Method for evaluating geological storage quantity of carbon dioxide by considering influence of sealing performance of cover layer

Abstract

The invention discloses a carbon dioxide geological sequestration quantity evaluation method considering the influence of sealing performance of a cover layer. The method comprises the following steps: acquiring a structural plane and a thickness distribution map of the cover layer by utilizing a three-dimensional geological model; obtaining the change rule of the cap layer breakthrough pressure along with the depth; the hydraulic fracturing pressure of the cover rock is obtained, and a cover rock damage envelope line and the cover rock breakthrough pressure are drawn; and finally determining and obtaining the maximum allowable reservoir pressure based on the cap stratum breakthrough pressure, the reservoir and the cap stratum fracture pressure. The maximum reservoir pressure after maximum permissible carbon dioxide injection of reservoirs in different regions is utilized to obtain a regional saline water layer carbon dioxide limit sequestration amount distribution map, the limit sequestration potential of the regions is determined, and the problem that an existing carbon dioxide geological sequestration amount evaluation method does not consider the influence of the sealing performance of a cover layer is solved. The method breaks through the basic theory that the current reservoir pressure cannot exceed the overburden breakthrough pressure, provides a new thought for carbon dioxide geological storage potential evaluation, and is suitable for large-scale carbon dioxide geological utilization and storage.

Description

Technical Field

[0001] The present invention relates to the field of geological utilization and storage of carbon dioxide, and in particular to a method for evaluating the geological storage amount of carbon dioxide taking into account the influence of cap rock tightness. Background Art

[0002] Carbon dioxide geological storage technology (CCS) is currently the most effective measure to reduce direct carbon dioxide emissions. It uses industrial technology to inject supercritical carbon dioxide into deep formations for long-term storage. How to ensure the safe and efficient storage of carbon dioxide is crucial. At present, the evaluation of carbon dioxide storage capacity is based on the material balance storage capacity calculation method, the effective volume storage capacity calculation method, the dissolution mechanism storage capacity calculation method, and the comprehensive storage capacity calculation method considering multiple capture mechanisms. However, these methods do not consider the impact of cap rock tightness.

[0003] At present, the assessment process and method of the limit of geological storage of carbon dioxide mainly have the following technical difficulties:

[0004] (1) There is a lack of a systematic assessment process for CO2 geological storage that takes into account the impact of cap rock tightness. Since the assessment of CO2 geological storage is a systematic project, the current calculation methods of storage capacity do not take into account the impact of cap rock tightness, which determines that the assessment process of CO2 geological storage capacity is different. Therefore, it is urgent to establish an assessment process for CO2 geological storage capacity.

[0005] (2) The assessment methods for CO2 geological storage are imperfect. Since the current assessment methods for CO2 geological storage limit do not take into account the impact of caprock tightness, the assessment methods for CO2 geological storage are imperfect. Therefore, it is urgent to improve the assessment methods for CO2 geological storage.

[0006] In summary, there is an urgent need to invent a process and method for assessing the geological storage of carbon dioxide that takes into account the tightness of the cap rock, so as to solve the current problems of lack of assessment process and imperfect assessment method for geological storage of carbon dioxide, and provide technical guarantee for ensuring the safe and efficient geological storage of carbon dioxide. Summary of the invention

[0007] Based on the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for assessing the geological storage capacity of carbon dioxide taking into account the influence of the tightness of the cap rock. The method is simple and easy to use, and provides technical support for the assessment of the geological storage capacity of carbon dioxide and its efficient and safe storage.

[0008] In order to achieve the above-mentioned purpose, the present invention adopts the following technical measures:

[0009] A method for assessing the geological storage capacity of carbon dioxide taking into account the influence of cap rock tightness, the steps are as follows:

[0010] Step 1: Using a three-dimensional geological model to obtain the structural surface and thickness distribution map of the cap layer;

[0011] Step 2: Based on the breakthrough pressure indoor experiment, the variation law of the breakthrough pressure of the cap rock with depth is obtained, and the relationship between the breakthrough pressure of the cap rock and the depth is fitted. The variation law of the breakthrough pressure of the cap rock with depth is:

[0012] P b =AH+B

[0013] Where: P b is the breakthrough pressure of the caprock, MPa; H is the thickness of the caprock, m; A and B are constants obtained through experimental tests;

[0014] Step 3: Based on the results of the indoor mechanical experiment, the hydraulic fracturing pressure of the cap rock is obtained, and the failure envelope of the cap rock is drawn. At the same time, the breakthrough pressure of the cap rock is drawn into the failure envelope of the cap rock;

[0015] Step 4: Assuming that the caprock thickness limit is 100m and its airtightness meets the requirements, in order to increase the storage capacity of carbon dioxide, the carbon dioxide can be injected into the reservoir to exceed the breakthrough pressure, but it must be less than the minimum horizontal principal stress of the caprock. The reservoir pore pressure is determined according to the depth of carbon dioxide penetrating the caprock;

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

[0017] ρg(H-100)MPa

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

[0019] P max =P b +ρg(H-100)

[0020] Where: ρ is the density of salt water, kg / m 3 ; g is the acceleration due to gravity, m / s 2 ;

[0021] In order to ensure that the reservoir and cap rock will not leak carbon dioxide due to hydraulic fracturing, the maximum reservoir pressure after carbon dioxide injection is guaranteed to be no greater than 0.85 times the minimum horizontal principal stress of the reservoir or cap rock, that is:

[0022] P max ≤min(0.85δ Hf , 0.85δ Hc )

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

[0024] Step 7: Based on the cap rock thickness map of different regions obtained in step 1, the maximum reservoir pressure after carbon dioxide is injected into reservoirs in different regions and the distribution map of the carbon dioxide storage limit of regional saline layers are determined through steps 1 to 6, and the limit storage potential of the region is determined.

[0025] Preferably, if P max ≤min(0.85δ Hf , 0.85δ Hc ), the reservoir pressure increment can be expressed as:

[0026] △P f =P b +ρg(H-100)-P fi

[0027] Where: P fi is the original reservoir pressure, MPa.

[0028] Preferably, if P max >min(0.85δ Hf , 0.85δ Hc ), the reservoir pressure increment can be expressed as:

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

[0030] Preferably, the calculation formula for the limit storage capacity of carbon dioxide in the regional saline aquifer is:

[0031] Q max =ρ CO2 ADΦ(CR+CW)ΔP f

[0032] Where Q is the storage capacity of the regional saline aquifer, kg; A is the theoretical area of ​​the reservoir, m 2 ; D is the reservoir thickness, m; Φ is the effective porosity (<1); ΔP f is the reservoir pressure increment (MPa); C R is the rock compressibility; C w is the water compressibility; ρ CO2 is the density of carbon dioxide, (kg / m 3 ).

[0033] Through the technical measures of the above seven steps, the key steps are 1-7, which mainly solve the problem that the current carbon dioxide geological storage assessment method does not consider the influence of the cap rock tightness, and realize the reasonable assessment of the carbon dioxide geological storage considering the influence of the cap rock tightness. Compared with the prior art, the beneficial effect of the present invention is to break through the current basic theory that the reservoir pressure cannot exceed the cap rock breakthrough pressure, provide a new idea for the evaluation of carbon dioxide geological storage potential, and be applicable to large-scale carbon dioxide geological utilization and storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The diagram shows the distribution characteristics and evaluation diagram of cap rock sealing pressure of a method for assessing the geological storage capacity of carbon dioxide taking into account the influence of cap rock tightness.

[0035] Figure 2 A schematic diagram of quantitative evaluation of the risk of cap rock hydraulic fracturing in a method for assessing geological storage of carbon dioxide taking into account the influence of cap rock tightness;

[0036] Figure 3 A schematic diagram of the ground stress field in the target area of ​​a method for assessing the geological storage capacity of carbon dioxide taking into account the influence of the tightness of the cap rock;

[0037] Figure 4 Schematic diagram of the risk of hydraulic fracture of reservoir caprocks for a method of assessing geological storage capacity of carbon dioxide taking into account the influence of caprock tightness.

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

[0039] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] Embodiment 1:

[0041] A method for assessing the geological storage capacity of carbon dioxide taking into account the influence of cap rock tightness, the steps are as follows:

[0042] (1) Distribution characteristics and evaluation of caprock plugging pressure

[0043] The basic parameters of the target block are shown in Table 1. At the same time, the formation pressure, caprock breakthrough pressure and formation temperature are determined through experiments and data research. Among them, the change law of formation pressure with depth is:

[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 law of formation temperature with depth is:

[0048] T=0.034z+0.125

[0049] Table 1 Basic parameters of the target area

[0050]

[0051] like Figure 1 As shown in the figure, the distribution characteristics and evaluation diagram of caprock plugging pressure, the plugging pressure in the northeast and southwest of the target block is large, and the plugging pressure in the southeast is small; the maximum plugging pressure in the northeast of the target block exceeds 50MPa; it is reasonable to recommend the setting of injection wells in the northeast block.

[0052] (2) Hydraulic fracturing of caprock and limit of safe CO2 storage

[0053] 1) Quantitative analysis of caprock hydraulic fracturing

[0054] like Figure 2 The figure shows a schematic diagram of the risk assessment of hydraulic fracturing of the cap rock. After CO2 is injected, the Mohr circle of the rock will move to the left until it reaches the composite fracture envelope and the rock fractures. Figure 3is the geostress field of the target block. The target reservoir is buried at a depth of 1400-1700m and the caprock is 1300-1400m. In this section, the minimum principal stress and maximum principal stress of the reservoir and caprock are plotted on the stress curve. By obtaining the composite fracture envelope, the hydraulic fracture risk of the reservoir and caprock is obtained, such as Figure 4 As shown by Figure 4 The pore pressure increment of reservoir hydraulic fracturing is 14.36-16.98MPa, the pore pressure increment of cap layer hydraulic fracturing is 10.86-12.75MPa, and the cap layer breakthrough pressure is 12.88-13.57MPa. The risk of cap layer hydraulic fracturing leakage is higher than the risk of CO2 breaking through the intact cap layer.

[0055] 2) CO2 storage limit considering the influence of caprock tightness

[0056] The calculation formula for the CO2 storage capacity of regional saline aquifers is:

[0057] Q=A·D·Φ·(C R +C W )·ΔP·ρ (4)

[0058] Where Q is the storage capacity, kg; A is the theoretical area of ​​the reservoir, m 2 ; D is the reservoir thickness, m; Φ is the effective porosity (<1); ΔP is the increased pressure difference (MPa); C R is the rock compressibility; C w is the water compressibility; ρ CO2 is the density of CO2, (kg / m 3 ).

[0059] The CO2 storage capacity of the target block’s first subsection, second subsection, and third subsection is obtained by formula (4), as shown in Table 2. In summary, the safe storage capacity of the target block is approximately (2.14-2.60)×10 7 ton.

[0060] Table 2 Safe storage capacity of CO2 in a certain block

[0061]

[0062] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for assessing the geological storage capacity of carbon dioxide taking into account the influence of caprock tightness, characterized in that: Here are the steps: Step 1: Using a three-dimensional geological model to obtain the structural surface and thickness distribution map of the cap layer; Step 2: Based on the breakthrough pressure indoor experiment, the variation law of the breakthrough pressure of the cap rock with depth is obtained, and the relationship between the breakthrough pressure of the cap rock and the depth is fitted. The variation law of the breakthrough pressure of the cap rock with depth is: P b =AH+B Where: P b is the breakthrough pressure of the caprock, MPa; H is the thickness of the caprock, m; A and B are constants obtained through experimental tests; Step 3: Based on the results of the indoor mechanical experiment, the hydraulic fracturing pressure of the cap rock is obtained, and the failure envelope of the cap rock is drawn. At the same time, the breakthrough pressure of the cap rock is drawn into the failure envelope of the cap rock; Step 4: Assuming that the caprock thickness limit is 100m and its airtightness meets the requirements, in order to increase the storage capacity of carbon dioxide, the carbon dioxide can be injected into the reservoir to exceed the breakthrough pressure, but it must be less than the minimum horizontal principal stress of the caprock. The reservoir pore pressure is determined according to the depth of carbon dioxide penetrating the caprock; Step 5: If the carbon dioxide cap layer is greater than 100 m, under the condition of ensuring the airtightness of the carbon dioxide storage body cap layer, the thickness of carbon dioxide entering the cap layer is (H-100) m, and the pressure generated by carbon dioxide entering the cap layer is ρg(H-100) MPa; Step 6: The maximum reservoir pressure after injection of carbon dioxide can be expressed as: P max =P b +ρg(H-100) Where: ρ is the density of salt water, kg / m 3 ; g is the acceleration due to gravity, m / s 2 ; In order to ensure that the reservoir and cap rock will not leak carbon dioxide due to hydraulic fracturing, the maximum reservoir pressure after carbon dioxide injection is guaranteed to be no greater than 0.85 times the minimum horizontal principal stress of the reservoir or cap rock, that is: P max ≤min(0.85δ Hf ,0.85δ Hc ) In the formula, δ Hf is the minimum horizontal principal stress of the reservoir, MPa; δ Hc is the minimum horizontal principal stress of the caprock, MPa. Step 7: Based on the cap rock thickness map of different regions obtained in step 1, the maximum reservoir pressure after carbon dioxide is injected into reservoirs in different regions and the distribution map of the carbon dioxide storage limit of regional saline layers are determined through steps 1 to 6, and the limit storage potential of the region is determined.

2. A method for assessing the amount of geological storage of carbon dioxide taking into account the influence of caprock tightness according to claim 1, characterized in that: The P max ≤min(0.85δ Hf , 0.85δ Hc ), the reservoir pressure increment can be expressed as: △P f =P b +ρg(H-100)-P fi Where: P fi is the original reservoir pressure, MPa.

3. The method for assessing the amount of geological storage of carbon dioxide taking into account the influence of caprock tightness according to claim 1, characterized in that: The P max >min(0.85δ Hf , 0.85δ Hc ), the reservoir pressure increment can be expressed as: △P f =min(0.85δ Hf ,0.85δ Hc )-P fi 。 4. The method for assessing the amount of geological storage of carbon dioxide taking into account the influence of caprock tightness according to claim 1, characterized in that: The calculation formula for the limit storage capacity of carbon dioxide in the regional saline aquifer is: Q max =ρ CO2 ADΦ(CR+CW)ΔP f Where Q is the storage capacity of the regional saline aquifer, kg; A is the theoretical area of ​​the reservoir, m 2 ; D is the reservoir thickness, m; Φ is the effective porosity (<1); ΔP f is the reservoir pressure increment (MPa); C R is the rock compressibility; C w is the water compressibility; ρ CO2 is the density of carbon dioxide, (kg / m 3 ).

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