough pressure, the greater the influence of readily soluble salts on the natural gas breakthrough pressure; the smaller the difference between the first breakthrough pressure and the second breakthrough pressure, the smaller the influence of readily soluble salts on the natural gas breakthrough pressure.

[0029] Furthermore, the simulated formation water has the same degree of mineralization.

[0030] Furthermore, the determination of the impact of simulated formation water containing different soluble salts on the natural gas breakthrough pressure of the test sample based on the natural gas breakthrough pressure of the test rock sample corresponding to distilled water and simulated formation water includes the following steps:

[0031] Based on the natural gas breakthrough pressures corresponding to distilled water and simulated formation water in the test rock samples, a breakthrough pressure influence diagram was drawn.

[0032] Based on the impact diagram of the breakthrough pressure, the target salts are determined, wherein the target salts are the easily soluble salts corresponding to the largest and smallest impacts.

[0033] The beneficial effects of the above-mentioned technical solutions provided by the embodiments of the present invention include at least the following: selecting dense carbonate rocks as test samples for caprocks; saturating the test samples with distilled water and simulated formation water containing different soluble salts to obtain test rock samples; measuring the natural gas breakthrough pressure of the test rock samples based on the free hydrocarbon concentration method; and determining the influence of simulated formation water containing different soluble salts on the natural gas breakthrough pressure of the test samples based on the natural gas breakthrough pressure of the test rock samples corresponding to distilled water and simulated formation water, thus providing data support for the study of caprock breakthrough pressure under saline formation water conditions, the evaluation of caprock sealing performance, and the determination of oil and gas reservoir preservation conditions.

[0034] Other features and advantages of the invention will be set forth in the following description or may be learned by practicing the invention.

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0036] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0037] Figure 1 This is a flowchart of the method in an embodiment of the present invention; Detailed Implementation

[0038] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0039] Extensive exploration has confirmed that most saline basins are also oil and gas basins, with proven oil and gas reserves in these saline-oil basins accounting for over 80% of the world's total. In China's Mesozoic and Cenozoic continental lacustrine basins, saline-lacustrine oil and gas accumulation is very common, and the study of saline-lacustrine oil and gas geology has always been a hot topic in petroleum geology. Typical examples include the Shahejie Formation (Sha-1) depositional period in the Bohai Bay Basin, the Paleogene and Neogene depositional periods in the Qaidam Basin, the Permian Fengcheng-Lucaogou Formation depositional period in the Junggar Basin, and the Paleogene Qianjiang Formation depositional period in the Jianghan Basin—all typical saline lacustrine environments. Source rocks, reservoirs, and caprocks are crucial conditions for oil and gas storage, playing a vital role in oil and gas enrichment.

[0040] A caprock is an impermeable or low-permeability layer located above the reservoir, preventing oil and gas from escaping upwards. The ability of any caprock in nature to isolate gaseous or liquid hydrocarbons is relative; an absolutely impermeable caprock does not exist. Extensive research and experimental analysis have been conducted on the formation mechanisms of source rocks and reservoirs in saline environments. Current studies indicate that the main factors influencing caprock breakthrough pressure are temperature, pressure, lithology, physical properties, and pore fracture development. However, changes in the properties of the pore medium fluid can also affect the caprock natural gas breakthrough pressure. Currently, the impact of salts on the caprock natural gas breakthrough pressure has not been quantitatively evaluated.

[0041] To address the problems existing in the prior art, embodiments of the present invention provide a method for testing the relationship between easily soluble salts and the breakthrough pressure of caprock natural gas, the process of which is as follows: Figure 1 As shown, it includes the following steps:

[0042] Step S1: Select dense carbonate rocks as test samples for the caprock.

[0043] Among them, dense carbonate rocks can be made of argillaceous or micritic carbonate rocks. To improve the accuracy of the test, the test samples should have the following characteristics: no cracks, no clay minerals, high hardness and not easily broken.

[0044] Step S2: The test sample is saturated with distilled water and simulated formation water containing different soluble salts to obtain the test rock sample.

[0045] Specifically, a core saturated water experimental device is used to fully saturate the test sample with distilled water and simulated formation water containing different soluble salts to obtain a test rock sample. There can be one or more test samples. For example, when there is only one test sample, the same test sample is used repeatedly to determine the breakthrough pressure of natural gas. After each measurement, the test sample is cleaned to avoid residual liquid affecting the measurement accuracy.

[0046] Step S3: Determine the natural gas breakthrough pressure of the test rock sample based on the free hydrocarbon concentration method.

[0047] Step S4: Based on the natural gas breakthrough pressure of the test rock sample corresponding to distilled water and simulated formation water, determine the influence of simulated formation water containing different soluble salts on the natural gas breakthrough pressure of the test sample.

[0048] Specifically, the natural gas breakthrough pressure corresponding to the test rock sample and distilled water is used as the benchmark value for comparison. The natural gas breakthrough pressure corresponding to the test rock sample and simulated formation water is compared with the benchmark value. The greater the difference between the two, the greater the influence of the corresponding simulated formation water on the natural gas breakthrough pressure.

[0049] In the method described in this embodiment, step S1 may include the following steps:

[0050] Test samples were drilled perpendicular to the bedding plane of the cap layer, and the test samples were plunger samples.

[0051] For example, the test sample has a diameter of 2.5 cm and a length of 1.0 cm to 2.5 cm.

[0052] In the method described above in this embodiment, after step S1, the following steps are included:

[0053] Water sensitivity and salt sensitivity tests are performed on the test sample. If the water sensitivity of the test sample is higher than the water sensitivity threshold, or the salt sensitivity of the test sample is higher than the salt sensitivity threshold, a new test sample is selected. If the water sensitivity of the test sample is lower than the water sensitivity threshold, and the salt sensitivity of the test sample is lower than the salt sensitivity threshold, the test sample is determined as the target test sample.

[0054] The method of saturating the test sample with simulated formation water containing different soluble salts to obtain the test rock sample includes the following steps: saturating the target test sample with simulated formation water containing different soluble salts to obtain the test rock sample.

[0055] Specifically, salt sensitivity refers to the probability and extent to which permeability changes as the salinity of the injected fluid decreases; water sensitivity refers to the probability and extent to which incompatible foreign fluids entering the reservoir cause hydration, swelling, and dispersion of clay minerals, resulting in a decrease in reservoir permeability. After the test samples are prepared, water sensitivity and salt sensitivity experiments are performed on the test samples to determine their water sensitivity and salt sensitivity. Based on the water sensitivity and salt sensitivity of the test samples, as well as the preset water sensitivity threshold and salt sensitivity threshold, the target test sample is determined.

[0056] Preferably, after conducting water sensitivity or salt sensitivity tests on the test samples, the test samples are cleaned and dried to ensure the cleanliness of the test samples.

[0057] In the method described in this embodiment, step S2 may include the following steps:

[0058] The same test sample was saturated with distilled water and simulated formation water to obtain the test rock sample;

[0059] After the natural gas breakthrough pressure of the test rock sample is measured, the test rock sample is cleaned and dried to obtain a clean test sample.

[0060] Specifically, test rock samples are prepared using the same test sample. After the natural gas breakthrough pressure of the test rock sample is measured, the test rock sample is cleaned and dried to obtain a clean test sample. The clean test sample is then saturated with distilled water or simulated formation water to complete the preparation of the test rock sample.

[0061] In the method described in this embodiment, step S2 may include the following steps:

[0062] The process of saturating the test sample with distilled water and simulated formation water containing different soluble salts to obtain the test rock sample includes the following steps:

[0063] Test rock samples were obtained by saturating distilled water and simulated formation water containing different soluble salts with the corresponding test samples.

[0064] For example, if there are seven types of simulated formation water, then there are eight test samples. One test sample is saturated with distilled water, and the other seven test samples are saturated with the seven types of simulated formation water respectively, resulting in eight test rock samples.

[0065] In the above method of this embodiment, there are seven types of simulated formation water, namely NaHCO3 type, CaCl2 type, Na2SO4 type, MgCl2 type, NaCl type, KCl type and standard brine type.

[0066] Specifically, the standard salt solution has a NaCl:CaCl2:MgCl2·6H2O mass ratio of 7:0.6:0.4. Understandably, the types of easily soluble salts can be reduced or further increased from the range of sodium, potassium, magnesium, and calcium chlorides, carbonates, and sulfates.

[0067] In the method described above in this embodiment, step S3 may include the following steps:

[0068] Based on the caprock parameters, the experimental parameters of the rock gas breakthrough pressure measuring device are adjusted; the inlet pressure of the rock gas breakthrough pressure measuring device is gradually increased; when the gas in the test rock sample breaks through and escapes, the outlet pressure of the rock gas breakthrough pressure measuring device is obtained; the natural gas breakthrough pressure is determined based on the inlet pressure and the outlet pressure.

[0069] The caprock parameters include temperature and pressure.

[0070] For example, the rock gas breakthrough pressure determination method and rock gas breakthrough pressure determination experimental apparatus specified in SY / T 5748-2020 are used to determine the test rock sample.

[0071] In the method described above in this embodiment, step S4 may include the following steps:

[0072] The determination of the impact of simulated formation water containing different soluble salts on the natural gas breakthrough pressure of the test rock sample based on the natural gas breakthrough pressure corresponding to distilled water and simulated formation water includes the following steps:

[0073] The influence of readily soluble salts on the natural gas breakthrough pressure of the test samples is determined based on the difference between the first breakthrough pressure and the second breakthrough pressure. The first breakthrough pressure is the natural gas breakthrough pressure of the test rock sample saturated with distilled water, and the second breakthrough pressure is the natural gas breakthrough pressure of the test rock sample saturated with simulated formation water. The larger the difference between the first breakthrough pressure and the second breakthrough pressure, the greater the influence of readily soluble salts on the natural gas breakthrough pressure; the smaller the difference between the first breakthrough pressure and the second breakthrough pressure, the smaller the influence of readily soluble salts on the natural gas breakthrough pressure.

[0074] Specifically, the natural gas breakthrough pressure of the test rock sample corresponding to distilled water is used as the benchmark value for comparison. The natural gas breakthrough pressure of the test rock sample corresponding to simulated formation water is compared with the benchmark value. The larger the difference between the two, the greater the influence of the corresponding simulated formation water on the natural gas breakthrough pressure. By calculating the difference between the first breakthrough pressure and the second breakthrough pressure, the influence of soluble salts on the natural gas breakthrough pressure of the test sample is determined.

[0075] In the method described above in this embodiment, step S4 may include the following steps:

[0076] Based on the natural gas breakthrough pressures corresponding to distilled water and simulated formation water in the test rock samples, a breakthrough pressure influence diagram was drawn.

[0077] Based on the impact diagram of the breakthrough pressure, the target salts are determined, wherein the target salts are the easily soluble salts corresponding to the largest and smallest impacts.

[0078] Specifically, after all test rock samples have completed the natural gas breakthrough pressure measurement, a breakthrough pressure influence diagram is plotted with water type (NaHCO3, CaCl2, Na2SO4, MgCl2, NaCl, KCl, standard brine, distilled water) as the x-axis and breakthrough pressure (in MPa) as the y-axis. Based on the breakthrough pressure influence diagram, the influence of different salts on the breakthrough pressure of rock natural gas can be compared, and the salts with the greatest and least influence can be identified.

[0079] Preferably, the simulated formation water has the same degree of mineralization.

[0080] For example, a brine with a simulated formation water salinity of 80 g / L was used.

[0081] The method for testing the relationship between soluble salts and caprock breakthrough pressure provided in this invention involves selecting tight carbonate rocks as test samples for the caprock; saturating the test samples with distilled water and simulated formation water containing different soluble salts to obtain test rock samples; determining the natural gas breakthrough pressure of the test rock samples based on the free hydrocarbon concentration method; and determining the influence of simulated formation water containing different soluble salts on the natural gas breakthrough pressure of the test samples based on the natural gas breakthrough pressure of the test rock samples corresponding to distilled water and simulated formation water. This provides data support for the study of caprock breakthrough pressure under saline formation water conditions, the evaluation of caprock sealing performance, and the determination of oil and gas reservoir preservation conditions.

[0082] Those skilled in the art can change the above order without departing from the scope of protection of this disclosure.

[0083] Unless otherwise stated, the term "connection" as used above refers to a logical relationship of current transmission and does not necessarily indicate a direct electrical connection. Furthermore, terms such as "first" and "second" do not indicate a sequential order but are merely used to identify related units or devices.

Claims

1. A method for testing the relationship between easily soluble salts and the breakthrough pressure of caprock natural gas, characterized in that, Includes the following steps: Dense carbonate rocks were selected as test samples for the caprock. Test rock samples were obtained by saturating the test samples with distilled water and simulated formation water containing different soluble salts. The natural gas breakthrough pressure of the test rock sample was determined based on the free hydrocarbon concentration method. Based on the natural gas breakthrough pressures of the test rock samples corresponding to distilled water and simulated formation water, the influence of simulated formation water containing different soluble salts on the natural gas breakthrough pressures of the test samples was determined.

2. The method as described in claim 1, characterized in that, The selection of dense carbonate rocks from the caprock as test samples includes the following steps: Test samples were drilled perpendicular to the bedding plane of the cap layer, and the test samples were plunger samples.

3. The method as described in claim 1, characterized in that, Following the step of selecting dense carbonate rocks as test samples for the caprock, the following steps are included: Water sensitivity test and salt sensitivity test are performed on the test sample. If the water sensitivity of the test sample is higher than the water sensitivity threshold or the salt sensitivity of the test sample is higher than the salt sensitivity threshold, the test sample is reselected. If the water sensitivity of the test sample is lower than the water sensitivity threshold and the salt sensitivity of the test sample is lower than the salt sensitivity threshold, the test sample is determined as the target test sample. The process of saturating test samples with simulated formation water containing different soluble salts to obtain test rock samples includes the following steps: The target test sample was saturated with simulated formation water containing different soluble salts to obtain the test rock sample.

4. The method as described in claim 1, characterized in that, The process of saturating the test sample with distilled water and simulated formation water containing different soluble salts to obtain the test rock sample includes the following steps: The same test sample was saturated with distilled water and simulated formation water to obtain the test rock sample; After the natural gas breakthrough pressure of the test rock sample is measured, the test rock sample is cleaned and dried to obtain a clean test sample.

5. The method as described in claim 1, characterized in that, The process of saturating the test sample with distilled water and simulated formation water containing different soluble salts to obtain the test rock sample includes the following steps: Test rock samples were obtained by saturating distilled water and simulated formation water containing different soluble salts with the corresponding test samples.

6. The method as described in claim 1, characterized in that, The simulated formation water consists of seven types, namely NaHCO3 type, CaCl2 type, Na2SO4 type, MgCl2 type, NaCl type, KCl type and standard saline type.

7. The method as described in claim 1, characterized in that, The determination of the natural gas breakthrough pressure of the test rock sample based on the free hydrocarbon concentration method includes the following steps: Based on caprock parameters, the experimental parameters of the rock gas breakthrough pressure measurement experimental device were adjusted. Gradually increase the inlet pressure of the rock gas breakthrough pressure measuring experimental device, and when the gas in the test rock sample breaks out, obtain the outlet pressure of the rock gas breakthrough pressure measuring experimental device. The natural gas breakthrough pressure is determined based on the inlet and outlet pressures.

8. The method as described in claim 1, characterized in that, The determination of the impact of simulated formation water containing different soluble salts on the natural gas breakthrough pressure of the test rock sample based on the natural gas breakthrough pressure corresponding to distilled water and simulated formation water includes the following steps: The influence of readily soluble salts on the natural gas breakthrough pressure of the test samples is determined based on the difference between the first breakthrough pressure and the second breakthrough pressure. The first breakthrough pressure is the natural gas breakthrough pressure of the test rock sample saturated with distilled water, and the second breakthrough pressure is the natural gas breakthrough pressure of the test rock sample saturated with simulated formation water. The larger the difference between the first breakthrough pressure and the second breakthrough pressure, the greater the influence of readily soluble salts on the natural gas breakthrough pressure; the smaller the difference between the first breakthrough pressure and the second breakthrough pressure, the smaller the influence of readily soluble salts on the natural gas breakthrough pressure.

9. The method as described in claim 1, characterized in that, The simulated formation water has the same degree of mineralization.

10. The method as described in claim 1, characterized in that, The determination of the impact of simulated formation water containing different soluble salts on the natural gas breakthrough pressure of the test rock sample based on the natural gas breakthrough pressure corresponding to distilled water and simulated formation water includes the following steps: Based on the natural gas breakthrough pressures corresponding to distilled water and simulated formation water in the test rock samples, a breakthrough pressure influence diagram was drawn. Based on the impact diagram of the breakthrough pressure, the target salts are determined, wherein the target salts are the easily soluble salts corresponding to the largest and smallest impacts.

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