A method for monitoring oil layer pressure during gas injection in oil and gas fields

Abstract

The present invention discloses a method for monitoring oil layer pressure for gas drive injection in oil and gas fields, the method comprising: step S1: the oil and gas field is divided into a plurality of measurement areas and monitoring arrangement points are preset; step S2: the first pressure value is collected in the downhole detection area, the initial injection parameters are preset, and monitoring stations are respectively set in the ground measurement area and the formation correction area; step S3: all monitoring data of the first monitoring station and the second monitoring station are collected; step S4: the monitoring data before and after the gas drive injection are respectively collected and pressure contour lines are correspondingly set; step S5: a gradient threshold is set for the contour line, the part of the pressure difference exceeding the gradient threshold is marked as the contour line overflow value, and the correction injection parameters are set. Setting different pressure contour lines realizes the analysis of the position and amplitude of the pressure gradient change in the oil and gas field, which has the advantages and beneficial effects of improving the pressure change monitoring efficiency of the oil layer in the oil and gas field, stabilizing the gas drive injection process and improving the recovery rate of the oil and gas field.

Description

Technical Field

[0001] The invention relates to the field of oil and gas field detection, and in particular to an oil layer pressure monitoring method for gas drive injection in oil and gas fields. Background Art

[0002] Gas injection technology is a commonly used production-increasing technology in oil and gas field development, which aims to improve the recovery rate of oil and gas fields and extend the production cycle of oil and gas fields. Gas injection is to inject high-pressure gas into the oil layer to push the crude oil to the wellhead, thereby increasing the recovery rate of crude oil. During the gas injection process, the monitoring of the oil layer pressure plays a vital role, because pressure is one of the key parameters for evaluating the effect of gas injection and optimizing production.

[0003] During the gas injection process, when a gas with a large pressure difference from the oil layer is injected into the oil layer, the gas will gradually fill the pores and cracks in the oil layer, or the crude oil and water will interact with the injected gas, thereby changing the original fluid distribution and pressure distribution pattern, thereby affecting the pressure transmission and diffusion process of the oil layer inside the oil layer, causing the original pressure gradient of the oil layer inside the oil and gas field to change. Due to the irregular changes in oil layer pressure caused by gas injection, the data processing method of directly monitoring the oil layer pressure at the commonly used monitoring station has poor monitoring accuracy in multi-directional pressure changes, resulting in insufficient monitoring accuracy of the overall pressure change, making it difficult to accurately stabilize the pressure fluctuation of the oil layer, which is not conducive to the oil layer pressure monitoring of the oil and gas field and the precise adjustment of the gas injection parameters, and ultimately it is easy to affect the recovery rate of the oil and gas field. Summary of the invention

[0004] The present invention provides an oil layer pressure monitoring method for gas drive injection in oil and gas fields, which solves the problem that it is difficult to accurately adjust gas drive injection parameters to stabilize pressure monitoring due to insufficient monitoring accuracy of multi-directional pressure changes during gas drive injection in oil and gas fields.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for monitoring oil layer pressure during gas injection in an oil and gas field, the method comprising:

[0007] Step S1: dividing the data collection area of ​​the oil and gas field into a downhole detection area, a ground measurement area and a formation correction area, wherein the downhole detection area, the ground measurement area and the formation correction area are respectively located in the oil well pipeline area downhole in the oil and gas field, the ground of the oil and gas field and the formation below the surface of the oil and gas field, and monitoring arrangement points are preset in the downhole detection area, the ground measurement area and the formation correction area, wherein the distribution positions of the monitoring arrangement points in the downhole detection area and the ground measurement area are consistent;

[0008] Step S2: multiple pressure sensors are set at the monitoring arrangement points in the downhole detection area to collect initial pressure data of the oil layer, all the initial pressure data are marked as first pressure values, initial injection parameters are preset as execution parameter values ​​of gas drive injection, multiple first monitoring stations are set at the monitoring arrangement points in the ground measurement area, and multiple second monitoring stations are set at the monitoring arrangement points in the formation correction area, wherein the first monitoring stations are integrated with pressure sensors, and the second monitoring stations are integrated with fluid sensors;

[0009] Step S3: during the gas drive injection process, all the monitoring pressure data and monitoring fluid data outputted from the first monitoring site and the second monitoring site are collected, and all the monitoring pressure data are marked as the second pressure value, and a corrected pressure value for current oil layer pressure monitoring correction is set based on the monitoring fluid data, and a data result after weighted calculation of the corrected pressure value and the second pressure value is used as the measured pressure value of the current oil layer during this gas drive injection process;

[0010] Step S4: constructing an xyz spatial rectangular coordinate system based on the oil and gas field, wherein the z-axis represents the numerical value of the pressure value, and the xy horizontal plane represents the positions of the monitoring arrangement points of the downhole detection area and the ground measurement area on the xy horizontal plane in the form of coordinates, and collecting all the first pressure values ​​and the measured pressure values ​​respectively and performing time series statistics to set all the first contour lines and the second contour lines representing the continuous pressure value distribution of the first pressure value and the measured pressure value respectively;

[0011] Step S5: Mark the first contour line and the second contour line in the xy horizontal plane, calculate the pressure difference at the same monitoring arrangement point on the first contour line and the second contour line, set a gradient threshold for the first contour line, mark the part of the pressure difference that exceeds the gradient threshold as the contour line overflow value, set a corrected injection parameter according to the pressure value of all contour line overflow values ​​and the distribution of the monitoring arrangement points for updating to the execution parameter value, complete the gas drive injection based on the execution parameter value and maintain pressure monitoring.

[0012] Due to the irregular changes in oil layer pressure caused by gas drive injection, the commonly used data processing method for directly monitoring oil layer pressure at monitoring stations has poor monitoring accuracy in terms of multi-directional pressure changes, which leads to insufficient monitoring accuracy of overall pressure changes, making it difficult to accurately stabilize the pressure fluctuation of the oil layer, which is not conducive to the oil layer pressure monitoring of the oil and gas field and the precise adjustment of the gas drive injection parameters, and ultimately easily affects the recovery rate of the oil and gas field. Based on this, the present invention provides an oil layer pressure monitoring method for gas drive injection in oil and gas fields, which solves the problem that it is difficult to accurately adjust the gas drive injection parameters to stabilize pressure monitoring due to insufficient monitoring accuracy of multi-directional pressure changes during gas drive injection in oil and gas fields.

[0013] Further, the corrected pressure value is set by using Jacobi iteration method, and the setting process of the corrected pressure value and the measured pressure value includes:

[0014] Step A1: The xy horizontal plane is evenly divided into a number of grid units, the time length of the gas drive injection is evenly divided into a number of discrete time steps, the number of time steps is set to be equal to the number of iterations, the initial pressure value for iteration is set for the corrected pressure value of each grid unit, and the monitored fluid data is set to include the fluid pressure value:

[0015] Step A2: Based on the monitored fluid data, a mass conservation equation including the fluid pressure value is constructed, the mass conservation equation is discretized according to the time step and brought into each grid unit, all the monitored fluid data in each time step are averaged and brought into the mass conservation equation, and the fluid pressure value of each grid unit in the current time step is calculated;

[0016] Step A3: The difference between the fluid pressure values ​​in two adjacent time steps is set as the iteration residual value, and the second threshold and the first threshold are set for the fluid pressure values ​​in order from large to small. When the iteration residual value is greater than the second threshold, less than the second threshold and greater than the first threshold, and less than the first threshold, the iteration result is respectively determined to be in the three states of non-convergence, near convergence, and convergence;

[0017] Step A4: Set the fluid pressure value at the end of the iteration as the corrected pressure value, and set the weight values ​​corresponding to the unconverged, nearly converged and converged corrected pressure values ​​to be the first corrected weight value, the second corrected weight value and the third corrected weight value, respectively, and the first corrected weight value, the second corrected weight value and the third corrected weight value increase sequentially.

[0018] Furthermore, the monitored fluid data also includes fluid velocity, fluid density and fluid cross-sectional area; the permeability of the current oil and gas field is obtained, and the mass conservation equation of the oil layer fluid is constructed based on the permeability, fluid velocity, fluid density and fluid cross-sectional area, and the source term value is calculated, and the source term value is used to represent the magnitude of the driving external force exerted on the oil layer fluid during the gas drive injection process, and the fluid pressure value calculated by using the source term value to Darcy's law is used as the initial pressure value for each grid unit iteration.

[0019] Furthermore, let the fluid density be ρ, the fluid cross-sectional area be A, the fluid velocity be V, let the differential operator be ∇, and the source term be Q.

[0020] Then the mass conservation equation is expressed as: .

[0021] Furthermore, k is set as the permeability of the current oil and gas field, P is the fluid pressure value,

[0022] Then the calculation formula of Darcy's law is set as: ;

[0023] The permeability k of the oil and gas field is obtained by measuring the pressure drop based on the ratio of the bottom hole pressure of the oil well to the production.

[0024] Furthermore, the calculation process of the first contour line and the second contour line includes:

[0025] The monitoring arrangement points of all measured pressure values ​​are matched with the second monitoring site, the setting process of the first contour line and the second contour line is the same and independent of each other, and the first monitoring site and the second monitoring site are collectively referred to as monitoring sites; the pressure value changes of the time series of the first pressure value and the measured pressure value are collected, and the linear interpolation method is used to predict the pressure value of the target area where the monitoring is missing around all monitoring sites; based on the xy horizontal plane of the spatial coordinate system, for each target position in the target area for which the current pressure value needs to be predicted, the time series position of each target position is determined according to the distance between each target position and the nearest monitoring site, and the corresponding time points and pressure values ​​of the two monitoring sites closest to the corresponding target position are used to perform linear interpolation calculations on each target position to output all the pressure prediction values ​​in the target area, and the pressure prediction values ​​are filled to the corresponding first pressure values ​​and measured pressure values ​​to convert discrete values ​​into continuous pressure curves.

[0026] Furthermore, the linear interpolation calculation process includes:

[0027] Assume that the coordinates of two monitoring stations in the same data collection area are expressed as and , and their corresponding pressure values ​​are set as P1 and P2 respectively.

[0028] Assume the target position is represented by The predicted current pressure value at is expressed as ,

[0029] Then the current pressure value calculation formula for target position prediction can be set as: ,

[0030] The initial time of gas injection is assumed to be time 0, t is the time size of the target location at the current time point, t1 and t2 are the time sizes of the two monitoring stations at the current time points, and t1 <t<t2。

[0031] Furthermore, the setting method of the correction injection parameter includes:

[0032] Based on the geological characteristics and well network structure of the oil and gas field, a numerical simulation model is established, which includes the geometric characteristics and rock formation parameters of the oil reservoir. The boundary conditions and injection parameters of gas drive injection are set in the model, and the gas drive injection is numerically simulated to evaluate the fluid migration and pressure change in the oil reservoir during gas drive injection. All contour overflow values ​​are brought into the calculation as independent variables of the numerical simulation model, and the output values ​​are used as corrected injection parameters for correcting the gas drive injection.

[0033] Compared with the prior art, the present invention collects pressure values ​​before and after gas drive injection in different data collection areas of the oil and gas field, corrects the pressure value based on the collection and analysis of oil layer fluid data in the formation, and sets different pressure contour lines to analyze the position and amplitude of pressure gradient changes in the oil and gas field, and adjusts the gas drive injection based on the analysis results, thereby reducing the fluctuation of oil layer pressure during gas drive injection. The present invention has the advantages and beneficial effects of improving the pressure change monitoring efficiency of oil layers in oil and gas fields, stabilizing the gas drive injection process and improving the recovery rate of oil and gas fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0035] Figure 1 It is a flowchart of the present invention. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention. Example

[0037] like Figure 1 As shown, this embodiment is a method for monitoring oil layer pressure for gas injection in oil and gas fields, the method comprising:

[0038] Step S1: dividing the data collection area of ​​the oil and gas field into a downhole detection area, a ground measurement area and a formation correction area, wherein the downhole detection area, the ground measurement area and the formation correction area are respectively located in the oil well pipeline area downhole in the oil and gas field, the ground of the oil and gas field and the formation below the surface of the oil and gas field, and monitoring arrangement points are preset in the downhole detection area, the ground measurement area and the formation correction area, wherein the distribution positions of the monitoring arrangement points in the downhole detection area and the ground measurement area are consistent;

[0039] Step S2: multiple pressure sensors are set at the monitoring arrangement points in the downhole detection area to collect initial pressure data of the oil layer, all the initial pressure data are marked as first pressure values, initial injection parameters are preset as execution parameter values ​​of gas drive injection, multiple first monitoring stations are set at the monitoring arrangement points in the ground measurement area, and multiple second monitoring stations are set at the monitoring arrangement points in the formation correction area, wherein the first monitoring stations are integrated with pressure sensors, and the second monitoring stations are integrated with fluid sensors;

[0040] Step S3: during the gas drive injection process, all the monitoring pressure data and monitoring fluid data outputted from the first monitoring site and the second monitoring site are collected, and all the monitoring pressure data are marked as the second pressure value, and a corrected pressure value for current oil layer pressure monitoring correction is set based on the monitoring fluid data, and a data result after weighted calculation of the corrected pressure value and the second pressure value is used as the measured pressure value of the current oil layer during this gas drive injection process;

[0041] Step S4: constructing an xyz spatial rectangular coordinate system based on the oil and gas field, wherein the z-axis represents the numerical value of the pressure value, and the xy horizontal plane represents the positions of the monitoring arrangement points of the downhole detection area and the ground measurement area on the xy horizontal plane in the form of coordinates, and collecting all the first pressure values ​​and the measured pressure values ​​respectively and performing time series statistics to set all the first contour lines and the second contour lines representing the continuous pressure value distribution of the first pressure value and the measured pressure value respectively;

[0042] Step S5: Mark the first contour line and the second contour line in the xy horizontal plane, calculate the pressure difference at the same monitoring arrangement point on the first contour line and the second contour line, set a gradient threshold for the first contour line, mark the part of the pressure difference that exceeds the gradient threshold as the contour line overflow value, set a corrected injection parameter according to the pressure value of all contour line overflow values ​​and the distribution of the monitoring arrangement points for updating to the execution parameter value, complete the gas drive injection based on the execution parameter value and maintain pressure monitoring.

[0043] The implementation process of this embodiment is mainly as follows: before gas drive injection, the oil layer of the oil and gas field is initially measured by the pressure sensor set at the monitoring arrangement point in the downhole detection area, and all the pressure data of the initial pressure measurement are marked as the first pressure value. The gas drive injection is started based on the initial injection parameters. At this time, the second monitoring station in the formation correction area starts to monitor the fluid state of the oil layer being injected with gas drive. At the same time, in the middle of the gas drive injection, the first monitoring station in the ground measurement area keeps monitoring the oil layer pressure and outputs the second pressure value. Based on the monitoring data of the fluid state, the oil layer pressure is set to a corrected pressure value for reference evaluation, and the corrected pressure value is added to the second pressure value according to the weight distribution to obtain the measured pressure value for comprehensive processing. Based on the oil and gas field, an xyz spatial rectangular coordinate system is constructed, in which the z axis represents the numerical value of the pressure value, and the xy horizontal plane represents the position of the monitoring arrangement points of the downhole detection area and the ground measurement area on the xy horizontal plane in the form of coordinates, that is, the coordinates of the xy horizontal plane are used to simultaneously represent the coordinate positions of the monitoring arrangement points of all data acquisition areas in the horizontal direction. A number of first contour lines and second contour lines are set based on the first pressure value and the measured pressure value. Since the distribution positions of the monitoring arrangement points in the underground detection area and the ground measurement area are consistent, and the measured pressure value is weighted and calculated based on the second pressure value, that is, only the pressure value is changed, but in the correspondence between the value and the measured position, each measured pressure value still corresponds to each first monitoring station. Therefore, the xy horizontal plane is used to intuitively compare the curve heights of all the first contour lines and the second contour lines according to the overlapping monitoring arrangement points, that is, the first contour line and the second contour line coincide on the xy horizontal plane, but on the z-axis, there is a height difference between the two at different positions due to the difference in pressure value. The height difference is set as the contour overflow value, and the injection parameter is corrected according to the pressure value of all the contour overflow values ​​and the distribution of the monitoring arrangement points for updating to the execution parameter value, so that the execution details of the gas drive injection are updated based on the current pressure fluctuation state, and the subsequent gas drive injection process is completed based on the execution parameter value, while continuing to maintain pressure monitoring.

[0044] The oil well pipeline area in the downhole detection area mainly refers to the inside of the wellbore of the oil well, including the collection layer section of the oil layer and the pipelines and equipment connected thereto. The oil and gas field surface in the ground measurement area mainly refers to the surface of the oil and gas field used to place production facility instruments and other equipment. The formation correction area covers the formation below the surface of the oil and gas field, and the main area is the underground formation where the oil and gas layer is located, which may include reservoirs, capping layers, etc. The distribution positions of the monitoring arrangement points in the downhole detection area and the ground measurement area are set to be consistent for subsequent accurate comparison of pressure contour lines to obtain contour line overflow values. The monitoring arrangement points in the downhole detection area are mainly used to set sensors or monitoring equipment at the bottom of the oil well for real-time monitoring of parameters such as oil layer pressure. The monitoring arrangement points in the ground measurement area are set on the ground to set pressure sensors for monitoring parameters such as oil layer pressure near the ground. The monitoring arrangement points in the formation correction area are set in the underground formation to set sensors or detection equipment for real-time monitoring of formation pressure or other related formation parameters. The initial pressure data is the oil layer pressure data of the current oil and gas field before gas injection. Since the location of the data acquisition point is closer to the oil layer, the use of the downhole detection area to monitor the output pressure data can more accurately reflect the actual situation of the oil layer, reduce delays in the transmission and acquisition of data, reduce environmental interference and noise interference, and improve data quality and reliability.

[0045] The initial injection parameters are conventional initial preset parameters for gas drive injection, including injection pressure value, injection rate value, type and ratio of injected gas or liquid, injection schedule, and injection wellbore type selection. The execution parameter value is the parameter used in the gas drive injection process. The corrected pressure value is the oil layer pressure value analyzed based on the monitoring fluid data. Since the data acquisition area is located in the formation closer to the oil layer, and the data acquisition method is different from the downhole detection area and the ground measurement area, the corrected pressure value is used as another way to obtain the pressure monitoring value. In the specific implementation, the deviation of the corrected pressure value can be evaluated to adjust the size of the assigned weight value. The xy horizontal plane can be represented as the ground of the oil and gas field, and the pressure contour line is represented in an intuitive and concrete form, and the different heights of the pressure contour line on the z-axis are the pressure value size. The time series statistics are statistics of the oil layer pressure data measured by the pressure sensors at different positions and the first monitoring station at different time points. Since the distribution positions of the monitoring points in the downhole detection area and the ground measurement area are consistent, there is a situation where the first contour line and the second contour line overlap at each monitoring point in the downhole detection area and the ground measurement area. That is, the purpose is to monitor the oil layer pressure value before and during the gas drive injection through different data acquisition areas, and compare the pressure size in the form of pressure contour lines based on the same monitoring position, and the difference compared is the contour line overflow value. There are many ways to set the gradient threshold of the first contour line. In specific applications, the pressure value that exceeds a certain percentile of the first contour line can be set as the gradient threshold; the pressure difference between adjacent pressure points of the first contour line can be calculated by statistical methods, and the mean of the pressure difference plus the absolute value of the standard deviation is used as the gradient threshold, etc. The injection parameter correction will be set according to the size and distribution of the contour line overflow value, which is used to update the execution parameter value of the gas drive injection, so as to accurately adjust the gas drive injection parameters through multi-directional pressure monitoring, so that the gas drive injection process can be more stable.

[0046] Further, as a feasible implementation, the Jacobi iteration method is used to set the corrected pressure value, and the setting process of the corrected pressure value and the measured pressure value includes:

[0047] Step A1: The xy horizontal plane is evenly divided into a number of grid units, the time length of the gas drive injection is evenly divided into a number of discrete time steps, the number of time steps is set to be equal to the number of iterations, the initial pressure value for iteration is set for the corrected pressure value of each grid unit, and the monitored fluid data is set to include the fluid pressure value:

[0048] Step A2: Based on the monitored fluid data, a mass conservation equation including the fluid pressure value is constructed, the mass conservation equation is discretized according to the time step and brought into each grid unit, all the monitored fluid data in each time step are averaged and brought into the mass conservation equation, and the fluid pressure value of each grid unit in the current time step is calculated;

[0049] Step A3: The difference between the fluid pressure values ​​in two adjacent time steps is set as the iteration residual value, and the second threshold and the first threshold are set for the fluid pressure values ​​in order from large to small. When the iteration residual value is greater than the second threshold, less than the second threshold and greater than the first threshold, and less than the first threshold, the iteration result is respectively determined to be in the three states of non-convergence, near convergence, and convergence;

[0050] Step A4: Set the fluid pressure value at the end of the iteration as the corrected pressure value, and set the weight values ​​corresponding to the unconverged, nearly converged and converged corrected pressure values ​​to be the first corrected weight value, the second corrected weight value and the third corrected weight value, respectively, and the first corrected weight value, the second corrected weight value and the third corrected weight value increase sequentially.

[0051] After the strata are divided into grid units, parallel computing and distributed computing methods can be used to improve computing efficiency. The calculations within each grid unit can be performed independently, and the internal geological features can be regarded as uniform, which makes it easier to apply numerical simulation methods for calculations. The mass conservation equation can be set as a continuity equation to describe the changes in fluid mass in space and time, or set as a state equation to describe the state parameters of the fluid and the load changes on the fluid pressure. The source term value describes the mass generation and consumption in the mass conservation equation, usually including factors such as chemical reactions, heat exchange, and material exchange. By discretizing the mass conservation equation in time and space and bringing it into each grid unit, the pressure value of each grid unit in each time step can be obtained. The difference between the fluid pressure values ​​in two adjacent time steps is calculated and used as the iterative residual value, which represents the degree of pressure change between two adjacent iterations and is an important indicator for evaluating iterative convergence. When the residual value is greater than the second threshold, it is determined to be in a non-convergent state; if the iterative residual value is between the second threshold and the first threshold, it is determined to be in a near-convergent state; if the iterative residual value is less than the first threshold, it is determined to be in a convergent state, and the weight distribution values ​​corresponding to the three states of non-convergent, near-convergent and convergent are set to increase in sequence from small to large. The fluid pressure value obtained based on the iterative calculation is set as the corrected pressure value, which more directly and accurately reflects the pressure state inside the oil layer than simply using the original value of the monitoring data.

[0052] Furthermore, as a feasible implementation method, the monitored fluid data also includes fluid velocity, fluid density and fluid cross-sectional area; the permeability of the current oil and gas field is obtained, and the mass conservation equation of the oil layer fluid is constructed based on the permeability, fluid velocity, fluid density and fluid cross-sectional area, and the source term value is calculated, and the source term value is used to represent the magnitude of the driving external force exerted on the oil layer fluid during the gas drive injection process, and the fluid pressure value calculated by using the source term value to Darcy's law is used as the initial pressure value for each grid unit iteration.

[0053] Furthermore, let the fluid density be ρ, the fluid cross-sectional area be A, the fluid velocity be V, let the differential operator be ∇, and the source term be Q, then the mass conservation equation is set as: .

[0054] Assuming k is the permeability of the current oil and gas field, and P is the fluid pressure value, the calculation formula of Darcy's law is set to:

[0055] ; wherein the permeability k of the oil and gas field is obtained by measuring the pressure drop based on the ratio of the bottom hole pressure of the oil well to the production.

[0056] The fluid velocity, fluid density and fluid cross-sectional area can provide information about the state of fluid movement inside the oil layer. The permeability is an important parameter that describes the permeability of oil and gas field rocks to fluids, and is one of the key factors affecting the efficiency of oil field production. In conventional technology, the physical parameters of the wellbore can be obtained by logging equipment to calculate the permeability, and the permeability can also be directly measured by exploration equipment based on the conductivity measurement method. The differential operator is usually called the gradient operator, which represents the gradient of a multivariable function in space, that is, the rate of change of the function in all directions; in the mass conservation equation, the differential operator ∇ usually represents the partial derivatives of parameters such as fluid density and velocity in the directions of each coordinate axis in space, which is used to describe the rate of change of these parameters at different spatial positions. The Darcy's law is an empirical law that describes the relationship between the fluid flow velocity and permeability, fluid viscosity, seepage distance and seepage pressure difference during seepage. (∂(A∙ρ)) / ∂t is represented as a time-varying term, which describes the rate of change of mass in the system over time. Where A represents the cross-sectional area and ρ represents the density. The calculation principle is to differentiate the rate of change of mass density in a given cross-sectional area with time, that is, to find the partial derivative with respect to time t. ∇∙(ρ∙A∙V) is expressed as a flux term, which describes the flow of mass in space, that is, flux. Among them, ∇ represents the gradient operator, ρ represents density, A represents the cross-sectional area, and V represents the velocity field. The calculation principle is to perform a gradient operation on the flow of fluid in a given cross-sectional area in space and calculate the flux of mass outflow. The source term Q represents the rate at which mass is generated or consumed in the system. The source term may include externally injected mass, mass generated by chemical reactions, etc. The calculation principle is to determine the rate at which mass is generated or consumed based on the physical process inside the system or external input.

[0057] During the gas injection process of an oil and gas field, the injection of gas will generate additional driving pressure, prompting crude oil to migrate to the wellhead. This additional driving pressure total external force is referred to as the source term value in this embodiment. In Darcy's law, the source term value represents the source or sink of the fluid in the porous medium, which describes the increase or decrease in mass due to external factors. In the fields of subsurface hydrology and petroleum engineering, the source term value usually represents the mass of fluid per unit volume per unit time. The calculated fluid pressure value is used as the initial pressure value for each grid unit iteration. In the Jacobi iteration method, the initial value of the iteration is crucial to the convergence speed of the iteration process and the accuracy of the results. Therefore, the fluid pressure value calculated using Darcy's law is used as the initial value, which can better reflect the actual pressure distribution and contribute to the convergence of the iteration and the accuracy of the results. In specific implementation, as a specific application, when Q>0, it means that external factors have injected fluid into the porous medium, such as injecting liquid or gas into an oil well, which leads to an increase in the mass of the fluid in the porous medium; when Q<0, it means that external factors have extracted fluid from the porous medium, such as oil well production, which leads to a decrease in the mass of the fluid in the porous medium.

[0058] In the calculation formula of Darcy's law, the negative sign indicates the opposite relationship between the direction of fluid pressure gradient and the direction of seepage. According to Darcy's law, fluid seeps from high pressure to low pressure, so the direction of fluid pressure gradient is negative, which is opposite to the direction of seepage. Permeability k indicates the difficulty of rock or porous medium for fluid penetration. It is one of the permeability characteristics of the medium and is a scalar. The larger the permeability k, the better the permeability of the medium to the fluid, and the greater the seepage rate. In Darcy's law, the differential operator ∇ indicates the conversion of the spatial rate of change of the pressure field into the magnitude and direction of the pressure gradient. Fluid pressure is the driving force of fluid in porous media, and the fluid pressure value P is an important parameter in the seepage process. The calculation result of ∇∙P is a vector, which indicates the magnitude and direction of the pressure gradient. In the calculation formula of Darcy's law, this term describes the driving effect of pressure gradient on fluid seepage and reflects the seepage law of fluid in porous media.

[0059] Furthermore, the calculation process of the first contour line and the second contour line includes:

[0060] The monitoring arrangement points of all measured pressure values ​​are corresponding to the positions of the second monitoring site, the setting process of the first contour line and the second contour line is the same and independent of each other, and the first monitoring site and the second monitoring site are collectively referred to as monitoring sites; the pressure value changes of the time series of the first pressure value and the measured pressure value are collected, and the pressure value of the target area with missing monitoring around all monitoring sites is predicted by using the linear interpolation method; based on the xy horizontal plane of the spatial coordinate system, for each target position in the target area that needs to predict the current pressure value, the time series position is determined according to the distance between each target position and the nearest monitoring site, and the corresponding time points and pressure values ​​of the two monitoring sites closest to the corresponding target position are used to perform linear interpolation calculations on each target position to output all the pressure prediction values ​​in the target area, and the pressure prediction values ​​are filled to the corresponding first pressure value and the measured pressure value to convert the discrete value into a continuous pressure curve. The pressure value changes of the time series of the first pressure value and the measured pressure value are collected, and the pressure value of the target area with missing monitoring around all monitoring sites is predicted by using the linear interpolation method. By using linear interpolation, the pressure value of the missing monitoring data in the target area can be estimated, making the monitoring data more complete. For each target location in the target area where the current pressure value needs to be predicted, the time series position is determined based on the distance between each target location and the nearest monitoring station. Then, linear interpolation calculations are performed between the corresponding time points and pressure values ​​using the two nearest monitoring stations to output all the pressure prediction values ​​in the target area. The linear interpolation method can fill in the missing values ​​in the monitoring data, thereby improving the integrity and continuity of the pressure contour lines.

[0061] Furthermore, as a feasible implementation, the linear interpolation calculation process includes:

[0062] Assume that the coordinates of two monitoring stations in the same data collection area are expressed as and , and their corresponding pressure values ​​are set as P1 and P2 respectively.

[0063] Assume the target position is represented by The predicted current pressure value at is expressed as ,

[0064] Then the current pressure value calculation formula for target position prediction can be set as: ,

[0065] The initial time of gas injection is assumed to be time 0, t is the time size of the target location at the current time point, t1 and t2 are the time sizes of the two monitoring stations at the current time points, and t1 <t<t2。

[0066] Among them, t1 and t2 are the current time points of the monitoring sites Z1 and Z2, respectively, and t represents the current time point at the target position C(x,y). Since linear interpolation assumes that the pressure value changes linearly with time, the pressure value at any time t between the two points Z1(x1,y1) and Z2(x2,y2) can be obtained by linear interpolation calculation. P1 and P2 are the pressure values ​​of the two monitoring sites at the current time points t1 and t2. These values ​​are known and can be obtained by monitoring or numerical simulation. P1 and P2 are the pressure values ​​at two time points and are used for linear interpolation. t1 and t2 are the time points corresponding to the two monitoring sites, respectively. These time points are also known and are used to determine the pressure values ​​at the monitoring sites. Usually, t1 and t2 are adjacent time points and are used for temporal interpolation. (t-t1) represents the time difference between the current time t and t1, while (t2-t1) represents the time interval between t2 and t1. These values ​​are used to normalize the time to ensure that the time is between 0 and 1 for linear interpolation. (P2-P1) represents the difference in pressure values ​​at the monitoring sites, that is, the change in pressure value. The product of this change and the time difference is used to represent the rate of change of the pressure value in a given time period. The product of the time difference and the pressure value difference divided by the time interval represents the rate of change of the pressure value in a given time period. Then this rate of change is added to the initial pressure value P1 to obtain the predicted pressure value P(x,y) at the target location.

[0067] By monitoring the location and pressure value of the site and determining the current time point, the current pressure value at the target location C(x, y) is calculated using the linear interpolation formula. In this way, the predicted pressure value at the target location can be obtained, thereby supplementing the monitoring data in the data collection area, making the pressure value more continuous and complete in space. Through this linear interpolation calculation process, the pressure value at the target location can be predicted, providing more data support for pressure monitoring and management of oil and gas fields.

[0068] Furthermore, the setting method of the correction injection parameter includes:

[0069] Based on the geological characteristics and well network structure of the oil and gas field, a numerical simulation model is established, which includes the geometric characteristics and rock formation parameters of the oil reservoir. The boundary conditions and injection parameters of gas drive injection are set in the model, and the gas drive injection is numerically simulated to evaluate the fluid migration and pressure change in the oil reservoir during gas drive injection. All contour overflow values ​​are brought into the calculation as independent variables of the numerical simulation model, and the output values ​​are used as corrected injection parameters for correcting the gas drive injection.

[0070] The numerical simulation is used to evaluate the fluid migration and pressure changes in the reservoir during gas drive injection. The geometric characteristics and formation parameters of the reservoir may include reservoir size and pore structure characteristics, and the formation parameters may include porosity and rock mechanical properties. The injection boundary and injection parameters mainly include the injection well coordinate position and the injected gas characteristics. The corrected injection parameters obtained by numerical simulation can more accurately guide the gas drive injection process and simulate the fluid migration and pressure changes in the reservoir during the gas drive injection process. Taking all contour overflow values ​​as independent variables can more comprehensively consider the dynamic response of the reservoir, thereby optimizing the gas drive injection strategy and improving the production efficiency. Using the simulation results as corrected injection parameters can help adjust key parameters in the gas drive injection process, such as injection pressure, injection rate, etc.

[0071] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for monitoring oil layer pressure during gas injection in oil and gas fields, characterized in that: The method includes: Step S1: dividing the data collection area of ​​the oil and gas field into a downhole detection area, a ground measurement area and a formation correction area, wherein the downhole detection area, the ground measurement area and the formation correction area are respectively located in the oil well pipeline area downhole in the oil and gas field, the ground of the oil and gas field and the formation below the surface of the oil and gas field, and monitoring arrangement points are preset in the downhole detection area, the ground measurement area and the formation correction area, wherein the distribution positions of the monitoring arrangement points in the downhole detection area and the ground measurement area are consistent; Step S2: multiple pressure sensors are set at the monitoring arrangement points in the downhole detection area to collect initial pressure data of the oil layer, all the initial pressure data are marked as first pressure values, initial injection parameters are preset as execution parameter values ​​of gas drive injection, multiple first monitoring stations are set at the monitoring arrangement points in the ground measurement area, and multiple second monitoring stations are set at the monitoring arrangement points in the formation correction area, wherein the first monitoring stations are integrated with pressure sensors, and the second monitoring stations are integrated with fluid sensors; Step S3: during the gas drive injection process, all the monitoring pressure data and monitoring fluid data outputted from the first monitoring site and the second monitoring site are collected, and all the monitoring pressure data are marked as the second pressure value, and a corrected pressure value for current oil layer pressure monitoring correction is set based on the monitoring fluid data, and a data result after weighted calculation of the corrected pressure value and the second pressure value is used as the measured pressure value of the current oil layer during this gas drive injection process; Step S4: constructing an xyz spatial rectangular coordinate system based on the oil and gas field, wherein the z-axis represents the numerical value of the pressure value, and the xy horizontal plane represents the positions of the monitoring arrangement points of the downhole detection area and the ground measurement area on the xy horizontal plane in the form of coordinates, and collecting all the first pressure values ​​and the measured pressure values ​​respectively and performing time series statistics to set all the first contour lines and the second contour lines representing the continuous pressure value distribution of the first pressure value and the measured pressure value respectively; Step S5: Mark the first contour line and the second contour line in the xy horizontal plane, calculate the pressure difference between the first contour line and the second contour line at the same monitoring arrangement point, set a gradient threshold for the first contour line, mark the part of the pressure difference that exceeds the gradient threshold as the contour line overflow value, set a modified injection parameter according to the pressure value of all contour line overflow values ​​and the distribution of the monitoring arrangement points for updating to the execution parameter value, complete the gas drive injection based on the execution parameter value and maintain pressure monitoring; The corrected pressure value is set by using the Jacobi iteration method, and the setting process of the corrected pressure value and the measured pressure value includes: Step A1: The xy horizontal plane is evenly divided into a number of grid units, the time length of the gas drive injection is evenly divided into a number of discrete time steps, the number of time steps is set to be equal to the number of iterations, the initial pressure value for iteration is set for the corrected pressure value of each grid unit, and the monitored fluid data is set to include the fluid pressure value: Step A2: Based on the monitored fluid data, a mass conservation equation including the fluid pressure value is constructed, the mass conservation equation is discretized according to the time step and brought into each grid unit, all the monitored fluid data in each time step are averaged and brought into the mass conservation equation, and the fluid pressure value of each grid unit in the current time step is calculated; Step A3: The difference between the fluid pressure values ​​in two adjacent time steps is set as the iteration residual value, and the second threshold and the first threshold are set for the fluid pressure values ​​in order from large to small. When the iteration residual value is greater than the second threshold, less than the second threshold and greater than the first threshold, and less than the first threshold, the iteration result is respectively determined to be in the three states of non-convergence, near convergence, and convergence; Step A4: setting the fluid pressure value at the end of the iteration as the corrected pressure value, assuming that the weight values ​​corresponding to the unconverged, nearly converged and converged corrected pressure values ​​are the first corrected weight value, the second corrected weight value and the third corrected weight value, respectively, and the first corrected weight value, the second corrected weight value and the third corrected weight value increase in sequence; The monitored fluid data also includes fluid velocity, fluid density and fluid cross-sectional area; the permeability of the current oil and gas field is obtained, and the mass conservation equation of the oil layer fluid is constructed based on the permeability, fluid velocity, fluid density and fluid cross-sectional area, and the source term value is calculated. The source term value is used to represent the magnitude of the driving external force exerted on the oil layer fluid during the gas drive injection process, and the fluid pressure value calculated by using the source term value to Darcy's law is used as the initial pressure value for each grid unit iteration.

2. The method for monitoring oil layer pressure for gas flooding injection in oil and gas fields according to claim 1, characterized in that: Let the fluid density be ρ, the fluid cross-sectional area be A, the fluid velocity be V, let the differential operator be ∇, and the source term be Q. Then the mass conservation equation is expressed as: .

3. The method for monitoring oil layer pressure for gas flooding injection in oil and gas fields according to claim 1, characterized in that: The calculation process of the first contour line and the second contour line includes: The monitoring arrangement points of all measured pressure values ​​are matched with the second monitoring site, the setting process of the first contour line and the second contour line is the same and independent of each other, and the first monitoring site and the second monitoring site are collectively referred to as monitoring sites; the pressure value changes of the time series of the first pressure value and the measured pressure value are collected, and the linear interpolation method is used to predict the pressure value of the target area where the monitoring is missing around all monitoring sites; based on the xy horizontal plane of the spatial coordinate system, for each target position in the target area for which the current pressure value needs to be predicted, the time series position of each target position is determined according to the distance between each target position and the nearest monitoring site, and the corresponding time points and pressure values ​​of the two monitoring sites closest to the corresponding target position are used to perform linear interpolation calculations on each target position to output all the pressure prediction values ​​in the target area, and the pressure prediction values ​​are filled to the corresponding first pressure values ​​and measured pressure values ​​to convert discrete values ​​into continuous pressure curves.

4. The method for monitoring oil layer pressure for gas flooding injection in oil and gas fields according to claim 3, characterized in that: The linear interpolation calculation process includes: Assume that the coordinates of two monitoring stations in the same data collection area are expressed as and , and their corresponding pressure values ​​are set as P1 and P2 respectively. Assume the target position is represented by The predicted current pressure value at is expressed as , Then the current pressure value calculation formula for target position prediction can be set as: , The initial time of gas injection is assumed to be time 0, t is the time size of the target location at the current time point, t1 and t2 are the time sizes of the two monitoring stations at the current time points, and t1 <t<t2。 5. The method for monitoring oil layer pressure for gas flooding injection in oil and gas fields according to claim 1, characterized in that: The setting method of the correction injection parameter includes: Based on the geological characteristics and well network structure of the oil and gas field, a numerical simulation model is established, which includes the geometric characteristics and rock formation parameters of the oil reservoir. The boundary conditions and injection parameters of gas drive injection are set in the model, and the gas drive injection is numerically simulated to evaluate the fluid migration and pressure change in the oil reservoir during gas drive injection. All contour overflow values ​​are brought into the calculation as independent variables of the numerical simulation model, and the output values ​​are used as corrected injection parameters for correcting the gas drive injection.

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