Method for identifying remaining reserves distribution of water-bearing gas reservoirs

Abstract

The application discloses a method for identifying remaining reserves distribution of a water-bearing gas reservoir, and belongs to the technical field of oil and gas field development. S1, a water body at the edge of a gas reservoir and internal gas wells are equivalent to separate units, and initial control volumes of each unit and between the units are calculated; S2, unit pressures and water contents are calculated, and the control volumes of each unit and between the units are corrected in real time; S3, initial control reserves and corrected control reserves are calculated according to the initial control volumes and the corrected control volumes, so that the remaining reserves and the remaining reserves distribution of the gas reservoir are determined. The application corrects the control volumes of each unit and between the units on the basis of the measured water content data of the gas well and the single-well testing interpretation result data, and on the basis of the gas reservoir engineering method and the intelligent optimization algorithm, so that the remaining reserves and the remaining reserves distribution of the water-bearing gas reservoir are determined, and the technical problem that the remaining reserves recovery efficiency cannot be improved because the natural gas is sealed by the water invasion in the water-bearing gas reservoir, and the sealed natural gas cannot be accurately identified is solved.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development technology, specifically relating to a method for identifying the distribution of remaining reserves in water-bearing gas reservoirs. Background Technology

[0002] For gas reservoirs experiencing water intrusion, the difference in seepage velocities between the gas and water phases, coupled with reservoir heterogeneity, can lead to formation water sealing off natural gas during development. This prevents the extraction of some natural gas, thus impacting the overall recovery rate. Accurately identifying the scale and distribution of remaining reserves is crucial for developing targeted enhanced oil recovery (EOR) strategies, and is of great significance for designing EOR programs for gas reservoirs.

[0003] Currently, most scholars determine the gas reservoir's reserves using analytical methods such as well test analysis and production decline analysis. However, these methods have limitations in determining dynamic reserves. Most analytical methods only consider the situation of a single well, failing to consider the overall gas reservoir and the influence of factors such as inter-well interference and water encroachment from the periphery. Furthermore, the dynamic reserves obtained are only data within the control range of a single well. On the one hand, they cannot accurately determine the overall remaining reserves of the gas reservoir; on the other hand, they cannot accurately determine the distribution location of the remaining reserves, thus hindering the development of targeted strategies to enhance the recovery rate of remaining reserves.

[0004] In summary, current methods for identifying the remaining reserves of water-bearing gas reservoirs after water intrusion all have certain limitations. Therefore, there is an urgent need for a method suitable for identifying the distribution of remaining reserves in water-bearing gas reservoirs. Summary of the Invention

[0005] The purpose of this invention is to provide a method for identifying the distribution of remaining reserves in water-bearing gas reservoirs, which solves the technical problem that water intrusion in water-bearing gas reservoirs causes formation water to seal natural gas, and the sealed natural gas cannot be accurately identified, thus making it impossible to carry out targeted research on the remaining reserves to enhance recovery rate.

[0006] The technical solution adopted in this invention is a method for identifying the distribution of remaining reserves in water-gas reservoirs, which is implemented according to the following steps: S1, treat the water body at the edge of the gas reservoir and the internal gas wells as separate units, and calculate the initial control volume of each unit and between units; S2 calculates the pressure and moisture content of each unit and corrects the control volume of each unit and between units in real time; S3. Calculate the initial controlled reserves and the corrected controlled reserves based on the initial controlled volume and the corrected controlled volume to determine the remaining reserves and distribution of the gas reservoir.

[0007] The invention is further characterized by: S1 specifically involves: equating the water bodies at the edge of the gas reservoir to water body units, equating the gas wells inside the gas reservoir to gas well units, and establishing connectivity between units; calculating the initial control volume of the water body units based on the size of the water bodies at the edge and the number of water body units; calculating the initial control volume of the gas well units based on the gas well control radius obtained from the well test interpretation results; and calculating the initial inter-unit control volume based on the static geological reserves of the gas reservoir and the distance between units.

[0008] The initial control volume of the water element in S1 is calculated as shown in the following formula:

[0009] in, Let m be the volume of water element i at the initial moment. 3 ; Let m be the volume of the water body at the edge. 3 ; The number of discrete water body units, dimensionless; The initial inter-element control volume is calculated in S1 as shown in the following formula:

[0010] in, and To control the volume between water element i and gas well element j in the initial element interval, m 3 ;n well The number of gas well units is dimensionless. h is the average porosity between water element i and gas well element j, dimensionless; ij The effective thickness, in meters, is the distance between water element i and gas well element j. The effective pore volume of the reservoir is m. 3 .

[0011] S2 specifically involves: calculating the pressure of each unit using the mass balance equation, calculating the water content of each unit using the gas-water two-phase motion equation, setting constraints on volume parameters, and using an intelligent fitting algorithm to correct the control volume of each unit and the control volume between units in real time based on the measured water content data of the gas well.

[0012] The mass balance equation in S2 is shown below:

[0013] in, Let be the gas volume coefficient of gas well unit j at time t, which is dimensionless; Let m be the inter-element conductivity between water element i and gas well element j at time t. 3 / (d·MPa); nwell is a gas well unit, dimensionless; Let be the water pressure of water element i at time t, in MPa; Let be the average bottom pressure of gas well unit j at time t, in MPa; Let m be the amount of water intrusion in unit i at time t. 3 / d; Let be the overall compressibility coefficient of the formation at time t, in MPa. -1 ; Let m be the element volume of element i at time t. 3 t represents time, in days; The two-phase motion equations for gas and water in S2 are shown below: , in, The relative permeability of the gas phase is %; The relative permeability of the aqueous phase is %; The volume ratio of water to air, m 3 / m 3 ; The viscosity is the gas phase viscosity, in mPa·s; The volume coefficient for the aqueous phase is m. 3 / m 3 ; The viscosity of the aqueous phase is given in mPa·s. m is the gas phase volume coefficient. 3 / m 3 .

[0014] The constraint in S2 is: the control volume of all elements and between elements is equal to the pore volume of the entire reservoir; the constraint of the method for identifying the distribution of remaining reserves in water-containing gas reservoirs is expressed by the following formula:

[0015] in, Let m be the initial control volume between connected units. 3 .

[0016] S3 specifically involves: calculating the initial controlled reserves and the corrected controlled reserves using the volumetric method based on the calculated initial controlled volume and the corrected controlled volume; and determining the remaining gas reserves and their distribution based on the initial controlled reserves between units and the determined controlled reserves between each unit.

[0017] The remaining gas reserves in S3 are calculated using the following formula:

[0018] in, m represents the remaining water seal capacity between connected units. 3 ; The volumetric method in method S3 for identifying the distribution of remaining reserves in water-bearing gas reservoirs is shown in the following formula:

[0019] in, m is the initial control storage between connected units. 3 ; Let m be the initial control volume between connected units. 3 ; To constrain water saturation, it is dimensionless.

[0020] Compared with the prior art, the beneficial effects of the present invention are: Based on measured water cut data from gas wells and interpretation results from single-well tests, this invention modifies the control volume between units and between units using gas reservoir engineering methods and intelligent optimization algorithms. It determines the remaining reserves and distribution of water-bearing gas reservoirs, solving the technical problem that water intrusion in water-bearing gas reservoirs can seal natural gas, and the sealed natural gas cannot be accurately identified, thus preventing targeted research on improving the recovery rate of remaining reserves. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the method for identifying the distribution of remaining reserves in water-gas reservoirs according to the present invention. Figure 2 This is a schematic diagram of the distribution of edge water body units and gas well units in the water-gas reservoir residual reserve distribution identification method of the present invention; Figure 3 This is a water cut fitting curve of well W1 in Embodiment 6 of the present invention; Figure 4 This is a water cut fitting curve of well W2 in Embodiment 6 of the present invention; Figure 5 This is a water cut fitting curve of well W3 in Embodiment 6 of the present invention; Figure 6 This is a water cut fitting curve of well W4 in Embodiment 6 of the present invention; Figure 7 This is a water cut fitting curve of well W5 in Embodiment 6 of the present invention; Figure 8 This is a water cut fitting curve of well W6 in Embodiment 6 of the present invention; Figure 9 This is a water cut fitting curve of well W7 in Embodiment 6 of the present invention; Figure 10 This is a schematic diagram of the distribution of remaining gas reserves in Embodiment 6 of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] Example 1 like Figure 1 , Figure 2 As shown, the method for identifying the distribution of remaining reserves in water-bearing gas reservoirs disclosed in this embodiment is implemented according to the following steps: S1: The water bodies at the edge of the gas reservoir are equivalent to water body units, and the gas wells inside the gas reservoir are equivalent to gas well units. A connection relationship is established between the units. The initial control volume of the water body unit is calculated based on the size of the water body at the edge and the number of water body units. The initial control volume of the gas well unit is calculated based on the control radius of the gas well obtained from the well test interpretation results. The initial control volume between units is calculated based on the static geological reserves of the gas reservoir and the distance between units. S2: The pressure of each unit is calculated using the material balance equation, the water content of each unit is calculated using the gas-water two-phase motion equation, and the constraints of the volume parameters are set to ensure that the model conforms to the physical meaning of the actual storage space during the water intrusion simulation. Based on the measured water content data of the gas well, the intelligent fitting algorithm is used to correct the control volume of each unit and the control volume between each unit in real time based on the measured water content of the gas well. S3: Based on the calculated initial control volume and the corrected control volume, the volumetric method is used to calculate the initial control reserves and the corrected control reserves; based on the initial control reserves between units and the determined control reserves between each unit, the remaining gas reserves and the distribution of remaining reserves are determined.

[0024] Example 2 Based on Example 1, the initial water unit control volume is calculated in step S1 as shown in the following formula:

[0025] in, Let m be the volume of water element i at the initial moment. 3 ; Let m be the volume of the water body at the edge. 3 ; The number of discrete water body units is dimensionless.

[0026] Furthermore, the initial inter-element control volume is calculated in step S1 as shown in the following formula:

[0027] in, and To control the volume between water element i and gas well element j in the initial element interval, m 3 ;n well The number of gas well units is dimensionless. h is the average porosity between water element i and gas well element j, dimensionless; ij The effective thickness, in meters, is the distance between water element i and gas well element j. The effective pore volume of the reservoir is m. 3 .

[0028] Example 3 Based on Example 1, the mass balance equation in S2 is as follows:

[0029] in, Let be the gas volume coefficient of gas well unit j at time t, which is dimensionless; Let m be the inter-element conductivity between water element i and gas well element j at time t. 3 / (d·MPa); nwell is a gas well unit, dimensionless; Let be the water pressure of water element i at time t, in MPa; Let be the average bottom pressure of gas well unit j at time t, in MPa; Let m be the amount of water intrusion in unit i at time t. 3 / d; Let be the overall compressibility coefficient of the formation at time t, in MPa. -1 ; Let m be the element volume of element i at time t. 3 t represents time, in days.

[0030] Furthermore, the gas-water two-phase motion equation in S2 is shown below: , in, The relative permeability of the gas phase is %; The relative permeability of the aqueous phase is %; The volume ratio of water to air, m 3 / m 3 ; The viscosity is the gas phase viscosity, in mPa·s; The volume coefficient for the aqueous phase is m. 3 / m 3 ; The viscosity of the aqueous phase is given in mPa·s. m is the gas phase volume coefficient. 3 / m 3 .

[0031] Example 4 Based on Example 1, the constraint in S2 is further defined as follows: the control volume of all units and between units is equal to the pore volume of the entire reservoir.

[0032] The constraint condition is expressed by the following formula:

[0033] in, Let m be the initial control volume between connected units. 3 .

[0034] Example 5 Based on Example 1, the calculation of the remaining gas reservoir reserves in step S3 is shown in the following formula:

[0035] in, m represents the remaining water seal capacity between connected units. 3 .

[0036] Furthermore, the volumetric method in S3 is shown in the following equation:

[0037] in, m is the initial control storage between connected units. 3 ; Let m be the initial control volume between connected units. 3 ; To constrain water saturation, it is dimensionless.

[0038] Example 6 Based on Examples 1-5, the following is an application of the present invention's method for identifying the distribution of remaining water gas reservoir reserves to specific examples: Taking a gas reservoir in the Sichuan Basin as an example, the system intelligently identifies the distribution of remaining gas reserves. First, water units and gas well units are set up based on the distribution of formation water at the reservoir's periphery and the distribution of gas wells within the reservoir. Figure 2 As shown. Production data of wells W1-W7 within the gas reservoir from 2015 to 2021 were tracked and recorded. The water cut data of each well in the production data was used as the objective function of the model. The water cut curve of each well was fitted as shown in the figure. Figures 3-9 As shown, the two characteristic parameters of control volume for each well and between units are corrected.

[0039] Furthermore, based on the corrected control volumes of each well and between units, the overall remaining gas reserves distribution of the reservoir can be determined, such as... Figure 10 As shown. According to Figure 10The diagram showing the distribution of remaining reserves indicates that the remaining reserves in well W4 and between W4 and W2, W3, and W5 are relatively large. This suggests that due to severe water intrusion from the northwest of the gas reservoir into the reservoir interior, the remaining water-sealed reserves in this area are substantial. Therefore, it is necessary to propose targeted measures to tap the potential of these remaining reserves, providing a reliable basis for designing enhanced oil recovery schemes for the gas reservoir.

[0040] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0041] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0042] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for identifying the distribution of remaining reserves in water-bearing gas reservoirs, characterized in that, The specific steps are as follows: S1, treat the water body at the edge of the gas reservoir and the internal gas wells as separate units, and calculate the initial control volume of each unit and between units; S2 calculates the pressure and moisture content of each unit and corrects the control volume of each unit and between units in real time; S3. Calculate the initial controlled reserves and the corrected controlled reserves based on the initial controlled volume and the corrected controlled volume to determine the remaining reserves and distribution of the gas reservoir.

2. The method for identifying the distribution of remaining reserves in water-bearing gas reservoirs according to claim 1, characterized in that, Specifically, S1 involves: equating the water bodies at the edge of the gas reservoir to water body units, equating the gas wells inside the gas reservoir to gas well units, and establishing connectivity between the units; calculating the initial control volume of the water body units based on the size of the water bodies at the edge and the number of water body units; calculating the initial control volume of the gas well units based on the gas well control radius obtained from the well test interpretation results; and calculating the initial inter-unit control volume based on the static geological reserves of the gas reservoir and the distance between the units.

3. The method for identifying the distribution of remaining reserves in water-bearing gas reservoirs according to claim 2, characterized in that, The initial control volume of the water body unit is calculated in S1 as shown in the following formula: in, Let m be the volume of water element i at the initial moment. 3 ; Let m be the volume of the water body at the edge. 3 ; The number of discrete water body units, dimensionless; The initial inter-unit control volume is calculated in S1 as shown in the following formula: in, and To control the volume between water element i and gas well element j in the initial element interval, m 3 ;n well The number of gas well units is dimensionless. h is the average porosity between water element i and gas well element j, dimensionless; ij The effective thickness between water element i and gas well element j, in meters; The effective pore volume of the reservoir is m. 3 .

4. The method for identifying the distribution of remaining reserves in water-bearing gas reservoirs according to claim 1, characterized in that, Specifically, S2 involves: calculating the pressure of each unit using the mass balance equation, calculating the water content of each unit using the gas-water two-phase motion equation, setting constraints on volume parameters, and using an intelligent fitting algorithm to correct the control volume of each unit and the control volume between units in real time based on the measured water content data of the gas well.

5. The method for identifying the distribution of remaining reserves in water-bearing gas reservoirs according to claim 4, characterized in that, The mass balance equation in S2 is shown below: in, Let be the gas volume coefficient of gas well unit j at time t, which is dimensionless; Let m be the inter-element conductivity between water element i and gas well element j at time t. 3 / (d·MPa); nwell is a gas well unit, dimensionless; Let be the water pressure of water element i at time t, in MPa; Let be the average bottom pressure of gas well unit j at time t, in MPa; Let m be the amount of water intrusion in unit i at time t. 3 / d; Let be the overall compressibility coefficient of the formation at time t, in MPa. -1 ; Let m be the element volume of element i at time t. 3 t represents time, in days; The two-phase motion equation of gas and water in S2 is shown in the following equation: ， in, The relative permeability of the gas phase is %; The relative permeability of the aqueous phase is %; The volume ratio of water to air, m 3 / m 3 ; The viscosity is the gas phase viscosity, in mPa·s; The volume coefficient for the aqueous phase is m. 3 / m 3 ; The viscosity of the aqueous phase is given in mPa·s. m is the gas phase volume coefficient. 3 / m 3 .

6. The intelligent identification method for the water intrusion front of a water-bearing gas reservoir according to claim 4, characterized in that, The constraint in S2 is that the control volume of all elements and between elements is equal to the pore volume of the entire reservoir; this constraint is expressed by the following formula: in, Let m be the initial control volume between connected units. 3 .

7. The method for identifying the distribution of remaining reserves in water-bearing gas reservoirs according to claim 1, characterized in that, Specifically, S3 involves: calculating the initial controlled reserves and the corrected controlled reserves using the volumetric method based on the calculated initial controlled volume and the corrected controlled volume; and determining the remaining gas reserves and their distribution based on the initial controlled reserves between units and the determined controlled reserves between each unit.

8. The method for identifying the distribution of remaining reserves in water-bearing gas reservoirs according to claim 7, characterized in that, The remaining gas reserves in S3 are calculated using the following formula: in, m represents the remaining water seal capacity between connected units. 3 ; The volumetric method in S3 is shown in the following formula: in, m is the initial control storage between connected units. 3 ; Let m be the initial control volume between connected units. 3 ; To constrain water saturation, it is dimensionless.

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