An experimental method for revealing the mechanism of carbonate rock pore formation and preservation
Patent Information
- Application Number
- CN202510512180.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-23
- Publication Date
- 2026-10-23
AI Technical Summary
[0030]本发明提供的揭示碳酸盐岩孔隙形成保持机理的实验方法，实验中采用高温高压环境，来模拟深层-超深层储层分别在静态与动态流体环境下(对应封闭体系和流动开放体系)的碳酸盐岩的溶蚀过程，真实还原深层-超深层地下溶蚀的化学平衡过程，能够系统揭示孔隙形成与保持机理，为深层-超深层碳酸盐岩储层评价与预测提供支持。
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Abstract
Description
Technical Field
[0001] This invention relates to the field of oil and gas exploration technology, and in particular to an experimental method for revealing the formation and maintenance mechanism of pores in carbonate rocks. Background Technology
[0002] In recent years, deep to ultra-deep carbonate rocks (internationally defined as those exceeding 4500 meters in depth) have become an important successor area for oil and gas exploration and development. Research on the porosity formation and retention mechanisms of deep to ultra-deep carbonate rocks is crucial for determining reservoir space formation and for reservoir evaluation and prediction. Currently, research has primarily focused on the porosity formation and retention mechanisms of shallow to medium-depth (<4500m) carbonate rocks. Results show that porosity in shallow to medium-depth rocks can be formed through dissolution or destroyed through precipitation. Deep to ultra-deep carbonate rocks, having undergone a long and complex process of reservoir formation, accumulation, and alteration, likely exhibit different porosity formation and retention mechanisms compared to shallow to medium-depth rocks. This significantly limits the evaluation and prediction of corresponding reservoirs. However, there are currently no reports on the porosity formation and retention mechanisms of deep to ultra-deep carbonate rocks. Summary of the Invention
[0003] In view of the above problems, the purpose of this invention is to provide an experimental method for revealing the formation and maintenance mechanism of pores in carbonate rocks.
[0004] This invention provides an experimental method for revealing the mechanism of pore formation and retention in carbonate rocks, comprising the following steps:
[0005] In a closed system, a first dissolution simulation experiment was conducted on the first carbonate rock sample under high temperature and high pressure.
[0006] In a fluid open system, a second dissolution simulation experiment was conducted on a second carbonate rock sample under high temperature and high pressure.
[0007] Based on the changes in ion concentration of the reaction liquid in the first and second dissolution simulation experiments, the mechanism of pore formation and maintenance in carbonate rocks in deep and ultra-deep reservoirs was analyzed.
[0008] In one embodiment, conducting the first dissolution simulation experiment under high temperature and high pressure environment includes:
[0009] Obtain a plunger-shaped first carbonate rock sample with an internal porous structure;
[0010] Under the closed system, the first carbonate rock sample was subjected to dissolution experiments at multiple temperature and pressure values in the high temperature and high pressure environment.
[0011] The ion concentration in the reaction solution is determined in real time.
[0012] Determine the relationship between the ion concentration and the temperature and pressure of the sample.
[0013] In one embodiment, the first carbonate rock sample is a dolomite sample; the dolomite sample may be one or a combination of the following types: porous dolomite, cavitary dolomite, fracture-porous dolomite;
[0014] The initial porosity of the selected dolomite samples was 8%–12%;
[0015] The initial permeability of the selected dolomite samples was 1–10 md;
[0016] The specific surface area of each of the selected dolomite samples remained consistent.
[0017] In one embodiment, the flow rate of the reaction solution in the closed system is 0.1 ml / min.
[0018] In one embodiment, conducting the second dissolution simulation experiment under high temperature and high pressure environment includes:
[0019] Obtain secondary carbonate rock samples with different mineral types and lithologies;
[0020] In the aforementioned open flow system, the second carbonate rock sample was subjected to dissolution experiments at multiple temperature and pressure values under the aforementioned high temperature and high pressure environment.
[0021] The ion concentration in the reaction solution is determined in real time.
[0022] Determine the relationship between the ion concentration and the temperature and pressure of the sample.
[0023] In one embodiment, the second carbonate rock sample obtained from different mineral types includes calcite and dolomite.
[0024] In one embodiment, the second carbonate rock samples with different lithologies obtained include: dolomite and limestone.
[0025] In one embodiment, the flow rate of the reaction solution in the open flow system is 1.0 ml / min.
[0026] In one embodiment, the temperature range is 130–250°C, and the pressure range is 80–150 MPa.
[0027] In one embodiment, the ion concentration is the Ca in the reaction solution. 2+ and Mg 2+ The sum of concentrations.
[0028] In one embodiment, the reaction solution is a saturated carbon dioxide acidic solution.
[0029] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following:
[0030] The experimental method provided by this invention, which reveals the porosity formation and retention mechanism of carbonate rocks, uses a high-temperature and high-pressure environment to simulate the dissolution process of carbonate rocks in deep and ultra-deep reservoirs under static and dynamic fluid environments (corresponding to closed systems and flowing open systems), respectively. This method realistically restores the chemical equilibrium process of deep and ultra-deep underground dissolution, and can systematically reveal the porosity formation and retention mechanism, providing support for the evaluation and prediction of deep and ultra-deep carbonate rock reservoirs.
[0031] Furthermore, experimental samples with different pore structures (pore type, void type, fracture-pore type), different mineral types (calcite, dolomite), and different lithologies (limestone and dolomite) were used to meet the research needs of diverse reservoir characteristics and provide support for the fine evaluation of complex carbonate reservoirs.
[0032] Furthermore, by clarifying key parameters such as the initial porosity, initial permeability, and fluid flow rate under different systems of the experimental samples, a dynamic quantitative relationship between the ion concentration in the reaction solution and the changes in temperature and pressure was established, providing direct experimental basis for predicting the reservoir porosity development potential and reducing the risks of oil and gas exploration and development.
[0033] 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
[0034] 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:
[0035] Figure 1 This is a flowchart of the experimental method for revealing the formation and retention mechanism of pores in carbonate rocks in an embodiment of the present invention;
[0036] Figure 2 This is a schematic diagram of the simulation experiment results of carbonate rock karstification with different pore structures in the embodiments of the present invention;
[0037] Figure 3a This is a schematic diagram of the simulation results of carbonate rock dissolution of different mineral types in the embodiments of the present invention;
[0038] Figure 3b This is a schematic diagram of the simulation results of carbonate rock karstification of different lithologies in the embodiments of the present invention. Detailed Implementation
[0039] This embodiment provides an experimental method for revealing the porosity formation and retention mechanism of carbonate rocks. Although exemplary embodiments of this disclosure are shown in the accompanying drawings, it should be understood that this disclosure can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of this disclosure and to fully convey the scope of this disclosure to those skilled in the art.
[0040] This invention provides an experimental method for revealing the mechanism of pore formation and retention in carbonate rocks, referring to... Figure 1 As shown, the method includes the following steps:
[0041] S11. Conduct a first dissolution simulation experiment on the first carbonate rock sample under high temperature and high pressure in a closed system;
[0042] S12. Under a flowing open system, a second dissolution simulation experiment was conducted on the second carbonate rock sample under high temperature and high pressure.
[0043] S13. Based on the changes in ion concentration of the reaction liquid in the first and second dissolution simulation experiments, analyze the mechanism of pore formation and maintenance in carbonate rocks in deep and ultra-deep reservoirs.
[0044] Deep to ultra-deep carbonate reservoirs are mostly closed systems, but may become open and flowing systems during special periods such as tectonic activity. This invention, in both of these systems and under high temperature and high pressure conditions, uses dissolution simulation experiments to determine the changes in ion concentration in the reaction solution. Based on the trend of ion concentration changes, it reveals the mechanism of pore formation and retention in carbonate rocks, providing support for subsequent evaluation and prediction of deep to ultra-deep carbonate reservoirs.
[0045] In one embodiment, the steps of conducting the first dissolution simulation experiment under high temperature and high pressure in step S11 are as follows: obtaining a plunger-shaped first carbonate rock sample with an internal porous structure; conducting dissolution experiments on the first carbonate rock sample under multiple temperature and pressure values in a closed system; determining the ion concentration in the reaction solution in real time; and determining the relationship between the ion concentration and the temperature and pressure of the sample.
[0046] In one embodiment, in step S11 above, the first carbonate rock sample is a dolomite sample; the dolomite sample may be one or a combination of the following types: porous dolomite, cavitary dolomite, fracture-porous dolomite; the initial porosity of the selected dolomite sample is 8% to 12%; the initial permeability of the selected dolomite sample is 1 to 10 md; and the specific surface area of each selected dolomite sample remains consistent.
[0047] In one embodiment, in step S11 above, the flow rate of the reaction solution in the closed system is 0.1 ml / min. Strictly speaking, this closed system is a near-closed system, not an absolutely closed system. In fact, all the closed systems appearing in the embodiments of this invention are near-closed systems.
[0048] In one embodiment, in step S11 above, the reaction solution is a saturated carbon dioxide acidic solution.
[0049] In one embodiment, in step S11 above, there are multiple temperature and pressure values in the high temperature and high pressure environment, with the temperature value ranging from 130 to 250°C and the pressure value ranging from 80 to 150 MPa.
[0050] In one embodiment, in step S11 above, the ion concentration is the sum of the concentrations of calcium ions and magnesium ions in the reaction solution.
[0051] In one embodiment, in step S11 above, the first carbonate rock sample comprises three groups: fractured porous sandy dolomite (initial porosity 9.85%, initial permeability 6.19 md), porous fine-grained dolomite (initial porosity 10.15%, initial permeability 2.17 md), and porous oolitic dolomite (initial porosity 11.78%, initial permeability 1.84 md). The flow rate of the reaction liquid in the closed system during the experiment was 0.1 ml / min. Four temperature and pressure values were set in the high-temperature and high-pressure environment: (150℃, 90 MPa), (180℃, 108 MPa), (210℃, 126 MPa), and (240℃, 144 MPa). Four temperature and pressure values were also set in a low-temperature, low-pressure environment to compare with the dissolution results of carbonate rocks in shallow and medium-depth reservoirs: (30℃, 18MPa), (60℃, 36MPa), (90℃, 54MPa), and (120℃, 72MPa). The results obtained using the aforementioned first carbonate rock sample and under the above controlled conditions are referenced... Figure 2 Specifically, experimental results show that in simulated acidic fluid dissolution experiments on shallow and medium-depth dolomite reservoirs, within a low-temperature and low-pressure range, for example, as the temperature of fracture-pore sand fragments gradually increases from 30℃ to 120℃ and the pressure increases from 18MPa to 72MPa, the ion concentration, or dissolution amount, in the reaction solution, i.e., Ca... 2+ and Mg 2+ The increasing sum of concentrations indicates a gradually increasing dissolution rate of dolomite. However, for porous fine-grained dolomite and porous oolitic dolomite, for example, during a process where the temperature gradually increases from 30℃ to 120℃ and the pressure increases from 18MPa to 72MPa, the ion concentration or dissolution rate in the reaction solution, i.e., Ca... 2+ and Mg 2+The sum of concentrations gradually decreases, seemingly indicating an anomalous decrease in the dolomite dissolution rate, but this is not actually the case. Porous dolomite possesses strong dissolving power under saturated carbon dioxide. Because the reaction system is closed (with a saturated carbon dioxide flow rate of 0.1 ml / min), the ion concentration in the reaction solution gradually increases but cannot be promptly removed, causing the chemical reaction between the reaction solution and the dolomite to gradually reach dynamic equilibrium. Therefore, as temperature and pressure gradually increase, the amount of dissolution—the ion concentration—gradually decreases in the reaction solution.
[0052] For fracture-porous dolomite, due to the lower permeability of pores compared to fractures, saturated carbon dioxide reaction solution has difficulty penetrating the internal pores of the dolomite. This significantly reduces the specific surface area of the sample under dissolution, resulting in a much lower ion concentration in the reaction solution at the beginning of the experiment compared to the ion concentration corresponding to porous dolomite samples. However, as temperature and pressure increase, the reaction solution gradually enters the dolomite pores, causing the dissolution amount and ion concentration to gradually increase. In simulated acidic fluid dissolution experiments on deep to ultra-deep dolomite reservoirs, it was found that within the high temperature and high pressure range, regardless of the sample's internal pore structure, such as porous dolomite and fracture-porous dolomite in this example, when the temperature and pressure reach 150℃ and 90MPa, the ion concentration in the reaction solution essentially reaches a common equilibrium point. That is, even if the temperature and pressure increase further under high temperature and pressure, the ion concentration hardly changes, indicating that the reaction solution and dolomite have fully reacted and reached chemical equilibrium, thus preserving the pore structure.
[0053] The above experimental results reveal that for deep-ultra-deep closed diagenetic systems, the continuous chemical reaction between acidic fluids and carbonate rocks reaches a dynamic equilibrium. At this point, neither secondary dissolution pores are formed nor existing pores are destroyed, thus preserving the existing pores.
[0054] In one embodiment, the steps of conducting the second dissolution simulation experiment under high temperature and high pressure environment in step S12 are as follows: obtaining second carbonate rock samples of different mineral types and different lithologies; conducting dissolution experiments on the second carbonate rock samples under multiple temperature and pressure values in a high temperature and high pressure environment in a flowing open system; determining the ion concentration in the reaction solution in real time; and determining the relationship between the ion concentration and the temperature and pressure of the sample.
[0055] In one embodiment, the second carbonate samples of different mineral types obtained in step S12 above include calcite and dolomite.
[0056] In one embodiment, the second carbonate rock samples with different lithologies obtained in step S12 above include: dolomite and limestone.
[0057] In one embodiment, in step S12 above, the flow rate of the reaction liquid in the flow development system is 1.0 ml / min.
[0058] In one embodiment, in step S12 above, the reaction solution is a saturated carbon dioxide acidic solution.
[0059] In one embodiment, in step S12 above, there are multiple temperature and pressure values in the high temperature and high pressure environment, with the temperature value ranging from 130 to 250°C and the pressure value ranging from 80 to 150 MPa.
[0060] In one embodiment, in step S12 above, the ion concentration is the sum of the concentrations of calcium ions and magnesium ions in the reaction solution.
[0061] In one embodiment, in step S12 above, calcite and dolomite were selected for dissolution experiments on different mineral types in the second carbonate rock sample. Oolitic dolomite and oolitic limestone were selected for dissolution experiments on different lithologies. In the experiment, the flow rate of the reaction liquid in the open flow system was 1.0 ml / min. Four temperature and pressure values were set in the high-temperature and high-pressure environment: (150℃, 90 MPa), (180℃, 108 MPa), (210℃, 126 MPa), and (240℃, 144 MPa). Four temperature and pressure values were also set in the low-temperature and low-pressure environment for comparison with the dissolution results of carbonate rocks in shallow and medium-depth reservoirs: (30℃, 18 MPa), (60℃, 36 MPa), (90℃, 54 MPa), and (120℃, 72 MPa). In addition, considering the temperature at which hydrocarbons mature into organic acids and the instability of acetic acid (organic acid) under high temperature and high pressure (pyrolysis), as well as the dominant role of deep-to-ultra-deep saturated carbon dioxide solution (inorganic acid), a 2.0 ml / L acetic acid solution was added to the dissolution simulation experiment of shallow-to-medium-depth carbonate reservoirs. Experimental results are referenced... Figure 3a and Figure 3b The results showed that, Figure 3a In the study, under high temperature and high pressure conditions and saturated carbon dioxide reaction solution, the ion concentration of different mineral types increased with increasing temperature and pressure. Under low temperature and low pressure conditions, regardless of the reaction solution, the ion concentration of different mineral types also increased with increasing temperature and pressure. Figure 3b In the experiment, under high temperature and high pressure conditions and saturated carbon dioxide reaction solution, the ion concentration of different lithological samples increased with increasing temperature and pressure. Under low temperature and low pressure conditions, regardless of the reaction solution, the ion concentration of different lithological samples also gradually increased with increasing temperature and pressure. These experimental results reveal that for deep-to-ultra-deep open-flow diagenetic systems, secondary dissolution pores can be continuously formed during the dissolution process of acidic fluids.
[0062] In one embodiment, based on the porosity formation and retention mechanism of carbonate rocks in deep-ultra-deep reservoirs disclosed in this invention, the inventors infer that with the uplift of carbonate strata and the decrease in temperature and pressure, mineral precipitation may occur under the action of saturated acidic fluids, forming cement that destroys porosity. Throughout geological history, closed systems and open flow systems have alternated; each regional tectonic activity leads to the disruption of closed systems and the formation of open flow systems. During periods of sustained tectonic stability and continuous fluid flow, energy equilibrium is reached, and the open flow system is broken, transitioning into a closed system. As energy continues to accumulate, regional tectonic activity occurs again, causing the closed system to be broken again and the open flow system to form again. Since the temperature and pressure values at which the chemical reaction reaches dynamic equilibrium are close to the critical points of the temperature and pressure values corresponding to the deep-ultra-deep and shallow-medium layers, for example, in the embodiments of this invention, this critical point is (150℃, 90MPa). Therefore, in the shallow-medium layer reservoirs under low temperature and low pressure environments, whether it is an open flow system or a closed system (except for absolutely closed systems), the characteristics are the continuous dissolution and porosity building in the deep burial background and the precipitation and porosity reduction in the uplifted geological background. Meanwhile, the preservation of carbonate rock porosity mainly occurs in the deep-ultra-deep reservoirs under high temperature and high pressure environments.
[0063] The experimental method provided by this invention, which reveals the porosity formation and retention mechanism of carbonate rocks, uses a high-temperature and high-pressure environment to simulate the dissolution process of carbonate rocks in deep and ultra-deep reservoirs under static and dynamic fluid environments (corresponding to closed systems and flowing open systems), respectively. This method realistically restores the chemical equilibrium process of deep and ultra-deep underground dissolution, and can systematically reveal the porosity formation and retention mechanism, providing support for the evaluation and prediction of deep and ultra-deep carbonate rock reservoirs.
[0064] Furthermore, experimental samples with different pore structures (pore type, void type, fracture-pore type), different mineral types (calcite, dolomite), and different lithologies (limestone and dolomite) were used to meet the research needs of diverse reservoir characteristics and provide support for the fine evaluation of complex carbonate reservoirs.
[0065] Furthermore, by clarifying key parameters such as the initial porosity, initial permeability, and fluid flow rate under different systems of the experimental samples, a dynamic quantitative relationship between the ion concentration in the reaction solution and the changes in temperature and pressure was established, providing direct experimental basis for predicting the reservoir porosity development potential and reducing the risks of oil and gas exploration and development.
[0066] Obviously, those skilled in the art can make various modifications to this invention without departing from its spirit and scope. Therefore, if these modifications fall within the scope of the claims and their equivalents, this invention is also intended to include these modifications.
Claims
1. An experimental method for revealing the mechanism of pore formation and retention in carbonate rocks, characterized in that, include: In a closed system, a first dissolution simulation experiment was conducted on the first carbonate rock sample under high temperature and high pressure. In a fluid open system, a second dissolution simulation experiment was conducted on a second carbonate rock sample under high temperature and high pressure. Based on the changes in ion concentration of the reaction liquid in the first and second dissolution simulation experiments, the mechanism of pore formation and maintenance in carbonate rocks in deep and ultra-deep reservoirs was analyzed.
2. The method as described in claim 1, characterized in that, The first dissolution simulation experiment under high temperature and high pressure environment includes: Obtain a plunger-shaped first carbonate rock sample with an internal porous structure; Under the closed system, the first carbonate rock sample was subjected to dissolution experiments at multiple temperature and pressure values in the high temperature and high pressure environment. The ion concentration in the reaction solution is determined in real time. Determine the relationship between the ion concentration and the temperature and pressure of the sample.
3. The method as described in claim 2, characterized in that, The first carbonate rock sample is a dolomite sample; the dolomite sample may be one or a combination of the following types: porous dolomite, cavitary dolomite, fracture-porous dolomite; The initial porosity of the selected dolomite samples was 8%–12%; The initial permeability of the selected dolomite samples was 1–10 md; The specific surface area of each of the selected dolomite samples remained consistent.
4. The method as described in claim 2, characterized in that, The flow rate of the reaction solution in the closed system is 0.1 ml / min.
5. The method as described in claim 1, characterized in that, The second dissolution simulation experiment under high temperature and high pressure environment includes: Obtain secondary carbonate rock samples with different mineral types and lithologies; In the aforementioned open flow system, the second carbonate rock sample was subjected to dissolution experiments at multiple temperature and pressure values under the aforementioned high temperature and high pressure environment. The ion concentration in the reaction solution is determined in real time. Determine the relationship between the ion concentration and the temperature and pressure of the sample.
6. The method as described in claim 5, characterized in that, The second carbonate rock samples obtained included different mineral types: calcite and dolomite.
7. The method as described in claim 5, characterized in that, The second carbonate rock samples with different lithologies obtained included dolomite and limestone.
8. The method as described in claim 5, characterized in that, The flow rate of the reaction solution in the open flow system is 1.0 ml / min.
9. The method as described in claim 2 or 5, characterized in that, Among the multiple temperature and pressure values, the temperature range is 130–250℃; the pressure range is 80–150MPa.
10. The method as described in claim 2 or 5, characterized in that, The ion concentration is the Ca in the reaction solution. 2+ and Mg 2+ The sum of concentrations.
11. The method as described in claim 2 or 5, characterized in that, The reaction solution is a saturated carbon dioxide acid solution.