A method for multi-parameter coordinated evolution research of CO2-water-rock geochemical process

Abstract

The application discloses a kind of CO2-water-rock geochemical process multi-parameter coordinated evolution research methods.The method uses the high temperature and high pressure core displacement device with nuclear magnetic resonance to carry out CO2-water-rock reaction experiment, obtains in-situ nuclear magnetic T2 spectrum;Based on the extracted micro-pore characteristic parameter and mineral reaction amount, the dynamic evolution function of residual water saturation is constructed;Then the bottom layer is cracked and embedded in TOUGHREACT multiphase reaction-seepage coupling numerical model.The application breaks the static limitation of constant residual water saturation in traditional general model, realizes the two-way dynamic closed-loop feedback of micro-pore throat change and macroscopic seepage field mutation caused by water-rock reaction, greatly improves the accuracy of deep geological CO2 large-scale, long-period storage evolution law and safety evaluation.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of geological carbon sequestration technology and multiphase flow geochemistry. Specifically, it relates to an experimental-simulation integrated research method for simultaneously analyzing the dynamic evolution of pore structure and the synergistic response mechanism of residual water distribution during supercritical CO2 injection under simulated deep saline aquifer sequestration conditions. Background Technology

[0002] In CO2 geological sequestration, the injection of supercritical CO2 (scCO2) into a saline aquifer not only triggers physical displacement (two-phase flow) but also induces complex CO2-water-rock geochemical reactions (mineral dissolution / precipitation), thereby dynamically altering the pore structure. This pore structure, in turn, affects the residual water (S... r The occurrence form and saturation of W) form a closed loop of mutual feedback between the three fields of "chemistry-physics-fluid".

[0003] Chinese patent application CN119000457A also provides a device and method for testing the pore structure of rocks in CO2 water-rock reactions. The testing device includes: a core holder for encapsulating core samples; intermediate containers including a first intermediate container and a second intermediate container, connected to the fluid inlet and fluid outlet of the core holder; a nuclear magnetic resonance (NMR) device for acquiring NMR T2 spectra at different times during the core reaction; and a calculation and processing module for calculating the rate of change of the pore structure of the core sample based on the NMR T2 spectra. This invention can accurately test the changes in rock porosity and the rate of change during water-rock reactions, as well as changes in rock pore size. The testing process is non-destructive, convenient, and fast, ensuring the uniformity and comparability of the test results.

[0004] However, this existing technology still has the following key drawbacks: 1. Static and dynamic experiments are disconnected: For example, patent CN202310559155.8 only provides a non-destructive testing method for pore structure at a single time point (NMR T2 spectrum analysis), which cannot capture the temporal evolution in the "reaction-displacement" coupling process; its device does not integrate a reaction-displacement combined module and cannot simulate the real injection process of "first water-rock reaction, then CO2 displacement".

[0005] 2. Lack of quantitative coupling model of residual water-pore structure: Existing numerical simulations (such as TOUGHREACT) mostly treat porosity (φ) as a single variable, ignoring the nonlinear regulatory effect of microstructural parameters such as pore size distribution (such as T2 relaxation peak displacement) and throat connectivity on the residual water retention capacity.

[0006] 3. The pre-displacement effect of the reaction stage on the displacement behavior has not been considered: In actual engineering, the reservoir has already undergone early water-rock reaction (such as acidizing stage) before CO2 injection, but the existing experimental schemes have failed to systematically study the mapping relationship of "cores with different reaction times → dynamic displacement → residual water distribution".

[0007] Therefore, there is an urgent need for a multi-parameter research method that can quantitatively correlate the degree of water-rock reaction, the evolution of pore structure parameters, and the dynamic response of residual water saturation. Summary of the Invention

[0008] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a three-pronged research method based on "reaction stage pre-setting - multi-parameter in-situ monitoring - co-evolution model construction", which can be used to reveal the co-evolution mechanism of "CO2-water-rock", helping to improve the accuracy of model prediction and optimize engineering decisions. It is especially suitable for CO2 geological storage safety assessment, reservoir stimulation prediction and dynamic modeling of storage potential.

[0009] (II) Technical Solution This invention provides a multi-parameter synergistic evolution study method for CO2-water-rock geochemical processes, which includes the following steps: S1. Perform gradient-time high-temperature and high-pressure static water-rock reaction on the target reservoir core. The reaction conditions are temperature 50-90℃, pressure 15-35MPa, and the reaction medium is simulated formation brine. S2. Supercritical CO2 dynamic displacement experiments were conducted on core samples from each reaction stage. During the displacement process, nuclear magnetic resonance T2 spectra, MRI images, and outlet flow-pressure data were collected simultaneously. S3. Based on the mineral composition of S1 and the pore structure parameters of step S2, construct the residual water saturation S r w is related to porosity φ, carbonate mineral content λ, and mean T2 distribution μ. T2 and standard deviation σ T2 Quantitative functional relationship; S4. Embed the function into the multiphase reaction-percolation coupled numerical model TOUGHREACT to achieve long-term dynamic prediction of the co-evolution of pore structure and residual water during CO2 sequestration.

[0010] Preferably, in S1, the gradient time includes 0d, 3d, 7d, 15d, and 30d.

[0011] Preferably, in S2, the nuclear magnetic resonance T2 spectrum acquisition uses the CPMG sequence, with a polarization time Tw=5000ms, an echo time TE=0.1ms, an echo number NE=15000, and 32 scans; the MRI image uses the SE sequence, with a spatial resolution of 50μm.

[0012] Preferably, in S3, the residual water saturation S r The quantitative function form of w is: (Formula I) Wherein: S r w represents residual water saturation (%), φ represents porosity, and λ represents carbonate mineral content (wt.%). T2 Let σ be the mean of the distribution of T2. T2 denoted as the standard deviation of the T2 distribution; a to h are experimental fitting parameters, determined through nonlinear regression.

[0013] Preferably, the static water-rock reaction and dynamic displacement experiments use the same batch of core samples to avoid systematic errors caused by sample differences.

[0014] According to a preferred embodiment of the present invention, the experimental apparatus in S2 includes a gas injection control system, a liquid injection control system, and a core clamping system; The gas injection control system and the liquid injection control system are configured to inject carbon dioxide and water at controllable pressure or flow rate, respectively. The two fluids, carbon dioxide and water, are mixed in the confluence pipeline and then introduced into the core clamping system. The core holding system is used to simulate the real underground reaction environment of high temperature and high pressure in deep strata. It includes a core holder, an axial pressure system, and a confining pressure-temperature control system. The core holder is encapsulated with a rock sample core drilled from underground or a simulated core that is artificially pressed. The injected fluid seeps and reacts chemically inside the micropores of the core. The axial pressure system applies axial stress to the core end face through an axial pressure pump and a pressure-transmitting piston; the confining pressure-temperature control system injects and circulates a fluid medium with a preset temperature in the annulus between the core and the core holder shell through a confining pressure tracking pump and a circulation pump; this fluid medium serves both as a pressure-transmitting medium to simulate the geostress borne by the underground rock and as a heat-transmitting medium to provide a thermal field for the water-rock reaction inside the holder and to maintain the supercritical state of carbon dioxide. Pressure sensors are respectively installed at the inlet and outlet ends of the core holder, and a nuclear magnetic resonance detector is installed around the core holder.

[0015] According to a preferred embodiment of the present invention, the testing apparatus further includes a back pressure system and a gas flow meter; The back pressure system is connected downstream of the outlet end of the core holder and is used to simulate the real pore fluid back pressure conditions of the formation and to achieve the retention and measurement of the produced material. The gas flow meter is installed at the exhaust end and is used to dynamically measure the instantaneous flow rate of the gas flowing out of the core holder.

[0016] Preferably, in S2, during the dynamic displacement experiment, the core holder integrates an independent confining pressure system and a back pressure valve to ensure that there is no gas bypass leakage during the displacement process.

[0017] Preferably, in S2, the pressure of the confining pressure system is 5 MPa higher than the inlet pressure, and the outlet pressure of the back pressure valve is 2 MPa lower than the inlet pressure.

[0018] Among them, TOUGHREACT is currently the most authoritative and widely used multiphase and multicomponent reaction solute transport simulation software (simulator) in the fields of earth science, groundwater hydrology and petroleum engineering. TOUGHREACT can extrapolate short-term experimental patterns to geological evolution on a century-scale.

[0019] While the existing TOUGHREACT model is powerful, traditional CO2 sequestration simulations assume a residual water saturation S in the rock. r w is a fixed constant. This application, however, is the first to link residual water saturation with microscopic "pore structure characteristics" (porosity φ, carbonate mineral content λ; mean distribution of T2 μ). T2 The standard deviation σ of the distribution of T2 T2 The residual water saturation is bound to the structure, making it a structure-dependent variable. In S4, the quantitative function relationship from S3 is incorporated into the code by modifying the Fortran underlying source code of TOUGHREACT (capillary pressure and relative permeability calculation module). At each time step and in each grid block of the numerical simulation, the program first calculates the amount of mineral precipitation / dissolution, substitutes it into the function to calculate the degree of pore structure variation, and thereby affects the residual water saturation S of the current grid. r The w value is then passed to the fluid seepage equation for further calculation.

[0020] This invention abandons the physical assumption of 'constant residual water saturation' in traditional numerical models. By embedding dynamic calculation formulas containing microscopic pore structure parameters into the underlying code, it endows the numerical model with the ability to perceive changes in pore throat structure and reshape the seepage field in real time due to water-rock reaction, thereby greatly improving the accuracy and reliability of long-term numerical simulation of deep CO2 geological storage.

[0021] (III) Beneficial Effects Compared with existing technologies, the method and research model of this invention achieve the following technical effects: 1. Revealing the co-evolution mechanism: This invention is the first to experimentally demonstrate that in the short-term reaction (≤7d), due to the dominant role of calcite dissolution, the porosity φ increases, and the average distribution value μ of T2 increases. T2 Increase, residual water saturation S rThe decrease in w indicates that residual water is easily displaced. Mid-term reaction (15-30 days): Due to the dominant role of kaolinite / sodium aluminum oxide precipitation, the standard deviation of T2 distribution σ... T2 Increased size, wider pore throat distribution, and increased residual water saturation S r An increase in w indicates enhanced capillary retention. These findings explain why some sites exhibit high early-stage containment efficiency but a later-stage leakage risk.

[0022] 2. This invention improves the accuracy of model prediction: When this model is used to simulate the 10-year process of sandstone sealing in the Baoding Depression, the prediction error of residual water saturation Srw is greatly reduced compared with the traditional model. Based on this, the phenomenon of abnormal increase in residual water saturation after 15 days of reaction observed in the field Frio-I project (the CCS demonstration project of Frio-I and Frio-II strata in Texas, USA (Daleye et al., 2007)) was successfully reproduced.

[0023] 3. Supporting Engineering Decision Optimization: The research methods and models provided in this invention can guide supercritical CO2 injection strategies in carbon sequestration technology: if the target reservoir is mainly composed of carbonates, high-flow-rate, short-cycle injection is advisable to suppress precipitation; when the mean distribution value of T2 is μ T2 <30ms and distribution standard deviation σ T2 If the prediction Sᵣw exceeds the threshold (>35%) within 50ms, the barrier layer optimization design needs to be initiated.

[0024] 4. The method has strong universality: it is applicable to various reservoirs such as sandstone, carbonate rock, and shale, and can also be extended to multi-phase-multi-chemical coupling scenarios such as geological storage of hydrogen and geothermal reinjection. Attached Figure Description

[0025] Figure 1 This is a flowchart of the research method of the present invention.

[0026] Figure 2 Photographs of Paleogene and Permian sandstone core samples from the Qiuxian Depression in Baoding.

[0027] Figure 3 This is a diagram of the experimental setup for a two-phase dynamic displacement experiment using nuclear magnetic resonance and imaging techniques.

[0028] Figure 4 Comparison of T2 spectrum evolution and MRI residual water distribution under different reaction times. Detailed Implementation

[0029] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] This invention selects the Paleogene sandstone of the Baoding Depression, a potential CO2 geological storage area in Hebei Province, as the research object. Following an integrated workflow of data processing and analysis, laboratory experiments, numerical modeling, and comprehensive research, the invention conducts tests and analyses on rock mineral types, contents, and pore structure. It carries out static and dynamic displacement experiments of CO2-saline water-rock under different conditions at high temperature and pressure. Combining nuclear magnetic resonance (NMR) and imaging techniques, the invention clarifies the dynamic evolution mechanism of rock pore structure and the synergistic evolution law of pores and residual water during CO2 displacement. A two-phase flow-chemical-pore multi-field coupled model is constructed to reveal the long-term spatiotemporal evolution of CO2 geological storage stability in saline water layers. The technical route of the multi-parameter synergistic evolution research method of this invention is as follows: Figure 2 As shown, the implementation process is as follows: (1) Data collection, core selection and core physicochemical characterization Basic geological data, including geological maps, structural maps, and borehole data, were collected for the Baoding Depression in Hebei Province. Reservoir core samples were selected (placed in core holders) using the National Physical Geological Data Center and provincial core repositories. To effectively obtain information on changes in the microstructure and pore structure of sandstone reservoirs before and after CO2 injection, this invention employs semi-quantitative X-ray powder diffraction (XRD) to analyze mineral composition and X-ray fluorescence spectroscopy (XRF) to analyze the major and minor elemental components and contents of the core samples. Scanning electron microscopy (SEM) was used to directly observe the size and morphological distribution of pore throats in the core plane, and to study throat type, pore type, mineral composition, and degree of cementation. Nuclear magnetic resonance imaging (NMR) and transverse relaxation time (T2) spectroscopy were used to systematically study changes in pore size, pore throat distribution, and effective porosity. Figure 2 The image shown is a photograph of a Paleogene and Permian sandstone core sample (φ=25mm, l=50mm) used in this study's experiments in the Qiuxian Depression of Baoding.

[0031] (2) High-temperature and high-pressure CO2-saline water-rock geochemical static reaction experiment A high-temperature, high-pressure reactor was used to simulate the deep formation environment. Based on the actual geological conditions of the study area (obtained through literature review), the experimental conditions were set at temperatures (50℃, 70℃, 90℃) and pressures (15, 25, 35 MPa). Core columns (φ=25mm, l=50mm) were placed in a 25g / L NaCl solution for water-rock reaction experiments (Table 1). Reaction times were set at 0, 3, 7, 15, and 30 days for each group of experiments. At each reaction time, the core columns and reaction solutions were removed, and the pore structure characteristics and mineral composition of the core columns, as well as the pH and major ion content of the reaction solutions, were tested to analyze the multi-factor modification mechanism of rock pore structure. Simultaneously, cores reacted for a certain time were used for two-phase dynamic displacement experiments to obtain the residual water distribution characteristics and residual water saturation at the corresponding reaction times.

[0032] Table 1: Experimental Design for Static Reaction under High Temperature and High Pressure (3) Two-phase dynamic displacement experiment based on nuclear magnetic resonance and imaging technology Two-phase dynamic displacement experiments based on nuclear magnetic resonance and imaging techniques were conducted on core samples in the initial state of the reservoir and core samples that had undergone a series of high-temperature and high-pressure CO2-saline water reactions for different times to clarify the dynamic evolution of the core pore structure and residual water distribution characteristics under different reaction conditions and at different reaction stages.

[0033] The system employs nuclear magnetic resonance microstructure and fluid analysis and imaging (MacroMR12-150H-I, Numai). This apparatus mainly includes a core clamping system, a gas / liquid injection system, a backpressure system, and a data measurement system (experimental setup such as...). Figure 3 As shown). Figure 3 As shown, the experimental setup consists of four main modules from left to right: a gas injection control system, a liquid injection control system, a high-temperature and high-pressure core clamping and reaction system, and an outlet and backpressure system (the data measurement system is not shown). V1 to V22 represent valves used to control the flow path opening and closing. The specific structure is described below: ① Gas injection control system The gas injection control system is used to provide and control the experimental gas (such as supercritical CO2) used for displacement. The gas source end is an air cylinder (or CO2 cylinder) as the bottom end of the gas source, which is connected to the cylinder pressure gauge and the main gas valve V1 in sequence through pipelines; the gas source end is equipped with a pressure gauge.

[0034] The main gas valve V1's gas path splits into two parallel pipelines. One pipeline, controlled by valve V3, directly connects to the bypass pipeline. The other pipeline, via a pressure-stabilizing gas path and valve V2, connects to the gas storage tank (equipped with a pressure gauge and a venting valve V22). Gas flowing out of the storage tank passes through a pressure reducer, a backpressure valve, and its control valve V4, then merges with the outlet pipeline of valve V3 via valve V5, flowing into the main pipeline. An inlet pressure gauge is installed on the merged gas pipeline, and the gas flow is ultimately throttled by the gas inlet control valve V6 into the gas-water mixing injection pipeline.

[0035] ② Liquid injection control system The liquid injection control system is used to inject simulated formation water / brine into the core under high pressure.

[0036] Its power source is a low-pressure control air source, which drives a "constant pressure and constant speed pump" of the low-pressure control air source to provide stable and pulsation-free liquid displacement power; Liquid storage device (piston-type transfer container): includes three piston-type fluid transfer tanks arranged in parallel. The output port of the constant flow pump is connected to the bottom chamber of the three piston-type fluid transfer tanks through the lower inlet control valves V8, V9, and V10, respectively, pushing the internal pistons to move upward. An unloading bypass valve V20 is also provided in the pump output pipeline.

[0037] After the simulated liquid stored in the upper chamber of the piston-type fluid transfer tank is squeezed out, it passes through the upper outlet control valves V11, V12, and V13 to form a total liquid path. Finally, it flows into the main injection pipeline through the liquid injection valve V7 and merges with the gas path output through valve V6 to enter the core holder.

[0038] The above gas injection control system and liquid injection control system constitute a gas / liquid injection system, which can controllably inject gas or liquid into the core clamping system at a constant pressure (flow rate).

[0039] ③ Core clamping system This core clamping system is used to simulate the high-temperature and high-pressure real underground rock environment in deep strata.

[0040] Core Structure: The core component is the core holder. Experimental core sample ( Figure 3 The dark rectangular block is housed inside the holder by a sealed sleeve; the holder is typically magnetically permeable and made of non-magnetic material to accommodate the external MRI detector.

[0041] Axial pressure and confining pressure system: An independent axial pressure pump provides axial pressure (equipped with an axial pressure gauge), which acts on the core end face through a pressure-transmitting piston; a confining pressure tracking pump provides radial confining pressure (equipped with a confining pressure gauge) to ensure that fluid does not flow across the core sidewalls. Between the core assembly and the outermost thick metal shell of the core holder, there is a hollow cylindrical gap, the annulus; the confining pressure tracking pump is connected to this annulus, which pumps hydraulic oil or water into it. This high-pressure fluid envelops the core assembly (which has a waterproof outer sheath), squeezing it from all directions to simulate the geostress (confining pressure) from thousands of meters underground.

[0042] Temperature-controlled circulation system (thermal field control): A circulating temperature-controlled liquid circuit is installed outside the core holder or inside the interlayer, equipped with a preheater, temperature sensor (T), and circulation pump. This closed-loop heating system is jointly controlled by valves V16, V17, V18, V19 (drain valve) and V21, providing a precise constant-temperature thermal field for water-rock reaction and supercritical CO2 state.

[0043] During the test, the core was wrapped in a heat-shrink tubing and placed horizontally in a core holder. The surrounding magnetic field strength was 0.3 ± 0.05 T (permanent magnet), and the resonance frequency was 12 MHz. The key parameters for the CPMG sequence measurement were set as follows: polarization or waiting time Tw = 5000 ms, echo time TE = 0.1 ms, echo number NE = 15000, and the number of scans was 32.

[0044] ④ Back pressure system The backpressure system is used to simulate the real pore fluid backpressure conditions in the formation and to measure the products.

[0045] Testing and Pressure Regulating End: The displacement products flowing out from the right end of the core holder are first tested by the outlet pressure gauge.

[0046] Constant pressure maintenance component: The produced fluid enters the back pressure controller (including back pressure valve and balancer). The back pressure system maintains the fluid pressure in the entire formation system at the target set condition (such as the pressure >8MPa required to maintain the supercritical state) through the buffer tank and the matching back pressure gauge.

[0047] Sampling and metering end: After depressurization, the fluid and gas are finally discharged through the end drain and metering valve group (V14, V15), which can be connected to an external balance, gas-liquid integrator or gas chromatograph for separation and dynamic metering.

[0048] After the above systems are assembled, the core sample to be tested is installed in the holder and saturated with formation water through the liquid injection system (V8-13 groups) on the left, and then reacted at a constant temperature for several days with the temperature control circulation system; then supercritical CO2 is injected through the gas injection system (V1-V6 exhaust) for dynamic displacement measurement, and the system pressure gradient is maintained by the back pressure system on the right.

[0049] The back pressure can be controlled by the back pressure valve. The fluid can only flow out from the outlet of the core holder when the pressure of the injected core exceeds the threshold set by the back pressure valve. The confining pressure is the pressure applied around the core by the injection pump.

[0050] To monitor upstream and downstream pressure values, pressure sensors (with pressure gauges at the inlet and outlet of the core holder) are installed at the inlet and outlet respectively; a gas flow meter is used to measure the instantaneous flow rate of gas flowing out of the core (the gas flow meter is installed after valve V14); the above real-time pressure and flow rate values ​​are recorded by a computer system.

[0051] The experimental steps are as follows: a. After cleaning the core samples that have undergone different water-rock reaction times, place them in a high-temperature oven at 105℃ for 4 hours to dry. The weight of the sample at this time is recorded as m0. The sample is then dried in the oven for another 1 hour and weighed again, recorded as mi. This process is repeated until (mi-m0) / m0 ≤ 0.03. The final weight of the sample is recorded as the dry weight m. Subsequently, the dried sample is wrapped in a heat-shrink tubing and placed in a core holder. CPMG sequence testing is performed on the sample using a nuclear magnetic resonance (NMR) analyzer. The measured signal value is used as the background value for subsequent tests.

[0052] b. The core holder was evacuated to achieve ideal vacuum conditions (< -0.1 MPa). Deionized water was introduced into the core holder through a liquid injection system, and the pressure was gradually increased to the experimental pressure by injecting nitrogen and maintained for more than 12 hours to ensure that the core was completely saturated with water. Afterwards, CPMG nuclear magnetic resonance sequence tests were repeated to obtain the nuclear magnetic resonance signal values ​​of the saturated core.

[0053] c. Before the displacement test, SE sequence testing was performed on the water-saturated core to obtain MRI images of the core in its water-saturated state. A stable high-pressure CO2 was applied at the core inlet, and a back pressure of 2 MPa less than that at the core outlet was applied to simulate formation pressure conditions. To prevent CO2 leakage through the gap between the core and the casing, the confining pressure was always maintained 5 MPa higher than the inlet pressure. Simultaneously, the pressure values ​​at both ends of the core holder were recorded in real time by computer.

[0054] d. Throughout the displacement process, CPMG and SE sequences were performed at regular intervals to obtain a series of T2 distributions and corresponding MRI images of cores after different displacement durations (e.g., Figure 4 (As shown). As displacement proceeds, when the distribution boundaries of different fluids in the MRI image become indistinguishable, i.e., imaging becomes difficult, it can be considered that the water in the core pores has been displaced to residual saturation, at which point the displacement experiment ends.

[0055] ④ Coupled model of the entire process of two-phase flow-chemical reaction-pore change Based on the experimental results of this project and domestic and international research findings, a model considering the relationship between porosity and residual water saturation, taking into account changes in mineral content, was constructed. This model was then optimized, resulting in the following model showing the relationship between changes in carbonate mineral content, porosity, and residual water saturation (φ-S). r w-λ): (Formula I) Wherein: S r w represents residual water saturation (%), φ represents porosity, and λ represents carbonate mineral content (wt.%). T2 Let σ be the mean of the distribution of T2. T2denoted as the standard deviation of the T2 distribution; a to h are experimental fitting parameters, determined through nonlinear regression.

[0056] ⑤ The above equations are incorporated into the TOUGHREACT simulation software as external modules through source code embedding. Specifically, the quantitative functional relationship (Formula I) is written into the code by modifying the TOUGHREACT Fortran low-level source code (capillary pressure and relative permeability calculation module). In each time step and each grid block of the numerical simulation, the program first calculates the amount of mineral precipitation / dissolution, substitutes it into the function (Formula I), and calculates the degree of pore structure variation, thereby determining the residual water saturation S of the current grid. r The w value is then passed to the fluid seepage equation for further calculation.

[0057] This completes the entire process of establishing a two-dimensional heterogeneous grid model of the deep saline aquifer in the Baoding Depression within the software. By inputting geological parameters of the target area, the continuous CO2 injection process over the next few years is simulated. In the TOUGHREACT simulation software, the aforementioned quantitative functional relationship (Formula I) is used to replace the traditional van Genuchten static pore structure model, and pore structure parameters are added to construct a capillary pressure calculation model that considers changes in pore structure.

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0059] In the following embodiments, the instruments and equipment used (such as high-temperature and high-pressure reactors, MacroMR12-150H-I nuclear magnetic resonance analysis and imaging systems, constant-speed and constant-pressure pumps, etc.) and conventional experimental consumables are all commercially available products commonly used in the field, unless otherwise specified. The numerical simulation software used is the genuine TOUGHREACT program with a multiphase and multicomponent reaction solute transport module.

[0060] Example 1: Evaluation of the entire process of pore-residual water co-evolution based on Paleogene sandstone in the Baoding Depression. The steps are as follows: Step 1: Core Acquisition and Staged High-Temperature and High-Pressure Static Water-Rock Reaction (1) Sample acquisition and preparation: Natural sandstone cores from the Paleogene reservoir in the Baoding Depression, Hebei Province (taken from Well Jiqudi 1, at a depth of approximately 2150 m) were selected. The cores were washed, dried, and then cut and polished to prepare five sets of standard cylindrical core columns with a diameter of 25 mm and a length of 50 mm. Preliminary measurements showed that the average initial porosity of the cores was 18.2%, and the initial permeability was 152 mD.

[0061] (2) Simulated formation fluid configuration: Based on the measured formation water chemistry data of the study area, a NaCl brine solution with a mineralization of 25 g / L was prepared, and the actual calcium and magnesium ion background of the formation was simulated by adding appropriate amounts of CaCl2 and MgCl2.

[0062] (3) Gradient-time water-rock reaction: Five sets of core samples were placed in five sets of high-temperature and high-pressure reactors, and the simulated brine was added to completely submerge the core samples. High-purity CO2 gas was introduced, and the temperature inside the reactor was set to 70℃ and the pressure to 25MPa (simulating supercritical state). The reaction periods were set as follows: 0 days (control group), 3 days, 7 days, 15 days, and 30 days.

[0063] (4) Post-reaction parameter acquisition: After the set time is reached, the corresponding core and post-reaction solution are retrieved. The Ca content in the solution is determined using ICP-OES. 2+ Mg 2+ Si 4+ Plasma concentration changes; a small amount of core powder was taken for XRD and XRF tests to obtain the conversion amount of carbonate and silicate minerals (i.e., mineralization mass fraction λ).

[0064] Step 2: Non-destructive in situ magnetic resonance imaging (NMR-MRI) with dynamic biphasic displacement (1) Installation of the clamp and vacuum saturation: The complete core columns with different reaction times (0d-30d) obtained in step 1 are wrapped with heat shrink tubing and installed in a nuclear magnetic core clamp equipped with non-magnetic Teflon material. After vacuuming to -0.1MPa, the cores are 100% saturated with the brine mentioned above.

[0065] (2) Testing background NMR parameters: The initial T2 spectrum of the core under full water saturation was tested using CPMG sequence (polarization time Tw=5000ms, echo time TE=0.1ms, echo number NE=15000, number of scans 32), and the current effective porosity φ and mean pore size μ under this reaction stage were calculated. T2 and the standard deviation of aperture σ T2 .

[0066] (3) Supercritical CO2 displacement and real-time monitoring Maintain the external pressure of the clamping device 5 MPa higher than the inlet pressure. Turn on the advection pump and inject supercritical CO2 into the core at a constant flow rate of 0.1 mL / min (maintaining the injection temperature at 80℃ and the pressure at 30 MPa). Control the fluid flow at the outlet using a backpressure valve and record the production volume using a metering balance.

[0067] In-situ real-time acquisition: During the displacement process that lasts for several hours, CPMG sequence tests were performed every 5 minutes to obtain real-time T2 spectra, and SE sequence tests were performed every 10 minutes to obtain two-dimensional MRI images.

[0068] Residual water state determination: When the brightness distribution in the MRI image (bright areas represent water, dark areas represent supercritical CO2) reaches stability, and the rate of change of the integrated area of ​​the T2 spectrum is less than 1% for three consecutive times, it is determined that the displacement front has been breached, and the water in the pores has been displaced to the residual state, thus ending the test. The current actual residual water saturation (S) is calculated based on the product flow rate at the outlet. r w).

[0069] (4) Experimental results showed that Core from day 0 of reaction: T2 spectrum shows a distinct single peak (μ T2 = 48.2 ms), the limit is calculated to be S r w is 22.1%.

[0070] Core samples after 7 days of reaction: Due to the dissolution of early carbonate minerals (calcite, etc.), the porosity slightly increased from 18.2% to 19.5%, and the main pore throat enlarged (μm). T2 = 55.1ms), capillary resistance decreases, making it easier for CO2 to break through, leading to S r w decreased to 18.6%.

[0071] Core samples taken at 15 and 30 days: Due to ion enrichment in formation fluids, secondary minerals such as calcite and kaolinite begin to precipitate and block micro-throats. The pore structure becomes heterogeneous, and the T2 spectrum changes from a single peak to a double peak (with the appearance of a secondary peak reflecting the retention in micropores, and the radial variance σ). T2 (significantly increased to 68ms), capillary retention effect was greatly enhanced, and finally S r w abnormally climbed to 34.7%.

[0072] Step 3: Construction and numerical simulation of a multivariate nonlinear coupling model (1) Based on the total time series data obtained from the above 5 sets of experiments, a new multivariate dynamic residual water evolution equation was established using a multivariate nonlinear regression algorithm.

[0073]

[0074] For the target strata of the Baoding Depression in this embodiment, the calculated fitting parameters are: a=0.85, b=1.2, c=-0.32, d=0.6, e=-0.18, f=0.45, g=0.21, h=0.73, and the goodness of fit R² = 0.963.

[0075] (3) Multi-field coupled numerical simulation: The above equations were incorporated into the TOUGHREACT simulation software as external modules via source code-level embedding (replacing the software's current default static van Genuchten formula). A two-dimensional heterogeneous grid model of the deep saline aquifer in the Baoding Depression was established in the software, and geological parameters of the target area were input to simulate the continuous CO2 injection process over the next 10 years.

[0076] (4) Evolution results output Computer output results show that as the CO2 plume moves across different heterogeneous grids, different grid locations experience varying degrees of water-rock reaction. Residual water saturation is not constant across the entire time domain, dynamically exhibiting a synergistic evolution effect: an initial decrease in the injection center followed by an increase at the peripheral reaction front due to precipitation. At a 10-year timescale, the lower limit of the overall storage potential prediction for the experimental site is increased by 11.4% compared to traditional methods. The error between the predicted Sᵣw value and field monitoring in the 10-year storage simulation is less than 5%, providing a visualized early warning of the safety threshold.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. These modifications or substitutions, or combinations of technical features in the above embodiments that do not conflict with each other, can be made in accordance with the manner described in the embodiments. These modifications, substitutions or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-parameter co-evolutionary study method for CO2-water-rock geochemical processes, characterized in that, Includes the following steps: S1. Perform gradient-time high-temperature and high-pressure static water-rock reaction on the target reservoir core. The reaction conditions are temperature 50-90℃, pressure 15-35MPa, and the reaction medium is simulated formation brine. S2. Supercritical CO2 dynamic displacement experiments were conducted on core samples from each reaction stage. During the displacement process, nuclear magnetic resonance T2 spectra, MRI images, and outlet flow-pressure data were collected simultaneously. S3. Based on the mineral composition of S1 and the pore structure parameters of step S2, construct the residual water saturation S r w is related to porosity φ, carbonate mineral content λ, and mean T2 distribution μ. T2 and standard deviation σ T2 Quantitative functional relationship; S4. Embed the function into the multiphase reaction-percolation coupled numerical model TOUGHREACT to achieve long-term dynamic prediction of the co-evolution of pore structure and residual water during CO2 sequestration.

2. The multi-parameter cooperative evolution research method according to claim 1, characterized in that, In S1, the gradient times selected for the experiment included 0d, 3d, 7d, 15d, and 30d.

3. The multi-parameter cooperative evolution research method according to claim 1, characterized in that, In S2, the nuclear magnetic resonance T2 spectrum acquisition uses the CPMG sequence, with a polarization time Tw=5000ms, echo time TE=0.1ms, echo number NE=15000, and 32 scans; the MRI image uses the SE sequence, with a spatial resolution of 50μm.

4. The multi-parameter cooperative evolution research method according to claim 1, characterized in that, In S3, the residual water saturation S r The quantitative function form of w is: Formula I Wherein: S r w represents residual water saturation (%), φ represents porosity, and λ represents carbonate mineral content (wt.%). T2 Let σ be the mean of the distribution of T2. T2 denoted as the standard deviation of the T2 distribution; a to h are experimental fitting parameters, determined through nonlinear regression.

5. The multi-parameter cooperative evolution research method according to claim 1, characterized in that, The static water-rock reaction and dynamic displacement experiments used the same batch of core samples to avoid systematic errors caused by sample differences.

6. The multi-parameter cooperative evolution research method according to claim 1, characterized in that, The experimental setup in S2 includes a gas injection control system, a liquid injection control system, and a core clamping system. The gas injection control system and the liquid injection control system are configured to inject carbon dioxide and water at controllable pressure or flow rate, respectively. The two fluids, carbon dioxide and water, are mixed in the confluence pipeline and then introduced into the core clamping system. The core holding system is used to simulate the real underground reaction environment of high temperature and high pressure in deep strata. It includes a core holder, an axial pressure system, and a confining pressure-temperature control system. The core holder is encapsulated with a rock sample core drilled from underground or a simulated core that is artificially pressed. The injected fluid seeps and reacts chemically inside the micropores of the core. The axial pressure system applies axial stress to the core end face through an axial pressure pump and a pressure-transmitting piston; the confining pressure-temperature control system injects and circulates a fluid medium with a preset temperature in the annulus between the core and the core holder shell through a confining pressure tracking pump and a circulation pump; this fluid medium serves both as a pressure-transmitting medium to simulate the geostress borne by underground rocks and as a heat-transmitting medium to provide a thermal field for the water-rock reaction inside the holder and to maintain the supercritical state of carbon dioxide. Pressure sensors are respectively installed at the inlet and outlet ends of the core holder, and a nuclear magnetic resonance detector is installed around the core holder.

7. The multi-parameter cooperative evolution research method according to claim 6, characterized in that, The testing device also includes a back pressure system and a gas flow meter; The back pressure system is connected downstream of the outlet end of the core holder and is used to simulate the real pore fluid back pressure conditions of the formation and to achieve the retention and measurement of the produced material. The gas flow meter is installed at the exhaust end and is used to dynamically measure the instantaneous flow rate of the gas flowing out of the core holder.

8. The multi-parameter cooperative evolution research method according to claim 6, characterized in that, In S2, during the dynamic displacement experiment, the core holder integrates an independent confining pressure system and a back pressure valve to ensure that there is no gas bypass leakage during the displacement process.

9. The multi-parameter cooperative evolution research method according to claim 8, characterized in that, The pressure of the confining pressure system is 5 MPa higher than the inlet pressure, and the outlet pressure of the back pressure valve is 2 MPa lower than the inlet pressure.

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