Tight sandstone gas reservoir working fluid reservoir damage evaluation system and method

Abstract

The invention discloses a compact sandstone gas reservoir working fluid reservoir damage evaluation system and method. The method comprises the steps that a plunger-shaped rock core of a target reservoir is dried and vacuumized, and simulated formation water is saturated; reducing the water saturation of the rock core to the original water saturation of the reservoir; the first container with the pressure being the maximum filtration loss pressure difference is communicated with the treated rock core, when the pressure in the first container is attenuated to a set value, the operation is stopped, and the pressure attenuation time is recorded; the working fluid in the rock core is saturated, then return pressure is applied to formation pressure, and gas is injected into the rock core until the gas in the rock core is saturated; and carrying out a working solution damage rock core experiment to obtain a rock core working solution damage rate and liquid saturation. According to the invention, the pressure when the actual reservoir working fluid invades is simulated by changing the return pressure, and the filtration pressure can be increased from 3.5 MPa to more than 15 MPa; reservoir damage evaluation is carried out by innovatively applying the rock core with the original water saturation of the reservoir, so that the evaluation result is more accurate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of natural gas development, and particularly relates to a tight sandstone gas reservoir working fluid reservoir damage evaluation system and method. BACKGROUND

[0002] The working fluid mainly refers to the drilling fluid and fracturing fluid used in the drilling and fracturing process of a natural gas well. In the drilling and fracturing process of a gas well, the high working pressure in the wellbore can cause the working fluid to leak, and the working fluid filtrate to invade the near-wellbore reservoir, causing reservoir damage and greatly reducing the seepage capacity of gas in the near-wellbore, thereby reducing the productivity of the gas well and affecting the ultimate recovery of the gas reservoir. This damage is more obvious in tight sandstone gas reservoirs. The degree of reservoir damage can be evaluated by experimental methods, which can improve the drilling and fracturing operation effect of tight sandstone gas reservoirs and achieve efficient development of gas reservoirs. At present, the experimental methods for reservoir damage of tight sandstone gas reservoirs mainly include the following aspects.

[0003] (1) The industry standard for working fluid reservoir damage, "Laboratory Evaluation Method for Oil Reservoir Damage of Drilling Fluids and Completion Fluids" (S / YT6540-2021). This standard is applicable to the evaluation of reservoir damage caused by external fluids such as drilling fluids, perforating fluids, and killing fluids for conventional sandstone, tight sandstone, and shale reservoirs. It specifies the instruments and materials, experimental procedures, experimental parameters, and result analysis methods for related experiments. The standard design has a maximum experimental confining pressure of 4.5-5 MPa and a maximum filtration pressure difference of 3.5 MPa. However, the actual reservoir pressure is above 30 MPa, and the filtration pressure difference is related to the construction pressure and liquid column pressure, so it should be designed in combination with the actual field pressure conditions. The standard requires that when calculating the pressure half-life damage rate, the pressure half-life before damage (T b ) is the denominator, and when the pressure half-life after damage (T a ) increases to 2T b , the pressure half-life damage rate calculated by (T a -T b ) / T b ×100% is greater than 100%, which does not conform to the physical reality.

[0004] (2) Patent CN113092266A, Evaluation device and method for reservoir damage mechanism of slick water fracturing fluid (2021), discloses an experimental method and process including injection control unit, reservoir simulation unit and evaluation analysis unit. The method simulates reservoir conditions by increasing injection pressure and increasing confining pressure on dry samples; there is no problem of changing the pressure difference and the actual pressure difference. Patent CN111967162A, A method for evaluating reservoir damage of tight sandstone gas reservoir drilling fluid (2020), establishes a tight sandstone borehole-reservoir physical model for dry samples, derives a drilling fluid reservoir invasion depth calculation equation, and evaluates the damage degree by using the permeability change of the damaged reservoir. It does not solve the problems existing in the experimental evaluation method. Patent CN104792683A, A device and method for evaluating the damage degree of working fluid to tight reservoirs (2015), discloses a reservoir damage evaluation device for dry samples, and realizes the evaluation of the liquid permeability damage degree of the tight reservoir core after being polluted by the working fluid by the change of the pressure difference with time in the liquid pressure pulse attenuation process. In addition, the experiments involved in the three patents all use dry core samples, and the influence of the original water saturation of the reservoir on the reservoir damage evaluation is not considered.

[0005] It can be seen that the three main problems existing in the current experimental method are: ① The core pressure difference is small, which does not conform to the actual production situation; ② The influence of the original water saturation of the reservoir on the reservoir damage degree in the experiment is not considered; ③ The half-life damage rate calculation method is unreasonable. SUMMARY

[0006] In order to overcome the problems of small core pressure difference, which does not conform to the actual production situation, and unreasonable half-life damage rate calculation in the prior art, an experimental method for evaluating the reservoir damage of working fluid in tight sandstone gas reservoirs is provided. The method considers the influence of the original water saturation of the reservoir on the reservoir damage degree in the experiment, so as to more accurately characterize the reservoir damage degree.

[0007] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0008] A method for evaluating the reservoir damage of working fluid in tight sandstone gas reservoirs, comprising the following steps:

[0009] (1) After drying the target reservoir plug-shaped core, measure the initial mass, then saturate with simulated formation water under vacuum and weigh to obtain the saturated core mass;

[0010] (2) The core treated in step (1) is treated to reduce the water saturation of the core to the original water saturation of the reservoir;

[0011] (3) connecting the first container with the maximum filter loss pressure difference with the treated core in step (2), stopping when the pressure in the first container decays to a set value, and recording the pressure decay time;

[0012] (4) driving the working fluid to flow through one end of the core to the other end of the core until the working fluid in the core is saturated, then applying back pressure to the formation pressure, and then filling the core with gas until the core is saturated with gas;

[0013] (5) performing a working fluid damage core experiment to obtain the working fluid damage rate of the core and the liquid saturation.

[0014] Further, the water saturation of the saturated core is reduced by using a gas drive water method.

[0015] Further, the water saturation of the saturated core is reduced to the original water saturation of the reservoir, comprising the following steps: gas driving the water-saturated core, and weighing the core every certain time to obtain the core mass after gas driving, until (m2-m0) / (m1-m0)×100% = S w .

[0016] In the formula, m2 is the core mass after gas driving, m0 is the initial mass, m1 is the saturated core mass, and S w is the original water saturation of the reservoir.

[0017] Further, for the drilling fluid damage experiment, the maximum filter loss pressure difference ΔP is calculated by the following formula:

[0018] ΔP = ρ 液 gh - P p Formula (1)

[0019] In the formula, ρ 液 is the working fluid density in the wellbore, g is the acceleration of gravity, h is the liquid column height, and P p is the formation pressure.

[0020] Further, for the fracturing fluid damage experiment:

[0021] ΔP = ρ 液 gh + P 井口 - f 摩阻 - P p Formula (2)

[0022] In the formula: ΔP is the maximum filter loss pressure difference; ρ 液 is the working fluid density in the wellbore; g is the acceleration of gravity; h is the liquid column height; P p is the reservoir pore pressure; P 井口 is the inlet pressure; f 摩阻 is the resistance generated by the pipe string to the working fluid.

[0023] Further, the working fluid damage core experiment is carried out, and the core working fluid damage rate and the liquid saturation are obtained, including the following steps:

[0024] After the damage setting time of the core is stopped, the working fluid unloading pressure in the core is discharged, the core is taken out, the core mass is weighed, and the core damage pressure half-life is measured;

[0025] According to the pressure decay time, the core damage pressure half-life, the core working fluid damage rate is calculated; and according to the initial mass, the saturated core mass and the core mass after the working fluid damage core experiment, the liquid saturation is calculated.

[0026] Further, the core working fluid damage rate I c is calculated by the following formula:

[0027]

[0028] In the formula, t0 is the pressure decay time, and t1 is the core damage pressure half-life.

[0029] Further, the liquid saturation S 液 is calculated by the following formula:

[0030]

[0031] In the formula, m0 is the initial mass, m1 is the saturated core mass, and m3 is the core mass after the working fluid damage core experiment.

[0032] A tight sandstone gas reservoir working fluid reservoir damage evaluation system, comprising a gas injection pump, a gas-liquid separator, a back pressure valve, a first valve, a second valve, a three-way valve, a third valve, a first container, a fourth valve, a clamp, a constant pressure pump and a back pressure pump;

[0033] The core is arranged on the clamp, one end of the core is an outlet end, and the other end is an inlet end;

[0034] The outlet of the gas-liquid separator is connected with the inlet of the back pressure valve, the outlet of the back pressure valve is divided into two paths, one path is connected with the back pressure pump, and the other path is connected with the first inlet of the three-way valve through the first valve, the gas injection pump is connected with the second inlet of the three-way valve through the second valve, the outlet of the three-way valve is connected with the inlet of the first container through the third valve, and the outlet of the first container is connected with the outlet end through the fourth valve;

[0035] The constant pressure pump is connected with a second container filled with working fluid, and the bottom of the second container is connected with the inlet end through a fifth valve and a second pressure gauge.

[0036] Further, one side of the core is provided with a confining pressure pump connected therewith;

[0037] A first pressure gauge is arranged on the pipeline between the third valve and the first container;

[0038] A flow meter and a liquid discharge valve are arranged on the gas-liquid separator;

[0039] The inlet end is further connected with a vent valve.

[0040] Compared with the prior art, the present application has the beneficial effects that:

[0041] The present application can increase the filtration pressure from 3.5 MPa to more than 15 MPa by changing the back pressure to simulate the pressure when the working fluid invades the actual reservoir, and overcomes the situation that the highest filtration pressure difference in the prior art is 3.5 MPa, which is not consistent with the actual situation; the present application innovatively applies the core with the original water saturation of the reservoir to carry out the reservoir damage evaluation, considers the damage of the original water saturation of the reservoir to the reservoir, and is closer to the actual situation of the core in the reservoir, so that the evaluation result is more accurate. The present application can carry out the working fluid filtration experiment under the conditions of the overlying rock pressure of the reservoir, the pore pressure, the original water saturation and the wellbore liquid column pressure, and calculate the reasonable reservoir damage degree evaluation data.

[0042] Further, in the present application, the core working fluid damage rate is obtained by calculating the half-life period change degree based on the damage half-life period under the condition of increasing the filtration pressure difference, the calculation is more reasonable, and the reservoir damage degree can be accurately characterized.

[0043] In the present application, by arranging the back pressure valve, the first valve and the back pressure pump, the back pressure device area is formed at the outlet end of the core, the pressure when the working fluid invades the actual reservoir is simulated by changing the back pressure, the filtration pressure can be increased from 3.5 MPa to more than 15 MPa, and the reservoir damage degree evaluation data is more reasonable. The evaluation system of the present application has simple structure, can realize the damage experiment of the core, and more accurately carries out the working fluid reservoir damage evaluation of the tight sandstone gas reservoir. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 It is a working fluid damage tight gas layer experiment flow chart;

[0045] In the figure, 1 is a flow meter, 2 is a gas injection pump, 3 is a gas-liquid separator, 4 is a liquid discharge valve, 5 is a back pressure valve, 6 is a first valve, 7 is a second valve, 8 is a three-way valve, 9 is a third valve, 10 is a first pressure gauge, 11 is a first container, 12 is a fourth valve, 13 is a back pressure pump, 14 is a constant pressure pump, 15 is a holder, 16 is a core, 17 is an outlet end, 18 is an inlet end, 19 is a confining pressure pump, 20 is a vent valve, 21 is a second pressure gauge, 22 is a fifth valve, 23 is a working fluid, and 24 is a second container. DETAILED DESCRIPTION

[0046] For the purpose of facilitating the understanding of the present application, a more complete description of the present application will be given below with reference to the relevant drawings. The preferred embodiments of the present application are shown in the drawings. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0047] Referring to Figure 1 , a reservoir damage evaluation system for a tight sand gas reservoir working fluid of the present application comprises a gas injection pump 2, a gas-liquid separator 3, a back pressure valve 5, a first valve 6, a three-way valve 8, a first container 11, a clamp 15, a confining pressure pump 19, a vent valve 20, a constant pressure pump 14 and a back pressure pump 13.

[0048] Among them, one end of the core 16 is the outlet end 17, and the other end is the inlet end 18.

[0049] The back pressure valve 5, the first valve 6 and the back pressure pump 13 are located in the back pressure device area.

[0050] The gas-liquid separator 3 is provided with a flowmeter 1 and a liquid discharge valve 4. The outlet of the gas-liquid separator 3 is connected with the inlet of the back pressure valve 5. The outlet of the back pressure valve 5 is divided into two routes. One route is connected with the back pressure pump 13, and the other route is connected with the first inlet of the three-way valve 8 through the first valve 6. The gas injection pump 2 is connected with the second inlet of the three-way valve 8 through the second valve 7. The outlet of the three-way valve 8 is connected with the inlet of the first container 11 through the third valve 9. The pipeline between the third valve 9 and the first container 11 is provided with a first pressure gauge 10. The outlet of the first container 11 is connected with the outlet end 17 through the fourth valve 12.

[0051] The constant pressure pump 14 is connected with the second container 24 containing the working fluid 23. The bottom of the second container 24 is provided with an outlet. The outlet is connected with the inlet end 18 through the fifth valve 22 and the second pressure gauge 21. The inlet end 18 is also connected with the vent valve 20.

[0052] The confining pressure pump 19 is connected with one side of the core 16.

[0053] Referring to Figure 1 , a reservoir damage evaluation method for a tight sand gas reservoir working fluid of the present application comprises the following steps:

[0054] (1) Select a target reservoir plug-shaped core. After drying for 24 hours, measure the initial mass m0;

[0055] (2) Vacuumize and saturate the target reservoir plug-shaped core in step (1) with simulated formation water, weigh m1, and pressurize the reservoir to the overburden pressure (P i ) of the reservoir according to the formula P Figure 1 After connecting the instruments, the target reservoir plug-shaped core is loaded into the clamp 15. The confining pressure is applied to the overburden pressure (P i ) of the reservoir through the confining pressure pump 19;

[0056] (3) Determine the initial water saturation S of the reservoir based on the well logging data and coring data w , using the gas-water drive method to reduce the core water saturation to the original reservoir water saturation S w , open the second valve 7, the third valve 9, the fourth valve 12 and the vent valve 20, start the air injection pump 2, and perform air drive on the saturated core. Weigh the core mass m2 every 15 minutes until (m2-m0) / (m1-m0)×100%=S w ;

[0057] (4) Close the fourth valve 12 and inject gas into the first container 11 until the reading on the first pressure gauge 10 rises to the maximum filtration pressure difference ΔP. Then, close the gas injection pump 2, the second valve 7, and the third valve 9. After stabilizing for 15 minutes, open the fourth valve 12 and stop when the pressure reading drops to ΔP / 2. Record the pressure decay time as t0.

[0058] (5) Open the fifth valve 22, start the constant pressure pump 14, and drive the working fluid to flow slowly toward the outlet 17 until the working fluid 23 flows out of the vent valve 20. Then stop driving and close the vent valve 20 and the fifth valve 22.

[0059] (6) Apply back pressure to the formation pressure (P p ), open the first valve 6, the second valve 7, the third valve 9, and the fourth valve 12, close the drain valve 4, start the gas injection pump 2, and inject gas into the core until gas begins to be produced by the flow meter;

[0060] (7) Start the constant pressure pump 14 to make the pressure inside the second container 24 (P t ) rises until ΔP=P t -P p , reaching the actual construction pressure difference of the wellbore, among which the drilling fluid damage test includes:

[0061] ΔP=ρ 液 gh-P p Formula (1)

[0062] For fracturing fluid damage experiments, there are:

[0063] ΔP=ρ 液 gh+P 井口 -f 摩阻 -P p Formula (2)

[0064] Where: ΔP is the maximum filtration pressure difference, MPa; ρ 液 is the density of the working fluid in the wellbore, kg / m 3 ; g is the acceleration due to gravity, 9.8m / s 2 ; h is the height of the liquid column, m; Pp P is the reservoir pore pressure, MPa; P 井口 P is the inlet pressure, MPa; f 摩阻 P is the resistance of the pipe string to the working fluid, MPa.

[0065] (8) Open the liquid discharge valve 4 and the fifth valve 22, start the working fluid damage core experiment, and start timing, record the cumulative invasion amount V of the working fluid 23 at different times with the flowmeter 1;

[0066] (9) After 120 minutes of core damage, stop the experiment, close the fifth valve 22, slowly open the vent valve 20, and flow back the working fluid 23 in the core. After the vent valve 20 has no liquid output, unload all pressures, take out the core, clean the core end face, weigh (m3), and measure the core damage pressure half-life t1 according to step (4);

[0067] (10) Calculate the core working fluid damage rate according to the improved half-life change degree calculation formula (3) and formula (4);

[0068]

[0069]

[0070] Wherein, I c P is the core working fluid damage rate, S 液 S is the liquid saturation;

[0071] (11) End the experiment and arrange the experimental instruments.

[0072] Example 1

[0073] In order to verify the reliability of the present application, the working fluid damage evaluation method for tight gas reservoir under reservoir conditions was actually carried out, the pressure half-life was taken as the evaluation index of the conductivity of the tight core, and the damage degree of the working fluid to the tight gas reservoir under the reservoir conditions was calculated. The embodiment of the present application is carried out by the following steps:

[0074] (1) Select a target reservoir to take a plunger-shaped core 16 with a diameter of 2.48 cm and a length of 3.65 cm, dry for 24 hours, and measure the initial mass m0=44.63g;

[0075] (2) Vacuum saturate the core 16 with water, weigh m1=45.32g, and follow the attached Figure 1 After connecting the instruments, the core 16 is loaded into the holder 2, and the confining pressure is applied to 35MPa;

[0076] (3) According to the gas reservoir logging data and coring data, the original water saturation S w=60%, open the second valve 7, the third valve 9, the fourth valve 12 and the vent valve 202, start the air injection pump 2, and perform air drive on the saturated core. The core mass m2 is weighed every 15 minutes. After 1 hour, m2 = 45.04 g, and the water saturation is (45.04-44.63) / (45.32-44.63)×100%=59%;

[0077] (4) Close the fourth valve 12 and inject gas into the first container 11. After the first pressure gauge 10 shows a maximum filtration pressure difference ΔP = 20 MPa, close the gas injection pump 2, the second valve 7, and the third valve 9. After stabilizing for 15 minutes, open the fourth valve 12 and stop when the pressure indicator drops to 10 MPa. Record the pressure decay time as t0 = 37.5 minutes.

[0078] (5) Open the fifth valve 22, start the constant pressure pump 14, and drive the working fluid to flow slowly toward the core outlet 17 until the working fluid 23 flows out of the vent valve 20. Stop driving and close the vent valve 20 and the fifth valve 22.

[0079] (6) After applying back pressure to the formation pressure of 35 MPa, open the first valve 6, the second valve 7, the third valve 9, and the fourth valve 12, close the drain valve 4, start the gas injection pump 2, and inject gas into the core until gas begins to be produced by the flow meter;

[0080] (7) Open 24 to make the pressure inside the second container 24 (P t ) rises until ΔP=P t —P p The actual construction pressure difference of the wellbore is reached, and the drilling fluid damage test includes:

[0081] ΔP=ρ 液 gh-P p Formula (1)

[0082] For fracturing fluid damage experiments, there are:

[0083] ΔP=ρ 液 gh+P 井口 -f 摩阻 -P p =20MPa Formula (2)

[0084] Where: ΔP——maximum filtration pressure difference, MPa; ρ 液 ——Density of working fluid in wellbore, kg / m 3 ; g - acceleration due to gravity, 9.8 m / s 2 ;h——height of liquid column, m; P p ——reservoir pore pressure, MPa; P 井口 ——Inlet pressure, MPa; f 摩阻Resistance of the pipe column to working fluid, MPa.

[0085] (8) Open the liquid drainage valve 4 and the fifth valve 22, start the working fluid damage core experiment, and start timing. Record the working fluid 23 invasion amount at different times with the flowmeter 1. The cumulative invasion amount is V 总 = 2.37 mL;

[0086] (9) Stop the experiment after 120 min of core damage, close the fifth valve 22, slowly open the vent valve 20, and flow back the working fluid 23 in the core. After no liquid is produced from the vent valve 20, unload all the pressure, take out the core 16, clean the core end face, weigh m3= 45.27, and measure the core damage pressure half-life t1= 91.8 min according to step (4);

[0087] (10) Calculate the core working fluid damage rate I c = 59.15% according to formula (3)-(4), and the liquid saturation S 液 = 92.75%;

[0088]

[0089]

[0090] (11) End the experiment and arrange the experimental instruments.

[0091] The above only describes the best embodiments of the present application, but cannot be understood as a limitation on the claims. The present application is not limited to the above embodiments, and the specific structure allows changes. Any changes made within the protection scope of the independent claims of the present application are within the protection scope of the present application.

[0092] Unless otherwise defined, 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 application belongs. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

Claims

1. A method for evaluating reservoir damage from a work fluid for a tight sand gas reservoir, the method comprising: The method comprises the following steps: (1) measuring the initial mass of the target reservoir plug-shaped core after drying, then vacuum-saturating the core with simulated formation water and weighing to obtain the saturated core mass; (2) processing the core after step (1) to reduce the water saturation of the core to the original water saturation of the reservoir; (3) connecting the first container with a pressure difference of the maximum filtration loss to the core after step (2), stopping when the pressure in the first container decays to a set value, and recording the pressure decay time; (4) driving the working fluid to flow through one end of the core to the other end of the core until the working fluid in the core is saturated, then applying back pressure to the formation pressure, and then filling the core with gas until the core is saturated with gas; (5) performing a working fluid damage core experiment on the core to obtain the working fluid damage rate of the core and the liquid saturation.

2. The method of claim 1, wherein, The water saturation of the core is reduced by using a gas-water displacement method.

3. The method of claim 1, wherein, Decreasing the water saturation of the saturated core to the original water saturation of the reservoir, comprising the following steps: gas flooding the water-saturated core, and weighing the core every set time to obtain the core mass after gas flooding until (m2-m0) / (m1-m0) x 100% = S w ; In the formula, m2 is the core mass after gas flooding, m0 is the initial mass, m1 is the saturated core mass, S w is the original water saturation of the reservoir.

4. The method of evaluating reservoir damage from a tight sand gas reservoir servicing fluid of claim 1, wherein, For the drilling fluid damage experiment, the maximum filtration loss pressure difference ΔP is calculated by the following formula: ΔP = p 液 gh-P p Equation (1) Where, ρ 液 is the density of the working fluid in the wellbore, g is the acceleration of gravity; h is the height of the liquid column, P p is the formation pressure.

5. The method of evaluating reservoir damage from a tight sand gas reservoir servicing fluid of claim 1, wherein, For the fracturing fluid damage experiment: ΔP = p 液 gh + P 井口 -f 摩阻 -P p Equation (2) Where: ΔP is the maximum filtration pressure difference; ρ 液 is the density of the working fluid in the wellbore; g is the acceleration of gravity; h is the height of the liquid column; P p is the reservoir pore pressure; P 井口 is the inlet pressure; f 摩阻 It is the resistance of the tubing string to the working fluid.

6. The method of evaluating reservoir damage from a tight sand gas reservoir servicing fluid of claim 1, wherein, The working fluid damage core experiment on the core is performed to obtain the working fluid damage rate of the core and the liquid saturation, comprising the following steps: After the core is damaged for a set time, the working fluid in the core is unloaded, the core is taken out, the mass of the core is weighed, and the pressure half-life of the damaged core is measured; According to the pressure decay time and the pressure half-life of the damaged core, the working fluid damage rate of the core is calculated; and according to the initial mass, the saturated core mass and the core mass after the working fluid damage core experiment, the liquid saturation is calculated.

7. The method of evaluating reservoir damage from a tight sand gas reservoir servicing fluid of claim 1, wherein, Core fluid loss rate I c is calculated by the formula: In the formula, t0 is the pressure decay time, and t1 is the pressure half-life of the damaged core.

8. The method of evaluating reservoir damage from a tight sand gas reservoir servicing fluid of claim 1, wherein, Liquid saturation S 液 is calculated by the formula: In the formula, m0 is the initial mass, m1 is the saturated core mass, and m3 is the core mass after the working fluid damage core experiment.

9. A system for evaluating reservoir damage of a tight sand gas reservoir working fluid as employed in the method of any one of claims 1 to 8, characterized in that, The apparatus comprises an air injection pump (2), a gas-liquid separator (3), a back pressure valve (5), a first valve (6), a second valve (7), a three-way valve (8), a third valve (9), a first container (11), a fourth valve (12), a holder (15), a constant pressure pump (14) and a back pressure pump (13); The core (16) is arranged on the holder (15), one end of the core (16) is an outlet end (17), and the other end is an inlet end (18); The outlet of the gas-liquid separator (3) is connected to the inlet of the back pressure valve (5), the outlet of the back pressure valve (5) is divided into two paths, one path is connected to the back pressure pump (13), and the other path is connected to the first inlet of the three-way valve (8) through the first valve (6), the air injection pump (2) is connected to the second inlet of the three-way valve (8) through the second valve (7), the outlet of the three-way valve (8) is connected to the inlet of the first container (11) through the third valve (9), and the outlet of the first container (11) is connected to the outlet end (17) through the fourth valve (12); The constant pressure pump (14) is connected to a second container (24) containing working fluid (23), and the bottom of the second container (24) is connected to the inlet end (18) through a fifth valve (22) and a second pressure gauge (21).

10. A system for evaluating reservoir damage from a tight sand gas reservoir servicing fluid according to claim 9, wherein, A confining pressure pump (19) is arranged on one side of the core (16); A first pressure gauge (10) is arranged on the pipeline between the third valve (9) and the first container (11). A flow meter (1) and a drain valve (4) are arranged on the gas-liquid separator (3); The inlet end (18) is further connected with a vent valve (20).

Images