A method for evaluating water-flooded gas well wetting reversal water lock breaking and production recovery potential

Abstract

The present application relates to a kind of water-flooded gas well wetting reversal water seal production potential evaluation experimental method, belong to oil and gas field development field;It establishes a kind of scientific analysis method based on wetting reversal for water-flooded gas well water seal effect evaluation, its technical scheme is: obtaining the wellbore pressure gradient distribution data of target gas well under current capacity;Respectively obtain the wetting angle and corresponding wellbore breakthrough pressure gradient distribution data before and after wetting reversal of reservoir core;The above three kinds of distribution data are compared, and the production potential of wetting reversal measure for the water seal of target gas well is evaluated according to the comparison result, the application effect of wetting reversal agent is quickly and intuitively evaluated;The present application has good practical application effect, reliable result, and strong generalizability.

Description

TECHNICAL FIELD

[0001] The application relates to a water-flooded gas well wetness reversal water seal breaking production recovery potential evaluation experimental method and belongs to the oil and gas field development field. BACKGROUND

[0002] With the deepening of natural gas field development, water invasion and water flooding problems of gas wells are increasingly serious in many old gas reservoirs. Water invasion refers to the invasion of formation water into a gas reservoir during development, which leads to the increase of water production rate of a gas well and the sharp decrease of gas phase permeability, and even causes the water flooding of the gas well and the shutdown of the gas well. Water seal breaking by injection of a wetness reversal agent is a common method in the field. The wetness reversal agent can change the wettability of a rock surface from hydrophilic to hydrophobic, reduce the water phase retention, and enhance the gas flow capacity. Therefore, quantitative evaluation of the water seal breaking production recovery potential of a water-flooded gas well by wetness reversal is beneficial to the optimization of drainage gas recovery technology and the accurate tapping of remaining gas.

[0003] Through extensive research, the application number CN201911199216.4 "Method for restoring production of sealed gas well" based on coiled tubing technology and chemical plugging remover can specifically remove the plugging of high molecular polymers and inorganic pollutants in the wellbore, and improve the seepage conditions of the reservoir near the well bottom. The application number CN202410013710.1 "Method for diagnosing production recovery capacity of water-producing gas well after shut-in" is based on the gas well node analysis theory. By establishing the inflow and outflow dynamic curves and combining the critical liquid-carrying flow rate, the natural production recovery capacity of the water-producing gas well after shut-in is diagnosed. The application number CN202011527150.X "Experimental evaluation method for water lock damage of gas reservoir" is based on the centrifuge control of water saturation, the mercury injection curve conversion of capillary pressure, the determination of the change of gas permeability, and the calculation of the damage degree coefficient.

[0004] In general, there are many methods for water seal breaking production recovery of a water-flooded gas well at present, but most of them focus on field operation, production dynamic diagnosis or damage evaluation. There are few methods for quantitative evaluation of water seal breaking potential based on wetness reversal. Therefore, a method for conveniently evaluating the water seal breaking production recovery potential of a water-flooded gas well by considering the influence of wetness reversal on the wellbore breakthrough pressure gradient after treatment of a wetness reversal agent is needed. SUMMARY

[0005] The application aims to establish a scientific analysis method for evaluating the water seal breaking effect of a water-flooded gas well based on wetness reversal. The application obtains the wellbore pressure gradient distribution data of a target gas well under the current production capacity. The wetting angles and the corresponding wellbore breakthrough pressure gradient distribution data of the reservoir core before and after wetness reversal are obtained respectively. The three types of distribution data are compared. According to the comparison result, the production recovery potential of the wetness reversal measure for the water seal breaking of the target gas well is evaluated. The application effect of the wetness reversal agent is quickly and intuitively evaluated. The application has good practical application effect, reliable result and strong generalizability.

[0006] To achieve the above object, the application provides a water-flooded gas well wetting reversal water seal breaking and production recovery potential evaluation experimental method, which comprises the following steps,

[0007] S100, obtaining wellbore pressure gradient distribution data of a target gas well under current productivity;

[0008] S200, obtaining a wetting angle before wetting reversal and wellbore breakthrough pressure gradient distribution data before wetting reversal of a target gas well reservoir core;

[0009] S300, obtaining a wetting angle after wetting reversal and wellbore breakthrough pressure gradient distribution data after wetting reversal of a target gas well reservoir core;

[0010] S400, comparing the wellbore pressure gradient distribution data, the wellbore breakthrough pressure gradient distribution data before wetting reversal and the wellbore breakthrough pressure gradient distribution data after wetting reversal, and evaluating the production recovery potential of the target gas well after wetting reversal according to the comparison result.

[0011] In the water-flooded gas well wetting reversal water seal breaking and production recovery potential evaluation experimental method, the wellbore pressure gradient distribution data of the target gas well under the current productivity is obtained by collecting production parameters and reservoir parameters of the target gas well and bringing them into a wellbore pressure gradient calculation formula , to obtain the wellbore pressure gradient distribution data of the target gas well under the current productivity, wherein, is a pressure gradient, and the unit is MPa / m; is a gas production, and the unit is m 3 / d; is a reservoir temperature, and the unit is K; is a gas compressibility factor, and the unit is dimensionless; is a gas average viscosity, and the unit is mPa·S; is a reservoir permeability, and the unit is mD; is a reservoir thickness, and the unit is m; is an average formation pressure, and the unit is MPa; is a wellbore radius, and the unit is m.

[0012] In the water-flooded gas well wetting reversal water seal breaking and production recovery potential evaluation experimental method, the method for obtaining the wetting angle before wetting reversal and the wetting angle after wetting reversal of the target gas well reservoir core is that a wetting angle measuring instrument is used to test the wetting angle of an outlet end surface of the target gas well reservoir core under the conditions of a reservoir temperature and a pressure.

[0013] In the water-flooded gas well wetting reversal water seal breaking and production recovery potential evaluation experimental method, the corresponding wellbore breakthrough pressure gradient distribution data is obtained by first performing a centrifugal dewatering experiment on the target gas well reservoir core, and then according to a formula The rotational speed is converted into the well radius to obtain the water saturation distribution data of the well, then the gas breakthrough pressure experiment is carried out on the target gas well reservoir core to obtain the water saturation and breakthrough pressure gradient data, finally the mapping relationship of the well radius to the breakthrough pressure gradient is established to obtain the corresponding well breakthrough pressure gradient distribution data, wherein, is the well radius, and the unit is m; is the gas well production, and the unit is m 3 / d; is the reservoir temperature, and the unit is K; is the gas compressibility factor, and the unit is dimensionless; is the average viscosity of the gas, and the unit is mPa·S; is the reservoir permeability, and the unit is mD; is the reservoir thickness, and the unit is m; is the average formation pressure, and the unit is MPa; is the formation water density, and the unit is kg / m 3 ; is the rotational speed, and the unit is rpm; is the centrifugal radius of the centrifuge, and the unit is m; is the core length, and the unit is m.

[0014] In the above-mentioned experimental method for evaluating the water breakthrough gas well wetness reversal water seal breaking and production recovery potential, the mapping relationship of the well radius to the breakthrough pressure gradient is finally established by directly matching the well radius and the breakthrough pressure gradient corresponding to the data points of the same water saturation in the same interval, matching the mapping relationship after shape-preserving interpolation of the data points of different water saturations in the same interval to the same point, and matching the mapping relationship by curve fitting of the data points of different water saturations in different intervals.

[0015] In the above-mentioned experimental method for evaluating the water breakthrough gas well wetness reversal water seal breaking and production recovery potential, the production recovery potential of the wetness reversal water seal breaking of the target gas well is evaluated according to the comparison result, that is, if the well pressure gradient is lower than the breakthrough pressure gradient before the wetness reversal but higher than the breakthrough pressure gradient after the wetness reversal, the wetness reversal water seal breaking and production recovery effect is remarkable, if the well pressure gradient is lower than the well breakthrough pressure gradient before the wetness reversal and after the wetness reversal, the wetness reversal water seal breaking and production recovery effect is not remarkable, and if the well pressure gradient is higher than the well breakthrough pressure gradient before the wetness reversal and after the wetness reversal, the wetness reversal has an improvement effect on the gas well production.

[0016] Compared with the prior art, the present application has the following beneficial effects: (1) the theory is combined with the practice to quickly and intuitively evaluate the water seal breaking potential of the gas well under different wetness angles; (2) the test process is simple and convenient to use; and (3) the present application has strong generalizability. BRIEF DESCRIPTION OF DRAWINGS

[0017] In the drawings:

[0018] Figure 1 is a method technical roadmap.

[0019] Figure 2 is an X-12# water-flooded gas well water seal breaking and production recovery potential evaluation chart.

[0020] Figure 3 is an X-19# water-flooded gas well water seal breaking and production recovery potential evaluation chart. DETAILED DESCRIPTION

[0021] The present application will be further described below in conjunction with embodiments and drawings.

[0022] The present application provides a water-flooded gas well wetness reversal water seal breaking and production recovery potential evaluation experimental method, Figure 1 is a technical roadmap of the method, which comprises the following steps:

[0023] S100, obtaining wellbore pressure gradient distribution data of the target gas well under current productivity;

[0024] S200, obtaining the wetting angle before wetness reversal and the wellbore breakthrough pressure gradient distribution data before wetness reversal of the target gas well reservoir core;

[0025] S300, obtaining the wetting angle after wetness reversal and the wellbore breakthrough pressure gradient distribution data after wetness reversal of the target gas well reservoir core;

[0026] S400, comparing the wellbore pressure gradient distribution data, the wellbore breakthrough pressure gradient distribution data before wetness reversal and the wellbore breakthrough pressure gradient distribution data after wetness reversal, and evaluating the production recovery potential of the target gas well water seal breaking by wetness reversal according to the comparison result.

[0027] Further, the wellbore pressure gradient distribution data of the target gas well under current productivity is obtained by collecting the production parameters and reservoir parameters of the target gas well and bringing them into the wellbore pressure gradient calculation formula, and the specific steps are,

[0028] S101, bringing the average gas viscosity, gas well production, reservoir temperature, reservoir permeability, gas compressibility factor, average formation pressure and reservoir thickness parameters into the wellbore pressure gradient calculation formula to obtain the discrete data set of the wellbore pressure gradient about the wellbore radius under current productivity, wherein, is the pressure gradient, and the unit is MPa / m; is the gas well production, and the unit is m 3 / d; is the reservoir temperature, and the unit is K; is the gas compressibility factor, dimensionless; is the gas average viscosity, mPa·S; is the reservoir permeability, mD; is the reservoir thickness, m; is the average formation pressure, MPa; is the wellbore radius, m.

[0029] Further, the method for obtaining the wetting angle of the target gas well reservoir core before and after the wetting reversal is that, through a wetting angle measuring instrument, the wetting angle of the outlet end surface of the target gas well reservoir core is tested under the reservoir temperature and pressure conditions.

[0030] Further, the specific steps for obtaining the corresponding wellbore breakthrough pressure gradient distribution data are that,

[0031] S201, after the core is cleaned and dried in a constant temperature drying box, the dry weight at this time is recorded, then the core is vacuumized, saturated with formation water and the wet weight at this time is recorded, and the core saturation is calculated according to the formula by using the weighing method;

[0032] S202, the core saturated with the formation water is placed in a centrifuge tube of a centrifuge for centrifugal dewatering experiment, the speed at this time is recorded, the water saturation at this time is calculated by using the weighing method, and then the speed is gradually increased for centrifugal dewatering, the step is repeated to obtain the data of the water saturation of the core before the wetting reversal about the speed;

[0033] S203, according to the formula, the speed is converted into the wellbore radius to obtain the water saturation distribution data of the wellbore, in which, is the wellbore radius, m; is the gas well production, m 3 / d; is the reservoir temperature, K; is the gas compressibility factor, dimensionless; is the gas average viscosity, mPa·S; is the reservoir permeability, mD; is the reservoir thickness, m; is the average formation pressure, MPa; is the formation water density, kg / m 3 ; is the speed, rpm; is the centrifugal radius of the centrifuge, m; is the core length, m;

[0034] S204, after the core is washed, the core is dried in a constant temperature drying box, then the core is vacuumized, and the core is resaturated with formation water;

[0035] S205, the core is loaded into a core holder with temperature control, a confining pressure is applied, an experimental temperature is a formation temperature, an outlet pressure is set to be higher than a saturated steam pressure of the formation water by 0.1 MPa to 1.0 MPa, a gas source is connected to an inlet end of the core, an inlet pressure is gradually increased, when an outlet flowmeter just shows a non-zero and constant value, a differential pressure between the inlet and the outlet at this time is recorded and divided by a length of the core, and the gas breakthrough pressure gradient of the core is obtained, the core is taken out, and a water saturation at this time is calculated by using a weighing method;

[0036] S206, the core is centrifugally dewatered by using a centrifuge, the water saturation of the core is reduced, the gas breakthrough pressure experiment is repeated, and data of the breakthrough pressure gradient before wetting reversal of the core with respect to the water saturation are obtained;

[0037] S207, finally, a mapping relationship of a well radius to the breakthrough pressure gradient is established, and corresponding breakthrough pressure gradient distribution data of the well are obtained.

[0038] Further, the last step of establishing the mapping relationship of the well radius to the breakthrough pressure gradient specifically comprises the following steps,

[0039] S301, for the same water saturation in the data of the centrifugal dewatering experiment and the gas breakthrough pressure experiment, corresponding breakthrough pressure gradients and well radii are associated by data matching, and a mapping relationship of the breakthrough pressure gradient with respect to the well radius is obtained;

[0040] S302, for the inner points of the overlapping interval in the data of the centrifugal dewatering experiment and the gas breakthrough pressure experiment, a conformal interpolation method is used to interpolate the data points, the data is unified to the same water saturation value, and then a mapping relationship of the breakthrough pressure gradient with respect to the well radius in the interval is established by data matching;

[0041] S303, for the outer points of the overlapping interval in the data of the centrifugal dewatering experiment and the gas breakthrough pressure experiment, a logarithmic fitting is performed on the data of the centrifugal dewatering experiment to obtain a logarithmic curve equation, an exponential fitting is performed on the data of the gas breakthrough pressure experiment to obtain an exponential curve equation, and the two equations are combined to obtain a mapping relationship of the breakthrough pressure gradient with respect to the well radius outside the interval.

[0042] Further, the evaluation of the potential of the wetness reversal for the water seal breaking and production recovery of the target gas well according to the comparison result is that, if the pressure gradient around the well is lower than the breakthrough pressure gradient before the wetness reversal but higher than the breakthrough pressure gradient after the wetness reversal, the effect of the wetness reversal for the water seal breaking and production recovery is remarkable; if the pressure gradient around the well is lower than the breakthrough pressure gradient before the wetness reversal and the breakthrough pressure gradient after the wetness reversal, the effect of the wetness reversal for the water seal breaking and production recovery is not remarkable; and if the pressure gradient around the well is higher than the breakthrough pressure gradient before the wetness reversal and the breakthrough pressure gradient after the wetness reversal, the wetness reversal has an improvement effect on the production of the gas well.

[0043] Taking X-12# and X-19# as examples, the evaluation experiment of the potential of the wetness reversal for the water seal breaking and production recovery of the water-flooded gas well is performed by using the No. 1 core of X-12# and the No. 2 core of X-19#, the average formation pressure of X-12# is 27.18 MPa, the reservoir temperature of X-12# is 379.62 K, the average viscosity of the gas of X-12# is 0.020164 mPa·s, the gas compressibility factor of X-12# is 0.99138, the reservoir thickness of X-12# is 30.86 m, the reservoir permeability of X-12# is 0.4 mD, and the daily production of X-12# is 6089 m 3 / d, the average formation pressure of X-19# is 6.5 MPa, the reservoir temperature of X-19# is 379.62 K, the average viscosity of the gas of X-19# is 0.014539 mPa·s, the gas compressibility factor of X-19# is 0.96696, the reservoir thickness of X-19# is 30.86 m, the reservoir permeability of X-19# is 3.25 mD, and the daily production of X-19# is 83521 m 3 / d, and the core geometric parameters and other detailed parameters are shown in Table 1.

[0044] Table 1 Detailed parameter table

[0045]

[0046] The average viscosity of the gas, the gas well production, the reservoir temperature, the reservoir permeability, the gas compressibility factor, the average formation pressure and the reservoir thickness parameters are brought into the pressure gradient calculation formula to obtain the pressure gradient distribution data around the well of the target gas well under the current production capacity, and the specific data are shown in Table 2.

[0047] Table 2 Pressure gradient distribution data around the well of the target gas well under the current production capacity

[0048]

[0049] The wetting angle test, centrifugal dehydration experiment and gas breakthrough pressure experiment are carried out to obtain the wetting angle of the target gas well reservoir core before the wetting reversal and the corresponding wellbore breakthrough pressure gradient distribution data, wherein the wetting angle of the No. 1 core of X-12# before the wetting reversal is 43.023°, the wetting angle of the No. 2 core of X-19# before the wetting reversal is 45.827°, and the specific data are shown in Tables 3, 4, 5 and 6.

[0050] Table 3 Centrifugal experiment and breakthrough pressure experiment data of the No. 1 core of X-12# before the wetting reversal

[0051]

[0052] Table 4 Wellbore breakthrough pressure gradient distribution data of X-12# corresponding to before the wetting reversal

[0053]

[0054] Table 5 Centrifugal experiment and breakthrough pressure experiment data of the No. 2 core of X-19# before the wetting reversal

[0055]

[0056] Table 6 Wellbore breakthrough pressure gradient distribution data of X-19# corresponding to before the wetting reversal

[0057]

[0058] The core is displaced with the wetting reversal agent, the wetting angle at the outlet end of the core is tested, and the wetting angle of the core after the wetting reversal and the corresponding wellbore breakthrough pressure gradient distribution data are obtained, wherein the wetting angle of the No. 1 core of X-12# after the wetting reversal is 83.926°, the wetting angle of the No. 2 core of X-19# after the wetting reversal is 86.321°, and the specific data are shown in Tables 7, 8, 9 and 10.

[0059] Table 7 Centrifugal experiment and breakthrough pressure experiment data of the No. 1 core of X-12# after the wetting reversal

[0060]

[0061] Table 8 Wellbore breakthrough pressure gradient distribution data of X-12# corresponding to after the wetting reversal

[0062]

[0063] Table 9 Centrifugal experiment and breakthrough pressure experiment data of the No. 2 core of X-19# after the wetting reversal

[0064]

[0065] Table 10. Wellbore breakthrough pressure gradient distribution data after wetting reversal of X-19#

[0066]

[0067] The wellbore pressure gradient distribution data, the wellbore breakthrough pressure gradient distribution data before wetting reversal, and the wellbore breakthrough pressure gradient distribution data after wetting reversal are compared. Based on the comparison results, the potential for wetting reversal to restore production in the target gas well by breaking the water seal is evaluated. Figure 2 and Figure 3 ,exist Figure 2 The pressure gradient around well X-12# remained consistently lower than the breakthrough pressure gradient, resulting in insignificant water seal release and production recovery due to wetting reversal, making production recovery difficult. Figure 3 The wetting reversal of the X-19# gas well has an improving effect on gas well production, increasing the wellbore control radius. Figure 2 and Figure 3 This allows for a direct and rapid evaluation of the potential for water-sealed gas wells to resume production under different wetting angles, providing a basis for decision-making regarding wetting reversal measures.

[0068] Compared with the prior art, the present invention has the following advantages: (1) It combines theory with practice, and the pressure response characteristic curve chart is more convenient and faster; (2) The testing process is simple and easy to use; (3) It has strong scalability.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An experimental method for evaluating the potential for water-seal reversal and recovery of production in water-flooded gas wells, characterized in that, The method includes the following steps: S100: Obtain the wellbore pressure gradient distribution data of the target gas well under the current production capacity; S200, acquiring the wetting angle and wellbore breakthrough pressure gradient distribution data of the target gas well reservoir core before wetting reversal, the specific steps are as follows: S201. After cleaning the core, dry it in a constant temperature drying oven and record the dry weight. Then, vacuum the core, saturate it with formation water and record the wet weight. Calculate the water saturation of the core using the weighing method. S202, put the core saturated with formation water into the centrifuge tube of a centrifuge for centrifugation dehydration experiment, record the rotation speed at this time, calculate the water saturation at this time by weighing method, and then gradually increase the rotation speed for centrifugation dehydration. Repeat this step to obtain the data of water saturation of the core before wetting reversal with respect to rotation speed. S203, according to the formula, Converting the rotational speed to the well circumference radius yields the well circumference water saturation distribution data, where, The radius of the well is in meters. Gas well production, in meters (m³) 3 / d; Reservoir temperature, in Kelvin (K). This is the gas compressibility factor, and its unit is dimensionless. The average viscosity of the gas is expressed in mPa·s. Reservoir permeability, in mD; The reservoir thickness is expressed in meters (m). Mean formation pressure, in MPa; This refers to the density of formation water, expressed in kg / m³. 3 ; Rotational speed, in rpm; This refers to the centrifugal radius of the centrifuge, expressed in meters (m). This refers to the core length, in meters (m). S204, after cleaning the core, it is dried in a constant temperature drying oven, then vacuumed, and then the core is resaturated with formation water. S205. The core is placed in a core holder with temperature control, and confining pressure is applied. The experimental temperature is the formation temperature, and the outlet pressure is set to be 0.1 MPa~1.0 MPa higher than the saturated vapor pressure of formation water. The gas source is connected to the inlet end of the core, and the inlet pressure is gradually increased. When the outlet flow meter just shows a non-zero and constant value, the pressure difference between the inlet and outlet is recorded and divided by the core length. This is the gas breakthrough pressure gradient of the core. The core is then removed, and the water saturation at this time is calculated using the weighing method. S206, the core was centrifuged and dehydrated to reduce the water saturation of the core. The gas breakthrough pressure experiment was repeated to obtain data on the breakthrough pressure gradient of the core before wetting reversal with respect to water saturation. S207 Finally, establish the mapping relationship between the well perimeter radius and the breakthrough pressure gradient to obtain the corresponding well perimeter breakthrough pressure gradient distribution data; S300, obtain the wetting angle and wellbore breakthrough pressure gradient distribution data of the target gas well reservoir core after wetting reversal; S400 compares the wellbore pressure gradient distribution data, the wellbore breakthrough pressure gradient distribution data before wetting reversal, and the wellbore breakthrough pressure gradient distribution data after wetting reversal, and evaluates the potential for wetting reversal to break the water seal and restore production of the target gas well based on the comparison results.

2. The method according to claim 1, characterized in that, In step S100, obtaining the wellbore pressure gradient distribution data of the target gas well under the current production capacity involves collecting the production parameters and reservoir parameters of the target gas well and inputting them into the wellbore pressure gradient calculation formula. The wellbore pressure gradient distribution data of the target gas well under the current production capacity is obtained, where, This represents the pressure gradient, in MPa / m. Gas well production, in meters (m³) 3 / d; Reservoir temperature, in Kelvin (K). This is the gas compressibility factor, and its unit is dimensionless. The average viscosity of the gas is expressed in mPa·s. Reservoir permeability, in mD; The reservoir thickness is expressed in meters (m). Mean formation pressure, in MPa; The radius of the well is in meters (m).

3. The method according to claim 1, characterized in that: The method for obtaining the wetting angle of the target gas well reservoir core before wetting reversal in S200 and the method for obtaining the wetting angle of the target gas well reservoir core after wetting reversal in S300 are as follows: the wetting angle of the target gas well reservoir core outlet end face is tested using a wetting angle measuring instrument under reservoir temperature and pressure conditions.

4. The method according to claim 1, characterized in that: In step S207, a mapping relationship is established between the well perimeter radius and the breakthrough pressure gradient to obtain the corresponding well perimeter breakthrough pressure gradient distribution data. For data points with the same water saturation in the same interval, the well perimeter radius and breakthrough pressure gradient are directly matched to establish a mapping relationship. For data points with different water saturation in the same interval, shape-preserving interpolation is performed to the same point before matching to establish a mapping relationship. For data points with different water saturation in different intervals, curve fitting is performed to establish a mapping relationship.

5. The method according to claim 1, characterized in that: The evaluation of the potential for water seal reversal in resuming production of the target gas well based on the comparison results is as follows: if the wellbore pressure gradient is lower than the breakthrough pressure gradient before water seal reversal but higher than the breakthrough pressure gradient after water seal reversal, then the water seal reversal effect of water seal reversal is significant; if the wellbore pressure gradient is lower than both the breakthrough pressure gradient before and after water seal reversal, then the water seal reversal effect of water seal reversal is not significant; if the wellbore pressure gradient is higher than both the breakthrough pressure gradient before and after water seal reversal, then water seal reversal has an improving effect on gas well production.

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