Method for evaluating dissolution and storage rate and storage quantity of CO2 in saline water layer by considering solid-phase dissolution

Abstract

The invention relates to the technical field of CO2 geological sequestration, in particular to a saline water layer CO2 dissolution sequestration rate and sequestration quantity evaluation method considering solid phase dissolution. The method comprises the steps that a salt water layer physical model is established, and stratum environment attribute values are obtained; carrying out computational domain grid division on the physical model, and determining a numerical simulation boundary condition according to the stratum environment attribute value; constructing a mathematical model related to dissolution and storage of CO2 in the saline water layer; coupling a mathematical model related to dissolution and storage of CO2 in the salt water layer, carrying out numerical simulation of dissolution and storage of CO2 in the salt water layer, and obtaining CO2 concentration distribution and calcium bicarbonate concentration distribution conditions of the salt water layer at different moments; according to the CO2 concentration distribution and calcium bicarbonate concentration distribution conditions of the salt water layer at different moments, the dissolution and storage rate and storage amount of CO2 in the salt water layer are evaluated. In the simulation process, the chemical reaction caused by the salt water layer CO2 dissolution process is considered, and the salt water layer CO2 dissolution storage rate and storage amount can be accurately evaluated.

Description

Technical Field

[0001] The present invention relates to CO 2 The technical field of geological storage specifically relates to a method for evaluating the CO2 dissolution storage rate and storage capacity of saline layers taking solid phase dissolution into consideration. Background Art

[0002] Saline CO 2 Geological storage is the process of storing large amounts of CO2 emitted by humans / industry. 2 The gas is injected into a large-scale saline aquifer with a stable closed structure, and the CO is stored in the aquifer based on the mechanisms of structural storage, dissolution storage, capillary storage and mineralization storage. 2 Long-term storage underground can achieve the purpose of carbon emission reduction. 2 Dissolution storage is recognized as the most promising long-term safe storage mechanism.

[0003] CO injected into saline aquifers 2 First, it contacts the underground fluid in the saline aquifer (i.e., formation brine) and reacts with CO 2 The molecular form dissolves in salt water, triggering the dissolution and storage mechanism. The dissolution rate and storage amount are usually closely related to the environmental conditions and the properties of the saline layer.

[0004] CO partially dissolved in brine 2 It reacts with salt water to form H 2 CO 3 , and ionizes to produce H + , making the underground fluid weakly acidic, destroying the original physical and chemical balance of the formation and inducing CO 2 The physical and chemical reaction between salt water and formation rock minerals. This reaction consumes a lot of H + , promoting dissolved H 2 CO 3 Ionization continues to occur, accelerating the CO 2 dissolution process. In addition, CO 2 - The brine-rock interaction will change the physical properties of the saline aquifer rock, such as porosity and permeability, which will further affect the CO 2 Dissolution storage rate and storage potential.

[0005] However, existing studies on saline CO 2 Evaluation of dissolution storage rate and storage capacity rarely considers CO 2 - The chemical reactions between salt water and rocks and their effects on the properties of saline aquifers cannot effectively guide the CO 2 Assessment of solution storage potential. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a method for evaluating the dissolution storage rate and storage capacity of saline CO2 taking into account solid phase dissolution. 2 The chemical reactions triggered by the dissolution process can more accurately assess the CO 2 Dissolution storage rate and storage volume.

[0007] In order to solve the above technical problems, the technical solution of the present invention is: a method for evaluating the dissolution storage rate and storage capacity of CO2 in saline water layers considering solid phase dissolution, the method comprising:

[0008] Establish a physical model of the saline layer and obtain the values ​​of the formation environment attributes;

[0009] Divide the computational domain of the physical model into grids and determine the numerical simulation boundary conditions according to the formation environment attribute values;

[0010] Constructing saline CO 2 Mathematical models involved in dissolution storage, including CO 2 The equations for flow and diffusion in saline aquifers, the kinetic equations for the evolution of solid concentration and reaction product concentration in saline aquifers, and the equations for updating fluid density, porosity, and permeability;

[0011] Coupled saline layer CO 2 The mathematical model involved in dissolution storage uses the rare species transport module and Darcy's law module in Comsol multi-physics simulation software to carry out the CO2 storage in saline aquifers. 2 Numerical simulation of dissolved storage to obtain CO in saline water layers at different times 2 Concentration distribution and calcium bicarbonate concentration distribution in saline water layer at different times;

[0012] According to the distribution of CO2 concentration in the saline layer at different times and the distribution of calcium bicarbonate concentration in the saline layer at different times, the CO 2 Dissolution storage rate and storage volume.

[0013] Furthermore, the boundary conditions of the numerical simulation are as follows: the upper boundary of the computational domain adopts the CO2 saturation concentration boundary, and the other three boundaries adopt the non-permeable boundaries;

[0014] CO 2 The saturation concentration is determined based on the ambient temperature and pressure of the formation environmental property values.

[0015] Furthermore, CO 2 The flow and diffusion equations in the saline layer are:

[0016]

[0017]

[0018] The kinetic equation for the evolution of solid phase concentration and reaction product concentration in the saline layer is:

[0019]

[0020] Fluid density real-time update equation:

[0021]

[0022] The updated equation for the porosity of saline water layer is:

[0023]

[0024] The updated equation for the permeability of the saline layer is:

[0025]

[0026] Where φ is the porosity of the saline layer (-); ρ w is the fluid density (kg / m 3 ); t is time (s); u is fluid velocity (m / s); k is the permeability of the saline layer (m 2 ); μ w is the fluid dynamic viscosity (Pa·s); p is the fluid pressure (Pa); g is the gravitational acceleration (m / s 2 );c CO2 CO in the fluid 2 Concentration (mol / m 3 ); D is the diffusion coefficient (m 2 / s); k r is the reaction rate constant (m 4 / (mol·s)); a v is the solid phase reaction specific surface area (m -1 ); is the concentration of calcium carbonate in the saline layer (mol / m 3 ), calcium carbonate is the main mineral that undergoes solid phase dissolution in saline water layers, and the dissolution product is Ca(HCO 3 ) 2 , is the concentration of calcium bicarbonate in the saline layer (mol / m 3 ), ρ w,0 is the initial density of the formation fluid (kg / m 3 ), β is the volume expansion coefficient (kg / mol), M CaCO3 and ρ CaCO3 The molar mass (kg / mol) and density (kg / m 3 );φ 0 With k 0 are the initial porosity (-) and permeability (m2 ).

[0027] Furthermore, the evaluation of saline CO 2 The evaluation model for dissolution storage rate is:

[0028]

[0029] In the formula, c CO2 CO in the fluid 2 Concentration (mol / m 3 ), is the concentration of calcium carbonate in the saline layer (mol / m 3 ), is the CO2 dissolution storage rate in saline water layer (mol / (m 3 ·s)).

[0030] Furthermore, the evaluation of saline CO 2 The storage volume assessment model is:

[0031]

[0032] In the formula, For saline layer CO 2 Total molar amount of dissolved and stored (mol); n CO2(aq) The CO in the saline layer 2 CO in the form of 2 Total molar amount (mol); n Ca(HCO3)2 V is the total molar amount of calcium bicarbonate produced by the dissolution of calcium carbonate in the saline layer (mol); 咸水层 To assess the volume of saline aquifer in the region (m 3 ); For saline layer CO 2 Total dissolved sealed mass (kg); For CO 2 Molar mass (kg / mol).

[0033] After adopting the above technical solution, the present invention fully considers CO 2 - Chemical reactions between fluids and rocks, changes in porosity and permeability of saline aquifers caused by chemical reactions, and CO 2The influence of the concentration of dissolved in formation fluid and the concentration of chemical reaction products on the density of formation fluid is coupled to the flow and diffusion model of CO2 in saline aquifers, the solid phase dissolution kinetic model, the fluid density update and the porosity and permeability evolution equation of saline aquifers, etc., to more comprehensively consider the dynamic evolution characteristics of the physical properties of rocks and fluids caused by physical and chemical reactions in the process of CO2 dissolution and storage in saline aquifers, and carry out numerical simulation of CO2 dissolution and storage in saline aquifers. According to the numerical simulation results, the dissolution and storage rate and storage capacity of CO2 dissolution and storage in saline aquifers under the condition of changes in the physical properties of saline aquifers can be effectively and accurately evaluated, thereby providing guidance for the geological storage of CO2 in saline aquifers. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A flow chart of a method for evaluating the CO2 dissolution storage rate and storage capacity of a saline layer taking solid phase dissolution into consideration according to the present invention;

[0035] Figure 2 A physical model diagram used for calculations in embodiments of the present invention;

[0036] Figure 3 The saltwater layer CO at different times obtained by simulation in the embodiment of the present invention 2 Schematic diagram of concentration distribution;

[0037] Figure 4 This is a schematic diagram of the calcium carbonate concentration distribution of the saline layer at different times obtained by simulation in an embodiment of the present invention;

[0038] Figure 5 This is a schematic diagram of the distribution of calcium bicarbonate concentration in the saline layer at different times obtained by simulation in an embodiment of the present invention;

[0039] Figure 6 The saline layer CO in the embodiment of the present invention 2 Schematic diagram of the evolution of dissolution and storage rate. DETAILED DESCRIPTION

[0040] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments in conjunction with the accompanying drawings.

[0041] This embodiment provides a saltwater layer CO considering solid phase dissolution 2 Methods for assessing dissolution storage rate and storage volume, such as Figure 1 As shown, the specific steps include:

[0042] Step S1, determining the saline layer CO 2In the dissolution and sealing assessment area, the physical property values ​​of the saline layer and formation fluid in the selected area, as well as the formation environmental property values, are obtained; wherein the physical property values ​​include the initial porosity and initial permeability of the saline layer, the fluid viscosity and initial density, and the formation environmental property values ​​include the ambient temperature and pressure.

[0043] Among them, in CO 2 During the dissolution process, the porosity and permeability of the saline layer and the fluid density change dynamically, while the fluid viscosity and the ambient temperature and pressure remain basically unchanged.

[0044] Step S2: Conduct saline CO2 analysis in the selected physical area. 2 Numerical simulation of dissolution storage, the specific steps include:

[0045] Step S21, divide the selected physical area into computational domain grids and determine the upper boundary of the computational domain using CO 2 The saturated concentration boundary is used, and the other three boundaries are impermeable boundaries; among them, CO 2 Saturation concentration is determined based on the ambient temperature and pressure of the formation environmental property values;

[0046] Step S22, constructing a saltwater layer CO 2 The mathematical models involved in dissolution storage include:

[0047] (i)CO 2 Flow and diffusion equations in a saline layer:

[0048]

[0049] Where φ is the porosity of the saline layer (-); ρ w is the fluid density (kg / m 3 ); t is time (s); u is fluid velocity (m / s); k is the permeability of the saline layer (m 2 ); μ w is the fluid dynamic viscosity (Pa·s); p is the fluid pressure (Pa); g is the gravitational acceleration (m / s 2 );c CO2 CO in the fluid 2 Concentration (mol / m 3 ); D is the diffusion coefficient (m 2 / s); k r is the reaction rate constant (m 4 / (mol·s)); a v is the solid phase reaction specific surface area (m -1 );c CaCO3 is the concentration of calcium carbonate in the saline layer (mol / m 3), calcium carbonate is the main mineral that undergoes solid phase dissolution in saline water layers, and the dissolution product is Ca(HCO 3 ) 2 , is the concentration of calcium bicarbonate in the saline layer (mol / m 3 ).

[0050] (ii) Kinetic equations for the evolution of solid phase concentration and reaction product concentration in the saline water layer:

[0051]

[0052] (iii) Considering CO in saline aquifers 2 The influence of concentration and solid dissolved products on fluid density is used to construct a real-time update equation for fluid density:

[0053]

[0054] In the formula, ρ w,0 is the initial density of the formation fluid (kg / m 3 );β is the volume expansion coefficient (kg / mol).

[0055] (iv) Considering the effect of solid phase dissolution on the pore structure and permeability of the saline aquifer, the porosity and permeability evolution equation of the saline aquifer is constructed:

[0056]

[0057] Where M CaCO3 and ρ CaCO3 The molar mass (kg / mol) and density (kg / m 3 );φ 0 With k 0 are the initial porosity (-) and permeability (m 2 ).

[0058] Step S23, coupling the mathematical model constructed in step S22, using the rare species transfer module and Darcy's law module in the Comsol multi-physics simulation software to carry out the saltwater layer CO 2 Numerical simulation of dissolved storage to obtain CO in saline water layers at different times 2 Concentration distribution and calcium bicarbonate concentration distribution in saline water layer at different times;

[0059] Step S3, establishing saline layer CO 2 Dissolution storage rate assessment model, assuming that CO dissolved in saline aquifers 2 Only CO 2 With Ca(HCO 3 ) 2 Existence in the form of:

[0060]

[0061] Step S4, using equations (1)-(7), calculate CO 2 Dissolution storage process CO 2 concentration, product Ca(HCO 3 ) 2 concentration and porosity of the saline layer, and then establish the saline layer CO 2 Model for evaluating the evolution of dissolved storage over time:

[0062]

[0063] Where n CO2,总 For saline layer CO 2 Total molar amount of dissolved and stored (mol); n CO2(aq) The CO in the saline layer 2 CO in the form of 2 Total molar amount (mol); n Ca(HCO3)2 V is the total molar amount of calcium bicarbonate produced by the dissolution of calcium carbonate in the saline layer (mol); 咸水层 To assess the volume of saline aquifer in the region (m 3 ); For saline layer CO 2 Total dissolved sealed mass (kg); For CO 2 Molar mass (kg / mol).

[0064] The solutions involved in the above embodiments are described in detail below in conjunction with specific embodiments.

[0065] The selected area of ​​the saline layer is a cube with a side length of 1m. Under given conditions, the formation fluid CO 2 The saturation concentration is about 1.2 mol / L, the volume fraction of calcium carbonate in the saline layer is about 30%, and the density of calcium carbonate is 2700 kg / m 3 , the molar mass fraction is 100g / mol.

[0066] Figure 2 This is the physical model diagram used for calculation. Through numerical simulation, Figure 3 The CO of the saline layer at different times obtained based on simulation 2 Schematic diagram of concentration distribution, Figure 4 This is a schematic diagram of the calcium carbonate concentration distribution in the saline layer at different times based on simulation. Figure 5 The schematic diagram of the calcium bicarbonate concentration distribution of the saline layer at different times obtained based on the simulation is shown in Figure 2. 2 The mathematical model involved in dissolution storage calculated that after the calcium carbonate was completely dissolved, the porosity of the saline layer was 0.55, and then the CO2 content of the selected area of ​​the saline layer was calculated.2 The dissolved storage volume is about 189.42kg. Figure 5 The CO in the saline layer at different times is shown. 2 Schematic diagram of the evolution of dissolution and storage rate.

[0067] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for evaluating the CO2 dissolution storage rate and storage capacity in saline water layers taking into account solid phase dissolution, characterized in that: Methods include: Establish a physical model of the saline layer and obtain the values ​​of the formation environment attributes; Divide the computational domain of the physical model into grids and determine the numerical simulation boundary conditions according to the formation environment attribute values; Construct mathematical models for CO2 dissolution storage in saline aquifers, including the flow and diffusion equations of CO2 in saline aquifers, the kinetic equations for the evolution of solid phase concentration and reaction product concentration in saline aquifers, and the equations for updating fluid density, porosity and permeability; Couple the mathematical models involved in the CO2 dissolution storage in saline aquifers, conduct numerical simulations of CO2 dissolution storage in saline aquifers, and obtain the distribution of CO2 concentration in saline aquifers at different times and the distribution of calcium bicarbonate concentration in saline aquifers at different times; According to the distribution of CO2 concentration in the saline aquifer at different times and the distribution of calcium bicarbonate concentration in the saline aquifer at different times, the dissolution and storage rate and storage capacity of CO2 in the saline aquifer are evaluated.

2. The method for evaluating the CO2 dissolution storage rate and storage capacity of saline water layers considering solid phase dissolution according to claim 1 is characterized in that: The boundary conditions of numerical simulation are as follows: the upper boundary of the computational domain adopts the CO2 saturation concentration boundary, and the other three boundaries adopt the non-permeable boundaries; The CO2 saturation concentration is determined based on the ambient temperature and pressure of the formation environmental property values.

3. The method for evaluating the CO2 dissolution storage rate and storage capacity of saline water layers considering solid phase dissolution according to claim 1, characterized in that: The flow and diffusion equation of CO2 in the saline layer is: The kinetic equation for the evolution of solid phase concentration and reaction product concentration in the saline layer is: Fluid density real-time update equation: The updated equation for the porosity of saline water layer is: The updated equation for the permeability of the saline layer is: Where φ is the porosity of the saline layer (-); ρ w is the fluid density (kg / m 3 ); t is time (s); u is fluid velocity (m / s); k is the permeability of the saline layer (m 2 ); μ w is the fluid dynamic viscosity (Pa·s); p is the fluid pressure (Pa); g is the gravitational acceleration (m / s 2 );c CO2 is the CO2 concentration in the fluid (mol / m 3 ); D is the diffusion coefficient (m 2 / s); k r is the reaction rate constant (m 4 / (mol·s)); a v is the solid phase reaction specific surface area (m -1 ); is the concentration of calcium carbonate in the saline layer (mol / m 3 ), calcium carbonate is the main mineral that undergoes solid phase dissolution in saline water layers, and the dissolution product is Ca(HCO3)2, is the concentration of calcium bicarbonate in the saline layer (mol / m 3 ), ρ w,0 is the initial density of the formation fluid (kg / m 3 ), β is the volume expansion coefficient (kg / mol), M CaCO3 and ρ CaCO3 The molar mass (kg / mol) and density (kg / m 3 ); φ0 and k0 are the initial porosity (-) and permeability (m 2 ).

4. The method for evaluating the CO2 dissolution storage rate and storage capacity of saline water layers considering solid phase dissolution according to claim 1, characterized in that: The evaluation model for assessing the CO2 dissolution storage rate in saline aquifers is: In the formula, c CO2 is the CO2 concentration in the fluid (mol / m 3 ), is the concentration of calcium bicarbonate in the saline layer (mol / m 3 ), is the CO2 dissolution storage rate in saline water layer (mol / (m 3 ·s)).

5. The method for evaluating the CO2 dissolution storage rate and storage capacity of saline water layers considering solid phase dissolution according to claim 1, characterized in that: The evaluation model for assessing the CO2 storage capacity of saline aquifers is: In the formula, is the total molar amount of CO2 dissolved and stored in the saline layer (mol); n CO2(aq) is the total molar amount of CO2 in the saline layer in the form of CO2 (mol); n Ca(HCO3)2 V is the total molar amount of calcium bicarbonate produced by the dissolution of calcium carbonate in the saline layer (mol); 咸水层 To assess the volume of saline aquifer in the region (m 3 ); is the total dissolved CO2 storage mass in the saline aquifer (kg); is the molar mass of CO2 (kg / mol).

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