Weakly cemented argillaceous siltstone starting pressure gradient law analysis method and device

Abstract

The invention discloses a weakly cemented argillaceous siltstone starting pressure gradient law analysis method and system. The method comprises the following steps: constructing a plurality of test cores; a displacement test is conducted on each core holder, timing is conducted on each displacement test, and the displacement pressure, the confining pressure change and the displacement fluid capacity of the core holder are recorded; determining a starting pressure gradient by combining the confining pressure change of the rock core holder in each displacement test, determining a real liquid outlet point of the test rock core in the displacement test process, and obtaining the minimum starting pressure gradient of each test rock core; fitting the relationship between the pressure gradient and the liquid production speed, and obtaining the quasi-starting pressure gradient of each test rock core; fitting to obtain a relationship between the minimum starting pressure gradient and the stratum parameters and between the quasi-starting pressure gradient and the stratum parameters; according to the method, the real liquid outlet point of effective displacement is determined, the accuracy of data analysis is improved, and the change rule of the low-permeability loose argillaceous siltstone water phase starting pressure gradient along with the rock core seepage characteristic and the formation fluid property is determined.

Description

Technical Field

[0001] The present invention relates to the technical field of sandstone displacement driving pressure, and specifically relates to a method and device for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone. Background Art

[0002] During the seepage process of natural gas hydrates in low-permeability loose argillaceous siltstone, there is a phenomenon of starting pressure gradient. Below this pressure gradient, natural gas hydrates do not flow. Due to different formation seepage conditions and injection fluid properties, the starting pressure gradients required for the flow of natural gas hydrates are different. With the development of natural gas hydrates, the starting pressure gradient has an unignorable impact on development, and it is a comprehensive manifestation of abnormal fluid boundary layer properties and fluid plasticity.

[0003] The methods for studying the starting pressure gradient mainly apply indoor physical experiment simulation methods and numerical experiment methods at most. Among them, the indoor physical experiment simulation method is the most intuitive and currently relatively recognized effective method. Specifically, the method of measuring the relationship between pressure difference and flow rate under a steady flow state is adopted, that is, after saturating the core or sand-packed tube with crude oil, the steady-state flow rate under a certain pressure difference is measured, and then the starting pressure gradient is obtained by using mathematical methods. Its basic principle is to measure the flow rate of the fluid through the core after stabilizing at different displacement pressure differences, draw a relationship diagram of flow rate and pressure gradient, and obtain the starting pressure gradient by regressing the curve. And the method for measuring the starting pressure gradient in the laboratory still adopts the conventional method of measuring the relationship between steady-state pressure difference and flow rate, that is, after saturating the core with crude oil, under a series of pressure differences, record the steady-state flow rate at each point.

[0004] Both the commonly used indoor physical experiment simulation method and numerical experiment method use oil-phase displacement test operations, and the oil phase affects the calculation of core permeability. At present, there is no set of accurate analysis methods for the analysis of the test results of water-phase displacement test operations. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and device for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone, so as to solve the technical problem that there is no set of accurate analysis methods for the analysis of the test results of water-phase displacement test operations in the prior art.

[0006] To solve the above technical problem, the present invention specifically provides the following technical solutions:

[0007] A system for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone, comprising:

[0008] A timing unit for timing each displacement test operation;

[0009] A pressure sensor is installed inside the core holder and is used to measure the confining pressure exerted on the weakly cemented argillaceous siltstone inside the core holder, as well as the displacement pressure corresponding to the inlet end of the core holder and the displacement pressure corresponding to the outlet end of the core holder;

[0010] A liquid level sensor is installed inside the graduated cylinder at the outlet end of the core holder and is used to measure the liquid production volume of the displacement test;

[0011] A processing system is communicatively connected to the pressure sensor, the timing unit, and the liquid level sensor respectively. There is also a data analysis module inside the processing system. The data analysis module constructs a core confining pressure change diagram based on the output data of the timing unit and the pressure sensor to determine the true liquid outlet point of the displacement test and the minimum starting pressure gradient corresponding to the moment before the true liquid outlet 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, the timing unit, and the liquid level sensor to determine the pseudo starting pressure gradient corresponding to the displacement test;

[0013] The data analysis module is used to collect the minimum starting pressure gradient and the pseudo starting pressure gradient obtained during the displacement test of multiple test cores corresponding to weakly cemented argillaceous siltstone, and fits to obtain the relationship between the minimum starting pressure gradient and the pseudo starting pressure gradient and the formation parameter K / μ.

[0014] As a preferred solution of the present invention, there is a data cleaning module inside the processing system. The data cleaning module cleans and screens out the output data corresponding to the pressure sensor and the output data corresponding to the liquid level sensor before the test time point corresponding to the true liquid outlet point in the core confining pressure change diagram.

[0015] As a preferred solution of the present invention, the processing system is communicatively connected to the displacement test device. The processing system is used to regulate the displacement test operation of the displacement test device, and the processing system associates the regulation time point of the displacement test operation of the displacement test device with the timing unit to determine the displacement test operation corresponding to after the true liquid outlet point.

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

[0017] Set the initial confining pressure to 2 MPa. The liquid variable speed displacement operation changes the displacement liquid pump speed according to 0.005 ml / min, 0.015 ml / min, 0.05 ml / min, 0.1 ml / min, 0.3 ml / min, 0.6 ml / min;

[0018] The variable-pressure displacement operation changes the displacement pressure in the sequence of 1.6 MPa - 2.2 MPa - 1.6 MPa;

[0019] Adjust the confining pressure to 4 MPa and 8 MPa in sequence, and under each confining pressure condition, conduct displacement tests in the order of liquid variable-speed displacement operation first and then variable-pressure displacement operation.

[0020] Combined with the time points corresponding to the true liquid production points in each displacement test, determine the displacement test operations corresponding to after the core of the rock sample truly produces liquid, as well as the pressure gradient and liquid production rate corresponding to the displacement test operations after the core of the rock sample truly produces liquid.

[0021] In addition, to solve the above solution, the present invention also provides an analysis method for an analysis system of the starting pressure gradient law of weakly cemented argillaceous siltstone, including the following steps:

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

[0023] Step 200: Conduct displacement tests on each core holder, time each displacement test, and record the displacement pressure, confining pressure change, and displacement fluid volume of the core holder;

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

[0025] Step 400: Clean the data of the displacement pressure and displacement fluid volume, fit the relationship between the pressure gradient and the liquid production rate, and obtain the pseudo starting pressure gradient of each test core;

[0026] Step 500: Combine the minimum starting pressure gradient, pseudo starting pressure gradient of all test cores, and the formation parameter K / μ, and fit to obtain the relationship between the minimum starting pressure gradient and the pseudo starting pressure gradient and the formation parameter K / μ.

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

[0028] Based on the monitoring data of the pressure sensor for measuring the confining pressure of the core and the displacement test time for conducting the displacement test on the core, construct a confining pressure change diagram of the core;

[0029] According to 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 then starts increasing is taken as the displacement starting point for the core to establish effective displacement, and the displacement starting point is taken as the true liquid production point, and the pressure gradient corresponding to the moment before this true liquid production point is set as the lower limit of the starting pressure gradient.

[0030] As a preferred solution of the present invention, in the step 400, data cleaning is performed on the monitoring data of the pressure sensor for measuring the displacement pressure in the core holder to screen out the pressure monitoring data before the true liquid production point;

[0031] Data cleaning is performed on the monitoring data of the liquid level sensor in the graduated cylinder at the outlet end of the core holder to screen out the liquid production monitoring data before the true liquid production point.

[0032] As a preferred solution of the present invention, the implementation method for determining the relationship between the pressure gradient and the liquid production rate is as follows:

[0033] Collect the core displacement pressure corresponding to the displacement test operation after the true liquid production 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 true liquid production point, and determine the liquid production rate corresponding to each displacement test operation;

[0035] Combining the core pressure gradient corresponding to each displacement test operation and the liquid production rate corresponding to each displacement test operation, construct a two-dimensional dot diagram of the pressure gradient and the liquid production rate;

[0036] Perform curve fitting on the dot diagram of the pressure gradient and the liquid production rate to construct a relationship curve between the pressure gradient and the liquid production rate, and take the intersection point of the curve segment with the largest slope in the relationship curve between the pressure gradient and the liquid production rate and the two-dimensional coordinate axes as the quasi-starting pressure gradient.

[0037] As a preferred solution of the present invention, in the step 500, the equivalent permeability is calculated in combination with 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 corresponding to each displacement test operation;

[0039] Among them, the equivalent permeability K = k * ρ * g / η, where k is the permeability of the weakly cemented argillaceous siltstone, κ is the permeability coefficient, and the permeability coefficient is calculated according to the displacement pressure difference corresponding to each displacement test operation and the liquid production data corresponding to each displacement test operation; η is the dynamic viscosity coefficient; ρ is the density of the aqueous fluid in the weakly cemented argillaceous siltstone; g is the acceleration due to gravity.

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

[0041]

[0042] By fitting the pseudo startup pressure gradient with the K / μ data, the calculation formula for the pseudo startup pressure gradient of the aqueous phase and K / μ is:

[0043]

[0044] The present invention has the following beneficial effects compared with the prior art:

[0045] The present invention takes the point where the confining pressure stops decreasing and then rises again as the true liquid production point for establishing effective displacement of the core. At this time, the liquid drainage at the outlet end is considered to be the actual production of the injected fluid. The pressure gradient corresponding to the moment before this point is the lower limit of the startup pressure gradient, which improves the accuracy of data analysis. Moreover, the variation law of the aqueous phase startup pressure gradient of low-permeability loose argillaceous siltstone with the core seepage characteristics and formation fluid properties is determined. The smaller the mobility, that is, the smaller the permeability of the core, the larger the minimum startup pressure gradient and the pseudo startup pressure gradient. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can be obtained by extending the provided drawings.

[0047] Figure 1 It is the overall structural schematic diagram of the startup pressure gradient test device provided in Embodiment 1 of the present invention;

[0048] Figure 2 It is the flow schematic diagram of the startup pressure gradient test method provided in Embodiment 1 of the present invention;

[0049] Figure 3 It is the structural block diagram of the startup pressure gradient law analysis system in Embodiment 2 of the present invention;

[0050] Figure 4 It is the flow schematic diagram of the startup pressure gradient law analysis method in Embodiment 2 of the present invention;

[0051] Figure 5 It is the core confining pressure change diagram in the embodiment of the present invention;

[0052] Figure 6 It is the relationship diagram between the displacement pressure difference and the permeability in the embodiment of the present invention;

[0053] Figure 7 The relationship diagram between the pressure gradient and the liquid production rate in the embodiment of the present invention;

[0054] Figure 8 The relationship curve diagram between the minimum startup pressure gradient and K / μ in the embodiment of the present invention;

[0055] Figure 9 The relationship curve diagram between the pseudo startup pressure gradient and K / μ in the embodiment of the present invention;

[0056] The labels in the figure are respectively shown as follows:

[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 manners

[0060] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0061] Embodiment 1

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

[0063] Pressure sensors 5 are provided at both the inlet end and the outlet end 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 the 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 the confining pressure injected into the core holder 1.

[0065] In this embodiment, a low-permeability loose argillaceous siltstone core sample is used. The argillaceous siltstone natural gas hydrate reservoir exhibits the characteristic of weak cementation. After the hydrate decomposes, the reservoir core presents a semi-fluidized state.

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

[0067] After filling the core sample into the core holder 1, permeable stones are placed at both ends of the cylindrical flexible tube. 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 there is no argillaceous leakage at both ends.

[0068] At least two piston containers 6 are connected to the inlet end of the six-way valve 2. The other end of the piston container 6 is connected to a high-pressure precision injection pump 4 through a valve. The high-pressure precision injection pump 4 injects pressure or evacuates the air into the core holder 1 through the piston container 6, and the high-pressure precision injection pump 4 also injects the displacement aqueous phase into the core holder 1 through the piston container 6.

[0069] The testing method of the above-mentioned weak cementation argillaceous siltstone starting pressure gradient testing device is as Figure 2 shown and includes the following steps:

[0070] Step 100: Place the weak cementation argillaceous siltstone into the core holder, connect the testing device, evacuate the core holder and the weak cementation argillaceous siltstone inside the core holder and saturate it with formation water.

[0071] Before step 100, connect the testing device and configure standard brine to test the sealing performance of the testing device.

[0072] After saturating the weak cementation argillaceous siltstone with formation water, the reservoir core of the weak cementation argillaceous siltstone presents a semi-fluidized state.

[0073] Step 200: Set the initial confining pressure, open the inlet end and the outlet end of the core holder, displace and pressurize the core holder multiple times until the pressure inside the core holder is stable and no liquid flows out from the outlet end of the core holder.

[0074] In step 200, after applying the displacement pressure to the core holder, the reservoir core of the semi-fluidized weak cementation argillaceous siltstone deforms, and the confining pressure drops. By displacing and pressurizing the core holder multiple times until the pressure is stable and no liquid flows out from the core holder.

[0075] That is, in this embodiment, after the core is saturated with formation water, the reservoir core after hydrate decomposition presents a semi-fluidized plastic state and is extremely prone to deformation under pressure. Therefore, when the core holder is pressurized at this time, the core is squeezed and deformed, and the confining pressure will continuously decrease.

[0076] Combined with the starting pressure gradient test device for weakly cemented argillaceous siltstone, use one of the piston containers 6 to apply a confining pressure with an initial value of 2 MPa to the core holder, and then use the other piston container 6 to apply a displacement pressure to the core holder until the reservoir core of the semi-fluidized plastic weakly cemented argillaceous siltstone is compacted and the core holder no longer discharges liquid after the pressure is stable.

[0077] Step 300: Conduct a displacement test on the core holder, and conduct the displacement test with the displacement fluid at an increasing pump speed in sequence. Time each displacement test, and record the displacement pressure, confining pressure change, and displacement fluid volume corresponding to the inlet and outlet ends 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, conduct a displacement test on the core holder according to the displacement pressure regulation process, time each displacement test, and record the displacement pressure, confining pressure change, and displacement fluid volume corresponding to the inlet and outlet ends of the core holder.

[0079] Step 500: Gradually increase the confining pressure in sequence, repeat the above steps 200 - step 400 until the outlet end of the core holder no longer overflows the displacement fluid, and stop the test.

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

[0081] Apply a confining pressure with an initial value of 2 MPa to the core holder;

[0082] Set the initial pump speed of the displacement aqueous phase to 0.005 ml / min, start the displacement and time it, and record the confining pressure inside the core holder throughout the process;

[0083] After the displacement test is stable according to the initial pump speed, change the pump speed to 0.015 ml / min, 0.05 ml / min, 0.1 ml / min, 0.3 ml / min, and 0.6 ml / min respectively in sequence, and then count the displacement fluid at the outlet end of the core holder again, and record the displacement time and the confining pressure inside the core holder 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, the displacement pressure at the inlet end of the core holder does not specifically exceed 80% of the set confining pressure in the core holder, adjust the displacement test to variable-pressure displacement, and change the displacement pressure in sequence according to 1.6 MPa - 2.2 MPa - 1.6 MPa.

[0085] Statistically analyze the displacement fluid at the outlet end of the core holder during each displacement test, and record in real time the displacement time, confining pressure, and displacement pressure difference in the core holder.

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

[0087] Based on the displacement time of the core holder recorded in real time in step 300 and step 400, as well as the confining pressure in the core holder, create a core confining pressure change diagram.

[0088] Based on the variable-speed displacement tests of 0.005 ml / min, 0.015 ml / min, 0.05 ml / min, 0.1 ml / min, 0.3 ml / min, 0.6 ml / min, and the displacement time and confining pressure corresponding to the variable-pressure displacement test of 1.6 MPa - 2.2 MPa - 1.6 MPa, determine the time point when the confining pressure stops decreasing and then rises, and take this time point as the true liquid production point.

[0089] Based on multiple displacement tests after the true liquid production point in step 300 and step 400, sequentially obtain the displacement pressures corresponding to the inlet and outlet ends of the core holder, and calculate the displacement pressure differences corresponding to each displacement test in step 300 and step 400.

[0090] Determine the equivalent permeability corresponding to multiple displacement tests after the true liquid production point in step 300 and step 400, and create a relationship diagram between the displacement pressure difference and the permeability to corroborate the true liquid production point.

[0091] In step 500, sequentially increase the confining pressure to 4 MPa, 8 MPa, and 12 MPa respectively. Specifically use it, and after each increase in the confining pressure, re-perform the displacement test according to steps 200 - 400 until the outlet end of the core holder no longer produces liquid. At this time, stop the pressurization work of the high-pressure precision injection pump, take out the weakly cemented argillaceous siltstone, and dry and weigh it.

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

[0093] Example 2

[0094] After conducting experiments according to the above-mentioned test method for the starting pressure gradient of weakly cemented argillaceous siltstone, a series of monitoring data of the measuring device are obtained. By processing this monitoring data, the law of the starting pressure gradient of weakly cemented argillaceous siltstone can be obtained. Therefore, in combination with the above-mentioned test device and method for the starting pressure gradient of weakly cemented argillaceous siltstone, the present invention also provides an analysis system for the starting pressure gradient law of weakly cemented argillaceous siltstone, as Figure 3 shown, including: a timing unit 7, a pressure sensor 5, a liquid level sensor 8, and a processing system 9.

[0095] The 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 different confining pressure conditions, with a liquid variable-speed displacement operation first and then a variable-pressure displacement operation;

[0097] The initial confining pressure is set to 2 MPa, and the liquid variable-speed displacement operation changes the displacement liquid pump speed according 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;

[0098] The variable-pressure displacement operation changes the displacement pressure according to 1.6 MPa - 2.2 MPa - 1.6 MPa;

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

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

[0101] The pressure sensor 5 is installed inside the core holder and is used to measure the confining pressure exerted on the weakly cemented argillaceous siltstone inside the core holder, as well as the displacement pressure corresponding to the inlet end of the core holder and the displacement pressure corresponding to the outlet end of the core holder.

[0102] The liquid level sensor 8 is installed in the graduated cylinder at the outlet end of the core holder and is used to measure the liquid production volume 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 respectively. A data analysis module 91 is further provided in the processing system 9. The data analysis module 91 constructs a core confining pressure change diagram based on the output data of the timing unit 7 and the pressure sensor 5 to determine the true liquid production point of the displacement test and the minimum starting pressure gradient corresponding to the moment before the true liquid production point.

[0104] 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 pseudo starting pressure gradient corresponding to the displacement test.

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

[0106] According to Example 1, the reservoir core after hydrate decomposition presents a semi-fluidized state and is extremely easy to deform after pressurization. Therefore, there will be a phenomenon that the confining pressure continuously decreases after pressurization. It is necessary to pressurize multiple times and let it stand until the pressure is stable and no liquid flows out from the outlet end of the core holder.

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

[0108] For each displacement test operation corresponding to the core pressure gradient and the liquid production rate after determining the starting point of effective displacement, a curve graph between the core pressure gradient and the liquid production rate is fitted, and by the steady-state method, the straight line segment of the stable non-Darcy seepage curve is extended to intersect with the coordinate axis, and the intersection point is the pseudo starting pressure gradient.

[0109] It should be supplemented and explained that a data cleaning module 92 is provided in the processing system 9. The data cleaning module 92 cleans and screens the output data of the pressure sensor 5 and the output data of the liquid level sensor 8 corresponding to the test time point before the true liquid production point in the core confining pressure change diagram, and cleans the output data of the pressure sensor 5 and the output data of the liquid level sensor 8 through the data cleaning module 92 before analyzing the relationship between the core pressure gradient and the liquid production rate.

[0110] The processing system 9 is communicatively connected to the displacement test device. The processing system 9 is used to regulate the displacement test operation of the displacement test device, and the processing system 9 associates the time points of the displacement test operation of the displacement test device with the timing unit 7 to determine the displacement test operations corresponding to before the true liquid production point and the displacement test operations corresponding to after the actual liquid production point, and combines with the data cleaning module 92 to filter and remove the monitoring data corresponding to the displacement test operations before the true liquid production point.

[0111] Combined with the time point corresponding to the true liquid production point of each displacement test, determine the displacement test operations corresponding to after the true liquid production of the rock sample core, as well as the pressure gradient and liquid production rate corresponding to the displacement test operations after the true liquid production of the rock sample core.

[0112] In addition, as Figure 4 shown, the present invention also provides an analysis method for the above-mentioned analysis system of the starting pressure gradient law of weakly cemented argillaceous siltstone, including the following steps:

[0113] Step 100: Inject the 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 change, 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 true liquid production point during the displacement test of the test core, and obtain the minimum starting pressure gradient of each test core.

[0116] Step 400: Clean the data of the displacement pressure and the displacement fluid volume, fit the relationship between the pressure gradient and the liquid production rate, and obtain the pseudo starting pressure gradient of each test core.

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

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

[0119] In step 300, the implementation method of 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 of the pressure sensor for measuring the confining pressure of the core and the displacement test time of the displacement test on the core, a core confining pressure change diagram is constructed;

[0121] According to 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 increasing is taken as the displacement starting point for the core to establish effective displacement, and the displacement starting point is taken as the true liquid production point, and the pressure gradient corresponding to the moment before the true liquid production 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 starts increasing is taken as the true liquid production point for the core to establish effective displacement. At this time, the liquid drainage at the outlet end is considered to be the production of the actual 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 starts increasing as the starting point for the core to establish effective displacement can improve the analysis accuracy. At this time, the liquid drainage at the outlet end is considered to be the production of the actual injected fluid (the liquid drainage at the outlet end before this point is the liquid drainage due to core deformation).

[0123] In step 400, the monitoring data of the pressure sensor for measuring the displacement pressure in the core holder is subjected to data cleaning to screen out the pressure monitoring data before the true liquid production point;

[0124] The monitoring data of the liquid level sensor in the graduated cylinder at the outlet end of the core holder is subjected to data cleaning to screen out the liquid production monitoring data before the true liquid production point.

[0125] Thus, for the analysis of the monitoring data of the pressure sensor and the analysis of the monitoring data of the liquid level sensor, only the monitoring data after the true liquid production point is targeted.

[0126] Furthermore, in step 400, the implementation method for determining the relationship between the pressure gradient and the liquid production rate is as follows:

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

[0128] Collect the monitoring data of the liquid level sensor after the true liquid production point, and determine the liquid production rate corresponding to each displacement test operation;

[0129] Combining the core pressure gradient corresponding to each displacement test operation and the liquid production rate corresponding to each displacement test operation, construct a two-dimensional dot diagram of the pressure gradient and the liquid production rate;

[0130] Perform curve fitting on the dot diagram of the pressure gradient and the liquid production rate to construct a relationship curve between the pressure gradient and the liquid production rate, and take the intersection point of the curve segment with the largest slope in the relationship curve between the pressure gradient and the liquid production rate and the two-dimensional coordinate axes as the quasi-starting 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 corresponding to each displacement test operation.

[0133] Among them, the equivalent permeability K = k*ρ*g / η, where k is the permeability of the weakly cemented argillaceous siltstone, κ is the permeability coefficient, and the permeability coefficient is calculated according to the displacement pressure difference corresponding to each displacement test operation and the liquid production data corresponding to each displacement test operation; η is the dynamic viscosity coefficient; ρ is the density of the aqueous fluid in the weakly cemented argillaceous siltstone; g is the acceleration due to gravity.

[0134] Fitting the minimum starting pressure gradient with the K / μ data, the calculation formula for the minimum starting pressure gradient of the aqueous phase and K / μ is obtained as:

[0135]

[0136] Fitting the pseudo-starting pressure gradient with the K / μ data, the calculation formula for the pseudo-starting pressure gradient of the aqueous phase and K / μ is obtained as:

[0137]

[0138] According to the above formula, the smaller the K / μ, that is, the smaller the permeability of the core, the greater the minimum starting pressure gradient, and the greater the same pseudo-starting pressure gradient. The specific reason is that the finer 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] After obtaining the low-permeability loose argillaceous siltstone rock samples provided by the Guangzhou Marine Geological Survey in this embodiment, the rock samples are numbered as: BC06B and BC08B respectively.

[0141] The total salinity of the formation water used to saturate the rock samples is 4500 mg / L, and the ion composition is shown in Table 1.

[0142] Table 1 Formation water ion composition

[0143]

[0144] Fix a large-diameter thermoplastic pipe outside a 2.5-cm-diameter and 26-cm-long core. After placing it in an oven and uniformly heating and shaping it, it becomes a cylindrical hose with an inner diameter of 2.5 cm and a length of 26 cm that can deform with the core under pressure. Fill the cylindrical hose with rock samples and place water-permeable stones at both ends. 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 there is no muddy leakage at both ends. A total of 13 core samples are filled in the experiment. Among them, the core parameters of the 13 core samples are shown in Table 2 below.

[0145] Table 2 Experimental core parameter table

[0146]

[0147]

[0148] According to the above test method of the weak-cemented argillaceous siltstone starting pressure gradient test device, displacement tests are carried out on each core in the order of first displacement with variable speed and then displacement with variable pressure. The displacement test is carried out at an initial confining pressure of 2 MPa, and the displacement speed is sequentially changed 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. Then, it is changed to the method of variable pressure displacement in the order of displacement pressure of 1.6 MPa - 2.2 MPa - 1.6 MPa to determine the change in the displacement fluid volume under this displacement test.

[0149] Then, displacement tests are carried out at confining pressures of 4 MPa and 8 MPa, respectively, to determine the change in the displacement fluid volume under each displacement test.

[0150] Specifically, for the core BC08B-1-2, the displacement method of this group of cores is horizontal displacement. The confining pressure is set at 2 MPa. During the displacement process, two injection methods of displacement with variable speed and displacement with variable pressure are used to measure the starting pressure gradient. The change in the confining pressure of the BC08B-1-2 core during the displacement process is as Figure 5 shown.

[0151] It can be seen from the change diagram of the confining pressure of the BC08B-1-2 core that at the initial stage of displacement, affected by the continuous deformation of the core, the confining pressure of the core continuously decreases. As the displacement progresses, the decreasing speed of the confining pressure of the core gradually decreases. When the displacement reaches 10113 s, the confining pressure stops decreasing and instead increases, indicating that due to continuous injection at the inlet end, the pressure at the inlet end continuously rises and then an effective displacement is formed.

[0152] The injected fluid flows in the core, so that the pressure can be transmitted in the core, causing reverse deformation of the core, and thus the confining pressure continues to rise. According to this experimental phenomenon and the corresponding principle, the point at which the confining pressure stops decreasing and then rises is taken as the starting point for establishing effective displacement in the core. At this time, the fluid discharged at the outlet end is considered to be the actual output of the injected fluid (the liquid discharged at the outlet end before this point is the liquid discharged due to the deformation of the core), that is, this point is the true liquid discharge point, and the pressure gradient corresponding to the previous moment of this point is the lower limit of the starting pressure gradient.

[0153] Furthermore, through the relationship between the displacement pressure difference and the equivalent permeability of the displacement fluid during the displacement process of the BC08B-1-2 core, the true liquid discharge point can also be determined, as Figure 6 shown, where the displacement pressure difference is the pressure difference between the outlet end and the inlet end of the core holder corresponding to each displacement test operation.

[0154] Among them, the equivalent permeability K = k*ρ*g / η, where k is the permeability of the weakly cemented argillaceous siltstone, κ is the permeability coefficient, and the permeability coefficient is calculated according to the displacement pressure difference corresponding to each displacement test operation and the liquid production data corresponding to each displacement test operation; η is the dynamic viscosity coefficient; ρ is the density of the aqueous fluid in the weakly cemented argillaceous siltstone; g is the acceleration due to gravity.

[0155] Since there is energy accumulation at the inlet end of the core before the establishment of effective displacement, in the initial stage after the injected fluid breaks through, the equivalent permeability of fluid seepage is significantly larger. As the displacement pressure difference increases, the equivalent permeability rapidly decreases and gradually stabilizes at about 0.014 md.

[0156] After the displacement pressure difference > 1.2 MPa, the equivalent permeability of the core shows a stepped jump to 0.025 md, reflecting the occurrence of channel deformation during the core displacement process, resulting in improved permeability. Therefore, the previous moment before the true liquid discharge point is taken as the starting analysis point, that is, the displacement test operation at 0.05 ml / min is taken as the true liquid discharge point and the starting analysis point.

[0157] The relationship between the pressure gradient and the liquid production rate of the BC08B-1-2 core is as Figure 7 shown. By analysis Figure 7 it is known that the pressure gradient corresponding to the previous moment before the liquid discharge at the outlet end of the core is 0.00026 MPa / cm, which is the minimum starting pressure gradient. And by the steady-state method, the straight line segment of the stable non-Darcy seepage curve is extended to intersect with the coordinate axis, and the intersection point is the pseudo-starting pressure gradient. The pseudo-starting pressure gradient of the BC08B-1-2 core is 0.04 MPa / cm.

[0158] Using this analysis method, 13 groups of core displacement experiments were analyzed. The minimum starting pressure gradients and pseudo-starting pressure gradients of different cores are shown in Table 3. The starting pressure gradients of the 13 groups of cores vary greatly. The minimum starting pressure gradient is 0.00026 MPa / cm, and the maximum minimum starting pressure gradient in the experiment is 457 times that of the minimum, which is 0.119 MPa / cm. The minimum pseudo-starting pressure gradient is 0.04 MPa / cm, and the maximum pseudo-starting pressure gradient is 8 times that of the minimum, which is 0.32 MPa / cm. Although the difference multiple of the minimum starting pressure gradient is large, the difference multiple of the pseudo-starting pressure gradient decreases.

[0159] Table 3 Minimum starting pressure gradients and pseudo-starting pressure gradients of different cores

[0160]

[0161]

[0162] According to Step 500, based on the displacement experiment pressure and production data, the permeability of the sand-packed core is calculated, and according to the viscosity of the displacement fluid, the mobility of the displacement phase is calculated. The relationship curve between the minimum starting pressure gradient and K / μ is as Figure 8 shown. It can be seen from Figure 8 that the smaller K / μ is, that is, the smaller the core permeability is, the larger the minimum starting pressure gradient is. The reason is that the thinner the rock throat is, the greater the force of the solid surface on the boundary layer fluid is, and the greater the resistance that the fluid flow needs to overcome.

[0163] When K / μ < 0.005 μm2 / (Pa·s) or the core permeability is less than 0.005×10-3 μm2, with the decrease of K / μ, the minimum starting pressure gradient of the core increases rapidly. The calculation formula of the minimum starting pressure gradient of the aqueous phase and K / μ is obtained by fitting the data of the minimum starting pressure gradient and K / μ.

[0164]

[0165] According to Step 500, the relationship between the pseudo-starting pressure gradient and K / μ is as Figure 9 shown. It can be seen from Figure 9 that the smaller K / μ is, that is, the smaller the core permeability is, the larger the pseudo-starting pressure gradient is. The reason is that the thinner the rock throat is, the greater the force of the solid surface on the boundary layer fluid is, and the greater the resistance that the fluid flow needs to overcome. When K / μ < 0.007 μm2 / (Pa·s) or the core permeability is less than 0.007×10-3 μm2, with the decrease of K / μ, the pseudo-starting pressure gradient of the core increases rapidly. The calculation formula of the pseudo-starting pressure gradient and K / μ is obtained by fitting:

[0166]

[0167] The calculation formula for the correlation law between the minimum startup pressure gradient and the pseudo startup pressure gradient obtained through the above fitting and the formation parameter K / μ can be used to quickly calculate the minimum startup pressure gradient value and the pseudo startup pressure gradient value of any target formation.

[0168] For the (minimum) startup 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 startup pressure gradient of the core increases rapidly with the decrease of mobility. For the pseudo startup 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 startup pressure gradient of the core increases rapidly with the decrease of mobility.

[0169] The above embodiments are only exemplary embodiments of the present application and are not used to limit the present application. The protection scope of the present application is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements within the essence and protection scope of the present application, and such modifications or equivalent replacements should also be regarded as falling within the protection scope of the present application.

Claims

1. An analysis system for the starting pressure gradient law of weakly cemented argillaceous siltstone, characterized in that Including: A timing unit (7) for timing each displacement test operation; A pressure sensor (5) installed inside the core holder for measuring the confining pressure on the weakly cemented argillaceous siltstone inside the core holder, as well as the displacement pressure corresponding to the inlet end of the core holder and the displacement pressure corresponding to the outlet end of the core holder; A liquid level sensor (8) installed in the graduated cylinder at the outlet end of the core holder for measuring the liquid production volume of the displacement test; A processing system (9) communicatively connected to the pressure sensor (5), the timing unit (7), and the liquid level sensor (8) respectively. A data analysis module (91) is further provided in the processing system (9). The data analysis module (91) constructs a core confining pressure change diagram based on the output data of the timing unit (7) and the pressure sensor (5) to determine the true liquid production point of the displacement test and the minimum starting pressure gradient corresponding to the moment before the true liquid production 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 pseudo starting pressure gradient corresponding to the displacement test; The data analysis module (91) is used to collect the minimum starting pressure gradient and the pseudo starting pressure gradient obtained during the displacement test of test cores corresponding to multiple weakly cemented argillaceous siltstones, and fit the relationship between the minimum starting pressure gradient and the pseudo 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, wherein A data cleaning module (92) is provided in the processing system (9). The data cleaning module (92) cleans and screens out the output data corresponding to the pressure sensor and the output data corresponding to the liquid level sensor (8) before the test time point corresponding to the true liquid production 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, wherein 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, and the processing system (9) associates the displacement test operation control time point of the displacement test device with the timing unit (7) to determine the displacement test operation corresponding to after the true liquid production point.

4. The system for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone according to claim 1 or 3, wherein The displacement test operation control of the displacement test device is divided into a liquid variable speed displacement operation and a variable pressure displacement operation under different confining pressure conditions; The initial confining pressure is set to 2 MPa, and the liquid variable speed displacement operation changes the displacement liquid pump speed according to 0.005 ml / min, 0.015 ml / min, 0.05 ml / min, 0.1 ml / min, 0.3 ml / min, 0.6 ml / min; The variable-pressure displacement operation changes the displacement pressure in the sequence of 1.6 MPa - 2.2 MPa - 1.6 MPa; The confining pressure is adjusted to 4 MPa and 8 MPa in sequence, and under each confining pressure condition, a displacement test is carried out according to the liquid variable-speed displacement operation first and then the variable-pressure displacement operation. Combined with the time point corresponding to the true liquid outlet point of each displacement test, determine the displacement test operation corresponding to the core of the rock sample after the true liquid outlet, and the pressure gradient and liquid production rate corresponding to the displacement test operation after the true liquid outlet of the core of the rock sample.

5. An analysis method of an analysis system for the starting pressure gradient law of weakly cemented argillaceous siltstone according to any one of claims 1-4, characterized in that, It 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 core holder, time each displacement test, and record the displacement pressure, confining pressure change, and displacement fluid volume of the core holder; Step 300: Combine the displacement test time of each displacement test and the confining pressure change of the core holder to determine the starting pressure gradient, determine the true liquid outlet point during the displacement test of the test core, and obtain the minimum starting pressure gradient of each test core; Step 400: Clean the data of the displacement pressure and displacement fluid volume, fit the relationship between the pressure gradient and the liquid production rate, and obtain the pseudo starting pressure gradient of each test core; Step 500: Combine the minimum starting pressure gradient, pseudo starting pressure gradient of all test cores, and the formation parameter K / μ, and fit to obtain the relationship between the minimum starting pressure gradient, pseudo starting pressure gradient and the formation parameter K / μ.

6. The test method of a system for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone according to claim 5, characterized in that In the 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: Based on the monitoring data of the pressure sensor for measuring the confining pressure of the core and the displacement test time for conducting the displacement test on the core, construct a confining pressure change diagram of the core; According to the confining pressure data corresponding to different displacement test conditions in the confining pressure change diagram of the core, take the time point when the confining pressure data stops decreasing and then rises as the displacement starting point for the core to establish effective displacement, and take the displacement starting point as the true liquid outlet point, and set the pressure gradient corresponding to the moment before the true liquid outlet point as the lower limit of the starting pressure gradient.

7. The test method of a system for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone according to claim 3, characterized in that In the step 400, clean the monitoring data of the pressure sensor for measuring the displacement pressure in the core holder to screen out the pressure monitoring data before the true liquid outlet point; Clean the monitoring data of the liquid level sensor in the graduated cylinder at the outlet end of the core holder to screen out the liquid production monitoring data before the true liquid outlet point.

8. The test method of a system for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone according to claim 7, characterized in that The implementation method for determining the relationship between the pressure gradient and the liquid production rate is: Collect the core displacement pressure corresponding to the displacement test operation after the true 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 true liquid outlet point, and determine the liquid production rate corresponding to each displacement test operation; Combine the core pressure gradient corresponding to each displacement test operation and the liquid production rate corresponding to each displacement test operation to construct a two-dimensional dot plot of the pressure gradient and the liquid production rate; Perform curve fitting on the dot plot of the pressure gradient and the liquid production rate, construct a relationship curve between the pressure gradient and the liquid production rate, and use the intersection point of the curve segment with the largest slope in the relationship curve between the pressure gradient and the liquid production rate and the two-dimensional coordinate axes as the quasi-starting pressure gradient.

9. The method and device for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone according to claim 8, characterized in that, In the step 500, calculate the equivalent permeability in combination with the properties of the test core and the displacement pressure difference corresponding to each displacement test operation; Wherein, the displacement pressure difference is the pressure difference between the outlet end and the inlet end of the core holder corresponding to each displacement test operation; Wherein, the equivalent permeability K = k*ρ*g / η, where k is the permeability of the weakly cemented argillaceous siltstone, κ is the permeability coefficient, and the permeability coefficient is calculated according to the displacement pressure difference corresponding to each displacement test operation and the liquid production data corresponding to each displacement test operation; η is the dynamic viscosity coefficient; ρ is the density of the aqueous fluid in the weakly cemented argillaceous siltstone; g is the acceleration due to gravity.

10. The method and device for analyzing the starting pressure gradient law of weakly cemented argillaceous siltstone according to claim 9, characterized in that, Use the minimum starting pressure gradient to fit with the K / μ data, and the calculation formula for the minimum starting pressure gradient of the aqueous phase and K / μ is: Use the quasi-starting pressure gradient to fit with the K / μ data, and the calculation formula for the quasi-starting pressure gradient of the aqueous phase and K / μ is:

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