A method for determining a breakthrough pressure based on digital cores
By using a breakthrough pressure determination method based on digital cores, the problems of data interpretation uncertainty and resource waste in traditional gas storage sealing evaluation have been solved, achieving more accurate and efficient sealing assessment and reducing damage to the rock structure.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-17
- Publication Date
- 2026-06-19
AI Technical Summary
Traditional gas storage sealing evaluation suffers from uncertainties in the interpretation of seismic exploration data and time-consuming and resource-intensive core experiments, and the core sampling process may damage the rock structure.
A breakthrough pressure determination method based on digital cores was adopted. Experiments were conducted by collecting core samples of caprock mudstone to build a digital core model. Fluent software was used for simulation calculations, and combined with gas-liquid two-phase flow simulation experiments. The model was adjusted until the breakthrough pressure judgment criteria were met, and the breakthrough pressure result was determined.
It improves the accuracy and efficiency of sealing performance evaluation, reduces damage to rock structures, and lowers resource consumption.
Smart Images
Figure CN122238093A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of gas storage sealing performance evaluation technology, and in particular to a method for determining breakthrough pressure based on digital core data. Background Technology
[0002] Currently, gas storage facilities are underground storage facilities used to store gases such as natural gas. One of the key issues to ensure the safe and reliable operation of gas storage facilities is the evaluation of their airtightness.
[0003] The sealing performance of a gas storage facility depends on the properties of the reservoir rock and the thickness of the overburden. Traditional methods for evaluating the sealing performance of gas storage facilities typically employ seismic exploration, well coring, and core testing to obtain relevant data, which is then used for evaluation. However, these methods have several drawbacks, including uncertainties in the interpretation of seismic exploration data, the high time and resource requirements of core testing, and the potential for rock structure damage during coring. Therefore, to address these shortcomings, a breakthrough pressure determination method based on digital core data is proposed. Summary of the Invention
[0004] (a) Technical problems to be solved
[0005] This invention provides a method for determining breakthrough pressure based on digital core samples, which overcomes the uncertainty in the interpretation of seismic exploration data in the sealing evaluation of traditional gas storage facilities in the prior art, the large amount of time and resources required for core experiments, and the potential for damage to the rock structure during the core sampling process.
[0006] (II) Technical Solution
[0007] To address the above problems, this invention provides a method for determining breakthrough pressure based on digital core data, comprising:
[0008] Step S1: Collect multiple caprock core samples, classify the collected caprock core samples according to permeability, preset the initial pressure difference of different types of caprock core samples, and conduct caprock core breakthrough pressure experiments on the collected caprock core samples under actual reservoir stress conditions, and obtain and record the experimental results of caprock core breakthrough pressure.
[0009] Step S2: Perform CT scans on the caprock mudstone core samples collected in Step S1, and build a digital core experimental model using image processing and analysis techniques.
[0010] Step S3: Based on the experimental results of the breakthrough pressure of the caprock mudstone core determined in Step S1, and the digital core experimental model determined in Step S2, and in conjunction with the capillary pressure formula, a digital core simulation calculation model is built using Fluent software.
[0011] Step S4: Using the digital core simulation calculation model determined in step S3, perform simulation calculations on the caprock mudstone core samples collected in step S1 to obtain the predicted value of the breakthrough pressure of the caprock mudstone core samples.
[0012] Step S5: Conduct a gas-liquid two-phase flow simulation experiment on the caprock mudstone core sample collected in step S1, observe the gas saturation diagram of the caprock mudstone core sample, and obtain the breakthrough pressure experimental value of the caprock mudstone core sample.
[0013] Step S6: Set a breakthrough pressure judgment standard, compare the predicted breakthrough pressure value determined in step S4 with the experimental breakthrough pressure value determined in step S5 to see if they meet the breakthrough pressure judgment standard. If they do not meet the standard, adjust the standard until it is met, and then determine the breakthrough pressure result value.
[0014] Preferably, in step S1, the number of caprock core samples is not less than 20, and the experimental results of the breakthrough pressure of the caprock core are the relationship between different permeability and breakthrough pressure corresponding to different formation pressures.
[0015] Preferably, in step S1, the classification criteria for the caprock mudstone core samples are: permeability less than 0.001 mD, permeability between 0.001 mD and 0.01 mD, and permeability greater than 0.01 mD; the criteria for the initial experimental pressure difference are: 8 MPa when the permeability is less than 0.001 mD, 6 MPa when the permeability is between 0.001 mD and 0.01 mD, and 1 MPa when the permeability is greater than 0.01 mD.
[0016] Preferably, in step S1, the experimental operation steps of the caprock mudstone core breakthrough pressure test are as follows: the caprock mudstone core sample is evacuated and saturated with water, and the volume of saturated water is recorded; the caprock mudstone core sample and saturated liquid are moved to an intermediate container, pressurized, and allowed to stand to fully saturate the caprock mudstone core sample; the saturated caprock mudstone core sample is loaded into a core holder and connected to the experimental device; the confining pressure is set according to the reservoir conditions; the gas source is connected to the inlet end of the rock sample, and the initial pressure difference and back pressure are set, and the pressure is gradually increased at certain time intervals; during the measurement, the condition of the rock sample outlet end is detected by a bubble monitoring device, and when the bubbles escape uniformly and continuously, the corresponding pressure difference between the inlet and outlet ends of the rock sample is the gas breakthrough pressure of the caprock mudstone core sample.
[0017] Preferably, in step S2, the digital core experimental model includes the pore structure of the caprock mudstone core sample, the connectivity of the caprock mudstone core sample, the gas-water distribution of the caprock mudstone core sample, the pore throat radius of the caprock mudstone core sample, and the pore throat radius distribution of the caprock mudstone core sample.
[0018] Preferably, in step S3, the capillary pressure formula is determined based on the displacement capillary force curve description model, and its calculation formula is as follows:
[0019]
[0020] Among them, P c Capillary pressure; S w S represents the water saturation level. wc S represents the initial water saturation. o S represents residual gas saturation. or Residual gas saturation; c wi c oi a wi a oi b i These are the curve fitting coefficients.
[0021] Preferably, in step S4, the process of determining the predicted value of the breakthrough pressure is as follows: determining the pore throat radius distribution of the caprock mudstone core sample, determining the correspondence between different permeabilities and breakthrough pressures corresponding to different formation pressures, calculating the capillary pressure corresponding to each pore throat radius, and finally determining the predicted value of the breakthrough pressure.
[0022] Preferably, in step S5, the breakthrough pressure experimental value is the value corresponding to the water saturation in the gas saturation diagram decreasing to 98%.
[0023] Preferably, in step S6, the condition for satisfying the breakthrough pressure judgment criterion is that the absolute value of the difference between the predicted breakthrough pressure value and the experimental breakthrough pressure value does not exceed 2, then the predicted breakthrough pressure value is the breakthrough pressure result value.
[0024] Preferably, in step S6, if the absolute value of the difference between the predicted breakthrough pressure value and the experimental breakthrough pressure value exceeds 2, the breakthrough pressure prediction value determination process needs to be repeated based on the experimental breakthrough pressure value until the absolute value of the difference between the predicted breakthrough pressure value and the experimental breakthrough pressure value does not exceed 2, and the breakthrough pressure result value is determined as the predicted breakthrough pressure value.
[0025] (III) Beneficial Effects
[0026] The present invention provides a method for determining breakthrough pressure based on digital cores. By conducting breakthrough pressure experiments on caprock mudstone cores, the relationship between different permeabilities and breakthrough pressure under formation conditions is established. Then, through core CT scanning and numerical core simulation, the breakthrough pressure and pore characteristics of cores with different permeabilities are determined. Based on the formula for calculating capillary pressure, the breakthrough pressure under different depth conditions is calculated. Furthermore, the pressure difference is set and the gas saturation map is observed using simulation software to determine whether gas has broken through. Attached Figure Description
[0027] Figure 1 This is a flowchart of the breakthrough pressure determination method based on digital core data according to an embodiment of the present invention;
[0028] Figure 2 The above are simulation diagrams of gas breakthrough in an embodiment of the present invention, wherein a is the gas saturation diagram at 0.05 seconds of simulation, b is the gas saturation diagram at 0.1 seconds of simulation, c is the gas saturation diagram at 0.15 seconds of simulation, and d is the gas saturation diagram at 0.2 seconds of simulation.
[0029] Figure 3 This is an observation diagram of the gas breakthrough curve in an embodiment of the present invention. Detailed Implementation
[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0031] Figure 1 This is a flowchart of the breakthrough pressure determination method based on digital core data according to an embodiment of the present invention, as shown below. Figure 1 As shown, this invention provides a method for determining breakthrough pressure based on digital core data, comprising:
[0032] Step S1: Collect multiple caprock core samples, classify the collected caprock core samples according to permeability, preset the initial pressure difference of different types of caprock core samples, and conduct caprock core breakthrough pressure experiments on the collected caprock core samples under actual reservoir stress conditions, and obtain and record the experimental results of caprock core breakthrough pressure.
[0033] Step S2: Perform CT scans on the caprock mudstone core samples collected in Step S1, and build a digital core experimental model using image processing and analysis techniques.
[0034] Step S3: Based on the experimental results of the breakthrough pressure of the caprock mudstone core determined in Step S1, and the digital core experimental model determined in Step S2, and in conjunction with the capillary pressure formula, a digital core simulation calculation model is built using Fluent software.
[0035] Step S4: Using the digital core simulation calculation model determined in step S3, perform simulation calculations on the caprock mudstone core samples collected in step S1 to obtain the predicted value of the breakthrough pressure of the caprock mudstone core samples.
[0036] Step S5: Conduct a gas-liquid two-phase flow simulation experiment on the caprock mudstone core sample collected in step S1, observe the gas saturation diagram of the caprock mudstone core sample, and obtain the breakthrough pressure experimental value of the caprock mudstone core sample.
[0037] Step S6: Set a breakthrough pressure judgment standard, compare the predicted breakthrough pressure value determined in step S4 with the experimental breakthrough pressure value determined in step S5 to see if they meet the breakthrough pressure judgment standard. If they do not meet the standard, adjust the standard until it is met, and then determine the breakthrough pressure result value.
[0038] In this method, in step S1, the number of caprock core samples is no less than 20, and the experimental results of the breakthrough pressure of the caprock core are the relationship between different permeability and breakthrough pressure corresponding to different formation pressures.
[0039] In practical applications, in step S1, the classification criteria for caprock mudstone core samples are: permeability less than 0.001 mD, permeability between 0.001 mD and 0.01 mD, and permeability greater than 0.01 mD; the criteria for the initial experimental pressure difference are: 8 MPa when permeability is less than 0.001 mD, 6 MPa when permeability is between 0.001 mD and 0.01 mD, and 1 MPa when permeability is greater than 0.01 mD.
[0040] In this method, the experimental procedure for the breakthrough pressure test of the caprock mudstone core in step S1 is as follows: the caprock mudstone core sample is evacuated and saturated with water, and the volume of saturated water is recorded; the caprock mudstone core sample and saturated liquid are moved to an intermediate container, pressurized, and allowed to stand to fully saturate the caprock mudstone core sample; the saturated caprock mudstone core sample is loaded into a core holder and connected to the experimental apparatus; the confining pressure is set according to the reservoir conditions; the gas source is connected to the inlet end of the rock sample, and the initial pressure difference and back pressure are set, and the pressure is gradually increased at certain time intervals; during the measurement, the condition of the outlet end of the rock sample is detected by a bubble monitoring device, and when the bubbles escape uniformly and continuously, the corresponding pressure difference between the inlet and outlet ends of the rock sample is the gas breakthrough pressure of the caprock mudstone core sample.
[0041] In practical applications, in step S2, the digital core experimental model includes the pore structure of the caprock mudstone core sample, the connectivity of the caprock mudstone core sample, the gas-water distribution of the caprock mudstone core sample, the pore throat radius of the caprock mudstone core sample, and the pore throat radius distribution of the caprock mudstone core sample.
[0042] In this method, in step S3, the capillary pressure formula is determined based on the displacement capillary force curve description model, and its calculation formula is as follows:
[0043]
[0044] Among them, P c Capillary pressure; S w S represents the water saturation level. wc S represents the initial water saturation. o S represents residual gas saturation. or Residual gas saturation; c wi c oi a wi a oi b i These are the curve fitting coefficients.
[0045] In practical applications, the process of determining the breakthrough pressure prediction value in step S4 is as follows: determine the pore throat radius distribution of the caprock mudstone core sample, determine the correspondence between different permeabilities and breakthrough pressures corresponding to different formation pressures, calculate the capillary pressure corresponding to each pore throat radius, and finally determine the predicted value of the breakthrough pressure.
[0046] In this method, in step S5, the breakthrough pressure experimental value is the value corresponding to the water saturation in the gas saturation diagram decreasing to 98%.
[0047] In practical applications, in step S6, the condition for meeting the breakthrough pressure judgment criterion is that the absolute value of the difference between the predicted breakthrough pressure value and the experimental breakthrough pressure value does not exceed 2, and the predicted breakthrough pressure value is the breakthrough pressure result value.
[0048] In this method, in step S6, if the absolute value of the difference between the predicted breakthrough pressure value and the experimental breakthrough pressure value exceeds 2, the breakthrough pressure prediction value determination process needs to be repeated based on the experimental breakthrough pressure value until the absolute value of the difference between the predicted breakthrough pressure value and the experimental breakthrough pressure value does not exceed 2, and the breakthrough pressure result value is determined to be the predicted breakthrough pressure value.
[0049] This invention provides a method for determining breakthrough pressure based on digital core data. It fully utilizes digital technology and numerical simulation methods to improve the accuracy of breakthrough pressure determination, and considers the heterogeneity and seepage characteristics of the formation. The working principle of this method based on digital core data determination is described in detail below:
[0050] Step 1: Collect multiple caprock mudstone core samples, classify the collected caprock mudstone core samples according to permeability, preset the initial pressure difference of different types of caprock mudstone core samples, and conduct caprock mudstone core breakthrough pressure experiments on the collected caprock mudstone core samples under actual reservoir stress conditions, and obtain and record the experimental results of caprock mudstone core breakthrough pressure.
[0051] Step 2: Perform CT scans on the collected caprock mudstone core samples, and build a digital core experimental model using image processing and analysis techniques;
[0052] Step 3: Based on the experimental results of the breakthrough pressure of the caprock mudstone core and the digital core experimental model, and in conjunction with the capillary pressure formula, a digital core simulation calculation model is built using Fluent software.
[0053] Step 4: Using a digital core simulation model, simulate and calculate the collected caprock mudstone core samples to obtain the predicted breakthrough pressure value of the caprock mudstone core samples.
[0054] Step 5: Conduct a gas-liquid two-phase flow simulation experiment on the collected caprock mudstone core samples, observe the gas saturation diagram of the caprock mudstone core samples, and obtain the breakthrough pressure experimental value of the caprock mudstone core samples.
[0055] Step 6: Set the breakthrough pressure judgment criteria, compare the predicted breakthrough pressure value with the experimental breakthrough pressure value to see if they meet the breakthrough pressure judgment criteria. If they do not meet the criteria, adjust the criteria until they are met, and then determine the breakthrough pressure result value.
[0056] In this embodiment, 20 caprock mudstone core samples were used, categorized into three types: permeability less than 0.001 mD, permeability between 0.001 mD and 0.01 mD, and permeability greater than 0.01 mD. The initial pressure difference was 8 MPa for permeability less than 0.001 mD, 6 MPa for permeability between 0.001 mD and 0.01 mD, and 1 MPa for permeability greater than 0.01 mD. The relationship between different permeabilities and breakthrough pressures under reservoir stress conditions was established by measuring the breakthrough pressures of the samples.
[0057] In practical applications, CT scans were performed on 20 caprock mudstone core samples to obtain detailed structural information inside the cores. A digital core experimental model was built using image processing and analysis techniques. The digital core experimental model was used to obtain the pore structure, connectivity, gas-water distribution, pore throat radius, and pore throat radius distribution of the caprock mudstone core samples.
[0058] In this embodiment, the experimental results of the breakthrough pressure of caprock mudstone cores, the digital core experimental model, and the simulation parameters derived from the capillary force formula are used as inputs. A digital core simulation calculation model is built using Fluent software. The breakthrough pressure of cores with different permeabilities is determined through the digital core simulation calculation model, different pore characteristics are determined, and the predicted value of the breakthrough pressure of caprock mudstone core samples is obtained.
[0059] In practical applications, the process of determining the breakthrough pressure prediction value is as follows: determine the pore throat radius distribution of the caprock mudstone core sample, determine the correspondence between different permeabilities and breakthrough pressures corresponding to different formation pressures, calculate the capillary pressure corresponding to each pore throat radius, and finally determine the predicted value of the breakthrough pressure.
[0060] In this embodiment, simulation software is used to simulate gas-liquid two-phase flow, and the gas saturation diagram is observed, such as... Figure 2 (a) to Figure 2 As shown in (d), to simulate the process of gas being injected from the right inlet to the left outlet, the presence or absence of obvious gas connectivity between the inlet and outlet ends of the model can be used as a criterion for determining whether gas leakage has occurred. Specifically, in Figure 2 Gas breakthrough can be observed at (c). Figure 3 As shown, by observing the gas saturation diagram, when the water saturation drops to 98%, it is considered a gas breakthrough, and the breakthrough pressure experimental value of the caprock mudstone core sample is obtained.
[0061] In practical applications, by comparing the predicted and experimental values of the breakthrough pressure, the breakthrough pressure can be further analyzed and optimized. If the absolute value of the difference between the predicted and experimental breakthrough pressure values does not exceed 2, the breakthrough pressure judgment criterion is met, and the predicted breakthrough pressure value is the final breakthrough pressure value. If the absolute value of the difference exceeds 2, parameter adjustments and optimizations can be made based on the simulation results. This means that the breakthrough pressure prediction process needs to be repeated based on the experimental breakthrough pressure values until the absolute value of the difference between the predicted and experimental breakthrough pressure values does not exceed 2, at which point the final breakthrough pressure value is determined as the predicted breakthrough pressure value.
[0062] Furthermore, besides oil exploration and underground engineering, this embodiment can also be applied to other fields, such as geological engineering and water resource development. Through continuous optimization and verification in practical applications across different fields, this method has broader application prospects and market potential.
[0063] The present invention provides a method for determining breakthrough pressure based on digital cores. By conducting breakthrough pressure experiments on caprock mudstone cores, the relationship between different permeabilities and breakthrough pressure under formation conditions is established. Then, through core CT scanning and numerical core simulation, the breakthrough pressure and pore characteristics of cores with different permeabilities are determined. Based on the formula for calculating capillary pressure, the breakthrough pressure under different depth conditions is calculated. Furthermore, the pressure difference is set and the gas saturation map is observed using simulation software to determine whether gas has broken through.
[0064] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.
Claims
1. A method for determining a breakthrough pressure based on digital cores, characterized in that, include: Step S1: Collect multiple caprock core samples, classify the collected caprock core samples according to permeability, preset the initial pressure difference of different types of caprock core samples, and conduct caprock core breakthrough pressure experiments on the collected caprock core samples under actual reservoir stress conditions, and obtain and record the experimental results of caprock core breakthrough pressure. Step S2: Perform CT scans on the caprock mudstone core samples collected in Step S1, and build a digital core experimental model using image processing and analysis techniques. Step S3: Based on the experimental results of the breakthrough pressure of the caprock mudstone core determined in Step S1, and the digital core experimental model determined in Step S2, and in conjunction with the capillary pressure formula, a digital core simulation calculation model is built using Fluent software. Step S4: Using the digital core simulation calculation model determined in step S3, perform simulation calculations on the caprock mudstone core samples collected in step S1 to obtain the predicted value of the breakthrough pressure of the caprock mudstone core samples. Step S5: Conduct a gas-liquid two-phase flow simulation experiment on the caprock mudstone core sample collected in step S1, observe the gas saturation diagram of the caprock mudstone core sample, and obtain the breakthrough pressure experimental value of the caprock mudstone core sample. Step S6: Set a breakthrough pressure judgment standard, compare the predicted breakthrough pressure value determined in step S4 with the experimental breakthrough pressure value determined in step S5 to see if they meet the breakthrough pressure judgment standard. If they do not meet the standard, adjust the standard until it is met, and then determine the breakthrough pressure result value.
2. The digital rock based breakthrough pressure determination method of claim 1, wherein, In step S1, the number of caprock core samples is no less than 20, and the experimental results of the breakthrough pressure of the caprock cores are the relationship between different permeability and breakthrough pressure corresponding to different formation pressures.
3. The digital rock based breakthrough pressure determination method of claim 1, wherein In step S1, the classification criteria for the caprock mudstone core samples are: permeability less than 0.001 mD, permeability between 0.001 mD and 0.01 mD, and permeability greater than 0.01 mD; the criteria for the initial experimental pressure difference are: 8 MPa when the permeability is less than 0.001 mD, 6 MPa when the permeability is between 0.001 mD and 0.01 mD, and 1 MPa when the permeability is greater than 0.01 mD.
4. The digital rock based breakthrough pressure determination method of claim 1, wherein In step S1, the experimental procedure for the breakthrough pressure test of the caprock mudstone core is as follows: The caprock mudstone core sample is evacuated and saturated with water, and the volume of saturated water is recorded; the caprock mudstone core sample and saturated liquid are moved to an intermediate container, pressurized, and allowed to stand until the caprock mudstone core sample is fully saturated; the saturated caprock mudstone core sample is loaded into a core holder and connected to the experimental apparatus; the confining pressure is set according to the reservoir conditions; a gas source is connected to the inlet end of the rock sample, and the initial pressure difference and back pressure are set, gradually increasing the pressure at certain time intervals; during the measurement, the condition at the outlet end of the rock sample is detected by a bubble monitoring device, and when the bubbles escape uniformly and continuously, the corresponding pressure difference between the inlet and outlet ends of the rock sample is the gas breakthrough pressure of the caprock mudstone core sample.
5. The digital rock based breakthrough pressure determination method of claim 1, wherein, In step S2, the digital core experimental model includes the pore structure of the caprock mudstone core sample, the connectivity of the caprock mudstone core sample, the gas-water distribution of the caprock mudstone core sample, the pore throat radius of the caprock mudstone core sample, and the pore throat radius distribution of the caprock mudstone core sample.
6. The digital rock-based breakthrough pressure determination method of claim 1, wherein, In step S3, the capillary pressure formula is determined based on the displacement capillary force curve description model, and its calculation formula is as follows: where P c is the capillary pressure; S w is the water saturation, S wc is the initial water saturation; S o is the residual gas saturation; S or is the residual gas saturation; c wi , c oi , a wi , a oi , b i are curve fitting coefficients.
7. The digital rock based breakthrough pressure determination method of claim 2, 5 or 6, wherein, In step S4, the process of determining the predicted breakthrough pressure is as follows: determine the pore throat radius distribution of the caprock mudstone core sample, determine the correspondence between different permeabilities and breakthrough pressures corresponding to different formation pressures, calculate the capillary pressure corresponding to each pore throat radius, and finally determine the predicted breakthrough pressure.
8. The digital rock-based breakthrough pressure determination method of claim 1, wherein, In step S5, the breakthrough pressure experimental value is the value corresponding to the water saturation in the gas saturation diagram decreasing to 98%.
9. The digital rock-based breakthrough pressure determination method of claim 1, wherein, In step S6, the condition for satisfying the breakthrough pressure judgment criterion is that the absolute value of the difference between the predicted breakthrough pressure value and the experimental breakthrough pressure value does not exceed 2, then the predicted breakthrough pressure value is the breakthrough pressure result value.
10. The digital rock-based breakthrough pressure determination method of claim 9, wherein, In step S6, if the absolute value of the difference between the predicted breakthrough pressure value and the experimental breakthrough pressure value exceeds 2, the breakthrough pressure prediction value determination process needs to be repeated based on the experimental breakthrough pressure value until the absolute value of the difference between the predicted breakthrough pressure value and the experimental breakthrough pressure value does not exceed 2, and the breakthrough pressure result value is determined to be the predicted breakthrough pressure value.