Method for evaluating influence of enveloped clay cladding on reservoir quality
By constructing a reactive transport model to simulate the mineral changes of clay cladding under different fluids, the problem of the dynamic impact of clay cladding on reservoir quality was solved, quantitative assessment and accurate prediction were achieved, and reliable exploration and development solutions were provided.
Patent Information
- Application Number
- CN202511635677.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-10
- Publication Date
- 2026-03-06
AI Technical Summary
Existing technologies cannot accurately predict the dynamic effects of clay crust in deep sandstone reservoirs, leading to difficulties in reservoir quality prediction. In particular, under high temperature, high pressure and acidic fluid environments, the dissolution and transformation of clay crust leads to porosity loss and blockage.
A reactive transport model was constructed, integrating thermodynamic databases and mineral reaction kinetic parameters, to simulate the mineral dissolution and precipitation process of clay coatings under CO2-enriched fluids and organic acid-enriched fluids. Through multi-scenario simulation, the net porosity change was evaluated, and a quantitative assessment of the dual effects of clay coatings was achieved.
It enables dynamic and quantitative assessment of clay cladding, improves the accuracy of reservoir quality prediction, and can identify the porosity evolution trend of reservoirs in future geological periods or under specific fluid injection, providing a reliable basis for exploration and development plans.
Smart Images
Figure CN121617486A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of oil and gas reservoir evaluation and petroleum geological exploration technology, specifically to a method for assessing the impact of coating clay on reservoir quality. Background Technology
[0002] In deep sandstone reservoirs, the development of authigenic clay mineral coatings (especially chlorite coatings) is considered a key factor in porosity preservation. Traditional evaluation methods, based on thin section observations and statistics, assume that the coatings protect porosity by inhibiting secondary quartz enlargement; therefore, high coating coverage is generally equated with high-quality reservoirs.
[0003] However, traditional views have serious flaws. In deep, high-temperature, high-pressure environments and acidic fluids (such as those rich in CO2 or organic acids), the clay cladding itself undergoes dissolution and geochemical transformation. This process not only causes it to lose its protective function, but its dissolution products also precipitate as secondary minerals such as siderite and kaolinite, clogging pores and leading to a net loss of porosity. This dual effect of "protection" and "destruction" makes it impossible to accurately predict reservoir quality based solely on static cladding parameters. Current technologies lack solutions for quantifying this dynamic process, increasing the risk of exploration decisions.
[0004] Therefore, it is necessary to develop and design a method for assessing the impact of clay-coated shells on reservoir quality, and to provide a dynamic, quantitative, and accurate assessment method to solve the problem of reservoir quality prediction caused by the dual effects of clay shells. This is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention
[0005] To address the aforementioned problems, this invention provides a method for evaluating the impact of clay-coated shells on reservoir quality, enabling dynamic, quantitative, and accurate assessment to solve the challenge of reservoir quality prediction caused by the dual effects of clay shells.
[0006] To achieve the above objectives, the present invention provides the following solution:
[0007] A method for evaluating the impact of clay-like coatings on reservoir quality includes the following steps:
[0008] S1. Acquisition of basic parameters: Obtain the petrological parameters, clay crust parameters, geochemical parameters and geological environment parameters of the target reservoir;
[0009] S2. Construction of reactive transport model: Based on the parameters obtained in S1, a reactive transport model is constructed. The model integrates a thermodynamic database and mineral reaction kinetic parameters, and has a built-in shell volume quantification module and a multi-mechanism reaction kinetics module.
[0010] S3. Multi-scenario simulation: Run the model to simulate the mineral dissolution and precipitation process and porosity evolution of the target reservoir under two scenarios: CO2 enriched fluid and organic acid enriched fluid.
[0011] S4. Comprehensive Assessment and Result Output: Compare and analyze the simulation results under the two scenarios of CO2 enriched fluid and organic acid enriched fluid, output the net porosity change value and the dominant diagenetic mechanism, and make a final assessment of the impact of clay-clad reservoir quality.
[0012] Preferably, the clay coating parameters in step S1 include coating mineral type, coverage, thickness, and pore-filled clay content.
[0013] Preferably, the coverage is 20% to 99%, the thickness is 4 μm to 20 μm, and the pore-filled clay content is 1% to 5%.
[0014] Preferably, the geochemical parameters in step S1 include the formation water chemical composition, the CO2 partial pressure of the injected fluid, or the concentration of organic acids.
[0015] Preferably, the shell volume quantification module in step S2 uses the specific surface area method for quantification, and its calculation formula is: total shell volume is... Where k is the proportionality coefficient, φ is the initial porosity, d is the average particle size, C is the coating coverage, h is the coating thickness, and μ is the coating microporosity correction coefficient.
[0016] Preferably, the proportionality coefficient k is 4.23 and the microporosity correction coefficient μ is 0.5.
[0017] Preferably, the reactive transport model further includes a reaction device for carrying the reactants. The reaction device includes at least two interconnected reaction tubes for placing sandstone. One end of each reaction tube is provided with an inlet for the inflow of CO2 enriched fluid or organic acid enriched fluid, and the other end of each reaction tube is provided with an outlet for the outflow of CO2 enriched fluid or organic acid enriched fluid.
[0018] Preferably, there are 100 reaction tubes, and the length of each reaction tube is 0.1 meters. Each reaction tube contains sandstone.
[0019] Preferably, the multi-mechanism reaction kinetics module in step S2 simulates secondary mineral precipitation including at least kaolinite, quartz, siderite, and magnesite.
[0020] Preferably, the clay coating is a chlorite coating.
[0021] The present invention achieves the following technical effects compared to the prior art:
[0022] By incorporating the "protective effect" and "self-dissolution and destruction effect" of clay cladding into a unified model, a complete quantitative assessment of the dual role of cladding is achieved. Through reactive transport simulation, quantitative changes in net porosity are output, rather than qualitative descriptions, greatly improving the accuracy of reservoir quality prediction. It can simulate the porosity evolution trend of reservoirs under future geological periods or specific fluid injections (such as CO2 geological sequestration). By comparing the results of two end-member fluid scenarios, the main risks (CO2 intrusion) or potentials (organic acid environment) of reservoir quality can be clearly identified, providing a direct and reliable decision-making basis for the selection of exploration targets and the formulation of development plans. Attached Figure Description
[0023] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0024] Appendix Figure 1 This is a schematic diagram of the reaction transport model structure of the method for evaluating the impact of encapsulated clay shells on reservoir quality disclosed in this invention;
[0025] Among them, 1. reaction tube; 2. water inlet; 3. water outlet. Detailed Implementation
[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0027] The purpose of this invention is to provide a method for evaluating the impact of clay-coated shells on reservoir quality, achieving dynamic, quantitative, and accurate evaluation, so as to solve the problem of reservoir quality prediction caused by the dual effects of clay shells.
[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0029] refer to Figure 1 The method for evaluating the impact of coated clay crust on reservoir quality disclosed in this embodiment of the invention includes the following steps:
[0030] S1. Obtain basic parameters: Obtain the petrological parameters, clay crust parameters, geochemical parameters, and geological environment parameters of the target reservoir;
[0031] S2. Constructing a reactive transport model: Based on the parameters obtained in S1, a reactive transport model is constructed. The model integrates a thermodynamic database and mineral reaction kinetic parameters, and has a built-in shell volume quantification module and a multi-mechanism reaction kinetics module.
[0032] S3. Multi-scenario simulation: Run the model to simulate the mineral dissolution and precipitation process and porosity evolution of the target reservoir under two scenarios: CO2 enriched fluid and organic acid enriched fluid.
[0033] S4. Comprehensive Assessment and Result Output: Compare and analyze the simulation results under the two scenarios of CO2 enriched fluid and organic acid enriched fluid, output the net porosity change value and the dominant diagenetic mechanism, and make a final assessment of the impact of clay coating on reservoir quality. If the net porosity decreases significantly under the CO2 charging scenario, the coating is judged to have a high risk; if the porosity remains stable or increases slightly under the organic acid charging scenario, the coating benefit is judged to be positive.
[0034] In this embodiment, the "protective effect" and "self-dissolution and destruction effect" of clay coating are incorporated into a unified model, achieving a complete quantitative assessment of the dual role of the coating. Through reactive transport simulation, the quantitative change value of net porosity is output, rather than a qualitative description, which greatly improves the accuracy of reservoir quality prediction. It can simulate the porosity evolution trend of the reservoir in future geological periods or under specific fluid injection (such as CO2 geological sequestration). By comparing the results of two end-member fluid scenarios, the main risks (CO2 intrusion) or potentials (organic acid environment) of reservoir quality can be clearly identified, providing a direct and reliable decision-making basis for the selection of exploration targets and the formulation of development plans.
[0035] It should be noted that, as one implementation method, the target layer is Triassic feldspar sandstone, with the initial mineral composition set as follows: quartz 40%, potassium feldspar 30%, initial porosity 30%, grain size 0.2 mm, chlorite coating coverage 99%, thickness 20 μm, formation temperature 100℃, and the injected fluid endmembers set as follows: pCO2 = 10 MPa, organic acid concentration = 2000 mg / L. A one-dimensional model was constructed using GWB software, and the initial volume of the chlorite coating was calculated to be 10.26% using the specific surface area method (k = 4.23, μ = 0.5). The LLNL (Lawrence Livermore National Laboratory) thermodynamic database and standard mineral kinetic parameters were integrated. The fluid flow rate was set to 0.1 m / year, and the simulation reaction time was 100 years. Two scenarios were run: CO2 enriched fluid and organic acid enriched fluid. The results of injecting CO2 enriched fluid showed that the net porosity decreased by a maximum of 2.5%, with the dominant mechanism being the precipitation of siderite / magnesite induced by chlorite dissolution.
[0036] Results of injecting organic acid enrichment fluid: net porosity change <0.5%, the dominant mechanism is near equilibrium of mineral dissolution and redistribution.
[0037] The final assessment concluded that the reservoir is extremely sensitive to CO2 intrusion, and the chlorite cladding presents a high-risk factor in this environment; however, it provides effective porosity protection in an organic acid environment. This conclusion provides crucial risk warnings for subsequent exploration, development, and CO2 storage site selection.
[0038] It should be noted that the porosity is determined by the helium porosity measurement method. This method utilizes the characteristic that helium molecules are small and can enter extremely small pores. The gas is injected into the rock core sample under a certain pressure, and the pressure change before and after the gas expansion is measured. Based on Boyle's law, the pore volume of the rock is accurately calculated, and thus the porosity is obtained.
[0039] refer to Figure 1 In one embodiment, the clay coating parameters in step S1 include coating mineral type, coverage, thickness, and pore-filling clay content. The coating parameters (type, coverage, and thickness) are mainly used to evaluate its protective function (inhibiting quartz cementation) and the pore volume it occupies. The pore-filling clay content directly evaluates its destructive function (blocking pores and throats, directly reducing porosity and permeability). By incorporating all of the above parameters into the experimental data, the model can quantify "porosity preserved due to protection" and "porosity lost due to space occupation" respectively, thereby calculating the net porosity change. The evaluation results are far more accurate than those of traditional methods.
[0040] refer to Figure 1 As one implementation method, the coverage rate is 20% to 99%, which can clearly compare the huge difference in porosity evolution under low coverage (poor suppression effect) and high coverage (good suppression effect) scenarios. It avoids the mathematical extreme value problem (such as zero effective surface area) that may be caused by 100% coverage, while still simulating almost complete suppression of quartz cementation. The thickness is 4μm to 20μm. This upper limit can be used to study the trade-off between the protective effect (inhibiting cementation) and its own harm (occupying pores). The clay content of pore filling is 1% to 5%, which can cover most real geological cases.
[0041] refer to Figure 1 As a preferred approach, the geochemical parameters in the S1 step include the formation water chemical composition, the CO2 partial pressure of the injected fluid, or the concentration of organic acids, to better simulate the true values of geochemical parameters.
[0042] refer to Figure 1 As a preferred method, the shell volume quantification module in step S2 uses the specific surface area method for quantification, and its calculation formula is: the total shell volume is... Where k is the proportionality coefficient, φ is the initial porosity, d is the average particle size, C is the coating coverage, h is the coating thickness, and μ is the coating microporosity correction coefficient.
[0043] refer to Figure 1 As one implementation method, the proportionality coefficient k is 4.23 and the microporosity correction coefficient μ is 0.5.
[0044] refer to Figure 1 As an implementation method, the reactive transport model also includes a reaction device for carrying the reactants. The reaction device includes at least two interconnected reaction tubes 1 for placing sandstone. One end of the reaction tube 1 is provided with an inlet 2 for the inflow of CO2 enriched fluid or organic acid enriched fluid, and the other end of the reaction tube 1 is provided with an outlet 3 for the outflow of CO2 enriched fluid or organic acid enriched fluid. This provides a physical support platform for the experiment. By performing fluid chemical analysis at the inlet and outlet of different reaction tubes 1, the migration of mineral dissolution fronts and the sequence of secondary mineral precipitation can be clearly captured, improving the accuracy of the experiment.
[0045] refer to Figure 1 There are 100 reaction tubes, each 0.1 meters long. Each reaction tube contains sandstone, which eliminates the interference of heterogeneity and can accurately reveal the complete sequence of chemical reaction evolution in space.
[0046] refer to Figure 1 As an implementation method, the multi-mechanism reaction kinetics module in step S2 simulates secondary mineral precipitation including at least kaolinite, quartz, siderite, and magnesite. Chlorite is a chemically complex mineral, mainly containing Fe, Mg, Al, Si, and O. When it dissolves, these elements must enter a new stable mineral phase. These four secondary minerals completely inherit all the major decomposition products of chlorite, which allows the model to accurately track the migration and fate of elements and strictly adhere to the most basic law of conservation of matter in geochemical simulation. By observing the precipitation amount and spatial distribution of these four minerals in the model, the specific causes of porosity changes can be directly diagnosed, improving experimental efficiency.
[0047] refer to Figure 1 As one implementation method, clay coating is chlorite coating.
[0048] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.
Claims
1. A method for evaluating the impact of a clay envelope on reservoir quality, characterized in that, The method comprises the following steps: S1, obtaining basic parameters: obtaining petrological parameters, clay coating parameters, geochemical parameters and geological environment parameters of the target reservoir; S2, constructing a reactivity transport model: based on the parameters obtained in S1, a reactivity transport model is constructed, which integrates a thermodynamic database and mineral reaction kinetics parameters, and internally contains a coating volume quantification module and a multi-mechanism reaction kinetics module; S3, multi-scenario simulation operation: running the model, respectively simulating the mineral dissolution and precipitation process and porosity evolution of the target reservoir under two scenarios of CO2-rich fluid and organic acid-rich fluid; S4, comprehensive evaluation and result output: comparative analysis of the simulation results under the two scenarios of CO2-rich fluid and organic acid-rich fluid, output of net porosity change value and dominant diagenetic mechanism, and final evaluation of the impact of clay coating on reservoir quality.
2. The method for evaluating the impact of an envelope of clay on reservoir quality according to claim 1, wherein, The clay coating parameters in the S1 step include coating mineral type, coverage, thickness and pore filling state clay content.
3. The method for evaluating the impact of a clay envelope on reservoir quality according to claim 2, wherein, The coverage is 20% to 99%, the thickness is 4 μm to 20 μm, and the pore filling state clay content is 1% to 5%.
4. The method for evaluating the impact of clay envelopes on reservoir quality of claim 1, wherein, The geochemical parameters in the S1 step include formation water chemical composition, CO2 partial pressure or organic acid concentration of the injected fluid.
5. The method for evaluating the impact of clay envelopes on reservoir quality of claim 1, wherein, The shell volume quantification module in the S2 step uses the specific surface area method for quantification, and the calculation formula is: total shell volume = k * φ * d * C * h * μ wherein k is a proportional coefficient, φ is the initial porosity, d is the average particle size, C is the shell coverage, h is the shell thickness, and μ is the shell microporosity correction coefficient.
6. The method for evaluating the impact of clay envelopes on reservoir quality according to claim 5, wherein, The proportion coefficient k is 4.23, and the microporosity correction coefficient μ is 0.
5.
7. The method for evaluating the impact of clay envelopes on reservoir quality of claim 1, wherein, The reactivity transport model further comprises a reaction device for carrying reaction substances, the reaction device comprising at least two reaction tubes for placing sandstone and being in communication with each other, one end of the reaction tube being provided with a water inlet for flowing in CO2-rich fluid or organic acid-rich fluid, the other end of the reaction tube being provided with a water outlet for flowing out CO2-rich fluid or organic acid-rich fluid.
8. The method for assessing the impact of envelope-shaped clay envelopes on reservoir quality according to claim 7, characterized in that, The reaction tube is 100, and the length of the reaction tube is 0.1 meters, and each reaction tube is placed with sandstone.
9. The method for evaluating the impact of clay envelopes on reservoir quality of claim 1, wherein, The multi-mechanism reaction kinetics module in the S2 step simulates at least the precipitation of secondary minerals including kaolinite, quartz, siderite and magnesite.
10. The method for evaluating the impact of clay envelopes on reservoir quality of claim 1, wherein, The clay coating is chlorite coating.