A water invasion identification method for water-drive gas reservoirs considering water-sealed gas

Abstract

This invention discloses a method for identifying water invasion in water-driven gas reservoirs considering water-sealed gas. The method includes collecting dynamic production data from single wells in the water-driven gas reservoir and the basic parameters required for calculation; preprocessing the collected dynamic production data and basic parameters to calculate the coefficients of the production capacity equation and obtain parameter fitting formulas; establishing a physical model of the water-driven gas reservoir considering water-sealed gas; establishing and deriving an improved material balance equation for the water-driven gas reservoir considering water-sealed gas, introducing the sealing effect coefficient and water invasion coefficient, and deriving the formation apparent pressure expression considering water-sealed gas; analyzing the fitting results of the comprehensive curve of water drive characteristics, and calculating the water invasion amount and water-sealed gas amount. Based on dynamic production data, this invention establishes an improved material balance equation considering water-sealed gas. The calculation method is simple and fast, achieving quantitative characterization and qualitative identification of water invasion throughout the entire process, avoiding the time lag problem caused by relying on chloride monitoring, and improving the accuracy of water invasion characteristic identification.

Description

Technical Field

[0001] This invention belongs to the field of gas reservoir engineering, and specifically relates to a method for identifying water intrusion in water-driven gas reservoirs that considers water-sealed gas. Background Technology

[0002] As water-driven gas reservoirs are further developed, reservoir gas is continuously extracted, leading to a decrease in formation pressure. This results in the non-uniform intrusion of water into the gas-bearing zone. The intruding water rapidly ascends or laterally along high-permeability zones or fractures, sealing off natural gas in low-permeability areas, forming "water-sealed gas." With continued extraction of natural gas from water-driven reservoirs, the intruding water occupies more of the high-permeability zones, and the amount of natural gas in the water-sealed low-permeability zones continues to increase. Due to the disruption of capillary forces and pressure systems, it is difficult to extract the gas using conventional depressurization methods, severely impacting the ultimate recovery rate of water-driven gas reservoirs.

[0003] Water intrusion identification in water-driven gas reservoirs based on material balance equations is the core of gas reservoir dynamic analysis, reflecting the technological development process from qualitative identification to quantitative characterization, and from general assessment to in-depth mechanism analysis.

[0004] Currently, the mainstream and relatively systematic methods for water intrusion identification mainly include analysis based on the gas reservoir mass balance principle, analysis based on production dynamic data, and analysis based on production well test data. Analysis based on the gas reservoir mass balance principle includes: the water intrusion coefficient method, the pressure drop curve method, and the apparent geological reserves method. The mass balance equation method does not consider complex fluid flow patterns and can be calculated with relatively little fluid property test data and production dynamic data. It is simple and practical, and widely used in gas reservoir engineering. However, the conventional water intrusion volume factor method is... Simplifying complex water bodies into steady-state or non-steady-state models and inversely estimating water intrusion volume is a direct method, but the formulas are highly theoretical. The derivation process ignores the effects of bound water expansion, rock and fluid compressibility, and changes in gas-bearing pore volume, resulting in certain theoretical deficiencies. It also has limitations and uncertainties in identifying non-uniform water intrusion in water-driven gas reservoirs. The pressure drop curve method qualitatively identifies water intrusion by observing the relationship curve between formation pressure and cumulative gas production. It is intuitive and fast and is a commonly used method for on-site diagnosis of water intrusion processes. However, similar to the water intrusion volume coefficient method, it is not sensitive to the identification of water drive characteristics in gas reservoirs, cannot quantify water intrusion parameters, and is easily affected by various factors, resulting in multiple solutions. The conventional method of observing geological reserves cannot be used to judge and identify water intrusion characteristics such as the activity level of water intrusion in gas reservoirs, and does not consider the influence of water-sealed gas during the water intrusion process.

[0005] When formulating development adjustment plans such as drainage and gas production for water-driven gas reservoirs, the impact of water-sealed gas becomes increasingly significant. It is necessary to consider water-sealed gas to obtain an objective assessment of the scale of water intrusion and the amount of water-sealed gas. However, existing water intrusion identification methods fail to systematically integrate the formation mechanism of water-sealed gas. Methods such as produced water analysis (relying on chloride monitoring, which has a lag), dynamic monitoring, and numerical simulation have inherent defects in water intrusion characteristic identification, water intrusion calculation, and development plan formulation. Overall, existing material balance equations considering water-sealed gas do not account for changes in the compressibility coefficients of reservoir rocks and fluids during water intrusion in water-driven gas reservoirs. They ignore the actual fluid flow process of water "channeling-fragmentation-isolation" along high-permeability channels in heterogeneous gas reservoirs. Based on conventional water intrusion coefficients, they cannot comprehensively determine reservoir isolation and water intrusion intensity, easily leading to misjudgments of water intrusion degree and the inability to identify water intrusion at all stages based on water intrusion characteristic curves, thus misleading development decisions. Summary of the Invention

[0006] This invention is proposed to solve the problems existing in the prior art, and its purpose is to provide a method for identifying water intrusion in water-driven gas reservoirs that takes into account water-sealed gas.

[0007] A method for identifying water intrusion in a water-driven gas reservoir considering water-sealed gas includes the following steps: S1. Collect data on water-driven gas reservoirs; S2. Based on the water-driven gas reservoir data collected in step S1, perform parameter processing; S3. Establish a physical model of a water-driven gas reservoir that takes into account water-sealed gas. S4. Derive the improved material balance equation for water-driven gas reservoirs considering water-sealed gas. S5. Combining the relative pseudo-pressure expression that takes into account the influence of water seal gas, and through actual measurements considering water seal gas... Curves and theories considering water-sealed gas The curve is fitted, and then compared with the R~water-gas ratio curve and the curve without considering the water seal gas. Curve comparison analysis yields curve fitting graphs and fitting parameter results.

[0008] In the above technical solution, the water-driven gas reservoir data includes single-well production dynamic data and basic parameters required for calculation; the production dynamic data includes the daily gas production, daily water production, water-gas ratio, and bottom hole flowing pressure of a single well in the water-driven gas reservoir; the basic parameters required for calculation include the original geological reserves G of the gas reservoir, the original formation pressure, PVT report data, porosity, initial water saturation, and pressure measurement data.

[0009] In the above technical solution, step S2 specifically includes the following steps: S21. Based on the daily gas production, daily water production, and water-to-gas ratio data of the single well in the water-driven gas reservoir collected in step S1, calculate the cumulative gas production G of the single well in the water-driven gas reservoir at each time. pCumulative water production W p and extraction degree R; S22. Combining the binomial equation for the productivity of water-driven gas reservoirs with pressure measurement data, perform linear regression on the data throughout the entire lifecycle. After curve regression fitting, calculate the laminar flow term coefficient of the binomial equation for the productivity of water-driven gas reservoirs. and turbulence term coefficient ; S23. Based on the basic data of single wells in water-driven gas reservoirs, the fitting formulas for the compressibility factor and volume coefficient of natural gas in single wells of different water-driven gas reservoirs are obtained through polynomial curve fitting. The compressibility factor of natural gas at different times is calculated. and volume factor ; S24. Calculate the relative pseudo-pressure. Pore ​​volume coefficient and original formation pressure With current formation pressure difference.

[0010] In the above technical solution, the formula for calculating the extraction degree R is: In the formula: The degree of extraction is dimensionless; Cumulative gas production, in m³ 3 ; Cumulative water production, in m³ 3 .

[0011] In the above technical solution, the binomial equation for the productivity of the water-driven gas reservoir is: In the formula: This refers to the bottom hole flowing pressure, expressed in MPa. Formation pressure, in MPa; This represents daily gas production, in units of 10. 4 m 3 / d; The coefficient for the laminar flow term is dimensionless. is the coefficient of the turbulence term, which is dimensionless.

[0012] In the above technical solution, the relative pseudo-pressure The calculation formula is: In the formula: The relative pressure is dimensionless; The volume factor of natural gas under the original formation conditions is m. 3 / m 3 Decimals, dimensionless; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; The original formation conditions and natural gas volume factor The calculation formula is: In the formula: The volume factor of natural gas under the original formation conditions is dimensionless. Standard pressure, unit is MPa. ; This represents the original formation pressure, expressed in MPa. The original condition natural gas deviation factor is a decimal, dimensionless. Reservoir temperature, in Kelvin (K). Standard temperature, in Kelvin (K). ; The current formation conditions and natural gas volume factor The calculation formula is: In the formula: The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; Standard pressure, unit is MPa. ; The current formation pressure is the pressure measurement data collected in step S1, in MPa. Reservoir temperature, in Kelvin (K). Standard temperature, in Kelvin (K). ; The natural gas compressibility factor under current conditions is a decimal and dimensionless.

[0013] In the above technical solution, the pore volume coefficient The calculation formula is: In the formula: Void volume factor, dimensionless; The formation water compressibility coefficient is expressed in MPa. -1 ; Rock compressibility coefficient, in MPa -1 ; The initial water saturation is a decimal, dimensionless.

[0014] In the above technical solution, step S4 specifically includes the following steps: S41. Establish a material balance equation for water-driven gas reservoirs that takes into account the changes in rock and fluid compressibility coefficients; The mass balance equation for the water-drive gas reservoir is: In the formula: Original geological reserves, in units of 10. 8 m 3 ; The volume factor of natural gas under the original formation conditions is dimensionless. The formation water compressibility coefficient is expressed in MPa. -1 ; The initial water saturation is a decimal, dimensionless. Rock compressibility coefficient, in MPa -1 ; Original formation pressure With current formation pressure The difference is expressed in MPa. Cumulative gas production, in units of 10. 8 m 3 ; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; The total water inundation volume is expressed in units of 10. 4 m 3 ; Cumulative water production, in units of 10. 8 m 3 ; This is the formation water volume factor, in cubic meters. 3 / m 3 ; S42. Using the material balance equation of a water-driven gas reservoir, and based on the physical model of a water-driven gas reservoir considering water-sealed gas, establish an improved material balance equation for a water-driven gas reservoir considering water-sealed gas. The improved material balance equation for the water-drive gas reservoir is as follows: In the formula: Original geological reserves, in units of 10. 8 m 3 ; The volume factor of natural gas under the original formation conditions is dimensionless. The formation water compressibility coefficient is expressed in MPa. -1 ; The initial water saturation is a decimal, dimensionless. Rock compressibility coefficient, in MPa -1 ; Original formation pressure With current formation pressure The difference is expressed in MPa. Cumulative gas production, in units of 10. 8 m 3 ; This refers to the water seal gas volume, in units of 10. 8 m 3 ; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; The total water inundation volume is expressed in units of 10. 4 m 3 ; Cumulative water production, in units of 10. 8 m 3 ; This is the formation water volume factor, in cubic meters. 3 / m 3 ; S43. Define the barrier effect coefficient. and water erosion coefficient The calculation formula; The sealing effect coefficient The water seal gas intensity, which varies due to reservoir heterogeneity, is calculated using the following formula: In the formula: The sealing effect coefficient is dimensionless. Original geological reserves, in units of 10. 8 m 3 ; The volume factor of natural gas under the original formation conditions is dimensionless. The total water inundation volume is expressed in units of 10. 4 m 3 ; Cumulative water production, in units of 10. 8 m 3 ; This refers to the water seal gas volume, in units of 10. 8 m 3 ; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; This is the formation water volume factor, in cubic meters. 3 / m 3 ; The water erosion coefficient The reservoir water intrusion intensity is expressed by the following formula: In the formula: The coefficient for water intrusion is dimensionless. The total water inundation volume is expressed in units of 10. 4 m 3 ; Cumulative water production, in units of 10. 8 m 3 ; This refers to the water seal gas volume, in units of 10. 8 m 3 ; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; The volume factor of natural gas under the original formation conditions is dimensionless. Cumulative gas production, in units of 10. 8 m 3 ; This is the formation water volume factor, in cubic meters. 3 / m 3 ; S44. Utilizing the sealing effect coefficient Water intrusion coefficient Extraction degree R, pore volume coefficient and relative pressure The improved material balance equation for the water-driven gas reservoir considering water-sealed gas, established in step S42, is simplified to obtain the relative pseudo-pressure expression considering the influence of water-sealed gas: In the formula: Void volume factor, dimensionless; Original formation pressure With current formation pressure The difference is expressed in MPa. The degree of extraction is dimensionless; The sealing effect coefficient is dimensionless. The coefficient for water intrusion is dimensionless. The relative pressure is dimensionless.

[0015] In the above technical solution, step S5 specifically includes the following steps: S51. Based on the geological characteristics of the single well reservoir in the water-driven gas reservoir, the initial values ​​of the parameters are given to fit the measured curve and the theoretical curve. Within a reasonable range, the values ​​of the fitting parameters are adjusted multiple times to make the measured curve and the theoretical curve considering water-sealed gas reach the fitting accuracy. Otherwise, this step is repeated to perform curve fitting, and finally the curve fitting graph and fitting parameter results are obtained. The fitting parameters include the sealing effect coefficient. Water intrusion coefficient And predict the timing of flooding; S52. Based on the fitting results, further, compared with the R~water-gas ratio curve and the curve without considering water seal gas... By comparing the curves and analyzing the water intrusion characteristic curves, we can characterize the water body's energy supply, containment, and intensity during the water intrusion process. Simultaneously, we can calculate the water-sealed gas volume at different times in the water-driven gas reservoir. and cumulative water intrusion .

[0016] The beneficial effects of this invention are: This invention provides a method for identifying water intrusion in water-driven gas reservoirs that considers water-sealed gas. Utilizing dynamic production data of the water-driven gas reservoir and an improved material balance equation considering water-sealed gas, field technicians can quickly identify water intrusion characteristics by obtaining water-driven characteristic curves through simple calculations. The calculation method is simple and fast. Furthermore, the method uses curve fitting results and the sealing effect coefficient... and water erosion coefficient It can quantitatively characterize reservoir isolation and water intrusion intensity, and simultaneously calculate water-sealed gas volume to achieve quantitative characterization; combined with characteristic curves that do not consider water-sealed gas and water-gas ratio curves, it can comprehensively judge different stages of isolation and water intrusion, and can be used for qualitative identification of water intrusion, realizing early warning of water intrusion risk and water-sealed gas formation. It changes the passive situation of traditional methods that rely on the time lag of chloride monitoring when water seeps from "lagging judgment" to "proactive early warning"; it is not limited by fluid flow laws, the method has high universality and strong scalability.

[0017] This invention avoids the time lag problem caused by relying on chloride monitoring, improves the accuracy of water intrusion feature identification, provides a theoretical basis and guidance for water control and management of water-driven gas reservoirs, and has practical significance for adjusting subsequent development schemes for such gas reservoirs. Attached Figure Description

[0018] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the physical model of a water-driven gas reservoir considering water-sealed gas in Embodiment 1 of the present invention; Figure 3 This is a fitting diagram of the water-drive characteristic curve considering water-sealed gas in this invention; Figure 4 This is a comprehensive analysis diagram of the water drive characteristic curves in this invention.

[0019] For those skilled in the art, other related figures can be obtained from the above figures without any creative effort. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1 like Figure 1 As shown, a method for identifying water intrusion characteristics of water-driven gas reservoirs considering water-sealed gas includes the following steps: S1. Collect data on water-driven gas reservoirs; The water-driven gas reservoir data includes single-well production dynamics data and basic parameters required for calculation. The production dynamic data includes the daily gas production, daily water production, water-to-gas ratio, and bottom hole flowing pressure of a single well in a water-driven gas reservoir; The basic parameters required for the calculation include the original geological reserves G of the gas reservoir and the original formation pressure. PVT report data, porosity Initial water saturation Pressure measurement data; The water-driven gas reservoir data for this embodiment are shown in Table 1.

[0022] Table 1: Water-driven gas reservoir data S2. Based on the water-driven gas reservoir data collected in step S1, perform parameter processing; Specifically, the following steps are included: S21. Based on the daily gas production, daily water production, and water-to-gas ratio data of the single well in the water-driven gas reservoir collected in step S1, calculate the cumulative gas production G of the single well in the water-driven gas reservoir at different production times (in days). p Cumulative water production W p and extraction degree R; The formula for calculating the extraction degree R is: In the formula: The degree of extraction is dimensionless; Cumulative gas production, in m³ 3 ; Cumulative water production, in m³ 3 ; S22. Combining the binomial equation for the productivity of water-driven gas reservoirs, linear regression is performed on the pressure measurement data. After curve regression fitting, the laminar flow term coefficient of the binomial equation for the productivity of water-driven gas reservoirs is calculated. and turbulence term coefficient ; The binomial equation for the productivity of the water-drive gas reservoir is as follows: In the formula: This refers to the bottom hole flowing pressure, expressed in MPa. Formation pressure, in MPa; This represents daily gas production, in units of 10. 4 m3 / d; The coefficient for the laminar flow term is dimensionless. The coefficients for the turbulence term are dimensionless. S23. Based on the basic data of single wells in water-driven gas reservoirs, the fitting formulas for the compressibility factor and volume coefficient of natural gas in single wells of different water-driven gas reservoirs are obtained through polynomial curve fitting. The compressibility factor of natural gas at different times is calculated. and volume factor ; The basic data for step S23 includes PVT report data and original formation pressure; S24. Calculate the relative pseudo-pressure. Pore ​​volume coefficient and original formation pressure With current formation pressure difference ( ); The relative pseudo-pressure The calculation formula is: In the formula: The relative pressure is dimensionless; The volume factor of natural gas under the original formation conditions is m. 3 / m 3 Decimals, dimensionless; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; The original formation conditions and natural gas volume factor The calculation formula is: In the formula: The volume factor of natural gas under the original formation conditions is dimensionless. Standard pressure, unit is MPa. ; This represents the original formation pressure, expressed in MPa. The original condition natural gas deviation factor is a decimal, dimensionless. Reservoir temperature, in Kelvin (K). Standard temperature, in Kelvin (K). ; The current formation conditions and natural gas volume factor The calculation formula is: In the formula: The natural gas volume factor under current formation conditions is m. 3 / m3 Decimals, dimensionless; Standard pressure, unit is MPa. ; This is the formation pressure, which is the formation pressure calculated in step S22, in MPa. Reservoir temperature, in Kelvin (K). Standard temperature, in Kelvin (K). ; The natural gas compressibility factor under current conditions is a decimal and dimensionless. The pore volume coefficient The calculation formula is: In the formula: Void volume factor, dimensionless; The formation water compressibility coefficient is expressed in MPa. -1 ; Rock compressibility coefficient, in MPa -1 ; The initial water saturation is a decimal, dimensionless. S3. Establish a physical model of a water-driven gas reservoir that takes into account water-sealed gas. During the development of water-driven gas reservoirs, formation water (edge ​​water or bottom water) invades the gas reservoir under the action of pressure difference, displacing and occupying part of the pore space. Some natural gas is sealed by water to form water-sealed gas. The physical model of water-driven gas reservoirs intuitively reflects the seepage mechanism such as water intrusion and gas being sealed by water. The physical model of the water-driven gas reservoir in this embodiment is as follows: Figure 2 As shown; S4. Derive the improved material balance equation for water-driven gas reservoirs considering water-sealed gas. Specifically, the following steps are included: S41. According to the principle of material balance, the original pore volume occupied by gas is equal to the sum of the current pore volume occupied by gas, the elastic expansion volume of the rock and bound water in the gas-bearing area, and the volume of pure water intrusion. Considering the changes in the compressibility coefficients of the rock and fluid, the material balance equation for a water-driven gas reservoir is established, namely: In the formula: Original geological reserves, in units of 10. 8 m 3 ; The volume factor of natural gas under the original formation conditions is dimensionless. The formation water compressibility coefficient is expressed in MPa. -1 ; The initial water saturation is a decimal, dimensionless. Rock compressibility coefficient, in MPa -1 ; Original formation pressure With current formation pressure The difference is expressed in MPa. Cumulative gas production, in units of 10. 8 m 3 ; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; The total water inundation volume is expressed in units of 10. 4 m 3 ; Cumulative water production, in units of 10. 8 m 3 ; This is the formation water volume factor, in cubic meters. 3 / m 3 ; S42. Using the material balance equation of a water-driven gas reservoir, and based on the physical model of a water-driven gas reservoir considering water-sealed gas, establish an improved material balance equation for a water-driven gas reservoir considering water-sealed gas, namely: In the formula: Original geological reserves, in units of 10. 8 m 3 ; The volume factor of natural gas under the original formation conditions is dimensionless. The formation water compressibility coefficient is expressed in MPa. -1 ; The initial water saturation is a decimal, dimensionless. Rock compressibility coefficient, in MPa -1 ; Original formation pressure With current formation pressure The difference is expressed in MPa. Cumulative gas production, in units of 10. 8 m 3 ; This refers to the water seal gas volume, in units of 10. 8 m 3 ; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; The total water inundation volume is expressed in units of 10. 4 m 3 ; Cumulative water production, in units of 10. 8 m 3 ; This is the formation water volume factor, in cubic meters.3 / m 3 ; S43. Define the barrier effect coefficient. and water erosion coefficient The calculation formula; The sealing effect coefficient The water seal gas intensity, which varies due to reservoir heterogeneity, is calculated using the following formula: In the formula: The sealing effect coefficient is dimensionless. Original geological reserves, in units of 10. 8 m 3 ; The volume factor of natural gas under the original formation conditions is dimensionless. The total water inundation volume is expressed in units of 10. 4 m 3 ; Cumulative water production, in units of 10. 8 m 3 ; This refers to the water seal gas volume, in units of 10. 8 m 3 ; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; This is the formation water volume factor, in cubic meters. 3 / m 3 ; The water erosion coefficient The reservoir water intrusion intensity is expressed by the following formula: In the formula: The coefficient for water intrusion is dimensionless. The total water inundation volume is expressed in units of 10. 4 m 3 ; Cumulative water production, in units of 10. 8 m 3 ; This refers to the water seal gas volume, in units of 10. 8 m 3 ; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; The volume factor of natural gas under the original formation conditions is dimensionless. Cumulative gas production, in units of 10. 8 m 3 ; This is the formation water volume factor, in cubic meters. 3 / m 3 ; S44. Utilizing the sealing effect coefficient Water intrusion coefficient Extraction degree R, pore volume coefficient and relative pressure The improved material balance equation for water-driven gas reservoirs considering water-sealed gas, established in step S42, is simplified by dividing both sides by [the formula is missing in the original text]. Then, we get: In the formula: Void volume factor, dimensionless; Original formation pressure With current formation pressure The difference is expressed in MPa. The degree of extraction is dimensionless; The sealing effect coefficient is dimensionless. The coefficient for water intrusion is dimensionless. The relative pressure is dimensionless; Furthermore, the relative quasi-pressure expression considering the influence of water seal gas can be obtained: In the formula: Void volume factor, dimensionless; Original formation pressure With current formation pressure The difference is expressed in MPa. The degree of extraction is dimensionless; The sealing effect coefficient is dimensionless. The coefficient for water intrusion is dimensionless. The relative pressure is dimensionless; S5. Combining the relative pseudo-pressure expression that takes into account the influence of water seal gas, and through actual measurements considering water seal gas... Curves and theories considering water-sealed gas The curve is fitted, and then compared with the R~water-gas ratio curve and the curve without considering the water seal gas. Curve comparison analysis yields curve fitting graphs and fitting parameter results.

[0023] Considering the actual measurement of water seal gas The x-coordinate of the curve is The vertical axis is Measured x-axis Step S21: Formula calculation; calculate using the formula from step S44. ; Theory of water-sealed gas The x-coordinate of the curve is The vertical axis is Theoretical x-axis These are theoretical values, such as 0.1, 0.2, 0.3, ..., 1, calculated using the formula in step S44. ; Without considering water seal gas The x-coordinate of the curve is The vertical axis is x-axis The measured data is calculated using the formula in step S21, and then calculated using the formula in step S24. ; The x-axis of the R-water-gas ratio curve is The vertical axis represents the water-to-air ratio, and the horizontal axis represents the water-to-air ratio. The measured data is calculated using the formula in step S21, and the water-air ratio is the production dynamic data collected in step S1. Specifically, the following steps are included: S51. Based on the geological characteristics of single-well reservoirs in water-driven gas reservoirs, the measured values ​​considering water-sealed gas are given. Curves and theories considering water-sealed gas The curve, within a reasonable range, was obtained by repeatedly adjusting the values ​​of the fitting parameters to account for the measured water seal gas. Curves and theories considering water-sealed gas If the curve reaches the required fitting accuracy, then repeat this step to perform curve fitting, and finally obtain the curve fitting graph. Figure 3 ), fitting parameter results (Table 2); The fitting parameters include the sealing effect coefficient. Water intrusion coefficient And predict the timing of flooding; S52. Based on the fitting results, further, compared with the R~water-gas ratio curve and the curve without considering water seal gas... Compare the curves, such as Figure 4 As shown; by analyzing the water drive characteristic curve ( Figure 3 , Figure 4 This characterizes the energy supply, containment, and intensity of water intrusion during the water intrusion process, and simultaneously calculates the water-sealed gas volume at different times in the water-driven gas reservoir. and cumulative water intrusion .

[0024] Water drive characteristic curves are curves used in gas reservoir engineering to describe the relationship between key dynamic parameters and production time or production indicators during the process of water intrusion into the gas reservoir. They can be used to identify water intrusion, determine the intensity of water intrusion, evaluate the water drive stage, and analyze development dynamics.

[0025] Table 2: Analysis Results of Water Drive Characteristic Curves in Examples This invention is based on the dual mechanism of water invasion into a water-driven gas reservoir, which replenishes formation energy and seals off natural gas in the reservoir. It considers the sealing effect of non-uniform water invasion on the gas reservoir, and uses data such as production dynamics and basic gas reservoir parameters to derive an improved material balance equation that considers water-sealed gas. By introducing a sealing effect coefficient A and a water invasion coefficient B, the energy supply, sealing, and water invasion strength of the reservoir water are characterized. The amount of water-sealed gas and water invasion at different times are calculated to clearly identify the entire process of non-uniform water invasion in the water-driven gas reservoir.

[0026] This invention directly considers the water-sealed gas term in the material balance equation, establishing an improved material balance equation that takes into account water-sealed gas. The theoretical derivation is not limited by the fluid flow pattern in the reservoir, quantifies the amount of water-sealed gas in water-driven gas reservoirs, and truly reflects the dual effects of water intrusion into the reservoir: the positive effect of replenishing formation energy and the negative impact of gas containment leading to the loss of recoverable reserves. This makes the theoretical model consistent with the actual process of water forming water-sealed gas along high-permeability channels. In the derivation of the improved material balance equation, water intrusion coefficients and containment effect coefficients considering water-sealed gas are introduced, and the changes in reservoir rock and fluid compressibility are simultaneously considered. Only production dynamic data and basic parameters are needed to plot the comprehensive water-drive characteristic identification curve considering the influence of water-sealed gas, and to calculate... The process is simple and convenient; by fitting the water drive characteristic curve, the water invasion coefficient and the sealing effect coefficient can be obtained, realizing the quantitative characterization of reservoir supply, sealing, and water invasion intensity. At the same time, the water invasion volume and water-sealed gas volume can be calculated, and the parameter solution is more comprehensive and accurate. The water invasion stage is qualitatively identified by the water drive characteristic curve, thereby classifying the water invasion mode and enriching the identification dimensions. The method of this invention can provide support for determining the optimal drainage timing and intensity and implementing drainage and gas production measures for water-driven gas reservoirs. The technical method of this invention can further amplify the water invasion signal, more sensitively identify water invasion characteristics, and realize early warning of water invasion risk and water-sealed gas formation. It changes the passive situation of traditional methods relying on the time lag of water exposure chloride monitoring from "lagging judgment" to "proactive early warning".

[0027] This invention, through theoretical innovation, develops an improved material balance method that considers water-sealed gas for quantitative and qualitative identification of water intrusion characteristics, which has practical application value for the efficient development of water-driven gas reservoirs.

[0028] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for identifying water intrusion in a water-driven gas reservoir considering water-sealed gas, characterized in that: Includes the following steps: S1. Collect data on water-driven gas reservoirs; S2. Based on the water-driven gas reservoir data collected in step S1, perform parameter processing; S3. Establish a physical model of a water-driven gas reservoir that takes into account water-sealed gas. S4. Derive the improved material balance equation for water-driven gas reservoirs considering water-sealed gas. S5. Combining the relative pseudo-pressure expression that takes into account the influence of water seal gas, and through actual measurements considering water seal gas... Curves and theories considering water-sealed gas The curve is fitted, and then compared with the R~water-gas ratio curve and the curve without considering the water seal gas. Curve comparison analysis yields curve fitting graphs and fitting parameter results.

2. The method for identifying water intrusion in a water-driven gas reservoir considering water-sealed gas according to claim 1, characterized in that: The water-driven gas reservoir data includes single-well production dynamic data and basic parameters required for calculation; the production dynamic data includes the daily gas production, daily water production, water-gas ratio, and bottom hole flowing pressure of a single well in the water-driven gas reservoir; the basic parameters required for calculation include the original geological reserves of the gas reservoir, the original formation pressure, PVT report data, porosity, initial water saturation, and pressure measurement data.

3. The water intrusion identification method for water-driven gas reservoirs considering water-sealed gas according to claim 1, characterized in that: Step S2 specifically includes the following steps: S21. Based on the daily gas production, daily water production, and water-to-gas ratio data of the single well in the water-driven gas reservoir collected in step S1, calculate the cumulative gas production G of the single well in the water-driven gas reservoir at each time. p Cumulative water production W p and extraction degree R; S22. Combining the binomial equation for the productivity of water-driven gas reservoirs with pressure measurement data, perform linear regression on the data throughout the entire lifecycle. After curve regression fitting, calculate the laminar flow term coefficient of the binomial equation for the productivity of water-driven gas reservoirs. and turbulence term coefficient ; S23. Based on the basic data of single wells in water-driven gas reservoirs, the fitting formulas for the compressibility factor and volume coefficient of natural gas in single wells of different water-driven gas reservoirs are obtained through polynomial curve fitting. The compressibility factor of natural gas at different times is calculated. and volume factor ; S24. Calculate the relative pseudo-pressure. Pore ​​volume coefficient and original formation pressure With current formation pressure difference.

4. The method for identifying water intrusion in a water-driven gas reservoir considering water-sealed gas according to claim 3, characterized in that: The formula for calculating the extraction degree R is: In the formula: The degree of extraction is dimensionless; Cumulative gas production, in m³ 3 ; Cumulative water production, in m³ 3 .

5. The water intrusion identification method for water-driven gas reservoirs considering water-sealed gas according to claim 3, characterized in that: The binomial equation for the productivity of the water-drive gas reservoir is as follows: In the formula: This refers to the bottom hole flowing pressure, expressed in MPa. Formation pressure, in MPa; This represents daily gas production, in units of 10. 4 m 3 / d; The laminar flow coefficient is dimensionless. is the coefficient of the turbulence term, which is dimensionless.

6. The method for identifying water intrusion in a water-driven gas reservoir considering water-sealed gas according to claim 3, characterized in that: The relative pseudo-pressure The calculation formula is: In the formula: The relative pressure is dimensionless; The volume factor of natural gas under the original formation conditions is m. 3 / m 3 Decimals, dimensionless; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; The original formation conditions and natural gas volume factor The calculation formula is: In the formula: The volume factor of natural gas under the original formation conditions is dimensionless. Standard pressure, unit is MPa. ; This represents the original formation pressure, expressed in MPa. The original condition natural gas deviation factor is a decimal, dimensionless. Reservoir temperature, in Kelvin (K). Standard temperature, in Kelvin (K). ; The current formation conditions and natural gas volume factor The calculation formula is: In the formula: The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; Standard pressure, unit is MPa. ; The current formation pressure is the pressure measurement data collected in step S1, in MPa. Reservoir temperature, in Kelvin (K). Standard temperature, in Kelvin (K). ; The natural gas compressibility factor under current conditions is a decimal and dimensionless.

7. The water intrusion identification method for water-driven gas reservoirs considering water-sealed gas according to claim 3, characterized in that: The pore volume coefficient The calculation formula is: In the formula: The pore volume coefficient is dimensionless. The formation water compressibility coefficient is expressed in MPa. -1 ; Rock compressibility coefficient, in MPa -1 ; The initial water saturation is a decimal, dimensionless.

8. The method for identifying water intrusion in a water-driven gas reservoir considering water-sealed gas according to claim 1, characterized in that: Step S4 specifically includes the following steps: S41. Establish a material balance equation for water-driven gas reservoirs that takes into account the changes in rock and fluid compressibility coefficients; The mass balance equation for the water-drive gas reservoir is: In the formula: Original geological reserves, in units of 10. 8 m 3 ; The volume factor of natural gas under the original formation conditions is dimensionless. The formation water compressibility coefficient is expressed in MPa. -1 ; The initial water saturation is a decimal, dimensionless. Rock compressibility coefficient, in MPa -1 ; Original formation pressure With current formation pressure The difference is expressed in MPa. Cumulative gas production, in units of 10. 8 m 3 ; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; The total water inundation volume is expressed in units of 10. 4 m 3 ; Cumulative water production, in units of 10. 8 m 3 ; is the formation water volume coefficient, dimensionless; S42. Using the material balance equation of a water-driven gas reservoir, and based on the physical model of a water-driven gas reservoir considering water-sealed gas, establish an improved material balance equation for a water-driven gas reservoir considering water-sealed gas. The improved material balance equation for the water-drive gas reservoir is as follows: In the formula: Original geological reserves, in units of 10. 8 m 3 ; The volume factor of natural gas under the original formation conditions is dimensionless. The formation water compressibility coefficient is expressed in MPa. -1 ; The initial water saturation is a decimal, dimensionless. Rock compressibility coefficient, in MPa -1 ; Original formation pressure With current formation pressure The difference is expressed in MPa. Cumulative gas production, in units of 10. 8 m 3 ; This refers to the water seal gas volume, in units of 10. 8 m 3 ; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; The total water inundation volume is expressed in units of 10. 4 m 3 ; Cumulative water production, in units of 10. 8 m 3 ; is the formation water volume coefficient, dimensionless; S43. Define the barrier effect coefficient. and water erosion coefficient The calculation formula; The sealing effect coefficient The water seal gas intensity, which varies due to reservoir heterogeneity, is calculated using the following formula: In the formula: The sealing effect coefficient is dimensionless. Original geological reserves, in units of 10. 8 m 3 ; The volume factor of natural gas under the original formation conditions is dimensionless. The total water inundation volume is expressed in units of 10. 4 m 3 ; Cumulative water production, in units of 10. 8 m 3 ; This refers to the water seal gas volume, in units of 10. 8 m 3 ; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; is the formation water volume coefficient, dimensionless; The water erosion coefficient The reservoir water intrusion intensity is expressed by the following formula: In the formula: The coefficient for water intrusion is dimensionless. The total water inundation volume is expressed in units of 10. 4 m 3 ; Cumulative water production, in units of 10. 8 m 3 ; This refers to the water seal gas volume, in units of 10. 8 m 3 ; The natural gas volume factor under current formation conditions is m. 3 / m 3 Decimals, dimensionless; The volume factor of natural gas under the original formation conditions is dimensionless. Cumulative gas production, in units of 10. 8 m 3 ; is the formation water volume coefficient, dimensionless; S44. Utilizing the sealing effect coefficient Water intrusion coefficient Extraction degree R, pore volume coefficient and relative pressure The improved material balance equation for the water-driven gas reservoir considering water-sealed gas, established in step S42, is simplified to obtain the relative pseudo-pressure expression considering the influence of water-sealed gas: In the formula: The pore volume coefficient is dimensionless. Original formation pressure With current formation pressure The difference is expressed in MPa. The degree of extraction is dimensionless; The sealing effect coefficient is dimensionless. The coefficient for water intrusion is dimensionless. The relative pressure is dimensionless.

9. The method for identifying water intrusion in a water-driven gas reservoir considering water-sealed gas according to claim 1, characterized in that: Step S5 specifically includes the following steps: S51. Based on the geological characteristics of the single well reservoir in the water-driven gas reservoir, the initial values ​​of the parameters are given to fit the measured curve and the theoretical curve. Within a reasonable range, the values ​​of the fitting parameters are adjusted multiple times to make the measured curve and the theoretical curve reach the fitting accuracy. Otherwise, this step is repeated to perform curve fitting, and finally the curve fitting graph and fitting parameter results are obtained. The fitting parameters include the sealing effect coefficient. Water intrusion coefficient And predict the timing of flooding; S52. Based on the fitting results, further, compared with the R~water-gas ratio curve and By comparing the curves and analyzing the water intrusion characteristic curves, we can characterize the water body's energy supply, containment, and intensity during the water intrusion process. Simultaneously, we can calculate the water-sealed gas volume at different times in the water-driven gas reservoir. and cumulative water intrusion .

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