A method for evaluating carbon dioxide geological storage capacity considering the influence of caprock tightness

Abstract

The application discloses a kind of carbon dioxide geological storage quantity evaluation methods considering the influence of caprock tightness, obtains the structural surface and thickness distribution of caprock using three-dimensional geological model;Obtain the variation law of caprock breakthrough pressure with depth;Obtain the hydraulic fracturing pressure of caprock rock, and draw the caprock rock failure envelope and caprock breakthrough pressure;Based on caprock breakthrough pressure, reservoir and caprock fracture pressure, finally determine the maximum allowable reservoir pressure;Using the maximum reservoir pressure after different regional reservoir maximum allowable carbon dioxide injection, obtain the regional saline aquifer carbon dioxide limit storage capacity distribution map, and determine the limit storage potential of region, solve the problem that current carbon dioxide geological storage quantity evaluation method does not consider the influence of caprock tightness;The method breaks through the current reservoir pressure cannot exceed the basic theory of caprock breakthrough pressure, provides a new idea for carbon dioxide geological storage potential evaluation, suitable for large-scale carbon dioxide geological utilization and storage.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide geological utilization and storage, specifically to a method for assessing the amount of carbon dioxide geologically stored, taking into account the influence of caprock sealing. Background Technology

[0002] Carbon dioxide geological storage (CCS) is currently one of the most effective measures to reduce direct carbon dioxide emissions, involving the long-term storage of supercritical carbon dioxide injected into deep formations using industrial technology. Ensuring safe and efficient carbon dioxide storage is crucial. Current methods for assessing carbon dioxide storage capacity include material balance calculations, effective volumetric storage methods, dissolution mechanism methods, and comprehensive methods considering multiple capture mechanisms. However, none of these methods take into account the impact of caprock tightness.

[0003] Currently, the assessment process and methods for the ultimate geological storage capacity of carbon dioxide mainly face the following technical challenges:

[0004] (1) Lack of a systematic assessment process for carbon dioxide geological reserves that considers the impact of caprock sealing. Since assessing carbon dioxide geological reserves is a systematic project, current methods for calculating reserves do not consider the impact of caprock sealing, resulting in different assessment processes for the ultimate geological reserves of carbon dioxide. Therefore, it is urgent to establish an assessment process for the ultimate geological reserves of carbon dioxide.

[0005] (2) The assessment methods for carbon dioxide geological reserves are inadequate. Current methods for assessing the ultimate potential for carbon dioxide geological reserves do not consider the impact of caprock sealing, thus the assessment methods are inadequate. Therefore, there is an urgent need to improve the assessment methods for carbon dioxide geological reserves.

[0006] In summary, there is an urgent need to invent a process and method for assessing carbon dioxide geological reserves that takes into account the airtightness of caprocks. This would solve the current problems of a lack of assessment processes and imperfect assessment methods for carbon dioxide geological reserves, and provide technical assurance for ensuring safe and efficient geological storage of carbon dioxide. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a method for assessing the geological carbon dioxide sequestration volume considering the influence of caprock sealing. This method is simple and easy to use, and provides technical support for the assessment of geological carbon dioxide sequestration volume and efficient and safe sequestration.

[0008] To achieve the above objectives, the present invention employs the following technical measures:

[0009] A method for assessing the geological carbon dioxide sequestration capacity considering the impact of caprock tightness, comprising the following steps:

[0010] Step 1: Use a 3D geological model to obtain the structural planes and thickness distribution maps of the caprock;

[0011] Step 2: Based on the breakthrough pressure laboratory experiment, the variation law of the caprock breakthrough pressure with depth was obtained. By fitting the relationship between the caprock breakthrough pressure and depth, the variation law of the caprock breakthrough pressure with depth is as follows:

[0012] P b =AH+B

[0013] In the formula: P b The caprock breakthrough pressure is MPa; H is the caprock thickness in meters; A and B are constants obtained through experimental testing.

[0014] Step 3: Based on the results of indoor mechanical experiments, obtain the hydraulic fracturing pressure of the caprock and draw the failure envelope of the caprock. At the same time, draw the breakthrough pressure of the caprock into the failure envelope of the caprock.

[0015] Step 4: Assuming that the sealing performance meets the requirements when the caprock thickness limit is 100m, in order to increase the carbon dioxide sequestration, the carbon dioxide can be injected into the reservoir at a pressure exceeding the breakthrough pressure, but it must be less than the minimum horizontal principal stress of the caprock. The reservoir pore pressure is determined based on the carbon dioxide penetration depth of the caprock.

[0016] Step 5: If the carbon dioxide cap layer is greater than 100m, under the condition of ensuring the airtightness of the carbon dioxide storage cap layer, the pressure generated by the carbon dioxide entering the cap layer is (H-100)m.

[0017] ρg(H-100)MPa

[0018] Step 6: The maximum reservoir pressure after carbon dioxide injection can be expressed as:

[0019] P max =P b +ρg(H-100)

[0020] In the formula: ρ is the density of saline water, kg / m³ 3 g is the acceleration due to gravity, in m / s². 2 ;

[0021] To ensure that the reservoir and caprock do not leak carbon dioxide due to hydraulic fracturing, the maximum reservoir pressure after carbon dioxide injection must not exceed 0.85 times the minimum horizontal principal stress of the reservoir or caprock, i.e.:

[0022] P max ≤min(0.85δ Hf 0.85δ Hc )

[0023] In the formula, δ Hf The minimum horizontal principal stress of the reservoir is given in MPa; δ Hc The minimum horizontal principal stress of the caprock is given in MPa.

[0024] Step 7: Based on the caprock thickness maps of different regions obtained in Step 1, determine the maximum reservoir pressure and the distribution map of the maximum carbon dioxide sequestration capacity of the saline water layer in different regions after carbon dioxide injection through Steps 1 to 6, and determine the ultimate sequestration potential of the region.

[0025] Preferably, if P max ≤min(0.85δ Hf 0.85δ Hc If the pressure increment of the reservoir is such that the pressure increment is 0, then the pressure increment of the reservoir can be expressed as:

[0026] △P f =P b +ρg(H-100)-P fi

[0027] In the formula: P fi The original reservoir pressure is given in MPa.

[0028] Preferably, if P max >min(0.85δ) Hf 0.85δ Hc If the pressure increment of the reservoir is such that the pressure increment is 0, then the pressure increment of the reservoir can be expressed as:

[0029] △P f =min(0.85δ) Hf 0.85δ Hc )-P fi

[0030] The preferred formula for calculating the maximum carbon dioxide sequestration capacity of a regional saline aquifer is as follows:

[0031] Q max =ρ CO2 ADΦ(CR+CW)ΔP f

[0032] In the formula, Q represents the regional saline aquifer sequestration capacity (kg); A represents the theoretical reservoir area (m²). 2 D is the reservoir thickness, in meters; Φ is the effective porosity (<1); ΔP f C represents the pressure increment of the reservoir (MPa); R C represents the rock compressibility. w ρ is the compressibility of water. CO2 The density of carbon dioxide (kg / m³) 3 ).

[0033] Through the above seven technical measures, steps 1-7 are the key steps. These key steps mainly solve the problem that current methods for assessing carbon dioxide geological reserves do not consider the influence of caprock tightness, thus achieving a reasonable assessment of carbon dioxide geological reserves that takes into account the caprock tightness. Compared with existing technologies, the beneficial effect of this invention is that it breaks through the current fundamental theory that reservoir pressure cannot exceed caprock breakthrough pressure, providing a new approach to evaluating carbon dioxide geological storage potential and making it applicable to large-scale carbon dioxide geological utilization and storage. Attached Figure Description

[0034] Figure 1 A schematic diagram illustrating the distribution characteristics and evaluation of caprock sealing pressure in a method for assessing the geological carbon dioxide sequestration capacity that takes into account the influence of caprock sealing.

[0035] Figure 2 This is a schematic diagram illustrating the quantitative assessment of the risk of caprock hydraulic fracturing in a method for assessing the geological carbon dioxide sequestration considering the impact of caprock tightness.

[0036] Figure 3 A schematic diagram of the geostress field of the target block for a method to assess the geological carbon dioxide sequestration capacity that takes into account the effect of caprock tightness.

[0037] Figure 4 This diagram illustrates the risk of hydraulic fracturing in the reservoir-caprock as part of a method for assessing the geological carbon dioxide sequestration capacity that takes into account the sealing properties of the caprock.

[0038] Figure 1 The target block shows high sealing pressure in the northeast and southwest, and low sealing pressure in the southeast. The maximum sealing pressure in the northeast exceeds 50 MPa; therefore, the injection well should be located in the northeast of the block. Figure 2 It can be seen that the Mohr circle of the caprock in the target block will move to the left, to the fracture envelope where the rock fractures. Figure 3 The geostress field of the reservoir (1400-1700m) and caprock (1300-1400m). Figure 4 The minimum and maximum principal stresses of the reservoir and caprock are then plotted on the stress curve. Figure 4 The pore pressure increment of hydraulic fracturing in the middle reservoir is 14.36-16.98 MPa, while that of hydraulic fracturing in the caprock is 10.86-12.75 MPa, and the caprock breakthrough pressure is 12.88-13.57 MPa. Therefore, the risk of leakage due to hydraulic fracturing in the caprock of the target block is higher than the risk of leakage due to carbon dioxide breakthrough in the intact caprock. Detailed Implementation

[0039] 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 merely illustrative and not intended to limit the invention.

[0040] Example 1:

[0041] A method for assessing the geological carbon dioxide sequestration capacity considering the impact of caprock tightness, comprising the following steps:

[0042] (1) Characteristics and evaluation of pressure distribution in caprock sealing

[0043] The basic formation parameters of the target block are shown in Table 1. Meanwhile, formation pressure, caprock breakthrough pressure, and formation temperature were determined through experiments and data surveys. The variation of formation pressure with depth is as follows:

[0044] P F =0.009897z - 0.0227

[0045] The variation law of caprock breakthrough pressure with depth is as follows:

[0046] P b =0.01z-0.125

[0047] The variation of formation temperature with depth is as follows:

[0048] T = 0.034z + 0.125

[0049] Table 1 Basic stratigraphic parameters of the target block

[0050]

[0051] like Figure 1 As shown in the figure, the sealing pressure distribution characteristics and evaluation diagram of the caprock are as follows: the sealing pressure is high in the northeast and southwest of the target block, and low in the southeast; the maximum sealing pressure in the northeast of the target block exceeds 50 MPa; it is reasonable to recommend that the injection well be set in the northeast block.

[0052] (2) Limits for hydraulic fracturing of caprock and safe CO2 sequestration

[0053] 1) Quantitative analysis of hydraulic fracturing of caprock

[0054] like Figure 2 The diagram shown illustrates the risk assessment of hydraulic fracturing in the caprock. When CO2 is injected, the Mohr's circle of the rock will move to the left until it reaches the composite fracturing envelope, at which point the rock will fracture. Figure 3The geostress field of the target block is shown, with the target reservoir at a depth of 1400-1700m and the caprock at 1300-1400m. This section plots the minimum and maximum principal stresses of the reservoir and caprock on stress curves. The hydraulic fracturing risk of the reservoir and caprock is obtained by deriving the composite fracturing envelope. Figure 4 As shown, by Figure 4 The pore pressure increments obtained from hydraulic fracturing of the reservoir were 14.36-16.98 MPa, those from hydraulic fracturing of the caprock were 10.86-12.75 MPa, and the caprock breakthrough pressure was 12.88-13.57 MPa. The leakage risk from hydraulic fracturing of the caprock was higher than the risk of CO2 breakthrough of the intact caprock.

[0055] 2) Limit values ​​for CO2 sequestration considering the impact of cap layer airtightness

[0056] Formula for calculating CO2 sequestration capacity in regional saline aquifers:

[0057] Q = A·D·Φ·(C R +C W )·ΔP·ρ (4)

[0058] In the formula, Q is the amount of material stored (kg); A is the theoretical area of ​​the reservoir (m²). 2 D is the reservoir thickness, in meters; Φ is the effective porosity (<1); ΔP is the increased pressure difference (MPa); C R C represents the rock compressibility. w ρ is the compressibility of water. CO2 The density of CO2 (kg / m³) 3 ).

[0059] The CO2 sequestration amounts for the first, second, and third sub-segments of the target block are obtained using equation (4), as shown in Table 2. In summary, the safe sequestration amount for the target block is approximately (2.14 - 2.60) × 10⁻⁶. 7 ton.

[0060] Table 2. CO2 safe storage capacity of a certain block

[0061]

[0062] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for assessing the geological reserves of carbon dioxide considering the influence of caprock sealing, characterized in that, The steps are as follows: Step 1: Use a 3D geological model to obtain the structural planes and thickness distribution maps of the caprock; Step 2: Based on the breakthrough pressure laboratory experiment, the variation law of the caprock breakthrough pressure with depth was obtained. By fitting the relationship between the caprock breakthrough pressure and depth, the variation law of the caprock breakthrough pressure with depth is as follows: P b =AH+B In the formula: P b The caprock breakthrough pressure is MPa; H is the caprock thickness in meters; A and B are constants obtained through experimental testing. Step 3: Based on the results of indoor mechanical experiments, obtain the hydraulic fracturing pressure of the caprock and draw the failure envelope of the caprock. At the same time, draw the breakthrough pressure of the caprock into the failure envelope of the caprock. Step 4: Assuming that the sealing performance meets the requirements when the caprock thickness limit is 100m, in order to increase the carbon dioxide sequestration, the carbon dioxide can be injected into the reservoir at a pressure exceeding the breakthrough pressure, but it must be less than the minimum horizontal principal stress of the caprock. The reservoir pore pressure is determined based on the carbon dioxide penetration depth of the caprock. Step 5: If the carbon dioxide cap layer is greater than 100m, under the condition of ensuring the airtightness of the carbon dioxide storage cap layer, the thickness of the carbon dioxide entering the cap layer is (H-100)m, and the pressure generated by the carbon dioxide entering the cap layer is ρg(H-100)Pa. Step 6: The maximum reservoir pressure after carbon dioxide injection is expressed as: P max =P b +ρg(H-100)×10 -6 In the formula: ρ is the density of saline water, kg / m³ 3 g is the acceleration due to gravity, in m / s². 2 ; To ensure that the reservoir and caprock do not leak carbon dioxide due to hydraulic fracturing, the maximum reservoir pressure after carbon dioxide injection must not exceed 0.85 times the minimum horizontal principal stress of the reservoir or caprock, i.e.: P max ≤min(0.85δ Hf ,0.85δ Hc ) In the formula, δ Hf The minimum horizontal principal stress of the reservoir is given in MPa; δ Hc The minimum horizontal principal stress of the caprock is given in MPa. The pressure increment of the reservoir is expressed as: ΔP f =P b +ρg(H-100)-P fi ; In the formula: P fi The original reservoir pressure is given in MPa. The P mentioned max >min(0.85δ) Hf 0.85δ Hc If the pressure increment of the reservoir is expressed as: △P f =min(0.85δ Hf ,0.85δ Hc )-P fi ; The formula for calculating the maximum carbon dioxide sequestration capacity of the saline aquifer is as follows: Q max =ρ CO2 ADΦ(CR+CW)ΔP f In the formula, Q represents the regional saline aquifer sequestration capacity (kg); A represents the theoretical reservoir area (m²). 2 D is the reservoir thickness, in meters; Φ is the effective porosity, Φ < 1; ΔP f For reservoir pressure increments, MPa; C R C represents the rock compressibility. w ρ is the compressibility of water. CO2 Density of carbon dioxide, kg / m³ 3 ; Step 7: Based on the caprock thickness maps of different regions obtained in Step 1, and then using the maximum reservoir pressure and the distribution maps of the maximum carbon dioxide sequestration potential of the saline water layer after carbon dioxide injection in different regions determined in Steps 1 to 6, determine the region's maximum sequestration potential.

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