Deepwater shallow CO2 injection rate determination method and device based on fracture pressure, medium and equipment

Abstract

The invention relates to a method, a device, a medium and equipment for determining the CO2 injection rate of a deep water shallow layer based on fracture pressure, and the method comprises the following steps: estimating the fracture pressure of a deep water shallow buried cover layer, and monitoring the pressure of a near wellbore zone of an injection port; setting the injection rate of CO2 according to the initial estimated permeability on the basis of estimating the fracture pressure of the deepwater shallow buried cover layer and monitoring the pressure of a near wellbore zone of an injection port; injecting liquid CO2 through an injection system on the basis of the injection rate; in the liquid CO2 injection process, the comparison between the near wellbore zone pressure and the fracture pressure is used as a judgment basis, and the injection rate is adjusted to achieve the optimal injection effect. According to the method, the maximum injection rate can be accurately determined, and the total CO2 injection amount is increased; and the operation time is shorter, and the operation cost is lower.

Description

Technical Field

[0001] This invention relates to the field of seabed carbon sequestration research technology, specifically to a method, apparatus, medium, and equipment for determining the deep-water shallow-layer CO2 injection rate based on rupture pressure. Background Technology

[0002] CO2 sequestration has become a key technological approach to mitigating the greenhouse effect. With the discovery of high-abundance deep-water shallow gas fields in the Qiongdongnan Basin, deep-water shallow environments have become important target areas for CO2 sequestration. These environments contain various caprock types, including deep-sea mud, block flows, and hydrate-bearing strata. To prevent injected CO2 from escaping from the bottom of these caprocks and ensure effective CO2 sequestration, it is crucial to maintain an injection pressure lower than the caprock fracturing pressure (when the non-wetting phase displaces the wetting phase, the transport resistance of fluids in the interconnected pores of the rock must be overcome). For deep-water shallow caprocks, the fracturing pressure mechanism is mainly divided into hydraulic sealing and capillary sealing. The former is linearly related to the vertical stress on the caprock, while the latter is inversely proportional to the size of the pore throats between particles.

[0003] When injecting carbon dioxide into deep-water shallow reservoirs, the key is to determine the maximum CO2 injection rate to maximize the storage capacity and optimize engineering efficiency and economy, while ensuring good capping of the CO2. In the process of multiphase CO2 storage and injection in deep-water shallow reservoirs, when the permeability is unknown, existing methods usually adopt a "low-to-high" injection rate strategy, that is, continuously increasing the injection rate until the pressure in the near-wellbore zone reaches the caprock fracture pressure.

[0004] However, in the initial stage of injection, the low-rate CO2 injection easily reacts with pore water around the well to form solid CO2 hydrates, causing reservoir pore blockage and preventing subsequent CO2 injection, thus limiting the CO2 diffusion range. Furthermore, existing methods often use excessively low initial injection rates when determining the maximum CO2 injection rate, resulting in longer implementation times and higher operating costs. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method, apparatus, medium, and equipment for determining the CO2 injection rate in deep-water shallow layers based on rupture pressure, which can accurately determine the maximum injection rate and increase the total amount of CO2 injected; and also has shorter operation time and lower operation cost.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: The method for determining the CO2 injection rate in deep-water shallow formations based on fracture pressure, as described in this invention, includes the following steps: Estimate the fracture pressure of the deep-water shallow caprock and monitor the pressure in the near-wellbore zone of the injection port; Based on the estimated fracture pressure of the deep-water shallow caprock and the pressure near the injection port near the well, the CO2 injection rate is set according to the initial estimated permeability. Liquid CO2 is injected through an injection system based on the injection rate; During liquid CO2 injection, the comparison between near-wellbore pressure and fracture pressure is used as the basis for judgment, and the injection rate is adjusted to achieve the best injection effect.

[0007] The method for determining the CO2 injection rate in deep water shallow layers, preferably, involves estimating the fracturing pressure of the deep water shallow caprock, specifically as follows: If the capping mechanism of the shallow-buried cap layer in the deep-water target area is mainly hydraulic sealing, the cap layer rupture pressure... The calculation formula is:

[0008] In the formula, It is an empirical constant and can be determined by triaxial stress experiments; The effective vertical stress at the bottom of the cap layer is calculated using the following formula:

[0009] In the formula, Density of the caprock skeleton; The density of seawater in the caprock pores; It is the acceleration due to gravity; The thickness of the capping layer; If the sealing mechanism of the shallow-buried caprock in the deep-water target area is mainly capillary force sealing, the caprock rupture pressure... The calculation formula is:

[0010] In the formula, For interfacial tension; For wetting angle; The radius of the capillary tube; The thickness of the water film.

[0011] The method for determining the CO2 injection rate in deep-water shallow layers, preferably, involves setting the CO2 injection rate based on an initial estimated permeability, specifically as follows: First, the maximum injection rate corresponding to different penetration rates is calculated using CMG professional software, and a graph showing the relationship between penetration rate and maximum injection rate is generated. If the reservoir permeability is unclear, an initial permeability is estimated based on well logging data. Then, according to the aforementioned relationship chart, CO2 is injected at the maximum injection rate corresponding to that permeability.

[0012] The method for determining the CO2 injection rate in deep-water shallow formations preferably uses the comparison between near-wellbore pressure and fracture pressure as the criterion for adjusting the injection rate during CO2 injection. Specifically: When the near-wellbore pressure is greater than the fracturing pressure during injection, the injection rate should be reduced; when the near-wellbore pressure is less than the fracturing pressure during injection, the injection rate should be increased.

[0013] The present invention also provides a device for determining the CO2 injection rate in deep-water shallow formations based on fracture pressure, comprising: The first processing unit is used to estimate the fracture pressure of the deep-water shallow caprock and monitor the pressure in the near-wellbore zone of the injection port. The second processing unit is used to set the CO2 injection rate based on the initial estimated permeability, based on the estimated fracture pressure of the deep-water shallow caprock and the pressure in the near-wellbore zone of the injection port. The third processing unit is used to inject liquid CO2 through the injection system based on the injection rate; The fourth processing unit is used to adjust the injection rate during the liquid CO2 injection process by comparing the near-wellbore pressure with the fracture pressure to achieve the best injection effect.

[0014] The present invention also provides a computer storage medium storing a computer program thereon, wherein the computer program, when executed by a processor, implements the steps of the method for determining the deep-water shallow-layer CO2 injection rate based on rupture pressure.

[0015] The present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method for determining the deep-water shallow-layer CO2 injection rate based on rupture pressure.

[0016] The present invention has the following advantages due to the adoption of the above technical solutions: It can accurately determine the maximum injection rate and increase the total amount of CO2 injected: The present invention adopts a high injection rate in the early stage. By injecting CO2 at high speed, CO2 can quickly diffuse into the surrounding reservoir with good porosity and permeability in a short time, avoiding the formation of CO2 hydrates around the well. This solves the problems of hydrate blockage, inability to inject subsequent carbon dioxide, and inability to determine the maximum injection rate caused by the low-speed injection strategy in the initial stage of the existing invention. Attached Figure Description

[0017] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. In the drawings: Figure 1 This is a schematic diagram of the deep-water shallow-layer CO2 injection system of the present invention.

[0018] The labels for the attached figures are as follows: 1 is seawater; 2 is a deep-water shallow-buried caprock; 3 is a reservoir beneath the caprock; 4 is a blowout preventer; 5 is a carbon dioxide booster injection pump; 6 is a carbon dioxide injection valve; 7 is a carbon dioxide storage and transportation pipeline; 8 is a casing; 9 is a carbon dioxide injection string; 10 is a perforation; 11 is a separator; 12-13 are ROVs (Remotely Operated Vehicles); 14 is an injection platform. Detailed Implementation

[0019] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0020] This invention provides a method for determining the CO2 injection rate in deep-water shallow formations based on fracture pressure. To address the problems of hydrate blockage and inability to determine the maximum injection rate caused by low injection rates in the initial stages of injection in existing technologies, this invention employs a high injection rate from the outset. By injecting CO2 at high speed, CO2 rapidly diffuses into surrounding reservoirs with good porosity and permeability, preventing the formation of CO2 hydrates around the wellbore. This facilitates subsequent CO2 injection, determines the maximum injection rate, and maximizes the total injection volume. Furthermore, a high-precision seabed CO2 leakage monitoring system is established by deploying a remotely operated underwater vehicle (ROV) on the seabed. Once the ROV detects CO2 gas leakage, injection is immediately stopped, and the injection rate at that moment is determined as the maximum injection rate, shortening operation time and reducing operating costs.

[0021] like Figure 1 As shown, the deep-water shallow-layer CO2 injection system of the present invention is as follows: The injection system is applied in scenarios consisting of a seawater layer 1, a deep-water shallow-buried caprock, and an underlying reservoir, arranged sequentially from top to bottom. The injection system includes: a blowout preventer 4, a carbon dioxide booster injection pump 5, a carbon dioxide injection valve 6, a carbon dioxide storage and transportation pipeline 7, a casing 8, a carbon dioxide injection string 9, a perforation 10, a packer 11, two remotely operated underwater vehicles 12 and 13, and an injection platform 14. The injection platform 14 is located on the sea surface of seawater layer 1. The casing 8 extends from the seabed of seawater layer 1 through the deep-water shallow-buried caprock 2 into the underlying reservoir 3. Carbon dioxide injection string 9 is inserted into casing 8, and the lower end of carbon dioxide injection string 9 is sealed by packer 11. Perforation 10 is set on the pipe wall near the lower end of casing 8. The upper end of carbon dioxide injection string 9 is connected to blowout preventer 4. Carbon dioxide storage and transportation pipeline 7 passes through blowout preventer 4 and is connected to carbon dioxide injection string 9. Carbon dioxide injection valve 6 and carbon dioxide booster injection pump 5 are installed on carbon dioxide storage and transportation pipeline 7 from upstream to downstream. Two remotely operated underwater robots 12 and 13 are respectively set on the seabed of seawater layer 1 and respectively set on both sides of casing 8.

[0022] This invention provides a method for determining the CO2 injection rate in deep-water shallow formations based on fracture pressure, comprising the following steps: S1. Estimate the fracture pressure of the deep-water shallow-buried caprock and monitor the pressure in the wellbore near the injection port; S2. Based on the estimated fracture pressure of the deep-water shallow caprock and the pressure in the near-wellbore zone near the injection port, the CO2 injection rate is set according to the initial estimated permeability. S3. Based on the injection rate, liquid CO2 is injected through the injection system; S4. During the liquid CO2 injection process, the injection rate is adjusted based on the comparison between the near-wellbore pressure and the fracture pressure to achieve the best injection effect.

[0023] In the above embodiments, preferably, the estimation of the fracturing pressure of the deep-water shallow-buried caprock specifically involves: If the capping mechanism of the shallow-buried cap layer in the deep-water target area is mainly hydraulic sealing, the cap layer rupture pressure... The calculation formula is:

[0024] In the formula, It is an empirical constant and can be determined by triaxial stress experiments; The effective vertical stress at the bottom of the cap layer is calculated using the following formula:

[0025] In the formula, Density of the caprock skeleton; The density of seawater in the caprock pores; It is the acceleration due to gravity; The thickness of the capping layer; If the sealing mechanism of the shallow-buried caprock in the deep-water target area is mainly capillary force sealing, the caprock rupture pressure... The calculation formula is:

[0026] In the formula, For interfacial tension; For wetting angle; The radius of the capillary tube; The thickness of the water film.

[0027] In the above embodiments, preferably, setting the CO2 injection rate based on the initial estimated permeability specifically involves: First, the maximum injection rate corresponding to different penetration rates is calculated using CMG professional software, and a graph showing the relationship between penetration rate and maximum injection rate is generated. If the reservoir permeability is unclear, first estimate an initial permeability, and then inject CO2 at the maximum injection rate corresponding to that permeability according to the aforementioned relationship chart.

[0028] In the above embodiments, preferably, the injection rate is adjusted based on the comparison between near-wellbore pressure and fracture pressure during CO2 injection, specifically as follows: When the near-wellbore pressure is greater than the fracturing pressure during injection, the injection rate should be reduced; when the near-wellbore pressure is less than the fracturing pressure during injection, the injection rate should be increased.

[0029] The present invention also provides a device for determining the CO2 injection rate in deep-water shallow formations based on fracture pressure, comprising: The first processing unit is used to estimate the fracture pressure of the deep-water shallow caprock and monitor the pressure in the near-wellbore zone of the injection port. The second processing unit is used to set the CO2 injection rate based on the initial estimated permeability, based on the estimated fracture pressure of the deep-water shallow caprock and the pressure in the near-wellbore zone of the injection port. The third processing unit is used to inject liquid CO2 through the injection system based on the injection rate; The fourth processing unit is used to adjust the injection rate during the liquid CO2 injection process by comparing the near-wellbore pressure with the fracture pressure to achieve the best injection effect.

[0030] The present invention also provides a computer storage medium storing a computer program thereon, wherein the computer program, when executed by a processor, implements the steps of the method for determining the deep-water shallow-layer CO2 injection rate based on rupture pressure.

[0031] The present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method for determining the deep-water shallow-layer CO2 injection rate based on rupture pressure.

[0032] 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 of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the CO2 injection rate in deep-water shallow formations based on fracture pressure, characterized in that, Includes the following steps: Estimate the fracture pressure of the deep-water shallow caprock and monitor the pressure in the near-wellbore zone of the injection port; Based on the estimated fracture pressure of the deep-water shallow caprock and the pressure near the injection port near the well, the CO2 injection rate is set according to the initial estimated permeability. Liquid CO2 is injected through an injection system based on the injection rate; During liquid CO2 injection, the comparison between near-wellbore pressure and fracture pressure is used as the basis for judgment, and the injection rate is adjusted to achieve the best injection effect.

2. The method for determining the CO2 injection rate in shallow deep water as described in claim 1, characterized in that, The estimation of the fracturing pressure of the deep-water shallow-buried caprock is specifically as follows: If the capping mechanism of the shallow-buried cap layer in the deep-water target area is mainly hydraulic sealing, the cap layer rupture pressure... The calculation formula is: In the formula, It is an empirical constant and can be determined by triaxial stress experiments; The effective vertical stress at the bottom of the cap layer is calculated using the following formula: In the formula, Density of the cover rock skeleton; The density of seawater in the caprock pores; It is the acceleration due to gravity; The thickness of the capping layer; If the sealing mechanism of the shallow-buried caprock in the deep-water target area is mainly capillary force sealing, the caprock rupture pressure... The calculation formula is: In the formula, For interfacial tension; For wetting angle; The radius of the capillary tube; The thickness of the water film.

3. The method for determining the CO2 injection rate in shallow deep water as described in claim 1, characterized in that, The step of setting the CO2 injection rate based on the initial estimated permeability is as follows: First, the maximum injection rate corresponding to different penetration rates is calculated using CMG professional software, and a graph showing the relationship between penetration rate and maximum injection rate is generated. If the reservoir permeability is unclear, an initial permeability is estimated based on well logging data. Then, according to the aforementioned relationship chart, CO2 is injected at the maximum injection rate corresponding to that permeability.

4. The method for determining the CO2 injection rate in shallow deep water as described in claim 1, characterized in that, During CO2 injection, the injection rate is adjusted based on the comparison between near-wellbore pressure and fracture pressure. Specifically: When the near-wellbore pressure is greater than the fracturing pressure during injection, the injection rate should be reduced; when the near-wellbore pressure is less than the fracturing pressure during injection, the injection rate should be increased.

5. A device for determining the CO2 injection rate in shallow deep water based on fracture pressure, characterized in that, include: The first processing unit is used to estimate the fracture pressure of the deep-water shallow caprock and monitor the pressure in the near-wellbore zone of the injection port. The second processing unit is used to set the CO2 injection rate based on the initial estimated permeability, based on the estimated fracture pressure of the deep-water shallow caprock and the pressure in the near-wellbore zone of the injection port. The third processing unit is used to inject liquid CO2 through the injection system based on the injection rate; The fourth processing unit is used to adjust the injection rate during the liquid CO2 injection process by comparing the near-wellbore pressure with the fracture pressure to achieve the best injection effect.

6. A computer storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the method for determining the deep-water shallow-layer CO2 injection rate based on the rupture pressure as described in any one of claims 1-4.

7. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method for determining the deep-water shallow-layer CO2 injection rate based on rupture pressure as described in any one of claims 1-4.

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