Method for determining relative permeability of loose sandstone gas, water phase

Abstract

The application discloses a method for determining relative permeability of loose sandstone gas and water, and comprises the following steps: drying and weighing a rock sample to obtain a dry weight, saturating the rock sample with formation water, applying a set confining pressure to obtain a wet weight, and calculating an effective pore volume of the rock sample; performing a non-steady-state gas displacement water relative permeability determination experiment on the rock sample according to a set displacement pressure difference, obtaining total sand water volume and gas volume change data over time; determining the volume of sand in the produced sand water, determining a water production volume correction coefficient according to the total sand water volume and the volume of sand in the produced sand water, and obtaining net water production volume change data over time; and determining the gas saturation of the rock sample and the gas and water relative permeability change data over time according to the effective pore volume and the net water production volume and gas volume change data over time. The method can obtain more accurate effective pore volume, accurately measure the sand volume, correct the net water production, and improve the accuracy of the determination of the relative permeability of loose sandstone gas and water.

Description

Technical Field

[0001] This invention relates to the field of rock property measurement technology in the development of oil and gas reservoirs, and particularly to a method for measuring the relative permeability of gas and water in loose sandstone. Background Technology

[0002] The relative permeability curves of gas and water are essential basic data for oil and gas field development research. Currently, the oil and gas field development industry mainly tests the relative permeability of gas and water according to the national standard GB / T28912-2012 "Method for Determination of Relative Permeability of Two-Phase Fluids in Rocks".

[0003] However, compared with ordinary sandstone, loose sandstone has special physical properties, with large rock porosity and loose pore structure. Studies have shown that, on the one hand, under the action of external force, the rock sample is easily deformed by compression, which causes a large change in the pore volume and permeability of the rock sample; on the other hand, during the water drive process of the rock sample, due to insufficient rock consolidation, sand is easily produced. Sand production not only causes changes in the pore volume and permeability of the rock sample, but also causes errors in the water production measurement ([1] Zhang Xueyou. Experimental study on stress sensitivity of physical parameters of loose sandstone [D]. China University of Petroleum, 2008. [2] Wang Xiaolu, et al. Sand production mechanism of loose sandstone and calculation method of critical pressure difference for sand production [J]. Natural Gas Industry, 2009, 29(7):72-75.). Summary of the Invention

[0004] The inventors discovered that in relative permeability determination, the values ​​and measurements of the effective pore volume of the sample and the net water production during gas-driven water flow are key parameters for calculating the relative permeability curve. Errors in these parameters inevitably lead to inaccurate relative permeability curve measurements, causing the experimentally obtained relative permeability curve to fail to reflect the true gas-water flow patterns of the sample. To at least partially address the technical problems existing in the prior art, the inventors developed this invention, which, through specific implementation methods, provides a method for determining the relative permeability of gas and water in loose sandstone. By obtaining a more accurate effective pore volume, accurately measuring the sand volume, and correcting the net water production, the accuracy of relative permeability determination of gas and water in loose sandstone is improved.

[0005] In a first aspect, embodiments of the present invention provide a method for determining the relative permeability of gas and water in loose sandstone, comprising:

[0006] The loose sandstone sample is dried and weighed as dry weight. After the sample is saturated with formation water, a set confining pressure is applied to obtain the wet weight of the sample. The effective pore volume of the sample is calculated based on the dry weight and wet weight.

[0007] An unsteady-state gas-driven water relative permeability determination experiment was conducted on rock samples according to the set displacement pressure difference, and the changes in the total volume of produced sand and water and the volume of produced gas over time were obtained.

[0008] Determine the volume of sand in the produced sand-water. Based on the total volume of the produced sand-water and the volume of sand in it, determine the water production volume correction coefficient. Use the water production volume correction coefficient to correct and obtain the data on the change of net produced water volume over time.

[0009] Based on the changes in effective pore volume and net produced water and gas volume over time, the changes in gas saturation, relative permeability of gas and water phases of the rock sample over time are determined.

[0010] Secondly, embodiments of the present invention provide a method for determining the relative permeability of loose sandstone, comprising:

[0011] Obtain data on the changes in gas saturation, relative permeability of gas and water phases over time in loose sandstone samples obtained by the above method;

[0012] For any given gas saturation level, the time corresponding to that gas saturation level is determined by using the obtained data on the change of gas saturation level over time.

[0013] The relative permeability of the gas phase at a given moment is determined by the data on the change of relative permeability of the gas phase over time, and is taken as the relative permeability of the gas phase of the rock sample under the gas saturation condition; and / or, the relative permeability of the water phase at a given moment is determined by the data on the change of relative permeability of the water phase over time, and is taken as the relative permeability of the water phase of the rock sample under the gas saturation condition.

[0014] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following:

[0015] The method for determining the relative permeability of gas and water in loose sandstone provided in this invention improves the experimental procedure to obtain a more accurate effective pore volume. Furthermore, by accurately measuring the sand volume and correcting the net water production, the accuracy of the measured data on the changes in gas saturation and relative permeability of the gas and water phases over time is improved. This method enables more accurate determination of the relative permeability curves of gas and water in loose sandstone. It is of great significance for studying the theory of gas and water two-phase flow, the water production law of oil and gas reservoirs, and the efficient development of oil and gas reservoirs.

[0016] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0019] Figure 1 This is a flowchart of the method for determining the relative permeability of gas and water in loose sandstone in Embodiment 1 of the present invention;

[0020] Figure 2 for Figure 1 The detailed implementation flowchart of step S14 is shown below;

[0021] Figure 3 This is a flowchart illustrating the specific implementation of the method for determining the relative permeability of gas and water in loose sandstone in Embodiment 2 of the present invention.

[0022] Figure 4 This is a comparison chart of the relative permeability curves of gas and water in loose sandstone before and after the correction in Embodiment 2 of the present invention. Detailed Implementation

[0023] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0024] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0025] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0026] In the description of this invention, it should be noted that the terms "comprising", "including", "having", "containing", etc., are all open-ended terms, meaning that they include but are not limited to.

[0027] To address the problems in existing technologies where the measurement of the effective pore volume of loose sandstone is subject to large errors, leading to changes in physical properties and deviations in water production measurement due to sand discharge, and consequently making it difficult to accurately measure the relative permeability curve of loose sandstone, this invention provides a method for measuring the relative permeability of gas and water in loose sandstone. By obtaining a more accurate effective pore volume, accurately measuring the sand discharge volume, and correcting the net water production, the method improves the accuracy of measuring the relative permeability of gas and water in loose sandstone.

[0028] Example 1

[0029] Embodiment 1 of the present invention provides a method for determining the relative permeability of gas and water in loose sandstone, the process of which is as follows: Figure 1 As shown, it includes the following steps:

[0030] Step S11: Dry the loose sandstone sample and weigh it. After saturating the sample with formation water, apply a set confining pressure to obtain the wet weight of the sample. Calculate the effective pore volume of the sample based on the dry and wet weights.

[0031] In this embodiment, loose sandstone refers to sandstone with incomplete diagenesis, weak diagenesis, and weak cementation. Loose sandstone often has relatively high porosity and permeability, and its pore structure is unstable.

[0032] The effective pore volume of the rock sample is calculated based on its dry and wet weights using the following formula (1):

[0033]

[0034] In formula (1), V p m2 is the effective pore volume of the rock sample, m0 is the wet weight of the rock sample, and ρ is the dry weight of the rock sample. w This represents the density of the formation water.

[0035] Step S12: Conduct a non-steady-state gas-driven water relative permeability measurement experiment on the rock sample according to the set displacement pressure difference, and obtain the data on the change of the total volume of produced sand and water and the volume of produced gas over time.

[0036] In some embodiments, before performing step S11, the method may further include obtaining a set displacement pressure difference and a set confining pressure by conducting a gas-driven water experiment on a loose sandstone sample, based on the minimum standard of the initial gas-driven water production rate.

[0037] Step S13: Determine the volume of sand in the produced sand-water. Based on the total volume of the produced sand-water and the volume of sand in it, determine the water production volume correction coefficient. Use the water production volume correction coefficient to correct the change data of the total volume of the produced sand-water over time, and obtain the change data of the net produced water volume over time.

[0038] In some embodiments, determining the volume of sand in the produced sand-water may include filtering all the produced sand-water with filter paper, drying the filter paper, and weighing it to obtain the total mass of the filter paper and sand; based on the total mass of the filter paper and sand, the mass of the filter paper, and the density of the rock sample, the volume of sand in the produced sand-water is determined by the following formula (2):

[0039]

[0040] In formula (2), V s Let m be the volume of sand in the produced sand-water. t m is the total mass of filter paper and sand. p For filter paper quality, ρ r This represents the density of the rock sample.

[0041] Optionally, the volume of sand in all the produced sand-water can be determined by other methods. The specific method is not limited in this embodiment, as long as it can accurately quantify the amount of sand.

[0042] Based on the total volume of the produced sand-water and the volume of sand within it, the production water volume correction factor is determined using the following formula (3):

[0043]

[0044] In formula (3), C is the product water volume correction factor, and V m1 V represents the total volume of sand and water produced. s This represents the volume of sand in the produced sand-water mixture.

[0045] Using the product water volume correction coefficient, the change data of the total volume of produced sand and water over time is corrected by the following formula (4) to obtain the change data of the volume of net produced water over time:

[0046] V w (t)=C·V w1 (t) (4)

[0047] In formula (4), V w (t) represents the actual (net) volume of water produced at time t, V w1 (t) represents the total volume of sand and water produced at time t.

[0048] Step S14: Based on the changes in effective pore volume and net produced water and gas volume over time, determine the changes in gas saturation, relative permeability of gas and water phases of the rock sample over time.

[0049] See Figure 2 As shown, the specific execution of step S14 may include the following steps:

[0050] Step S141: Based on the changes in effective pore volume and net produced water and gas volume over time, determine the changes in dimensionless water production, dimensionless total gas and water production, water content, and relative injection capacity over time.

[0051] Based on the changes in effective pore volume and net produced water volume over time, the changes in dimensionless water production over time are determined using the following formula (5):

[0052]

[0053] In formula (5), V p V is the effective pore volume of the rock sample. w (t) represents the volume of water produced at time t. Let t be the dimensionless water production at time t.

[0054] Based on the data on the changes in the volume of net produced water and produced gas over time, the data on the changes in the total volume of produced gas and water over time are determined. Based on the data on the changes in the effective pore volume and the total volume of produced gas and water over time, the data on the changes in the total dimensionless gas and water production over time are determined using the following formula (6):

[0055]

[0056] In formula (6), V t (t) represents the total volume of gas and water produced at time t. Let t be the dimensionless total gas and water production at time t.

[0057] Based on the data on the change of dimensionless water production over time and the data on the change of dimensionless total gas and water production over time, the data on the change of water content over time are determined by the following formula (7):

[0058]

[0059] In formula (7), f w (S w ( ) represents the water content. Based on the different dimensionless water production and the total dimensionless gas-water production at different times, the water content at different times can be obtained, and finally, the data on the change of water content over time can be obtained.

[0060] Based on the data on the changes in the volume of net produced water and produced gas over time, the data on the changes in the total gas and water flow rate at the rock sample outlet face over time and the total gas and water flow rate at the rock sample outlet face at the initial moment of the experiment are determined. Then, the data on the changes in the relative injection capacity over time are determined by the following formula (8):

[0061]

[0062] In formula (8), I is the relative injection capacity at time t, Q(t) is the total gas-water flow rate at the rock sample outlet end face at time t, and Q0 is the total gas-water flow rate at the rock sample outlet end face at the initial moment of the experiment. The initial moment here is not the moment when time is 0. The specific definition is the same as the initial moment in the national standard GBT28912-2012 "Method for Determination of Relative Permeability of Two-Phase Fluids in Rock".

[0063] Step S142: Based on the changes in dimensionless water production, total dimensionless gas and water production, and water content over time, determine the changes in gas saturation at the rock sample outlet face over time, and use this data as the changes in gas saturation of the rock sample over time.

[0064] Based on the changes in dimensionless water production, total dimensionless gas-water production, and water content over time, the changes in gas saturation at the rock sample outlet face over time are determined using the following formula (9):

[0065]

[0066] In formula (9), S g The gas saturation at the outlet end face of the rock sample. Let t be the dimensionless water production at time t. Let f be the dimensionless total gas and water production at time t. w (S w Let t be the water content, specifically the water content at time t. Based on the dimensionless water production, the total dimensionless gas-water production, and the water content at different times, the gas saturation at the rock sample outlet face at different times can be obtained, and finally, the data on the change of gas saturation at the rock sample outlet face over time can be obtained.

[0067] Step S143: Based on the data on the change of dimensionless total gas and water production and water content over time, determine the data on the change of relative permeability of the water phase in the rock sample over time.

[0068] Based on the changes in dimensionless gas-water total production and water content over time, the changes in the relative permeability of the water phase in the rock sample over time are determined using the following formula (10):

[0069]

[0070] In formula (9), k rw f is the relative permeability of the aqueous phase. w (S w () represents the moisture content. Let t represent the dimensionless total gas and water production, and I represent the relative injection capacity. Based on the water content, dimensionless total gas and water production, and relative injection capacity at different times, the relative permeability of the water phase at different times can be obtained, ultimately yielding data on the change of the relative permeability of the water phase over time.

[0071] Step S144: Based on the data on the change of relative permeability of the water phase over time and the data on the change of water content over time, determine the data on the change of relative permeability of the gas phase of the rock sample over time.

[0072] Based on the data on the change of relative permeability of the aqueous phase over time and the data on the change of water content over time, the data on the change of relative permeability of the gas phase over time of the rock sample are determined by the following formula (11):

[0073]

[0074] In formula (11), k rg k is the relative permeability of the gas phase. rw The relative permeability of the aqueous phase, μ g and μ w The viscosities f of the gas and formation water are respectively. w (S w ( ) represents the water content. Based on the relative permeability and water content of the water phase at different times, the relative permeability of the gas phase at different times can be obtained, and finally, the data on the change of the relative permeability of the gas phase over time can be obtained.

[0075] The method for determining the relative permeability of gas and water in loose sandstone provided in Embodiment 1 of the present invention improves the experimental procedure to obtain a more accurate effective pore volume; and further improves the accuracy of the measured data on the changes in gas saturation and relative permeability of gas and water phases over time by accurately measuring the sand volume and correcting the net water production.

[0076] Example 2

[0077] Embodiment 2 of this invention provides a specific implementation flow for determining the relative permeability of gas and water in loose sandstone. It improves and modifies the key testing procedures and calculation methods for relative permeability of gas and water in the national standard GB / T 28912-2012 "Methods for Determining the Relative Permeability of Two-Phase Fluids in Rocks," resulting in a more suitable method for determining the relative permeability of gas and water in loose sandstone. Figure 3 As shown, it includes the following steps:

[0078] Step S31: Improve the method for testing the effective pore volume of rock samples to obtain the effective pore volume of rock samples under experimental pressure conditions.

[0079] (1) The effective pore volume of rock samples was tested using the conventional rock sample effective pore volume test method specified in GB-T28912-2012. p1 .

[0080]

[0081] In formula (12), m1 is the mass of the rock sample after it is saturated with formation water, and m0 is the dry weight of the rock sample.

[0082] (2) Conduct gas-driven water experiments to determine the driving conditions for gas-driven water, including driving pressure difference and confining pressure.

[0083] According to GB-T28912-2012, when using gas-driven water, the initial displacement pressure differential should be sufficient to overcome the end effect without generating turbulence, and the initial gas-driven water production rate should preferably be between 7 mL / min and 30 mL / min. Considering the special characteristics of loose sandstone, the production rate is set to the lower limit of 7 mL / min. Record the displacement pressure differential ΔP and confining pressure p at an initial production rate of 7 mL / min. h The gas injection rate should be set to the smallest possible value according to the standard requirements.

[0084] (3) Determine the effective pore volume of the rock sample under experimental pressure conditions.

[0085] The rock sample was dried and weighed to a dry weight of m1, then saturated with formation water. The saturated rock sample was placed in a gas-driven water experimental apparatus, and a confining pressure p was applied to the sample using a core holder. h At this point, the rock sample is compressed under stress, the effective pore volume decreases, and some of the saturated water is squeezed out.

[0086] Take out the rock sample and weigh the confining pressure p. h Given the sample's wet weight (m²) under the given conditions, calculate the actual effective pore volume (V) of the rock sample. p .

[0087] Comparison of pore volume V of conventional rock samples p1 Effective pore volume V of rock sample under experimental pressure conditions p (See Table 1 below), and it can be seen that there is a significant difference between the two, indicating that by improving the testing method, the effective pore volume V of the rock sample under experimental pressure conditions can be obtained. p It is absolutely necessary.

[0088] Step S32: Conduct unsteady-state gas and water relative permeability experiments, and determine the amount of sand produced from the rock sample after the experiment.

[0089] (1) Conduct the unsteady-state gas-driven water relative permeability determination experiment according to the equipment and procedures described in "7.2 Unsteady-state gas-water relative permeability determination" in standard GBT28912-2012.

[0090] (2) During the gas-driven water experiment, although the displacement pressure difference ΔP was controlled to the minimum range, sand was usually produced during the experiment due to the loose sandstone reservoir. Sand production accompanied the entire experimental process. Since sand and water were produced at the same time, they entered the gas-water separation metering device in a muddy water mixture, which made the metering of produced water too large.

[0091] (3) After the experiment, measure the total volume V of the mud and water (water and sand). m1 .

[0092] (4) Using the known mass m p All the muddy water produced during the filter paper filtration experiment was filtered, and the solid matter (sand) was separated. The filter paper was dried and weighed to obtain the total mass m of the filter paper and solid matter. t Calculate the mass m of sand. s :m s =m t -m p .

[0093] (5) Based on the density ρ of the loose sandstone sample r Calculate the sand volume V s .

[0094] Step S33: Calculate the dimensionless sand production, assess the severity of sand production in the rock sample, and determine whether the rock sample is suitable for conducting relative permeability measurement experiments.

[0095] Based on the total mass of filter paper and sand, the mass of filter paper, and the dry weight of the rock sample, the dimensionless sand yield is determined using the following formula (13):

[0096]

[0097] In formula (13), m0 represents the dimensionless sand yield, and m0 represents the dry weight of the rock sample.

[0098] Determine whether the determined dimensionless sand output is not greater than the set dimensionless sand output threshold; if so, proceed with the next steps.

[0099] Specifically, the dimensionless sand yield threshold can be set to 3%. If the dimensionless sand yield is greater than 3%, it indicates that the loose sandstone is severely exuding sand, meaning that the gas-driven water experiment has caused excessive changes in the core quality and pore structure, and the rock sample is not suitable for relative permeability curve determination. If the dimensionless sand yield is less than or equal to 3%, the water production caused by the sand yield of the rock sample during the experiment can be further corrected to obtain a more accurate gas and water relative permeability curve.

[0100] Table 1 shows the basic parameters and related test results of two loose sandstone samples. According to the embodiment of the present invention, the sand yield is dimensionless. Rock sample S1 was found to have a dimensionless sand yield greater than 3%, indicating a high sand yield; therefore, this sample is unsuitable for relative permeability testing. S2's dimensionless sand yield... If the value is less than 3%, a more ideal relative permeability curve can be obtained through correction.

[0101] Table 1. Basic parameters and related test results of permeable sandstone reservoir samples.

[0102]

[0103] Step S34: For rock samples deemed suitable for relative permeability curve determination, correct the measurement error of water production caused by sand production during the experiment to obtain the actual water production at any given time.

[0104] (1) Based on the total volume V of mud and water (water and sand) produced after the experiment. m1 and sand output volume V s The product water volume correction factor C is obtained.

[0105] (2) Since the displacement pressure is stable, the ratio of sand production to water production in the rock sample can be considered consistent throughout the experiment. During the experiment, the mud-water production at any given moment was recorded as V. w1 (t), based on the correction coefficient, the actual water production V at any given time is obtained. w (t), the output of metered gas and water at the outlet.

[0106] Step S35: Using the corrected effective pore volume and actual water production of the rock sample, calculate the changes in gas saturation, relative permeability of the gas phase and water phase over time according to the method described in national standard GB-T28912-2012.

[0107] Some of the calculation methods in the above steps are described in Example 1, and will not be repeated here.

[0108] Figure 4 Table 2 shows the comparison of the relative permeability curves of S2 gas and water in loose sandstone before and after correction in Example 2 of the present invention; Table 2 shows the key parameters of the relative permeability curves of S2 in loose sandstone before and after correction in Example 2 of the present invention. Figure 4 As shown in Table 2, there are significant differences in the shape of the S2 relative permeability curve and key parameters of loose sandstone before and after the correction, which fully demonstrates that the improved and corrected method for measuring the relative permeability of loose sandstone gas and water described in this invention is necessary.

[0109] Table 2 compares the key parameters of the relative permeability curves of loose sandstone S2 before and after correction in the embodiments of the present invention.

[0110]

[0111] Based on the inventive concept of this invention, embodiments of this invention also provide a method for determining the relative permeability of loose sandstone, including:

[0112] Obtain data on the changes in gas saturation, relative permeability of gas and water phases over time in loose sandstone samples obtained by the above method;

[0113] For any given gas saturation level, the time corresponding to that gas saturation level is determined by using the obtained data on the change of gas saturation level over time.

[0114] The relative permeability of the gas phase at a given moment is determined by the data on the change of relative permeability of the gas phase over time, and is taken as the relative permeability of the gas phase of the rock sample under the gas saturation condition; and / or, the relative permeability of the water phase at a given moment is determined by the data on the change of relative permeability of the water phase over time, and is taken as the relative permeability of the water phase of the rock sample under the gas saturation condition.

[0115] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process may be rearranged without departing from the scope of this disclosure. The appended method claims provide elements of various steps in an exemplary order and are not intended to limit the specific order or hierarchy described.

[0116] In the detailed description above, various features are combined together in a single embodiment to simplify this disclosure. This approach to disclosure should not be construed as reflecting an intention that embodiments of the claimed subject matter require more features than are explicitly stated in each claim. Rather, as reflected in the appended claims, the invention is presented with fewer features than all of the features in a single disclosed embodiment. Therefore, the appended claims are hereby explicitly incorporated into the detailed description, with each claim representing a separate preferred embodiment of the invention.

[0117] The foregoing description includes examples of one or more embodiments. It is certainly impossible to describe all possible combinations of components or methods in order to describe the above embodiments, but those skilled in the art will recognize that further combinations and arrangements of the various embodiments are possible. Therefore, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, the term "comprising" as used in the specification or claims is interpreted in a manner similar to the term "including," as interpreted when used as a conjunction in the claims. Additionally, the use of any term "or" in the specification of the claims is intended to mean "non-exclusive or."

Claims

1. A method for determining the relative permeability of gas and water in loose sandstone, characterized in that, include: The loose sandstone sample was dried and weighed as dry weight. After the sample was saturated with formation water, a set confining pressure was applied to obtain the wet weight of the sample. The effective pore volume of the sample was calculated based on the dry weight and wet weight. An unsteady-state gas-driven water relative permeability determination experiment was conducted on rock samples according to the set displacement pressure difference, and the changes in the total volume of produced sand and water and the volume of produced gas over time were obtained. Determine the volume of sand in the produced sand-water. Based on the total volume of the produced sand-water and the volume of sand in it, determine the water production volume correction coefficient. Use the water production volume correction coefficient to correct the change data of the total volume of the produced sand-water over time, and obtain the change data of the net produced water volume over time. Based on the changes in effective pore volume and net produced water and gas volume over time, the changes in gas saturation, relative permeability of gas and water phases of the rock sample over time are determined.

2. The method as described in claim 1, characterized in that, Before drying and weighing the loose sandstone sample, the process also includes: Through gas-driven water experiments on loose sandstone samples, the set displacement pressure difference and set confining pressure were obtained according to the minimum standard of initial gas-driven water production rate.

3. The method as described in claim 1, characterized in that, The calculation of the effective pore volume of the rock sample based on the dry weight and wet weight specifically includes: Based on the dry and wet weights, the effective pore volume of the rock sample is calculated using the following formula (1): In formula (1), V p The effective pore volume of the rock sample is m2, the wet weight is m0, and the dry weight is ρ. w The density of the formation water is given.

4. The method as described in claim 1, characterized in that, Determining the volume of sand in the produced sand-water specifically includes: The sand-water mixture is filtered through filter paper, the filter paper is dried, and the total mass of the filter paper and sand is obtained by weighing. Based on the total mass of filter paper and sand, the mass of filter paper, and the density of the rock sample, the volume of sand in the produced sand-water is determined using the following formula (2): In formula (2), V s Let m be the volume of sand in the produced sand-water. t m is the total mass of filter paper and sand. p For filter paper quality, ρ r This represents the density of the rock sample.

5. The method as described in claim 4, characterized in that, After obtaining the total mass of the filter paper and sand by weighing, the process also includes: Based on the total mass of filter paper and sand, the mass of filter paper, and the dry weight of the rock sample, the dimensionless sand yield is determined using the following formula (3): In formula (3), m0 represents the dimensionless sand yield, and m0 represents the dry weight of the rock sample. Determine whether the determined dimensionless sand output is not greater than the set dimensionless sand output threshold. If so, the volume of sand in the produced sand-water is determined based on the total mass of the filter paper and sand, the mass of the filter paper, and the density of the rock sample.

6. The method as described in claim 1, characterized in that, The step of determining the water production volume correction coefficient based on the total volume of the produced sand-water and the volume of sand within it specifically includes: Based on the total volume of the produced sand-water and the volume of sand within it, the production water volume correction factor is determined using the following formula (4): In formula (4), C is the product water volume correction factor, and V m1 V represents the total volume of sand and water produced. s This represents the volume of sand in the produced sand-water mixture.

7. The method as described in claim 1, characterized in that, The determination of the changes in gas saturation, relative permeability of gas, water, and water phases of the rock sample over time based on the changes in the effective pore volume and the net produced water and gas volumes over time specifically includes: Based on the changes in effective pore volume and net produced water and gas volume over time, the changes in dimensionless water production, dimensionless total gas and water production, water content, and relative injection capacity over time are determined respectively. Based on the data on the changes in dimensionless water production, total dimensionless gas and water production, and water content over time, the data on the changes in gas saturation at the outlet end of the rock sample over time were determined and used as the data on the changes in gas saturation of the rock sample over time. Based on the data on the changes in dimensionless gas-water total production and water content over time, the data on the changes in the relative permeability of the water phase in the rock sample over time were determined. Based on the data on the change of relative permeability of the aqueous phase over time and the data on the change of water content over time, the data on the change of relative permeability of the gas phase over time of the rock sample were determined.

8. The method as described in claim 7, characterized in that, The step of determining the changes in dimensionless water production, dimensionless total gas-water production, water content, and relative injection capacity over time based on the changes in effective pore volume and net produced water and gas volumes over time includes: Based on the changes in effective pore volume and net produced water volume over time, the changes in dimensionless water production over time are determined using the following formula (5): In formula (5), V p V is the effective pore volume of the rock sample. w (t) represents the volume of water produced at time t. Let t be the dimensionless water production at time t; Based on the changes in the volume of net produced water and produced gas over time, the changes in the total volume of produced gas and water over time are determined. Based on the changes in the effective pore volume and the total volume of produced gas and water over time, the changes in the total dimensionless gas and water production over time are determined using the following formula (6): In formula (6), V t (t) represents the total volume of gas and water produced at time t. Let t be the dimensionless total gas and water production at time t; Based on the data on the change of dimensionless water production over time and the data on the change of dimensionless total gas and water production over time, the data on the change of water content over time are determined by the following formula (7): In formula (7), f w (S w () represents the moisture content; Based on the data on the changes in the volume of net produced water and produced gas over time, the data on the changes in the total gas and water flow rate at the rock sample outlet face over time and the total gas and water flow rate at the rock sample outlet face at the initial moment of the experiment are determined. Then, the data on the changes in the relative injection capacity over time are determined by the following formula (8): In formula (8), I is the relative injection capacity, Q(t) is the total gas and water flow rate at the rock sample outlet end face at time t, and Q0 is the total gas and water flow rate at the rock sample outlet end face at the initial time of the experiment.

9. The method as described in claim 7, characterized in that, The step of determining the change in gas saturation at the rock sample outlet face over time based on the changes in dimensionless water production, total dimensionless gas-water production, and water content over time specifically includes: Based on the changes in dimensionless water production, total dimensionless gas-water production, and water content over time, the changes in gas saturation at the rock sample outlet face over time are determined using the following formula (9): In formula (9), S g The gas saturation at the outlet end face of the rock sample. Let t be the dimensionless water production at time t. Let f be the dimensionless total gas and water production at time t. w (S w () represents the moisture content.

10. The method as described in claim 7, characterized in that, The determination of the relative permeability of the water phase in the rock sample over time, based on the changes in dimensionless gas-water total production and water content over time, specifically includes: Based on the changes in dimensionless gas-water total production and water content over time, the changes in the relative permeability of the water phase in the rock sample over time are determined using the following formula (10): In formula (9), krw is the relative permeability of the aqueous phase, and f w (S w () represents the moisture content. Let be the dimensionless total gas and water production at time t, and I be the relative injection capacity at time t.

11. The method as described in claim 7, characterized in that, The step of determining the change in the gas phase relative permeability of the rock sample over time based on the changes in the relative permeability of the aqueous phase and the changes in water content over time specifically includes: Based on the data on the change of relative permeability of the aqueous phase over time and the data on the change of water content over time, the data on the change of relative permeability of the gas phase over time of the rock sample are determined by the following formula (11): In formula (11), k rg k is the relative permeability of the gas phase. rw The relative permeability of the aqueous phase, μ g and μ w The viscosities f of the gas and formation water are respectively. w (S w () represents the moisture content.

12. A method for determining the relative permeability of loose sandstone, characterized in that, include: Obtain data on the changes in gas saturation, relative permeability of gas phase and water phase over time of loose sandstone samples obtained by the method of any one of claims 1 to 11; For any given gas saturation level, the time corresponding to that gas saturation level is determined by using the obtained data on the change of gas saturation level over time. The relative permeability of the gas phase at a given moment is determined by the data on the change of relative permeability of the gas phase over time, and is taken as the relative permeability of the gas phase of the rock sample under the gas saturation condition; and / or, the relative permeability of the water phase at a given moment is determined by the data on the change of relative permeability of the water phase over time, and is taken as the relative permeability of the water phase of the rock sample under the gas saturation condition.

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