Fractured-vuggy gas reservoir bottom hole flowing pressure calculation method considering fracture water evolution

Abstract

The invention provides a fractured-vuggy gas reservoir bottom hole flowing pressure calculation method considering fractured water evolution, and belongs to the field of oil and gas field development. In order to solve the problems that in a fracture-vug type gas reservoir, a fracture water body participates in seepage, and pressure response is complex, a coupling calculation process between a water body-fracture system and flowing bottomhole pressure is established. According to the method, a fracture water infiltration mechanism is introduced, the change of the fracture water content state along with the production process is dynamically described, a formation pressure iterative calculation model considering the water supply influence is constructed on the basis, and then hourly calculation of the flowing bottomhole pressure is achieved. The method only depends on conventional production data and basic geological parameters, the calculation process is clear, and the physical significance of the parameters is clear. Through comparison of example calculation and field actual measurement of flowing bottomhole pressure data, the result shows that the method can reasonably reflect the change characteristics of the bottomhole pressure in the production process of the gas well of the fracture-vug type gas reservoir, and technical support can be provided for dynamic analysis and production management of the fracture-vug type gas reservoir.

Description

Technical Field

[0001] This invention relates to a method for calculating bottom-hole flowing pressure in fractured-vuggy gas reservoirs that takes into account the evolution of fractured water bodies, and belongs to the field of oil and gas field development engineering. Background Technology

[0002] Fractured-vuggy gas reservoirs are characterized by fractures, pore development, strong heterogeneity, and complex water effects. During gas well production, formation water can infiltrate into the reservoir through the fracture system, causing the water-bearing state of the fractures to evolve continuously. This alters the gas-water two-phase flow capacity and further affects formation pressure changes and bottom hole flowing pressure response.

[0003] Existing methods for calculating bottom-hole flowing pressure in gas wells are mostly based on a constant production index or a simplified material balance assumption. They typically fail to explicitly consider the coupling effect of the dynamic evolution of fracture water during the production process on relative permeability and formation pressure. This results in insufficient accuracy of bottom-hole flowing pressure calculations in gas reservoirs with significant water intrusion or well-developed fractures, making it difficult to accurately reflect the production characteristics of gas wells.

[0004] Therefore, it is necessary to propose a calculation method that can comprehensively consider the evolution of fractured water, changes in formation pressure, and bottom hole flowing pressure response, so as to improve the rationality and applicability of bottom hole flowing pressure calculation for fractured-vuggy gas reservoirs. Summary of the Invention

[0005] The purpose of this invention is to provide a method for calculating bottom-hole flowing pressure in fractured-vuggy gas reservoirs that takes into account the evolution of fractured water. By establishing a coupled calculation relationship between water infiltration into the fracture system, the evolution of fracture water-bearing state, and formation pressure changes, the method achieves coordinated calculation of formation pressure and bottom-hole flowing pressure under the influence of fractured water, thereby improving the rationality and applicability of bottom-hole flowing pressure calculation in fractured-vuggy gas reservoirs.

[0006] To achieve the above objectives, this invention provides a method for calculating the bottom-hole flowing pressure of fractured-vuggy gas reservoirs that considers the evolution of fractured water. This method includes the following steps: S100, Data and parameter input and initial calculation state; S101, Obtain the production time series. Daily gas production Daily water production Input the original formation pressure Formation temperature Dynamic reserves of gas reservoirs Gas phase productivity index Water Productivity Index Crack volume Initial water saturation Corey Index , , water saturation Residual gas saturation heterogeneity coefficient Water erosion shape index Water body energy replenishment coefficient ; S102, Calculate the initial gas compressibility factor And obtained: ; Initialize cumulative gas production Water content of the crack ; in, This is the compressibility factor under the original formation pressure, expressed as a decimal. This is a function for calculating the gas compressibility factor based on pressure and temperature. For the first The total gas production of all gas wells in the world, in ten thousand cubic meters; For the first i The water volume of the fissures in the sky, in meters. 3 ; The crack volume is expressed in meters (m). 3 ; The initial water saturation is dimensionless. S200, for each production day Update cumulative gas production ; in Daily gas production, in units of For the first Daily gas production volume, expressed in 10,000 cubic meters per day; S300, fracture water content evolution and relative permeability calculation; S301. Calculate the effective water saturation. Corey's relative penetration rate is , ; in, Effective water saturation, dimensionless; For the first The water saturation of the day is dimensionless. The water saturation is dimensionless. Residual gas saturation, dimensionless; , For the first Relative permeability of the weather phase and the liquid phase, dimensionless; , The Corey exponent is dimensionless. S400, Water Infiltration into Fracts and Update of Fract Water Content Status; S401, in the Each computation time step calculates the amount of water infiltrating into the fracture system based on the pressure difference between the formation pressure and the fracture control body pressure. Among them, the pressure of the crack control body The fracture-wellbore equivalent pressure is calculated nonlinearly using formation mass balance and gas compressibility factor, with its initial value taken from the previous time step. The fracture water infiltration driving pressure difference is defined as... The driving pressure difference is used to characterize the effective pressure difference when formation water invades the fracture system. S402, the infiltration rate of water in the crack is calculated using the following formula: ; in, This is the water productivity index, expressed in m³ / (d·MPa). The infiltration rate is expressed in m³ / d; when When the differential pressure is less than the preset starting threshold, let And the daily infiltration amount does not exceed the preset maximum value; S403. Update the fracture water content based on the infiltration water volume. And further update the water saturation of the cracks. ; S500, Establish a nonlinear iteration of formation pressure-compressibility factor considering water intrusion; S501. Convert the infiltration volume of water in the fracture into an equivalent water infiltration energy: ; in, The total equivalent water intrusion is expressed in units of 10. 4 m³; where 10000 is a volume unit conversion factor used to convert the daily infiltration volume from m³ / d to a volume unit consistent with the dynamic storage. The conversion is used to convert the effect of fracture water intrusion on formation pressure maintenance into the water intrusion energy term in the mass balance equation. S502, the equivalent recovery ratio is: and constraints ; The water body energy amplification factor is used to characterize the equivalent contribution of a unit volume of water to the formation pressure maintenance capacity relative to gas during the intrusion of water into the fracture. It is dimensionless. S503, Calculate the following using the water seal material balance equation. Formation pressure to compressibility factor ratio constraint for the day: ; And by using nonlinear iteration of formation pressure and gas compressibility factor, the first... i The pressure of the crack control body at each time step The water seal material balance equation is used to describe the relationship between formation pressure and the degree of extraction under the combined effects of gas production and water intrusion. S600, Bottomhole flowing pressure calculation; wherein, the fracture control body pressure As the upstream equivalent pressure in the wellbore productivity equation, it is used to characterize the pressure supply capacity of the fracture-wellbore system to the bottom of the well; S601. Based on the gas seepage characteristics, establish a production capacity relationship in the form of square pressure. ; S602, Production Capacity Relationship under Pressure Squared Get the first i Wellbore pressure ; in, This is the gas phase productivity index, in units of (10). 4 m³ / d) / MPa²; S603. Output the bottom hole flowing pressure calculation results for each production time step; Attached Figure Description

[0007] Figure 1 This is the technical roadmap for this method; Figure 2 This is a schematic diagram of a fracture-water coupling model for fractured-vuggy gas reservoirs; Figure 3 This is a graph showing the calculated bottom-hole flowing pressure of a water-bearing fractured-vuggy gas well. Detailed Implementation

[0008] This invention provides a method for calculating bottom-hole flowing pressure in fractured-vuggy gas reservoirs that takes into account the evolution of fractured water. Figure 1 This is the technical roadmap for this method. For a fractured-vuggy gas well in China, the following steps are implemented: S100: As Figure 2 As shown, fractured-vuggy gas reservoirs are divided into three parts: external water body, fracture or pore control body, and wellbore system. The fracture or pore control body serves as an intermediate coupling unit between the water body and the wellbore, used to characterize the evolution of the water-bearing state of the fractures and its impact on the gas well's pressure supply capacity. S200: , such as Figure 1 The figure shows how to obtain the production time series. Daily gas production Daily water production Input the original formation pressure Formation temperature Dynamic reserves of gas reservoirs Gas phase productivity index Water Productivity Index Crack volume Initial water saturation Corey Index , , water saturation Residual gas saturation heterogeneity coefficient Water erosion shape index Water body energy replenishment coefficient ; Calculate the initial water-bearing volume of the fracture based on the initial fracture water saturation, and calculate the initial gas compressibility factor and initial pressure compressibility ratio; S300: In each calculation time step, the cumulative gas production is updated based on the daily gas production of the corresponding time step, providing a basis for the production volume for subsequent formation material balance calculations. S400: such as Figure 2 As shown, the intrusion of water into the fracture system alters the water-bearing state of the fractures. In the first... i At each time step, the water saturation of the fracture is calculated based on the water volume of the fracture. Under the condition of considering the immobile water saturation and residual gas saturation, the effective water saturation is calculated. Based on the effective water saturation, the Corey relative permeability model is used to calculate the relative permeability of the gas phase and the water phase, so as to characterize the influence of the gas-water two-phase flow capacity in the fracture system on the change of water state. S500: such as Figure 2 As shown, external water infiltrates into the fracture system driven by the pressure difference between the formation pressure and the fracture control body pressure. This occurs at the [number]th [time / period]. At each time step, the pressure of the crack control body... The fracture-wellbore equivalent pressure is calculated nonlinearly from the formation material balance and gas compressibility factor. Its initial value is taken from the calculation result of the previous time step. The fracture water infiltration driving pressure difference is defined as the difference between the formation pressure and the fracture control volume pressure. Based on this driving pressure difference, the water infiltration rate is calculated by combining the water productivity index and the relative permeability of the water phase, and the fracture water volume is updated accordingly.

[0009] S600: The infiltration volume of fracture water is converted into equivalent water intrusion energy, and together with the cumulative gas production, it is used to calculate the equivalent production ratio considering water intrusion correction. Based on the equivalent production ratio, the pressure compression ratio at the current time step is calculated using the material balance relationship considering the influence of water intrusion. The formation pressure at the corresponding time step is obtained through nested iterative calculation of formation pressure and gas compressibility factor.

[0010] S700: The gas phase productivity index is corrected based on the relative permeability of the gas phase. Based on the corrected gas phase productivity index, a gas well productivity relationship in the form of square pressure is established. The fracture control body pressure is used as the upstream equivalent pressure in the wellbore productivity equation to calculate the bottom hole flowing pressure at the corresponding time step.

[0011] Using the established method for calculating bottom-hole flowing pressure in fractured-vuggy gas reservoirs that considers the evolution of fractured water, and combined with self-developed calculation software, this paper takes a fractured-vuggy gas well as an example to calculate and analyze the pressure response of the well during actual production. Based on the well's production data, the input parameters are: original formation pressure of 72.4 MPa, dynamic reserves of 170,000,000 cubic meters, gas phase productivity index of 0.04, water productivity index of 0.91, heterogeneity coefficient of 4.1, and water intrusion index of 2.3. Incorporating production time series, daily gas production, and daily water production data, the changes in formation pressure and bottom-hole flowing pressure at the corresponding production time are calculated daily.

[0012] The calculated bottom hole flowing pressure versus time curve was compared with the actual measured bottom hole flowing pressure at the field site. The comparison results are as follows: Figure 3 As shown in the figure, the calculation results are combined with the pressure change characteristics during the well's production process for comprehensive analysis. As can be seen from the figure, the bottom-hole flowing pressure change trend calculated by the method of this invention has good consistency with the field measurement results, and can reasonably reflect the bottom-hole pressure evolution characteristics of fractured-vuggy gas reservoirs during the production process, verifying the applicability and reliability of the method of this invention in calculating bottom-hole flowing pressure in fractured-vuggy gas reservoirs.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) The fracture water body is introduced as an independent control unit in the calculation process. By describing the evolution of fracture water content, the influence of water replenishment on formation pressure and bottom hole flowing pressure of fractured-vuggy gas reservoirs can be reflected. This overcomes the problem that the prior art simplifies water intrusion into a single correction term and is difficult to reflect the dynamic changes of fracture water body; (2) The nonlinear iterative calculation method between formation pressure and gas compressibility factor is adopted to make the formation pressure calculation process continuous and stable, avoiding the discontinuity caused by pressure segment calculation in the traditional method and improving the rationality of bottom hole flowing pressure calculation results; (3) The influence of fracture water content change, gas phase productivity decay and production system change on bottom hole flowing pressure is comprehensively considered in the same calculation process. It can realize the dynamic calculation of bottom hole flowing pressure of fractured-vuggy gas reservoirs without complex numerical simulation. The calculation efficiency is high and the engineering applicability is strong.

[0014] Finally, it should be noted that the above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for calculating the bottom hole flowing pressure of a fractured-vuggy gas reservoir considering the evolution of fracture water, characterized in that, The method includes the following steps: S100, Data and parameter input and initial calculation state; S101, Obtain the production time series. Daily gas production Daily water production Input the original formation pressure Formation temperature Dynamic reserves of gas reservoirs Gas phase productivity index Water Productivity Index Crack volume Initial water saturation Corey Index , , water saturation Residual gas saturation heterogeneity coefficient Water erosion shape index Water body energy replenishment coefficient ; S102, Calculate the initial gas compressibility factor And obtained: ； Initialize cumulative gas production Water content of the crack ; in, This is the compressibility factor under the original formation pressure, expressed as a decimal. This is a function for calculating the gas compressibility factor based on pressure and temperature. For the first The total gas production of all gas wells in the world, in ten thousand cubic meters; For the first i The water volume of the fissures in the sky, in meters. 3 ; The crack volume is expressed in meters (m). 3 ; The initial water saturation is dimensionless. S200, for each production day Update cumulative gas production ; in Daily gas production, in units of For the first Daily gas production volume, expressed in 10,000 cubic meters per day; S300, fracture water content evolution and relative permeability calculation; S301. Calculate the effective water saturation. Corey's relative penetration rate is , ; in, Effective water saturation, dimensionless; For the first The water saturation of the day is dimensionless. The water saturation is dimensionless. Residual gas saturation, dimensionless; , For the first Relative permeability of the weather phase and the liquid phase, dimensionless; , The Corey exponent is dimensionless. S400, Water Infiltration into Fracts and Update of Fract Water Content Status; S401, in the Each computation time step calculates the amount of water infiltrating into the fracture system based on the pressure difference between the formation pressure and the fracture control body pressure. Among them, the pressure of the crack control body The fracture-wellbore equivalent pressure is calculated nonlinearly using formation mass balance and gas compressibility factor, with its initial value taken from the previous time step. The fracture water infiltration driving pressure difference is defined as... The driving pressure difference is used to characterize the effective pressure difference when formation water invades the fracture system. S402, the infiltration rate of water in the crack is calculated using the following formula: ； in, This is the water productivity index, expressed in m³ / (d·MPa). The infiltration rate is expressed in m³ / d; when When the differential pressure is less than the preset starting pressure threshold, let And the daily infiltration amount does not exceed the preset maximum value; S403. Update the fracture water content based on the infiltration water volume. And further update the water saturation of the cracks. ; S500, Establish a nonlinear iteration of formation pressure-compressibility factor considering water intrusion; S501. Convert the infiltration volume of water in the fracture into an equivalent water infiltration energy: ； in, The total equivalent water intrusion is expressed in units of 10. 4 m³; where 10000 is a volume unit conversion factor used to convert the daily infiltration volume from m³ / d to a volume unit consistent with the dynamic storage. The conversion is used to convert the effect of fracture water intrusion on formation pressure maintenance into the water intrusion energy term in the mass balance equation. S502, the equivalent recovery ratio is: and constraints ; The water body energy amplification factor is used to characterize the equivalent contribution of a unit volume of water to the formation pressure maintenance capacity relative to gas during the intrusion of water into the fracture. It is dimensionless. S503, Calculate the following using the water seal material balance equation. Formation pressure to compressibility factor ratio constraint for the day: ； And by using nonlinear iteration of formation pressure and gas compressibility factor, the first... i The pressure of the crack control body at each time step The water seal material balance equation is used to describe the relationship between formation pressure and the degree of extraction under the combined effects of gas production and water intrusion. S600, Bottomhole flowing pressure calculation; wherein, the fracture control body pressure As the upstream equivalent pressure in the wellbore productivity equation, it is used to characterize the pressure supply capacity of the fracture-wellbore system to the bottom of the well; S601. Based on the gas seepage characteristics, establish a production capacity relationship in the form of square pressure. ; S602, Production Capacity Relationship under Pressure Squared Get the first i Well Bottom Flow Pressure ; in, This is the gas phase productivity index, in units of (10). 4 m³ / d) / MPa²; S603, Output the bottom hole flowing pressure calculation results for each production time step.

2. The method according to claim 1, characterized in that: The Corey relative permeability and water replenishment are subject to the following constraints: S100, effective water saturation according to calculate; S200, relative permeability according to , calculate; S300 and water saturation updates simultaneously satisfy both the physical boundary of fracture water volume and the smoothing boundary of daily increment: ； ； This is a truncation function used to ensure that variables are within a physically reasonable range.

3. The method according to claim 1, characterized in that, The method further includes a parameter inversion step: using the stability constraint of the inversion results of measured daily gas production and bottom hole flowing pressure, or the fitting error with external test data, as the objective function, to perform parameter inversion on dynamic reserves. Gas phase productivity index Water Productivity Index and water intrusion parameters , , At least two parameters in the objective function are iteratively updated to make the objective function converge or be less than a preset threshold.

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