Method for determining storage capacity of gas storage
By injecting perdeuterium methane and carbon 14 methane into the gas storage, and sampling and analysis were performed during the gas extraction period, the storage capacity was calculated using the physical properties of isotopes, and the problem of low storage capacity calculation accuracy in the existing technology was solved, achieving a higher Accuracy and cost-effectiveness.
Patent Information
- Application Number
- CN202310805650.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-07-03
- Publication Date
- 2025-01-03
AI Technical Summary
The calculation results of the prior art are relatively low when determining the capacity of the gas storage reservoir, which is greatly affected by the heterogeneity of the gas reservoir and the formation pressure, and the model cannot be reused in the evaluation of other gas storage reservoir capacity.
Perdeuterium methane and carbon 14 methane are used as isotope markers, and the gas storage is injected into the gas storage and sampled and analyzed during the gas collection period. The storage capacity of the gas storage is calculated by the physical properties of the isotope to avoid the influence of gas reservoir heterogeneity and formation pressure.
It improves the calculation accuracy of the gas storage capacity, reduces errors, can evaluate the storage capacity more accurately, and reduces costs.
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Figure BDA0004317650130000043
Abstract
Description
Technical Field
[0001] The invention relates to a method for determining the storage capacity of a gas storage reservoir, and belongs to the technical field of oil and gas exploitation. Background Art
[0002] Underground gas storage is an important facility for smoothing the peak and valley consumption of natural gas and the smooth operation of the pipeline network. Underground gas storage is mainly divided into two types: salt cavern type and depleted oil and gas reservoir type. The injection and production cycle of gas storage is generally set as follows: the injection period is 180 days and the gas production period is 150 days. The injection and production intensity is 10 to 20 times that of conventional gas reservoir development.
[0003] The storage capacity of a gas storage reservoir is an important parameter for designing the density of injection and production wells and the injection and production intensity. At present, the storage capacity of a gas storage reservoir is calculated using the volumetric method, material balance method and numerical simulation method. The volumetric method is the basic principle for calculating oil and gas reserves. It is based on the pore volume, gas saturation and other parameters of the reservoir to calculate the volume of natural gas in the reservoir, that is, the storage capacity of the gas storage reservoir. The principle of the material balance method is based on the law of conservation of mass of the reservoir. At present, the commonly used method based on the material balance method is the pressure drop method, that is, the storage capacity of the gas storage reservoir is calculated based on the relationship between parameters such as the natural gas pressure and cumulative production of the gas storage reservoir. The numerical simulation method uses a combination of seismic phases, logging phases and sedimentation to establish a detailed reservoir model with a single sand body as a unit, and uses software for fitting calculations to ultimately determine the storage capacity of the gas storage reservoir.
[0004] However, the above three methods all rely on various geological, injection and production data of the gas storage, and are affected by the heterogeneity of the reservoir. For example, when there is less logging data for the gas storage, the accuracy of the calculation will be affected. For example, Chinese patent document CN108625823A provides a method for determining the capacity of a gas storage, including the following steps: establishing a formation pressure model based on the real-time radius of the gas layer in the gas storage; establishing a bottom hole flow pressure model based on the effective permeability and gas layer skin coefficient of the gas storage; establishing a wellhead oil pressure model and a gas injection model of the wellhead of the gas storage based on the formation pressure model and the bottom hole flow pressure model; and finally determining the capacity of the gas storage based on the wellhead oil pressure model and the gas injection model. This method indirectly calculates the storage capacity based on the pressure model, flow pressure model, oil pressure model and gas injection model. Its accuracy is affected by the heterogeneity of the gas reservoir and the accuracy of the model. Moreover, due to differences in gas storages, the model formed by this method cannot be reused in the storage capacity evaluation of other gas storages. Summary of the invention
[0005] The object of the present invention is to provide a method for determining the storage capacity of a gas storage reservoir, which can solve the problem of low calculation accuracy when determining the storage capacity of a gas storage reservoir.
[0006] In order to achieve the above objectives, the technical solution adopted by the method for determining the storage capacity of a gas storage reservoir of the present invention is:
[0007] A method for determining the storage capacity of a gas storage reservoir comprises the following steps:
[0008] (1) When the gas storage is in the gas injection period, deuterated methane, carbon-14 methane and natural gas are injected into the gas storage; the total molar amount of deuterated methane injected into the gas storage is x, and the total molar amount of carbon-14 methane injected into the gas storage is y;
[0009] (2) When the gas storage is in the gas production period, the natural gas produced in the gas storage is sampled and analyzed at a certain period to determine the molar volume concentration of deuterated methane and carbon 14 methane in the samples taken in each period; when the ratio of the molar volume concentration of deuterated methane to carbon 14 methane in the samples taken in each period is equal to a×(x / y), the average value of the molar volume concentration of deuterated methane and the average value of the molar volume concentration of carbon 14 methane in all samples are respectively calculated; wherein 0.95≤a≤1.05;
[0010] (3) Calculating the storage capacity of the gas storage reservoir; the storage capacity of the gas storage reservoir is equal to the ratio of x to the average value of the molar volume concentration of deuterated methane in step (2) or the ratio of y to the average value of the molar volume concentration of carbon-14 methane in step (2).
[0011] The method for determining the storage capacity of a gas storage reservoir of the present invention first injects deuterated methane, carbon 14 methane and natural gas into a gas storage reservoir in a gas injection period, and then samples and analyzes the natural gas produced in the gas storage reservoir at a certain period when the gas storage reservoir is in a gas production period, and calculates the storage capacity of the gas storage reservoir based on the molar volume concentrations of deuterated methane and carbon 14 methane obtained by the test. The method for determining the storage capacity of a gas storage reservoir of the present invention is based on the physical properties of isotopes and is not affected by the heterogeneity of the gas reservoir, gas reservoir development and formation pressure, thus avoiding errors caused by uncertain factors and being able to more accurately evaluate the storage capacity of the gas storage reservoir.
[0012] In the present invention, the deuterated methane refers to CD4, and carbon 14 methane refers to 14 CH4. In order to improve the solubility of the injected gas and the natural gas injected into the gas storage, methane is selected as the isotope labeling object. Methane is composed of hydrogen and carbon. The isotopes of hydrogen are protium, deuterium, and tritium. Considering that the natural abundance of protium is high and tritium is radioactive, the present invention selects deuterium as the isotope replacement element. The compound after replacement is deuterium methane (CD4); at the same time, the isotopes of carbon are 12 C. 13 C. 14 C. Consider 12 C and 13 The abundance of C is relatively high, and the present invention selects 14 C is used as an isotope replacement element, and the compound after replacement is carbon 14 methane ( 14CH4). When compounds containing elements with low abundance are injected into gas storage, it can ensure that a large difference can be made with a small amount, which is conducive to reducing costs.
[0013] It is understandable that the total molar amount of deuterated methane injected into the gas storage reservoir and the total molar amount of carbon 14 methane injected into the gas storage reservoir need to meet the minimum gas concentration value that can be detected by existing instruments. Preferably, when the storage capacity design value of the gas storage reservoir is M, then x / M≥0.22×10 -7 mol / m 3 , y / M≥0.22×10 -4 mol / m 3 .
[0014] In order to ensure that the deuterated methane, carbon-14 methane and natural gas injected into the gas storage can be dispersed better and faster, preferably, the time required to inject deuterated methane into the gas storage and the time required to inject carbon-14 methane into the gas storage are not greater than the time to inject natural gas into the gas storage.
[0015] In order to ensure that the deuterated methane, carbon-14 methane and natural gas injected into the gas storage reservoir can be quickly and evenly dispersed, preferably, in the early stage of the gas injection period, the deuterated methane and carbon-14 methane are continuously and uniformly injected into the gas storage reservoir along with the natural gas.
[0016] Preferably, the early stage of the gas injection period refers to the time period of the first 70% of the total time of the gas injection period. It can be understood that the early stage of the gas injection period refers to the time period between the moment when the gas injection starts and the moment corresponding to 70% of the time required for gas injection. For example, the moment when the gas injection starts is a, and the time required for gas injection is b, then the early stage of the gas injection period refers to the time period a to (a+70%×b).
[0017] It can be understood that in the early stage of the gas injection period, continuously and uniformly injecting deuterated methane and carbon-14 methane into the gas storage reservoir along with natural gas means continuously and uniformly injecting deuterated methane and carbon-14 methane into the gas storage reservoir along with natural gas in any time period within the first 70% of the total gas injection period.
[0018] It can be understood that when the ratio of the molar volume concentrations of deuterated methane and carbon-14 methane in the samples taken in each cycle is equal to a×(x / y), it means that the deuterated methane and carbon-14 methane are evenly dispersed in the gas storage reservoir, and the molar volume concentration at this time can be used to calculate the gas storage reservoir capacity with better accuracy.
[0019] Preferably, in step (2), the number of cycles for sampling and analyzing the natural gas produced in the gas storage is not less than 3.
[0020] It can be understood that both x and y are greater than 0.
[0021] Preferably, the rate of injecting deuterated methane into the gas storage reservoir is 10 to 20 mol / d; the rate of injecting carbon-14 methane into the gas storage reservoir is 10 to 20 mol / d.
[0022] Preferably, when x>y, the storage capacity of the gas storage reservoir is equal to the ratio of x to the average value of the molar volume concentration of deuterated methane in step (2); when x<y, the storage capacity of the gas storage reservoir is equal to the ratio of y to the average value of the molar volume concentration of carbon 14 methane in step (2). Selecting a substance with a larger injection volume as the calculation result of the storage capacity of the gas storage reservoir can reduce the accuracy requirements for the measuring instrument and reduce the absolute error.
[0023] Preferably, in step (2), the molar volume concentration refers to the molar volume concentration at standard atmospheric pressure and 20° C. The unit of the molar volume concentration is mol / m 3 .
[0024] It can be understood that in step (2), the molar volume concentration of deuterated methane in the sample taken in each cycle is the ratio of the molar amount of deuterated methane in the sample to the volume of deuterated methane at standard atmospheric pressure and room temperature; the molar volume concentration of carbon-14 methane in the sample taken in each cycle is the ratio of the molar amount of carbon-14 methane in the sample to the volume of carbon-14 methane at standard atmospheric pressure and room temperature.
[0025] The conventional method for evaluating the storage capacity of a gas storage reservoir is to calculate the parameters such as permeability, porosity and relative permeability of the gas storage reservoir structural model. The parameters of the gas storage reservoir structural model are determined based on the results of well logging and coring rock physics analysis of the drilled wells, and the data of the drilled wells can only cover a limited local area of the gas reservoir. The accuracy of the conventional method for evaluating the storage capacity of a gas storage reservoir is greatly affected by the heterogeneity of the gas reservoir, gas reservoir development and formation pressure. The method for determining the storage capacity of a gas storage reservoir of the present invention, because it is based on the physical properties of isotopes, is not affected by the heterogeneity of the gas reservoir, gas reservoir development and formation pressure, avoids errors caused by uncertain factors, and can more accurately evaluate the storage capacity of the gas storage reservoir. DETAILED DESCRIPTION
[0026] The technical solution of the present invention is further described below in conjunction with specific embodiments.
[0027] Example
[0028] Taking a gas storage reservoir as an example, the method for determining the storage capacity of the gas storage reservoir in this embodiment specifically includes the following steps:
[0029] (1) When the gas storage is in the gas injection period, deuterated methane, carbon 14 methane and natural gas are injected into the gas storage in a balanced manner (deuterated methane, carbon 14 methane and natural gas are continuously injected into the gas storage, and the time required to inject deuterated methane into the gas storage and the time required to inject carbon 14 methane into the gas storage are ensured to be no longer than the time required to inject natural gas into the gas storage;
[0030] In this embodiment, the start time of injecting deuterated methane, carbon 14 methane and natural gas into the gas storage is the same, the total time of injecting deuterated methane and carbon 14 methane is 10 days, and after the injection of deuterated methane and carbon 14 methane is completed, natural gas continues to be injected into the gas storage until the injection period ends; the rate of deuterated methane injected into the gas storage is 10 mol / d, and the total molar amount injected is 750 mol; the rate of carbon 14 methane injected into the gas storage is 20 mol / d, and the total molar amount injected is 1500 mol; after the injection period ends, the gas storage enters the equilibrium period; the ratio of the molar amount of deuterated methane and carbon 14 methane injected into the gas storage to the design value of the gas storage capacity is greater than 0.22×10 -4 mol / m 3 ;
[0031] (2) After the gas storage equilibrium period, when the gas storage is in the gas production period, the natural gas produced in the gas storage is sampled and analyzed at a certain period (every 3 days) (the total sampling period is n, n=3), and the molar volume concentrations of deuterated methane and carbon 14 methane in the samples taken in each period are determined (the molar volume concentration of deuterated methane in the samples taken in each period is the ratio of the molar amount of deuterated methane to the volume of deuterated methane at standard atmospheric pressure and room temperature; the molar volume concentration of carbon 14 methane in the samples taken in each period is the ratio of the molar amount of carbon 14 methane to the volume of carbon 14 methane at standard atmospheric pressure and room temperature); the molar volume concentration of deuterated methane in the samples taken in each period is B i (mol / m 3 ), the molar volume concentration of carbon 14 methane is C i (mol / m 3 ), where 1≤i≤n, and i is an integer;
[0032] Then the molar volume concentration ratio of deuterated methane and carbon-14 methane in the samples taken in each cycle was calculated. The results showed that the molar volume concentration ratio of deuterated methane and carbon-14 methane in the samples taken in each cycle (B i / C i ) are all equal to a×(x / y), where 0.95≤a≤1.05; this indicates that the deuterated methane and carbon-14 methane are evenly dispersed in the gas storage reservoir, and the molar volume concentration at this time is used to calculate the gas storage reservoir capacity with good accuracy;
[0033] Then, the average molar volume concentration of deuterated methane and the average molar volume concentration of carbon 14 methane in all samples are calculated respectively; among which, the average molar volume concentration of deuterated methane is Average value of molar volume concentration of carbon 14 methane
[0034] (3) Calculate the storage capacity of the gas storage reservoir. Since the total molar amount of carbon-14 methane injected is greater than the total molar amount of deuterated methane injected, the calculation method for the storage capacity of the gas storage reservoir is as follows:
[0035]
[0036] Where V is the storage capacity of the gas storage, n is the total molar amount of carbon 14 methane injected into the gas storage, ave is the average value of the molar volume concentration of carbon-14 methane.
[0037] The method for determining the gas storage capacity of the present invention is compared with the conventional method for determining the gas storage capacity. As a result, it is found that the difference percentage between the gas storage capacity determined by the method for determining the gas storage capacity of the present invention and the gas storage capacity determined by the conventional method is no more than 5%. The method for determining the gas storage capacity of the present invention is a method for obtaining the gas storage capacity through physical experiments, and can determine, verify and check the gas storage capacity.
Claims
1. A method for determining the storage capacity of a gas storage reservoir, characterized in that: The following steps are involved: (1) When the gas storage is in the gas injection period, deuterated methane, carbon-14 methane and natural gas are injected into the gas storage; the total molar amount of deuterated methane injected into the gas storage is x, and the total molar amount of carbon-14 methane injected into the gas storage is y; (2) When the gas storage is in the gas production period, the natural gas produced in the gas storage is sampled and analyzed at a certain period to determine the molar volume concentration of deuterated methane and carbon 14 methane in the samples taken in each period; when the ratio of the molar volume concentration of deuterated methane to carbon 14 methane in the samples taken in each period is equal to a×(x / y), the average value of the molar volume concentration of deuterated methane and the average value of the molar volume concentration of carbon 14 methane in all samples are respectively calculated; wherein 0.95≤a≤1.05; (3) Calculating the storage capacity of the gas storage reservoir; the storage capacity of the gas storage reservoir is equal to the ratio of x to the average value of the molar volume concentration of deuterated methane in step (2) or the ratio of y to the average value of the molar volume concentration of carbon-14 methane in step (2).
2. The method for determining the storage capacity of a gas storage reservoir according to claim 1, characterized in that: The time required to inject deuterated methane into a gas storage reservoir and the time required to inject carbon-14 methane into a gas storage reservoir shall not be greater than the time required to inject natural gas into a gas storage reservoir.
3. The method for determining the storage capacity of a gas storage reservoir according to claim 1, characterized in that: In the early stage of the gas injection period, deuterated methane and carbon-14 methane are continuously and uniformly injected into the gas storage reservoir along with natural gas.
4. The method for determining the storage capacity of a gas storage reservoir according to claim 3, characterized in that: The early stage of the gas injection period refers to the time period of the first 70% of the entire gas injection period.
5. The method for determining the storage capacity of a gas storage reservoir according to claim 1, characterized in that: In step (2), the molar volume concentration refers to the molar volume concentration at standard atmospheric pressure and 20°C.
6. The method for determining the storage capacity of a gas storage reservoir according to any one of claims 1 to 5, characterized in that: When x>y, the storage capacity of the gas storage reservoir is equal to the ratio of x to the average value of the molar volume concentration of deuterated methane in step (2); when x<y, the storage capacity of the gas storage reservoir is equal to the ratio of y to the average value of the molar volume concentration of carbon-14 methane in step (2).