A method and device for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone

Abstract

The application discloses a weakly cemented argillaceous siltstone starting pressure gradient law analysis method and device, which comprises the following steps: constructing multiple test cores; performing displacement tests on each core holder, timing each displacement test, and recording the displacement pressure, confining pressure change and displacement fluid capacity of the core holder; determining the starting pressure gradient in combination with the confining pressure change of the core holder in each displacement test, determining the real liquid production point of the test core in the displacement test process, and obtaining the minimum starting pressure gradient of each test core; fitting the relationship between the pressure gradient and the liquid production rate to obtain the pseudo starting pressure gradient of each test core; and fitting the relationship between the minimum starting pressure gradient and the pseudo starting pressure gradient and the formation parameters; the application determines the real liquid production point of effective displacement, improves the accuracy of data analysis, and determines the change law of the water phase starting pressure gradient of low-permeability loose argillaceous siltstone with the core seepage characteristics and the properties of formation fluid.

Description

Technical Field

[0001] This invention relates to the field of sandstone displacement driving pressure technology, specifically to a method and apparatus for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone. Background Technology

[0002] During the seepage of natural gas hydrates in low-permeability, loose argillaceous siltstone, there exists a starting pressure gradient. Below this pressure gradient, the natural gas hydrates do not flow. Due to differences in formation seepage conditions and the properties of the injected fluid, the starting pressure gradient required for the flow of natural gas hydrates varies. As natural gas hydrates are developed, the starting pressure gradient has a significant impact on development. It is a comprehensive manifestation of abnormal fluid boundary layer properties and fluid plasticity.

[0003] The most commonly used methods for studying the initiation pressure gradient are indoor physical simulation and numerical experiments. Among these, indoor physical simulation is the most intuitive and currently widely recognized as an effective method. Specifically, it employs the conventional method of measuring the relationship between pressure difference and flow rate under steady-state flow conditions. This involves saturating a core or sand-filled pipe with crude oil, measuring the steady-state flow rate under a certain pressure difference, and then using mathematical methods to calculate the initiation pressure gradient. The basic principle is to measure the flow rate of the fluid through the core after different displacement pressure differences have stabilized, plot the relationship between flow rate and pressure gradient, and use regression curves to determine the initiation pressure gradient. The laboratory method for measuring the initiation pressure gradient also uses the conventional method of measuring the relationship between steady-state pressure difference and flow rate. This involves saturating a core with crude oil and recording the steady-state flow rate at each point under a series of pressure differences.

[0004] Commonly used indoor physical simulation and numerical experimental methods both use oil phase displacement tests to calculate the effect of the oil phase on core permeability. However, there is currently no accurate analytical method for analyzing the test results of water phase displacement tests. Summary of the Invention

[0005] The purpose of this invention is to provide a method and apparatus for analyzing the starting pressure gradient law of weakly cemented silty mudstone, in order to solve the technical problem that there is no accurate analytical method for analyzing the test results of aqueous phase displacement test operations in the existing technology.

[0006] To solve the above-mentioned technical problems, the present invention specifically provides the following technical solution:

[0007] A system for analyzing the initiation pressure gradient law of weakly cemented argillaceous siltstone includes:

[0008] The timing unit is used to time each displacement test operation;

[0009] A pressure sensor is installed inside the core holder to measure the confining pressure on the weakly cemented silty mudstone inside the core holder, as well as the displacement pressure at the inlet end of the core holder and the displacement pressure at the outlet end of the core holder.

[0010] A liquid level sensor is installed in a graduated cylinder at the outlet end of the core holder to measure the liquid production during the displacement test.

[0011] The processing system is communicatively connected to the pressure sensor, timing unit, and liquid level sensor. The processing system also includes a data analysis module. Based on the output data of the timing unit and the pressure sensor, the data analysis module constructs a core confining pressure change map to determine the actual liquid discharge point of the displacement test and the minimum starting pressure gradient corresponding to the moment before the actual liquid discharge point.

[0012] The data analysis module analyzes the relationship between the core pressure gradient and the liquid production rate based on the output data of the pressure sensor, timing unit and liquid level sensor, so as to determine the proposed start-up pressure gradient for the displacement test.

[0013] The data analysis module is used to collect the minimum initiation pressure gradient and the proposed initiation pressure gradient obtained from the displacement test of multiple weakly cemented argillaceous siltstone cores, and to fit the relationship between the minimum initiation pressure gradient and the proposed initiation pressure gradient and the formation parameter K / μ.

[0014] As a preferred embodiment of the present invention, the processing system includes a data cleaning module, which cleans and filters out the output data of the pressure sensor and the output data of the liquid level sensor before the actual liquid outlet point in the core confining pressure change diagram based on the test time point.

[0015] In a preferred embodiment of the present invention, the processing system is communicatively connected to the displacement test device. The processing system is used to control the displacement test operation of the displacement test device, and the processing system links the control time point of the displacement test operation of the displacement test device with the timing unit to determine the displacement test operation corresponding to the actual liquid outlet point.

[0016] As a preferred embodiment of the present invention, the displacement test operation control of the displacement test device is divided into liquid variable speed displacement operation and pressure variable displacement operation under different confining pressure conditions.

[0017] The initial confining pressure was set to 2 MPa, and the liquid displacement operation was performed by changing the pump speed of the displacement liquid at 0.005 ml / min, 0.015 ml / min, 0.05 ml / min, 0.1 ml / min, 0.3 ml / min, and 0.6 ml / min.

[0018] The variable displacement operation changes the displacement pressure from 1.6MPa to 2.2MPa to 1.6MPa;

[0019] The confining pressure was adjusted to 4 MPa and 8 MPa in sequence, and under each confining pressure condition, the displacement test was carried out by first performing liquid variable speed displacement operation and then pressure variable displacement operation.

[0020] By combining the time points corresponding to the actual effluent points of each displacement test, the displacement test operations corresponding to the actual effluent effluent of the rock sample core are determined, as well as the pressure gradient and production rate corresponding to the displacement test operations after the actual effluent effluent effluent of the rock sample core.

[0021] In addition, to address the above-mentioned issues, this invention also provides an analytical method for analyzing the initiation pressure gradient law of weakly cemented silty mudstone, comprising the following steps:

[0022] Step 100: Inject weakly cemented argillaceous siltstone into the core holder to construct multiple test cores;

[0023] Step 200: Conduct a displacement test on each of the core holders, time each displacement test, and record the displacement pressure, confining pressure changes, and displacement fluid volume of the core holders.

[0024] Step 300: Combine the displacement test time of each displacement test with the confining pressure change of the core holder to determine the starting pressure gradient, and determine the actual liquid outlet point of the test core during the displacement test, and obtain the minimum starting pressure gradient of each test core.

[0025] Step 400: Clean the displacement pressure and displacement fluid capacity data, fit the relationship between pressure gradient and production rate, and obtain the proposed start-up pressure gradient for each test core.

[0026] Step 500: Combining the minimum initiation pressure gradient, the proposed initiation pressure gradient, and the formation parameter K / μ from all test cores, fit the relationship between the minimum initiation pressure gradient, the proposed initiation pressure gradient, and the formation parameter K / μ.

[0027] As a preferred embodiment of the present invention, in step 300, the method for determining the starting pressure gradient by combining the displacement test time and the confining pressure change of the core holder is as follows:

[0028] Based on the monitoring data from the pressure sensor used to measure the confining pressure of the core, and the displacement test time for the core displacement test, a map of the change in confining pressure of the core is constructed.

[0029] Based on the confining pressure data corresponding to different displacement test conditions in the core confining pressure change diagram, the time point when the confining pressure data stops decreasing and starts to increase is taken as the displacement starting point for establishing effective displacement of the core, and the displacement starting point is taken as the actual liquid outlet point, and the pressure gradient corresponding to the moment before the actual liquid outlet point is set as the lower limit of the starting pressure gradient.

[0030] As a preferred embodiment of the present invention, in step 400, the monitoring data of the pressure sensor used to measure the displacement pressure in the core holder is cleaned to screen out the pressure monitoring data before the actual liquid outlet point.

[0031] The monitoring data from the liquid level sensor in the measuring cylinder at the outlet end of the core holder is cleaned to filter out production monitoring data prior to the actual liquid outlet point.

[0032] As a preferred embodiment of the present invention, the method for determining the relationship between the pressure gradient and the product fluid rate is as follows:

[0033] Collect the core displacement pressure corresponding to the displacement test operation after the actual liquid outlet point, and determine the core pressure gradient corresponding to each displacement test operation in combination with the core length;

[0034] Collect the monitoring data of the liquid level sensor after the actual liquid outlet point to determine the liquid production rate corresponding to each displacement test operation;

[0035] By combining the core pressure gradient and the fluid production rate corresponding to each displacement test operation, a two-dimensional dot plot of pressure gradient and fluid production rate is constructed.

[0036] Curve fitting was performed on the scatter plot of pressure gradient versus product velocity to construct a curve relating pressure gradient and product velocity. The intersection point of the curve segment with the steepest slope with the two-dimensional coordinate axis was taken as the proposed start-up pressure gradient.

[0037] As a preferred embodiment of the present invention, in step 500, the equivalent permeability is calculated by combining the properties of the test core and the displacement pressure difference corresponding to each displacement test operation.

[0038] Among them, the displacement pressure difference is the pressure difference between the outlet end and the inlet end of the core holder during each displacement test operation;

[0039] Wherein, the equivalent permeability K = κ * ρ * g / η, where K is the permeability of the weakly cemented argillaceous siltstone, κ is the permeability coefficient, calculated based on the displacement pressure difference and the produced fluid data corresponding to each displacement test operation; η is the dynamic viscosity coefficient; ρ is the density of the aqueous phase fluid in the weakly cemented argillaceous siltstone; and g is the gravitational acceleration.

[0040] As a preferred embodiment of the present invention, by fitting the minimum initiation pressure gradient with formation parameter K / μ data, the calculation formula for the minimum initiation pressure gradient of the aqueous phase and formation parameter K / μ is obtained as follows:

[0041] ;

[0042] By fitting the hypothetical initiation pressure gradient with formation parameter K / μ data, the calculation formulas for the hypothetical initiation pressure gradient and formation parameter K / μ in the water phase are obtained as follows:

[0043] .

[0044] Compared with the prior art, the present invention has the following advantages:

[0045] This invention takes the point where the confining pressure stops decreasing and then increases as the actual point of fluid discharge for effective displacement of the core. At this point, the discharge at the outlet end is considered to be the actual production of injected fluid. The pressure gradient corresponding to this point is the lower limit of the starting pressure gradient, which improves the accuracy of data analysis. Furthermore, it determines the variation law of the starting pressure gradient of the aqueous phase in low-permeability loose argillaceous siltstone with the seepage characteristics of the core and the properties of the formation fluid. The smaller the mobility, that is, the smaller the permeability of the core, the larger the minimum starting pressure gradient and the proposed starting pressure gradient. Attached Figure Description

[0046] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of the overall structure of the starting pressure gradient testing device provided in Embodiment 1 of the present invention;

[0048] Figure 2 This is a flowchart illustrating the initiation pressure gradient test method provided in Embodiment 1 of the present invention;

[0049] Figure 3 This is a structural block diagram of the starting pressure gradient law analysis system of Embodiment 2 of the present invention;

[0050] Figure 4 This is a flowchart illustrating the starting pressure gradient law analysis method of Embodiment 2 of the present invention;

[0051] Figure 5 This is a diagram showing the variation of confining pressure in the core sample according to an embodiment of the present invention.

[0052] Figure 6This is a graph showing the relationship between displacement pressure difference and permeability in an embodiment of the present invention.

[0053] Figure 7 This is a graph showing the relationship between pressure gradient and liquid production rate in an embodiment of the present invention.

[0054] Figure 8 This is a graph showing the relationship between the minimum starting pressure gradient and K / μ in an embodiment of the present invention.

[0055] Figure 9 This is a graph showing the relationship between the proposed start-up pressure gradient and K / μ in an embodiment of the present invention.

[0056] The labels in the diagram represent the following:

[0057] 1-Core holder; 2-Six-way valve; 3-Measuring cylinder; 4-High-pressure precision injection pump; 5-Pressure sensor; 6-Piston container.

[0058] 7-Timing unit; 8-Liquid level sensor; 9-Processing system;

[0059] 91 - Data Analysis Module; 92 - Data Cleaning Module; Detailed Implementation

[0060] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] Example 1

[0062] like Figure 1 As shown, the present invention provides a starting pressure gradient testing device for weakly cemented argillaceous siltstone, including a core holder 1 for clamping the weakly cemented argillaceous siltstone. The inlet end of the core holder 1 is provided with a six-way valve 2, which is used to apply displacement pressure, confining pressure and displacement of water phase to the core holder 1 respectively. The outlet end of the core holder 1 is connected to a measuring cylinder 3, which measures the volume of liquid overflowing from the weakly cemented argillaceous siltstone through a liquid level sensor inside the measuring cylinder 3.

[0063] Pressure sensors 5 are provided at both the inlet and outlet ends of the core holder 1. The pressure sensor 5 at the inlet end of the core holder 1 is used to measure the displacement pressure and confining pressure inside the core holder 1.

[0064] A pressure sensor 5 is also provided at the outlet end of the six-way valve 2. The pressure sensor 5 at the outlet end of the six-way valve 2 is used to measure the displacement pressure and confining pressure injected into the core holder 1.

[0065] In this embodiment, the core sample used is a low-permeability, loose argillaceous siltstone. The argillaceous siltstone natural gas hydrate reservoir exhibits weak cementation characteristics, and the reservoir core after hydrate decomposition exhibits a semi-fluid plastic state.

[0066] The core holder 1 is specifically a large-diameter thermoplastic tube. The large-diameter thermoplastic tube is fixed to the outside of the core. After the core holder 1 is placed in an oven, it is heated and shaped evenly, so that the core holder 1 becomes a cylindrical flexible tube that can deform with the core after being pressurized.

[0067] After the rock sample is filled into the core holder 1, permeable stones are placed at both ends of the cylindrical hose. During the filling process, the core is fully compacted. This sand filling mold can ensure that the core does not leak during the displacement process and that there is no mud leakage at both ends.

[0068] The inlet end of the six-way valve 2 is connected to at least two piston containers 6. The other end of the piston containers 6 is connected to a high-pressure precision injection pump 4 through a valve. The high-pressure precision injection pump 4 injects pressure or draws a vacuum into the core holder 1 through the piston containers 6. The high-pressure precision injection pump 4 also injects a displacement water phase into the core holder 1 through the piston containers 6.

[0069] The test method for the above-mentioned starting pressure gradient test device for weakly cemented silty mudstone is as follows: Figure 2 As shown, it includes the following steps:

[0070] Step 100: Place the weakly cemented argillaceous siltstone into the core holder, connect the testing device, and vacuum and saturate the core holder and the weakly cemented argillaceous siltstone inside the core holder with formation water.

[0071] Before step 100, the testing device is turned on and a standard saline solution is prepared to perform a sealing test on the testing device.

[0072] After saturating formation water, the reservoir core of the weakly cemented argillaceous siltstone exhibits a semi-fluid state.

[0073] Step 200: Set the initial confining pressure, open the inlet and outlet ends of the core holder, and repeatedly displace and pressurize the core holder until the pressure inside the core holder is stable and no more liquid is discharged from the outlet end of the core holder.

[0074] In step 200, after applying displacement pressure to the core holder, the semi-liquid, weakly cemented argillaceous siltstone reservoir core deforms, causing a decrease in confining pressure. By repeatedly displacing and pressurizing the core holder until the pressure stabilizes, the core holder stops releasing liquid.

[0075] In this embodiment, after the core is saturated with formation water, the reservoir core after the hydrate decomposes is semi-liquid and plastic, and is easily deformed after pressure is applied. Therefore, when pressure is applied to the core holder, the core is squeezed and deformed, and the confining pressure will continue to decrease.

[0076] Combined with the pressure gradient test device for weakly cemented argillaceous siltstone, one piston container 6 was used to apply an initial confining pressure of 2 MPa to the core holder, and then the other piston container 6 was used to apply a displacement pressure to the core holder until the semi-liquid, weakly cemented argillaceous siltstone reservoir core was compacted and the core holder stopped leaking liquid after the pressure stabilized.

[0077] Step 300: Conduct a displacement test on the core holder, and increase the displacement fluid rate sequentially according to the pump speed. Time each displacement test and record the displacement pressure, confining pressure changes, and displacement fluid volume at the inlet and outlet of the core holder.

[0078] Step 400: After the inlet end of the core holder reaches the upper limit of the safe injection pressure, switch to pressure displacement. Perform displacement tests on the core holder according to the displacement pressure control process. Timing is recorded for each displacement test, and the displacement pressure, confining pressure changes, and displacement fluid volume corresponding to the inlet and outlet ends of the core holder are recorded.

[0079] Step 500: Increase the confining pressure sequentially, and repeat steps 200-400 above until the core holder no longer overflows with displacement fluid, then stop the test.

[0080] In step 300, the method for conducting a displacement test on the core holder is as follows:

[0081] An initial confining pressure of 2 MPa was applied to the core holder;

[0082] The initial pump speed for displacing the aqueous phase was set to 0.005 ml / min. Displacement was started and timing was initiated. The confining pressure inside the core holder was recorded throughout the process.

[0083] After the displacement test at the initial pump speed stabilized, the pump speed was changed sequentially to 0.015 ml / min, 0.05 ml / min, 0.1 ml / min, 0.3 ml / min, and 0.6 ml / min. The displacement fluid at the outlet of the core holder was counted again, and the displacement time and confining pressure inside the core holder were recorded in real time.

[0084] In step 400, after the pressure at the inlet end of the core holder reaches the upper limit of the safe injection pressure, when the displacement pressure at the inlet end of the core holder reaches the upper limit of the safe injection pressure, that is, when the displacement pressure at the inlet end of the core holder does not exceed 80% of the set confining pressure inside the core holder, the displacement test is adjusted to variable pressure displacement, and the displacement pressure is changed sequentially according to 1.6MPa-2.2MPa-1.6MPa.

[0085] The displacement fluid at the outlet of the core holder during each displacement test was statistically analyzed, and the displacement time, confining pressure, and displacement pressure difference inside the core holder were recorded in real time.

[0086] Based on the displacement time of the core holder recorded in real time in step 300, the displacement process of the variable speed displacement test on the core holder is determined. Based on the displacement time of the core holder recorded in real time in step 400, the displacement process of the variable pressure displacement test on the core holder is determined.

[0087] Based on the displacement time of the core holder and the confining pressure inside the core holder recorded in real time in steps 300 and 400, a core confining pressure variation map is created.

[0088] Based on the displacement tests at varying speeds of 0.005 ml / min, 0.015 ml / min, 0.05 ml / min, 0.1 ml / min, 0.3 ml / min, and 0.6 ml / min, as well as the displacement times and confining pressures corresponding to the pressure variations from 1.6 MPa to 2.2 MPa to 1.6 MPa, the time points corresponding to the cessation of confining pressure decrease and subsequent increase are determined, and these time points are taken as the actual liquid discharge points.

[0089] Based on the multiple displacement tests conducted after the actual liquid outlet point in steps 300 and 400, the displacement pressures corresponding to the inlet and outlet ends of the core holder are obtained sequentially, and the displacement pressure difference corresponding to each displacement test in steps 300 and 400 is calculated.

[0090] Determine the equivalent permeability corresponding to multiple displacement tests after the actual outlet point in steps 300 and 400, and create a graph showing the relationship between displacement pressure difference and permeability to corroborate the actual outlet point.

[0091] In step 500, the confining pressure is increased sequentially by 4MPa, 8MPa, and 12MPa. After each increase in confining pressure, the displacement test is repeated according to steps 200-400 until the outlet end of the core holder no longer produces liquid. At this point, the pressurization of the high-pressure precision injection pump is stopped, and the weakly cemented argillaceous siltstone is taken out, dried, and weighed.

[0092] This embodiment designs a method and device for testing the water phase initiation pressure gradient of low-permeability loose argillaceous siltstone cores under normal temperature and pressure conditions. By creating test conditions with different confining pressures, the water phase initiation pressure gradient of the cores corresponding to different confining pressures can be obtained, and then the variation law of water phase initiation pressure gradient of low-permeability loose argillaceous siltstone with core permeability can be analyzed.

[0093] Example 2

[0094] After conducting the above-described method for testing the starting pressure gradient of weakly cemented silty mudstone, a series of monitoring data regarding the measuring device were obtained. By processing this monitoring data, the starting pressure gradient law of the weakly cemented silty mudstone can be obtained. Therefore, combining the above-described device and method for testing the starting pressure gradient of weakly cemented silty mudstone, this invention also provides a system for analyzing the starting pressure gradient law of weakly cemented silty mudstone, such as... Figure 3 As shown, it includes: a timing unit 7, a pressure sensor 5, a liquid level sensor 8, and a processing system 9.

[0095] Timing unit 7 is used to time each displacement test operation.

[0096] Among them, the displacement test operation control of the displacement test device is divided into liquid variable speed displacement operation and pressure variable displacement operation under different confining pressure conditions.

[0097] The initial confining pressure was set to 2 MPa, and the liquid displacement operation was performed by changing the displacement liquid pump speed at 0.005 ml / min, 0.015 ml / min, 0.05 ml / min, 0.1 ml / min, 0.3 ml / min, and 0.6 ml / min.

[0098] The displacement pressure is changed from 1.6MPa to 2.2MPa to 1.6MPa during the variable displacement operation.

[0099] The confining pressure was adjusted to 4 MPa and 8 MPa in sequence, and under each confining pressure condition, the displacement test was carried out by first performing liquid variable speed displacement operation and then pressure variable displacement operation.

[0100] The timing unit 7 is used to time the operation duration of each displacement test.

[0101] Pressure sensor 5 is installed inside the core holder to measure the confining pressure on the weakly cemented silty mudstone inside the core holder, as well as the displacement pressure at the inlet end and the outlet end of the core holder.

[0102] The liquid level sensor 8 is installed inside the measuring cylinder at the outlet end of the core holder and is used to measure the liquid production of the displacement test.

[0103] The processing system 9 is communicatively connected to the pressure sensor 5, the timing unit 7, and the liquid level sensor 8. The processing system 9 is also equipped with a data analysis module 91. Based on the output data of the timing unit 7 and the pressure sensor 5, the data analysis module 91 constructs a core confining pressure change map to determine the actual liquid discharge point of the displacement test and the minimum starting pressure gradient corresponding to the moment before the actual liquid discharge point.

[0104] The data analysis module 91 analyzes the relationship between the core pressure gradient and the production rate based on the output data of the pressure sensor 5, the timing unit 7 and the liquid level sensor 8, so as to determine the proposed start-up pressure gradient corresponding to the displacement test.

[0105] The data analysis module 91 is used to collect the minimum initiation pressure gradient and the proposed initiation pressure gradient obtained from the displacement test of multiple weakly cemented argillaceous siltstone cores, and to fit the relationship between the minimum initiation pressure gradient and the proposed initiation pressure gradient and the formation parameter K / μ.

[0106] As can be seen from Example 1, the reservoir core after hydrate decomposition is semi-fluid and plastic, and is easily deformed after pressurization. Therefore, the confining pressure will continue to drop after pressurization, and multiple pressurizations are required. The core is allowed to stand until the pressure is stable and no more liquid is discharged from the outlet end of the core holder.

[0107] Therefore, this embodiment determines the starting point of effective displacement based on the confining pressure change corresponding to the displacement test operation of the displacement test device, and then determines the minimum starting pressure gradient for the displacement test of weakly cemented argillaceous siltstone.

[0108] After determining the effective displacement initiation point, the core pressure gradient and production rate corresponding to each displacement test operation are fitted to obtain a curve between the core pressure gradient and the production rate. Then, using the steady-state method, the straight line segment of the steady non-Darcy flow curve is extended to intersect the coordinate axis, and the intersection point is the proposed initiation pressure gradient.

[0109] It should be noted that the processing system 9 is equipped with a data cleaning module 92. The data cleaning module 92 cleans and filters out the output data of the pressure sensor 5 and the liquid level sensor 8 before the actual liquid outlet point in the core confining pressure change diagram. Before analyzing the relationship between the core pressure gradient and the liquid production rate, the data cleaning module 92 cleans the output data of the pressure sensor 5 and the liquid level sensor 8.

[0110] The processing system 9 is communicatively connected to the displacement test device. The processing system 9 is used to control the displacement test operation of the displacement test device. The processing system 9 also connects the control time point of the displacement test operation of the displacement test device with the timing unit 7 to determine the displacement test operation corresponding to the actual discharge point and the displacement test operation corresponding to the actual discharge point. In conjunction with the data cleaning module 92, the monitoring data corresponding to the displacement test operation before the actual discharge point is filtered out.

[0111] By combining the actual effluent point corresponding to each displacement test, the displacement test operation corresponding to the actual effluent point of the rock sample core is determined, as well as the pressure gradient and effluent production rate corresponding to the displacement test operation after the actual effluent point of the rock sample core.

[0112] In addition, such as Figure 4 As shown, the present invention also provides an analysis method for the above-mentioned weakly cemented silty mudstone initiation pressure gradient law analysis system, including the following steps:

[0113] Step 100: Inject weakly cemented argillaceous siltstone into the core holder to construct multiple test cores.

[0114] Step 200: Conduct a displacement test on each core holder, time each displacement test, and record the displacement pressure, confining pressure changes, and displacement fluid volume of the core holder.

[0115] Step 300: Combine the displacement test time and the confining pressure change of the core holder to determine the starting pressure gradient, and determine the actual liquid outlet point of the test core during the displacement test, and obtain the minimum starting pressure gradient of each test core.

[0116] Step 400: Perform data cleaning on the displacement pressure and displacement fluid capacity, fit the relationship between the pressure gradient and the production rate, and obtain the proposed start-up pressure gradient for each test core.

[0117] Step 500: Combining the minimum starting pressure gradient, the proposed starting pressure gradient, and the formation parameter K / μ of all determined test cores, fit the relationship between the minimum starting pressure gradient, the proposed starting pressure gradient, and the formation parameter K / μ.

[0118] It should be noted that in step 200 of the analysis method for the starting pressure gradient law analysis system of weakly cemented argillaceous siltstone, the displacement test implementation method for each core holder is specifically the complete steps of the test method for the starting pressure gradient test device of weakly cemented argillaceous siltstone.

[0119] In step 300, the method for determining the starting pressure gradient by combining the displacement test time and the confining pressure change of the core holder is as follows:

[0120] Based on the monitoring data from the pressure sensor used to measure the confining pressure of the core, and the displacement test time for the core displacement test, a map of the change in confining pressure of the core is constructed.

[0121] Based on the confining pressure data corresponding to different displacement test conditions in the confining pressure change diagram of the core, the time point when the confining pressure data stops decreasing and starts to increase is taken as the displacement starting point for establishing effective displacement of the core, and the displacement starting point is taken as the actual liquid outlet point, and the pressure gradient corresponding to the moment before the actual liquid outlet point is set as the lower limit of the starting pressure gradient.

[0122] In this embodiment, the point where the confining pressure stops decreasing and then increases is taken as the actual point of fluid discharge for the establishment of effective displacement of the core. At this point, the discharge at the outlet end is considered to be the actual production of injected fluid. The pressure gradient corresponding to the moment before this point is the lower limit of the starting pressure gradient. Taking the point where the confining pressure stops decreasing and then increases as the starting point for the establishment of effective displacement of the core can improve the accuracy of the analysis. At this point, the discharge at the outlet end is considered to be the actual production of injected fluid (the discharge at the outlet end before this point is the core deformation discharge).

[0123] In step 400, the monitoring data of the pressure sensor in the core holder used to measure the displacement pressure is cleaned to filter out the pressure monitoring data before the actual liquid outlet point.

[0124] Data cleaning was performed on the liquid level sensor in the measuring cylinder at the outlet of the core holder to remove production monitoring data prior to the actual liquid outlet point.

[0125] Therefore, the analysis of monitoring data from pressure sensors and liquid level sensors only applies to monitoring data after the actual liquid outlet point.

[0126] Furthermore, in step 400, the method for determining the relationship between the pressure gradient and the product fluid velocity is as follows:

[0127] Collect the core displacement pressure corresponding to the displacement test operation after the actual liquid outlet point, and determine the core pressure gradient corresponding to each displacement test operation in combination with the core length;

[0128] Collect monitoring data from the liquid level sensor after the actual liquid outlet point to determine the liquid production rate corresponding to each displacement test operation;

[0129] By combining the core pressure gradient and the fluid production rate corresponding to each displacement test operation, a two-dimensional dot plot of pressure gradient and fluid production rate is constructed.

[0130] Curve fitting was performed on the scatter plot of pressure gradient versus product velocity to construct a curve relating pressure gradient and product velocity. The intersection point of the curve segment with the steepest slope with the two-dimensional coordinate axis was taken as the proposed start-up pressure gradient.

[0131] In step 500, the equivalent permeability is calculated by combining the properties of the test core and the displacement pressure difference corresponding to each displacement test operation;

[0132] Among them, the displacement pressure difference is the pressure difference between the outlet end and the inlet end of the core holder during each displacement test operation;

[0133] Wherein, the equivalent permeability K = κ * ρ * g / η, where K is the permeability of the weakly cemented argillaceous siltstone, κ is the permeability coefficient, calculated based on the displacement pressure difference and the produced fluid data corresponding to each displacement test operation; η is the dynamic viscosity coefficient; ρ is the density of the aqueous phase fluid in the weakly cemented argillaceous siltstone; and g is the gravitational acceleration.

[0134] By fitting the minimum initiation pressure gradient with the formation parameter K / μ data, the formula for calculating the minimum initiation pressure gradient of the water phase and the formation parameter K / μ is obtained as follows:

[0135] ;

[0136] By fitting the hypothetical initiation pressure gradient with formation parameter K / μ data, the calculation formulas for the hypothetical initiation pressure gradient and formation parameter K / μ in the water phase are obtained as follows:

[0137] .

[0138] According to the above formula, the smaller K / μ is, the smaller the permeability of the core, the larger the minimum starting pressure gradient, and the larger the pseudo-starting pressure gradient. The specific reason is that the narrower the rock throat, the greater the force of the solid surface on the boundary layer fluid, and the greater the resistance that the fluid flow needs to overcome.

[0139] Example 3

[0140] In this embodiment, after obtaining low-permeability loose argillaceous siltstone samples provided by the Guangzhou Marine Geological Survey, the samples were numbered BC06B and BC08B, respectively.

[0141] The total mineralization of the formation water used in the saturated rock samples was 4500 mg / L, and the ionic composition is shown in Table 1.

[0142] Table 1. Ionic composition of formation water

[0143] ion Na+ K+ Mg2+ Ga2+ Cl- S042- HCO3- Concentration (mg / L) 1380 49 166 52 2494 347 19

[0144] A large-diameter thermoplastic tube was fixed to the outside of a 2.5cm diameter rock core. After being uniformly heated and shaped in an oven, it became a cylindrical flexible tube with an inner diameter of 2.5cm and a length of 26cm, which could deform with the rock core under pressure. Rock samples were filled into the cylindrical flexible tube, and permeable stones were placed at both ends. The rock core was fully compacted during the filling process. This sand-filling mold ensured that the rock core would not leak during displacement and that there was no mud leakage at both ends. A total of 13 rock core samples were prepared for the experiment. The core parameters of the 13 rock core samples are shown in Table 2 below.

[0145] Table 2 Experimental Core Parameters

[0146] Experiment number Core number Core diameter, cm Core length, cm Initiating pressure gradient measurement method 1 BC06B-1-2 2.5 23.5 steady state method 2 BC06B-1-4 2.5 23.5 steady state method 3 BC06B-1-8 2.5 23.5 steady state method 4 BC06B-1-12 2.5 23.5 steady state method 5 BC06B-2-2 2.5 24.9 steady state method 6 BC06B-2-4 2.5 24.9 steady state method 7 BC06B-2-8 2.5 24.9 steady state method 8 BC06B-2-12 2.5 24.9 steady state method 9 BC08B-1-2 2.5 24.9 steady state method 10 BC08B-1-4 2.5 24.9 steady state method 11 BC08B-1-8 2.5 24.9 steady state method 12 BC08B-2-8 2.5 24.9 steady state method 13 BC08B-2-12 2.5 24.9 steady state method

[0147] Following the testing method of the aforementioned pressure gradient test device for weakly cemented argillaceous siltstone, displacement tests were conducted on each core sample using a combination of variable displacement rate and variable displacement pressure. The initial confining pressure was 2 MPa, and the displacement rate was changed sequentially to 0.005 ml / min, 0.015 ml / min, 0.05 ml / min, 0.1 ml / min, 0.3 ml / min, and 0.6 ml / min. Then, the displacement pressure was changed to 1.6 MPa-2.2 MPa-1.6 MPa for sequential pressure variation, and the change in displacement fluid volume under this displacement test was determined.

[0148] Then, displacement tests were conducted at confining pressures of 4 MPa and 8 MPa to determine the change in displacement fluid volume for each displacement test.

[0149] Specifically, for core BC08B-1-2, horizontal displacement was performed using a long core displacement method, with a confining pressure of 2 MPa. During displacement, two injection methods—variable displacement rate and variable displacement pressure—were used to measure the initiation pressure gradient. The changes in confining pressure of core BC08B-1-2 during displacement are as follows: Figure 5 As shown.

[0150] As shown in the confining pressure variation diagram of core BC08B-1-2, the confining pressure of the core continued to decrease during the initial stage of displacement due to the continuous deformation of the core. As displacement progressed, the rate of decrease in confining pressure gradually slowed down. At 10113s, the confining pressure stopped decreasing and started to rise again, reflecting that effective displacement was achieved after the continuous injection at the inlet end and the continuous rise in inlet pressure.

[0151] The injected fluid flows through the core, allowing pressure to propagate within it and causing reverse deformation, thus leading to a continuous increase in confining pressure. Based on this experimental phenomenon and its corresponding principle, the point where the confining pressure stops decreasing and begins to increase is taken as the starting point for establishing effective displacement of the core. The fluid discharged from the outlet at this point is considered to be the actual output of the injected fluid (the fluid discharged from the outlet before this point is due to core deformation), meaning this point is the true fluid discharge point, and the pressure gradient corresponding to this point is the lower limit of the starting pressure gradient.

[0152] Furthermore, by analyzing the relationship between the displacement pressure difference and the equivalent permeability of the displacing fluid in the BC08B-1-2 core during the displacement process, the actual effluent point can also be determined, such as... Figure 6 As shown, the displacement pressure difference is the pressure difference between the outlet and inlet ends of the core holder during each displacement test operation.

[0153] Wherein, the equivalent permeability K = κ * ρ * g / η, where K is the permeability of the weakly cemented argillaceous siltstone, κ is the permeability coefficient, calculated based on the displacement pressure difference and the produced fluid data corresponding to each displacement test operation; η is the dynamic viscosity coefficient; ρ is the density of the aqueous phase fluid in the weakly cemented argillaceous siltstone; and g is the gravitational acceleration.

[0154] Because energy accumulates at the core inlet before effective displacement is established, the equivalent permeability of the fluid flow is significantly higher in the initial stage after the injected fluid breaks through. As the displacement pressure difference increases, the equivalent permeability decreases rapidly and gradually stabilizes at around 0.014 md.

[0155] After the displacement pressure difference was greater than 1.2 MPa, the equivalent permeability of the core showed a stepwise jump, reaching 0.025 md, which reflects the channel deformation during the core displacement process, resulting in improved permeability. Therefore, the moment before the actual effluent point was taken as the starting point for analysis, that is, the displacement test operation of 0.05 ml / min was taken as the actual effluent point and the starting point for analysis.

[0156] The relationship between the pressure gradient and the production rate of the BC08B-1-2 core is as follows: Figure 7 As shown, analysis Figure 7 It is known that the minimum starting pressure gradient is 0.00026 MPa / cm at the moment before the liquid exits the core outlet. According to the steady-state method, the intersection of the extended straight line segment of the steady non-Darcy flow curve with the coordinate axis is the proposed starting pressure gradient. The proposed starting pressure gradient of the BC08B-1-2 core is 0.04 MPa / cm.

[0157] Using this analytical method, 13 core displacement experiments were analyzed. The minimum initiation pressure gradient and the pseudo-initiation pressure gradient of different cores are shown in Table 3. The initiation pressure gradients of the 13 cores differed significantly. The minimum initiation pressure gradient was 0.00026 MPa / cm. The largest minimum initiation pressure gradient in the experiment was 457 times that of the smallest minimum initiation pressure gradient, which was 0.119 MPa / cm. The smallest pseudo-initiation pressure gradient was 0.04 MPa / cm. The largest pseudo-initiation pressure gradient was 8 times that of the smallest pseudo-initiation pressure gradient, which was 0.32 MPa / cm. Although the minimum initiation pressure gradients differed significantly, the differences in the pseudo-initiation pressure gradients decreased.

[0158] Table 3. Minimum initiation pressure gradient and potential initiation pressure gradient for different core samples

[0159] rock core K(mD) <![CDATA[K / μ(um 2 / Pa.s)]]> Minimum starting pressure gradient (MPa / cm) The proposed pressure gradient (MPa / cm) will be activated. BC08B-1-2 0.0195 0.0195 0.00026 0.04 BC08B-1-4 0.014 0.014 0.00036 0.076 BC08B-1-8 0.00335 0.00335 0.0361 0.15 BC06B-1-2 0.0205 0.0205 0.0102 0.024 BC06B-1-4 0.0122 0.0122 0.0255 0.06 BC06B-1-8 0.00305 0.00305 0.051 0.17 BC06B-1-12 0.0021 0.0021 0.119 0.2 BC08B-2-8 0.0043 0.0043 0.061 0.2 BC08B-2-12 0.0025 0.0025 0.083 0.32 BC06B-2-2 0.00835 0.00835 0.0094 0.11 BC06B-2-4 0.0068 0.0068 0.031 0.12 BC06B-2-8 0.0031 0.0031 0.015 0.25 BC06B-2-12 0.0018 0.0018 0.072 0.28

[0160] Following step 500, based on the displacement experiment pressure and production data, the permeability of the sand-filled core is calculated, and the mobility of the displacing phase is calculated based on the viscosity of the displacing fluid. The relationship curve between the minimum initiation pressure gradient and the formation parameter K / μ is shown below. Figure 8 As shown, by Figure 8 It can be seen that the smaller the formation parameter K / μ, i.e. the lower the permeability of the core, the greater the minimum initiation pressure gradient. This is because the narrower the rock throat, the greater the force exerted by the solid surface on the boundary layer fluid, and the greater the resistance that the fluid flow needs to overcome.

[0161] When the formation parameter K / μ < 0.005 μm² / (Pa·s) or the core permeability is less than 0.005 × 10⁻³ μm², the minimum initiation pressure gradient of the core increases rapidly as the formation parameter K / μ decreases. A formula for calculating the minimum initiation pressure gradient of the water phase relative to the formation parameter K / μ is obtained by fitting the minimum initiation pressure gradient with the formation parameter K / μ data.

[0162] ;

[0163] Following step 500, the relationship between the proposed pressure gradient and formation parameter K / μ is as follows: Figure 9 As shown, by Figure 9 It can be seen that the smaller the formation parameter K / μ, i.e., the smaller the core permeability, the larger the proposed initiation pressure gradient. This is because the narrower the rock throat, the greater the force exerted by the solid surface on the boundary layer fluid, and the greater the resistance that the fluid flow needs to overcome. When the formation parameter K / μ < 0.007 μm² / (Pa·s) or the core permeability is less than 0.007 × 10⁻³ μm², the proposed initiation pressure gradient increases rapidly as the formation parameter K / μ decreases. The formula for calculating the proposed initiation pressure gradient in relation to the formation parameter K / μ is obtained through fitting:

[0164] ;

[0165] The correlation formula between the minimum initiation pressure gradient, the proposed initiation pressure gradient and the formation parameter K / μ obtained from the above fitting can be used to quickly calculate the minimum initiation pressure gradient value and the proposed initiation pressure gradient value of any target formation.

[0166] For the (minimum) initiation pressure gradient, when the mobility is less than 0.005 μm² / (Pa•s) or the core permeability is less than 0.005 × 10⁻³ μm², the minimum initiation pressure gradient increases rapidly with decreasing mobility. However, for the pseudo-initiation pressure gradient, when the mobility is less than 0.007 μm² / (Pa•s) or the core permeability is less than 0.007 × 10⁻³ μm², the minimum initiation pressure gradient increases rapidly with decreasing mobility.

[0167] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.

Claims

1. A system for analyzing the initiation pressure gradient law of weakly cemented argillaceous siltstone, characterized in that, include: The timing unit (7) is used to time each displacement test operation; Pressure sensor (5) is installed in the core holder to measure the confining pressure on the weakly cemented silty mudstone in the core holder, as well as the displacement pressure at the inlet end of the core holder and the displacement pressure at the outlet end of the core holder. A liquid level sensor (8) is installed in a measuring cylinder at the outlet end of the core holder to measure the liquid production of the displacement test. The processing system (9) is connected to the pressure sensor (5), the timing unit (7) and the liquid level sensor (8) respectively. The processing system (9) is also equipped with a data analysis module (91). The data analysis module (91) constructs a core confining pressure change map based on the output data of the timing unit (7) and the pressure sensor (5) to determine the actual liquid discharge point of the displacement test and the minimum starting pressure gradient corresponding to the moment before the actual liquid discharge point. Specifically, the core confining pressure change map is constructed. According to the confining pressure data corresponding to different displacement test conditions in the core confining pressure change map, the time point when the confining pressure data stops falling and rises is taken as the displacement starting point for the core to establish effective displacement, and the displacement starting point is taken as the actual liquid discharge point. The data analysis module (91) analyzes the relationship between the core pressure gradient and the liquid production rate based on the output data of the pressure sensor (5), the timing unit (7) and the liquid level sensor (8) to determine the proposed starting pressure gradient corresponding to the displacement test. The data analysis module (91) is used to collect the minimum starting pressure gradient and the proposed starting pressure gradient obtained when conducting displacement tests on test cores of multiple weakly cemented argillaceous siltstones, and to fit the relationship between the minimum starting pressure gradient and the proposed starting pressure gradient and the formation parameter K / μ.

2. The system for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone according to claim 1, characterized in that, The processing system (9) is equipped with a data cleaning module (92). The data cleaning module (92) cleans and filters out the output data of the pressure sensor and the output data of the liquid level sensor (8) before the actual liquid outlet point in the core confining pressure change diagram.

3. The system for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone according to claim 1, characterized in that, The processing system (9) is communicatively connected to the displacement test device. The processing system (9) is used to control the displacement test operation of the displacement test device. The processing system (9) also connects the control time point of the displacement test operation of the displacement test device with the timing unit (7) to determine the displacement test operation corresponding to the actual liquid outlet point.

4. The system for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone according to claim 3, characterized in that, The displacement test device is divided into two operation modes under different confining pressure conditions: first, liquid variable speed displacement operation, and then pressure variable displacement operation. The initial confining pressure was set to 2 MPa, and the liquid displacement operation was performed by changing the pump speed of the displacement liquid at 0.005 ml / min, 0.015 ml / min, 0.05 ml / min, 0.1 ml / min, 0.3 ml / min, and 0.6 ml / min. The variable displacement operation changes the displacement pressure from 1.6MPa to 2.2MPa to 1.6MPa; The confining pressure was adjusted to 4 MPa and 8 MPa in sequence, and under each confining pressure condition, the displacement test was carried out by first performing liquid variable speed displacement operation and then pressure variable displacement operation. By combining the time points corresponding to the actual effluent points of each displacement test, the displacement test operations corresponding to the actual effluent effluent of the rock sample core are determined, as well as the pressure gradient and production rate corresponding to the displacement test operations after the actual effluent effluent effluent of the rock sample core.

5. An analytical method based on the starting pressure gradient law analysis system for weakly cemented argillaceous siltstone according to any one of claims 1-4, characterized in that, Includes the following steps: Step 100: Inject weakly cemented argillaceous siltstone into the core holder to construct multiple test cores; Step 200: Conduct a displacement test on each of the core holders, time each displacement test, and record the displacement pressure, confining pressure changes, and displacement fluid volume of the core holders. Step 300: Combine the displacement test time of each displacement test with the confining pressure change of the core holder to determine the starting pressure gradient, and determine the actual liquid outlet point of the test core during the displacement test, and obtain the minimum starting pressure gradient of each test core. Step 400: Clean the displacement pressure and displacement fluid capacity data, fit the relationship between pressure gradient and production rate, and obtain the proposed start-up pressure gradient for each test core. Step 500: Combining the minimum initiation pressure gradient, the proposed initiation pressure gradient, and the formation parameter K / μ from all test cores, fit the relationship between the minimum initiation pressure gradient, the proposed initiation pressure gradient, and the formation parameter K / μ.

6. The analytical method according to claim 5, characterized in that, In step 300, the method for determining the starting pressure gradient by combining the displacement test time and the confining pressure change of the core holder is as follows: Based on the monitoring data from the pressure sensor used to measure the confining pressure of the core, and the displacement test time for the core displacement test, a map of the change in confining pressure of the core is constructed. Based on the confining pressure data corresponding to different displacement test conditions in the core confining pressure change diagram, the time point when the confining pressure data stops decreasing and starts to increase is taken as the displacement starting point for establishing effective displacement of the core, and the displacement starting point is taken as the actual liquid outlet point, and the pressure gradient corresponding to the moment before the actual liquid outlet point is set as the lower limit of the starting pressure gradient.

7. The analytical method according to claim 5, characterized in that, In step 400, the monitoring data of the pressure sensor used to measure the displacement pressure in the core holder is cleaned to filter out the pressure monitoring data before the actual liquid outlet point. The monitoring data from the liquid level sensor in the measuring cylinder at the outlet end of the core holder are cleaned to filter out production monitoring data prior to the actual liquid outlet point.

8. The analytical method according to claim 7, characterized in that, The method for determining the relationship between pressure gradient and product fluid velocity is as follows: Collect the core displacement pressure corresponding to the displacement test operation after the actual liquid outlet point, and determine the core pressure gradient corresponding to each displacement test operation in combination with the core length; Collect the monitoring data of the liquid level sensor after the actual liquid outlet point to determine the liquid production rate corresponding to each displacement test operation; By combining the core pressure gradient and the fluid production rate corresponding to each displacement test operation, a two-dimensional dot plot of pressure gradient and fluid production rate is constructed. Curve fitting was performed on the scatter plot of pressure gradient versus product velocity to construct a curve relating pressure gradient and product velocity. The intersection point of the curve segment with the steepest slope with the two-dimensional coordinate axis was taken as the proposed start-up pressure gradient.

9. The analytical method according to claim 8, characterized in that, In step 500, the equivalent permeability is calculated by combining the properties of the test core and the displacement pressure difference corresponding to each displacement test operation; Among them, the displacement pressure difference is the pressure difference between the outlet end and the inlet end of the core holder during each displacement test operation; Wherein, the equivalent permeability K = κ * ρ * g / η, where K is the permeability of the weakly cemented argillaceous siltstone, κ is the permeability coefficient, calculated based on the displacement pressure difference and the produced fluid data corresponding to each displacement test operation; η is the dynamic viscosity coefficient; ρ is the density of the aqueous phase fluid in the weakly cemented argillaceous siltstone; and g is the gravitational acceleration.

10. The analytical method according to claim 9, characterized in that, By fitting the minimum initiation pressure gradient with the formation parameter K / μ data, the formula for calculating the minimum initiation pressure gradient of the water phase and the formation parameter K / μ is obtained as follows: ； By fitting the hypothetical initiation pressure gradient with formation parameter K / μ data, the calculation formulas for the hypothetical initiation pressure gradient and formation parameter K / μ in the water phase are obtained as follows: 。

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