Method for determining reasonable well spacing of overseas natural gas project gas field

Abstract

The invention discloses a reasonable well spacing determination method for a gas field of an overseas natural gas project. The reasonable well spacing determination method comprises the steps of (1) determining a reasonable technical well spacing, (2) determining an economic well spacing and (3) performing optimal well spacing-comprehensive selection. According to the method, the technical well spacing is determined through the maximum recovery degree chart method, the method can be used in the whole area or other gas fields of the same type only by building a typical well area chart, the method has the advantages of being good in universality and easy and convenient to use, the working efficiency is improved, and the research cost is saved; an overseas natural gas project can obtain as many natural gas resources as possible at the end of the project period, reasonable profits are obtained, the concept of the simulated well spacing is innovatively put forward, a relation chart of the recovery degree and the simulated well spacing of different exploitation age series is obtained through derivation and solving, and meanwhile the method for determining the technical well spacing through the maximum recovery degree is formed. Product division proportion parameters are added into a conventional economic well spacing calculation formula, the economic well spacing in a product division contract mode is obtained, and a reasonable profit economic technical well spacing method is formed.

Description

Technical Field

[0001] The invention belongs to the technical field of carbonate oil and gas reservoir development, and in particular relates to a method for determining a reasonable well spacing of a gas field in an overseas natural gas project. Background Art

[0002] Gas field development generally goes through the capacity construction stage, the natural stable production stage, the development adjustment and pressure-boosting stable production stage, the decline stage, and finally the abandonment. Usually, the distribution of gas wells in the gas field is planned in the capacity construction stage, and the distribution of gas wells is adjusted in the development adjustment stage, including well network improvement and rolling expansion. The key to gas field development is to rationally use the accumulated dynamic and static data of the gas field to layout the gas wells in the gas field to improve the recovery rate and economic benefits of the gas field.

[0003] For integrated gas fields with good connectivity and little difference in physical properties, the scale of gas field construction is usually determined based on the reserve scale and gas production rate, and the number of gas wells required is calculated based on the single well production, thereby determining the reasonable well spacing. Assuming a rectangular gas field with stable gas layer thickness, the required number of wells and well spacing can be calculated according to equations (1) and (2) respectively.

[0004]

[0005]

[0006] In the early stage of gas field development, the number of wells and well spacing calculated by equations (1) and (2) are appropriate, but other influencing factors such as contract life, gas well production decline and other parameters are not considered. Therefore, it is necessary to demonstrate the reasonable technical well spacing from the perspective of the entire project life cycle. The well spacing of a gas field has a great influence on the gas production rate and the stage recovery degree, that is, the smaller the well spacing, the more wells there are, and the higher the recovery degree at the end of the mining period. When the well spacing is small to a certain value, the recovery degree within the contract period reaches the maximum recovery factor value, and even if the well spacing is reduced in time, the cumulative gas production will not increase. For overseas oil and gas projects, if they belong to the product sharing contract (PSC) model, operators often hope to obtain the maximum recovery degree within the contract period.

[0007] When developing a gas field, the well network should consider not only reasonable technical well spacing, but also economic benefit indicators. First, the economic limit well spacing and economic reasonable profit well spacing of the gas field are calculated based on parameters such as drilling, surface engineering, operating fees, natural gas prices, and taxes. The economic limit well spacing is generally used as the lower limit of the development well spacing. Actual natural gas projects often need to consider a certain profit, that is, economic reasonable profit, which can also be considered as the minimum profit indicator. For overseas product sharing contracts, the project sharing ratio must also be considered.

[0008] Therefore, it is an urgent problem for technical personnel in this field to provide a method for determining the reasonable well spacing of gas fields in overseas natural gas projects to maximize the exploitation of natural gas within the remaining exploitation period and ensure reasonable profits. Summary of the invention

[0009] The present invention aims to provide a method for determining reasonable well spacing in gas fields of overseas natural gas projects, establish a method for determining technical well spacing (maximum recovery method and plate method) and an economic well spacing (reasonable profit method) suitable for overseas natural gas projects, and form a comprehensive selection method for the best well spacing based on technical well spacing and economic well spacing.

[0010] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is as follows:

[0011] A method for determining a reasonable well spacing of a gas field in an overseas natural gas project comprises the following steps:

[0012] 1) Determine the reasonable technical well spacing, including the following steps:

[0013] a. According to the exploitation characteristics of natural gas fields, the entire development life cycle is divided into two stages: the stable production period and the decline period. Assuming that the initial production and decline rules of the gas well are basically the same, the functional expression of the recovery degree can be obtained as 1, where the remaining exploitation life t is a variable,

[0014]

[0015] Where: t is the remaining mining life, years; T s is the stable production time, year; L psd is the simulated well spacing, year -1 ;D i is the initial decline rate, a decimal;

[0016] b. According to the average effective thickness, porosity and permeability parameters of the gas field and the physical properties of natural gas, the numerical simulation mechanism model of the typical well area is established using the numerical simulation software Eclipse or CMG, and a series of production scenarios with different well spacings are set to predict the relationship between the future daily gas production and the cumulative gas production and time. Based on the relationship between the future daily gas production and the cumulative gas production and time, T is calculated in the mechanism model. s Stable production time and D i Initial decline rate, calculate the recovery degree according to the cumulative gas production and geological reserves, draw the relationship curve between the actual well spacing and the recovery degree under different remaining mining years, and calculate the simulated well spacing L according to the actual well spacing psd , and calculate the pseudo well spacing L by formula 1 described in step a above psd The relationship between the recovery rate R(t) and the simulated well spacing L is plotted. psd Theoretical diagram of the recovery degree R(t);

[0017] c. In the above step b, the simulated well spacing L psd In the theoretical diagram of the recovery degree R(t), according to the remaining exploitation years of the gas reservoir, find the minimum pseudo-well spacing L corresponding to the maximum recovery degree psd value;

[0018] d. According to the minimum simulated well spacing L described in step c above psd The corresponding actual well spacing is calculated as the reasonable technical well spacing L t ;

[0019] 2) Determine the economic well spacing and calculate the economic limit well spacing L of the gas field min and economically reasonable profit well spacing L a ;

[0020] 3) According to the steps 1) and 2), the reasonable technical well spacing L is obtained. t , Economic limit well spacing L min and reasonable profit well spacing L a Then, determine the optimal well spacing L opt ;

[0021] a. When reasonable technical well spacing L t Greater than reasonable profit well spacing L a Time and economic limit well spacing L min , select reasonable technical well spacing L t As the optimal well spacing L opt ;

[0022] b. When the reasonable technical well spacing L t Less than reasonable profit well spacing L a , greater than the economic limit well spacing L min When selecting a reasonable profit well spacing L a As the optimal well spacing;

[0023] c. When the reasonable technical well spacing L t Less than the economic limit well spacing L min When the gas field is abandoned,

[0024] Furthermore, the pseudo well spacing L in formula 1 in step 1) is psd The definition is shown in formula 2:

[0025]

[0026] Where L is the distance between production wells, m; h is the effective thickness, m; φ is the porosity, decimal; S g is the gas saturation, decimal; η is the comprehensive utilization rate of gas wells, decimal; q g is the average single well production, ×10 4 m 3 / d; B giis the original volume coefficient of natural gas, a decimal.

[0027] Further, in step 1), the pseudo well spacing L is calculated according to the actual well spacing in step b. psd The calculation method is to input the corresponding actual well spacing as the actual well spacing L, the effective thickness of the reservoir in the specific well area, the natural gas compressibility coefficient, the porosity, the gas saturation, the comprehensive utilization rate of the gas well, the single well production and the original volume coefficient of the natural gas in Formula 2 to calculate the simulated well spacing L psd .

[0028] Furthermore, the actual well spacing calculated in step d in step 1) is used as the reasonable technical well spacing L t The calculation method is to enter the minimum simulated well spacing L described in step c of step 1) into formula 2 psd The corresponding actual well spacing L is calculated based on the parameters of the effective reservoir thickness, natural gas compressibility, porosity, gas saturation, comprehensive utilization rate of gas wells, single well production and original volume coefficient of natural gas, as the reasonable technical well spacing L. t .

[0029] Furthermore, step b in step 1) establishes a numerical simulation mechanism model for a typical well area, specifically: 1) establishes a grid model; 2) obtains porosity, effective thickness, and permeability based on geological results to establish an attribute field; 3) inputs PVT parameters, relative permeability curves, and refers to the gas-water interface and pressure; 4) sets up a gas well working system; 5) calculates and predicts production results.

[0030] Furthermore, in step 2), the economic limit well spacing L of the gas field min The calculation method is shown in Equation 3 and Equation 4.

[0031]

[0032]

[0033] Among them: F min , Economic limit well pattern density, mouth / m 2 ; E R , recovery rate, %; α, natural gas commodity rate, %; G, geological reserves of the gas field, ×10 8 m 3 ; T a , gas tax rate, %; P, gas unit price, yuan / m 3 ; O, operation fee, yuan / m 3 ; A, gas-bearing area, m 2 ; I, total investment per well, 10,000 yuan; R, loan interest rate, %; T, evaluation period, years; L min , economic limit well spacing, m.

[0034] Furthermore, in step 2), the economically reasonable profit well spacing L of the gas field a The calculation method is shown in Equation 5 and Equation 6.

[0035]

[0036]

[0037] Among them: F a , Economically reasonable profit well pattern density, mouth / m 3 ; E R , recovery rate, %; α, natural gas commodity rate, %; G, geological reserves of the gas field, ×10 8 m 3 ; T a , gas tax rate, %; P, gas unit price, yuan / m 3 ; O, operation fee, yuan / m 3 ; A, gas-bearing area, m 2 ; I, total investment per well, 10,000 yuan; R, loan interest rate, %; T, evaluation period, years; P sc , project sharing ratio, %; β, reasonable gross profit margin, usually greater than 0.2; L a , reasonable profit well spacing, year -1 .

[0038] Furthermore, the gas reservoirs are classified according to the reservoir permeability. For different types of gas reservoirs, the pseudo-well spacing L is established according to the reservoir type. psd Theoretical graph of the recovery rate R(t).

[0039] Furthermore, the classification is specifically that gas reservoirs with a permeability of more than 50 mD are high permeability gas reservoirs, permeabilities of 5 to 50 mD are medium permeability gas reservoirs, permeabilities of 0.1 to 5 mD are low permeability gas reservoirs, and permeabilities of ≤0.1 mD are tight gas reservoirs.

[0040] Furthermore, if the effective thickness and porosity vary greatly on the plane, the gas field is divided into high-position well area, wing well area and edge well area according to the structure and gas column height to ensure that the effective thickness and porosity in the area are close. Each well area is established with a pseudo well spacing L. psd The theoretical plate calculation of the recovery degree R(t) determines the reasonable well spacing to ensure the pseudo well spacing L in formula 2 psd Representative.

[0041] Beneficial effects of the present invention:

[0042] 1. The present invention adopts the maximum recovery degree plate method to determine the technical well spacing. It only needs to establish a typical well area plate, and it can be used in the whole area or other gas fields of the same type. It has the characteristics of good universality and easy use, improves work efficiency, and saves research costs. Using this method, overseas natural gas projects can obtain as much natural gas resources as possible at the end of the project period and obtain reasonable profits.

[0043] 2. In the present invention, the concept of pseudo-well spacing is innovatively proposed by integrating reserve parameters and production capacity parameters, and the relationship between the recovery degree and pseudo-well spacing of different mining years is derived and solved, forming a method for determining the technical well spacing of the maximum recovery degree. At the same time, the product sharing ratio parameter is added to the conventional economic well spacing calculation formula to obtain the economic well spacing under the product sharing contract model, forming a reasonable profit economic technical well spacing method.

[0044] 3. In the present invention, the gas field development well network not only considers the reasonable technical well spacing, but also the economic benefit index. First, the economic limit well spacing and the economic reasonable profit well spacing of the gas field are calculated according to the parameters such as drilling, surface engineering, operating fees, natural gas prices, and taxes; if the input and output are balanced, the economic limit well network density and the economic limit well spacing are obtained respectively using formula 3 and formula 4, and the economic limit well spacing is generally used as the lower limit of the development well spacing. Actual natural gas projects often need to consider a certain profit, that is, the economic reasonable profit, which can also be considered as the minimum profit index. For overseas product sharing contracts, the project sharing ratio must also be considered, and the reasonable profit well network density and reasonable profit well spacing of overseas natural gas projects are obtained respectively using formula 5 and formula 6.

[0045] 4. In the present invention, when the reasonable technical well spacing L t Greater than reasonable profit well spacing L a When the well spacing is obviously greater than the economic limit, the reasonable technical well spacing L is selected in this case. t As the optimal well spacing L opt , that is, to obtain the maximum recovery degree and obtain greater economic profit; when the reasonable technical well spacing L t Less than reasonable profit well spacing L a When selecting a reasonable profit well spacing L a As the optimal well spacing L opt That is, to ensure that the project has a certain economic profit, part of the recoverable reserves have to be abandoned, and the optimal well spacing is comprehensively selected to form a reasonable profit economic and technical well spacing method. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A graph showing the relationship between future daily gas production and time in Example 1 of the present invention.

[0047] Figure 2 This is a diagram showing the relationship between the simulated well spacing and the degree of recovery in Example 1 of the present invention.

[0048] Figure 3 It is a schematic diagram of the relationship between the economic and technical well spacing intervals of the present invention.

[0049] Figure 4 This is a schematic diagram of the division of the high-position well area, wing well area and edge well area in Example 1 of the present invention.

[0050] Figure 5 This is a graph showing the relationship between the simulated well spacing and the degree of recovery in Examples 2 and 3 of the present invention. DETAILED DESCRIPTION

[0051] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0052] Embodiment 1:

[0053] This embodiment provides a method for determining a reasonable well spacing of a gas field in an overseas natural gas project, comprising the following steps:

[0054] 1) Determine the reasonable technical well spacing, including the following steps:

[0055] a. According to the exploitation characteristics of natural gas fields, the entire development life cycle is divided into the stable production period (stable production time T s ) and the decline period. Assuming that the initial production of the gas well is basically consistent with the decline law, the functional expression of the recovery degree can be obtained as 1, where the remaining mining life t is a variable;

[0056]

[0057] The pseudo well spacing L in Eq. psd The definition is shown in formula 2:

[0058]

[0059] Where: t is the remaining mining life, years; T s is the stable production time, year; L psd is the simulated well spacing, year -1 ;D i is the initial decline rate, decimal; L is the distance between production wells, m; h is the effective thickness, m; φ is the porosity, decimal; S g is the gas saturation, decimal; η is the comprehensive utilization rate of gas wells, decimal; q g is the average single well production, ×10 4 m 3 / d; B gi is the original volume coefficient of natural gas, decimal;

[0060] b. According to the average effective thickness, porosity and permeability parameters of the gas field and the physical properties of natural gas, the numerical simulation mechanism model of the typical well area is established using the numerical simulation software Eclipse or CMG, and a series of production scenarios with different well spacings are set to predict the relationship between the future daily gas production and the cumulative gas production and time. Figure 1 As shown in the figure, T is calculated in the mechanism model based on the relationship between the future daily gas production and cumulative gas production and time. s Stable production time and D i The initial decline rate is shown in Table 1. The recovery degree is calculated based on the cumulative gas production and geological reserves. The relationship curve between the actual well spacing and the recovery degree under different remaining mining years is drawn, and the simulated well spacing L is calculated based on the actual well spacing. psd , and calculate the pseudo well spacing L by formula 1 described in step a above psd The relationship between the recovery rate R(t) and the simulated well spacing L is plotted. psd The theoretical diagram of the recovery degree R(t) is as follows: Figure 2 As shown;

[0061] The pseudo well spacing L is calculated based on the actual well spacing. psd The calculation method is to input the corresponding actual well spacing as the actual well spacing L, the effective thickness of the reservoir in the specific well area, the natural gas compressibility coefficient, the porosity, the gas saturation, the comprehensive utilization rate of the gas well, the single well production and the original volume coefficient of the natural gas in Formula 2 to calculate the simulated well spacing L psd ;

[0062] The specific steps of establishing the numerical simulation mechanism model of a typical well area are as follows: 1) establishing a grid model; 2) obtaining porosity, effective thickness, and permeability based on geological results to establish an attribute field; 3) inputting PVT parameters and relative permeability curves, and referring to the gas-water interface and pressure; 4) setting up the gas well working system; 5) calculating and predicting the production results;

[0063] Table 1 Annual decline rate of production in different well spacing schemes in each year (unit, %)

[0064]

[0065]

[0066] c. In the above step b, the simulated well spacing L psd In the theoretical diagram of the recovery degree R(t), according to the remaining exploitation years of the gas reservoir, find the minimum pseudo-well spacing L corresponding to the maximum recovery degree psd value;

[0067] d. Enter the minimum simulated well spacing L described in step c of step 1) in equation 2 psdThe corresponding actual well spacing L is calculated based on the parameters of the effective reservoir thickness, natural gas compressibility, porosity, gas saturation, comprehensive utilization rate of gas wells, single well production and original volume coefficient of natural gas, as the reasonable technical well spacing L. t .

[0068] 2) Determine the economic well spacing. According to the following formulas 3 to 6, calculate the economic limit well spacing Lmin and the economically reasonable profit well spacing La of the gas field.

[0069]

[0070]

[0071]

[0072]

[0073] Among them: F min , Economic limit well pattern density, mouth / m 2 ; E R , recovery rate, %; α, natural gas commodity rate, %; G, geological reserves of the gas field, ×10 8 m 3 ; T a , gas tax rate, %; P, gas unit price, yuan / m 3 ; O, operation fee, yuan / m 3 ; A, gas-bearing area, m 2 ; I, total investment per well, 10,000 yuan; R, loan interest rate, %; T, evaluation period, years;

[0074] L min , economic limit well spacing, m; F a , Economically reasonable profit well pattern density, mouth / m 3 ;P sc , project sharing ratio, %; β, reasonable gross profit margin, usually greater than 0.2; L a , reasonable profit well spacing, year -1 ;

[0075] 3) Determine the optimal well spacing. Steps 1) and 2) above obtain a reasonable technical well spacing L. t , Economic limit well spacing L min and reasonable profit well spacing L a Finally, a comprehensive comparative analysis is needed to determine the optimal well spacing L for the gas field. opt There are three situations in which the size relationship between reasonable technical well spacing and reasonable profit well spacing exists:

[0076] a. When reasonable technical well spacing L t Greater than reasonable profit well spacing L aWhen the well spacing is obviously greater than the economic limit, the reasonable technical well spacing L is selected in this case. t As the optimal well spacing L opt , that is, to obtain the maximum degree of recovery and obtain greater economic profits;

[0077] b. When the reasonable technical well spacing L t Less than reasonable profit well spacing L a When selecting a reasonable profit well spacing L a As the optimal well spacing L opt , that is, to ensure that the project has a certain economic profit, some recoverable reserves have to be abandoned;

[0078] c. When the reasonable technical well spacing L t Less than the economic limit well spacing L min When the gas field is abandoned,

[0079] In this example, the BP gas field on the right bank of the Amu Darya River was developed with a non-uniform well pattern in the early stage of development. After entering the mid-term development, the gas reservoir reserves were basically confirmed and the development characteristics were deeply understood. In order to give full play to the development potential of the gas field, it is necessary to optimize the existing well pattern. In the western well area of ​​the gas field, research on the evaluation of well pattern densification potential, reasonable well spacing, densification well location deployment and well type optimization was carried out.

[0080] The western block of the gas field is taken as the research object. Figure 4 As shown, the main geological and development parameters include: gas-bearing area A is 66.3km 2 The average effective thickness of the gas layer is 57m, of which the high part is 85m, the wing part is 65m, and the edge part is 40m. The average porosity is 7.0%, and the average gas saturation is S g 60%, permeability 55mD, recovery factor E R The volume coefficient of natural gas at the original pressure is 80%. gi The contract type is a production sharing contract, and the operator has a remaining mining period of 20 years. The average production of a single well is q g 40×10 4 m 3 / d, of which the high part is 50×10 4 m 3 / d, wing 45×10 4 m 3 / d, edge 30×10 4 m 3 / d, gas reservoir engineering demonstration gas production rate of 3.7%, a year is calculated as 365 days, the comprehensive utilization rate of gas wells η is 0.93, production well spacing L is 1900m. The calculation results show that the technical well spacing of the middle and high wells is 1638m, the technical well spacing of the wing wells is 1777m, and the technical well spacing of the edge wells is 1849m.

[0081] Based on the current status of well pattern, formation pressure, remaining reserves and water breakthrough risk assessment, it is believed that the well pattern in the western block of the gas field has the potential to be further improved. Figure 1 The R(t)-Lpsd chart shown in the figure shows that the series corresponding to the 20-year mining period is selected, and the maximum simulated well spacing value corresponding to the maximum recovery degree is 0.18 years. -1 Considering the reserve abundance and gas well productivity of different structural positions, the reasonable technical well spacing of the corresponding structural position is calculated by reverse calculation using the pseudo-well spacing formula as shown in Table 1. According to the relevant economic parameters: the reasonable gross profit rate β is 0.25, the project share ratio P SC The gas unit price P is 1.47 yuan / m 3 , gas tax rate Ta is 15%, loan interest rate R is 6.5%, natural gas commodity rate α is 0.96, evaluation period is the remaining mining period, total investment per well I is 10.03 million yuan and operating fee O is 0.2 yuan / m 3 , the economic limit well spacing was obtained, among which the economic limit well spacing of high-position wells is 443m, the economic limit well spacing of wing wells is 507m, and the economic limit well spacing of edge wells is 646m, and the economically reasonable profit well spacing, among which the economically reasonable profit well spacing of high-position wells is 736m, the economically reasonable profit well spacing of wing wells is 841m, and the economically reasonable profit well spacing of edge wells is 1072m.

[0082] According to the optimal well spacing determination principle, Figure 3 As shown in (a), the optimal well spacing in Example 1 is 1638m at the high part, 1777m at the wing part, and 1840m at the edge part, as shown in Table 2.

[0083] Table 2 Summary of optimal well spacing in Example 1

[0084]

[0085] Embodiment 2:

[0086] This embodiment provides a method for determining a reasonable well spacing of a gas field in an overseas natural gas project, comprising the following steps:

[0087] 1) Determine the reasonable technical well spacing, including the following steps:

[0088] a. According to the exploitation characteristics of natural gas fields, the entire development life cycle is divided into the stable production period (stable production time T s ) and the decline period. Assuming that the initial production of the gas well is basically consistent with the decline law, the functional expression of the recovery degree can be obtained as 1, where the remaining mining life t is a variable;

[0089]

[0090] The pseudo well spacing L in Eq.psd The definition is shown in formula 2:

[0091]

[0092] Where: t is the remaining mining life, years; T s is the stable production time, year; L psd is the simulated well spacing, year -1 ;D i is the initial decline rate, decimal; L is the distance between production wells, m; h is the effective thickness, m; φ is the porosity, decimal; S g is the gas saturation, decimal; η is the comprehensive utilization rate of gas wells, decimal; q g is the average single well production, ×10 4 m 3 / d; B gi is the original volume coefficient of natural gas, decimal;

[0093] b. According to the average effective thickness, porosity and permeability parameters of the gas field and the physical properties of natural gas, the numerical simulation mechanism model of the typical well area is established using the numerical simulation software Eclipse or CMG, and a series of production scenarios with different well spacings are set to predict the relationship between the future daily gas production and the cumulative gas production and time. Based on the relationship between the future daily gas production and the cumulative gas production and time, T is calculated in the mechanism model. s Stable production time and D i Initial decline rate, calculate the recovery degree according to the cumulative gas production and geological reserves, draw the relationship curve between the actual well spacing and the recovery degree under different remaining mining years, and calculate the simulated well spacing L according to the actual well spacing psd , and calculate the pseudo well spacing L by formula 1 described in step a above psd The relationship between the recovery rate R(t) and the simulated well spacing L is plotted. psd The theoretical diagram of the recovery degree R(t) is as follows: Figure 5 As shown;

[0094] The pseudo well spacing L is calculated based on the actual well spacing. psd The calculation method is to input the corresponding actual well spacing as the actual well spacing L, the effective thickness of the reservoir in the specific well area, the natural gas compressibility coefficient, the porosity, the gas saturation, the comprehensive utilization rate of the gas well, the single well production and the original volume coefficient of the natural gas in Formula 2 to calculate the simulated well spacing L psd ;

[0095] The specific steps of establishing the numerical simulation mechanism model of a typical well area are as follows: 1) establishing a grid model; 2) obtaining porosity, effective thickness, and permeability based on geological results to establish an attribute field; 3) inputting PVT parameters and relative permeability curves, and referring to the gas-water interface and pressure; 4) setting up the gas well working system; 5) calculating and predicting the production results;

[0096] c. In the above step b, the simulated well spacing L psd In the theoretical diagram of the recovery degree R(t), according to the remaining exploitation years of the gas reservoir, find the minimum pseudo-well spacing L corresponding to the maximum recovery degree psd value;

[0097] d. Enter the minimum simulated well spacing L described in step c of step 1) in equation 2 psd The corresponding actual well spacing L is calculated based on the parameters of the effective reservoir thickness, natural gas compressibility, porosity, gas saturation, comprehensive utilization rate of gas wells, single well production and original volume coefficient of natural gas, as the reasonable technical well spacing L. t .

[0098] 2) Determine the economic well spacing. According to the following formulas 3 to 6, calculate the economic limit well spacing Lmin and the economically reasonable profit well spacing La of the gas field.

[0099]

[0100]

[0101]

[0102]

[0103]

[0104] Among them: F min , Economic limit well pattern density, mouth / m 2 ; E R , recovery rate, %; α, natural gas commodity rate, %; G, geological reserves of the gas field, ×10 8 m 3 ; T a , gas tax rate, %; P, gas unit price, yuan / m 3 ; O, operation fee, yuan / m 3 ; A, gas-bearing area, m 2 ; I, total investment per well, 10,000 yuan; R, loan interest rate, %; T, evaluation period, years;

[0105] L min , economic limit well spacing, m; F a , Economically reasonable profit well pattern density, mouth / m 3 ;P sc , project share ratio, %;

[0106] β, reasonable gross profit margin, usually greater than 0.2; L a , reasonable profit well spacing, year -1 ;

[0107] 3) Determine the optimal well spacing. Steps 1) and 2) above obtain a reasonable technical well spacing L. t , Economic limit well spacing L min and reasonable profit well spacing L a Finally, a comprehensive comparative analysis is needed to determine the optimal well spacing L for the gas field. opt There are three situations in which the size relationship between reasonable technical well spacing and reasonable profit well spacing exists:

[0108] a. When reasonable technical well spacing L t Greater than reasonable profit well spacing L a When the well spacing is obviously greater than the economic limit, the reasonable technical well spacing L is selected in this case. t As the optimal well spacing L opt , that is, to obtain the maximum degree of recovery and obtain greater economic profits;

[0109] b. When the reasonable technical well spacing L t Less than reasonable profit well spacing L a When selecting a reasonable profit well spacing L a As the optimal well spacing L opt , that is, to ensure that the project has a certain economic profit, some recoverable reserves have to be abandoned;

[0110] c. When the reasonable technical well spacing L t Less than the economic limit well spacing L min When the gas field is abandoned,

[0111] In this example, the gas field permeability is 4.5mD, and the effective reservoir thickness is 20m. For this type of low permeability gas reservoir, a chart is established as follows: Figure 4 As shown, the remaining mining life is 7 years, and the other parameters are the same as those in Example 1;

[0112] This embodiment determines the reasonable well spacing of the gas field using the same method as in Embodiment 1.

[0113] In such Figure 5 The R(t)-Lpsd chart shown in the figure shows that the series corresponding to the mining period of 7 years is selected, and the maximum simulated well spacing value corresponding to the maximum recovery degree is 0.032 years. -1 The reasonable technical well spacing of the corresponding structural position is 1097m by reverse calculation using the pseudo well spacing formula. According to the relevant economic parameters: reasonable gross profit rate is 0.25, project share ratio is 60%, and gas unit price is 1.47 yuan / m 3 , gas tax rate 15%, loan interest rate 6.5%, total investment per well 10.03 million yuan and operating fee 0.2 yuan / m 3 , the economic limit well spacing is 745m and the economic reasonable profit well spacing is 1236m.

[0114] According to the optimal well spacing determination principle, Figure 3(b) shows that the optimal well spacing for Example 2 is 1236 m as shown in Table 3.

[0115] Table 3 Summary of optimal well spacing in Example 2

[0116]

[0117] Embodiment 3:

[0118] This embodiment provides a method for determining a reasonable well spacing of a gas field in an overseas natural gas project. The difference from Embodiment 2 is that in this embodiment, the remaining mining period in Embodiment 2 is increased to 15 years through negotiation. This embodiment determines the reasonable well spacing of a gas field in the same manner as Embodiment 2.

[0119] In such Figure 5 The R(t)-Lpsd chart shown in the figure shows that the series corresponding to the 15-year mining period is selected, and the maximum simulated well spacing value corresponding to the maximum recovery degree is 0.096 years. -1 The reverse calculation using the pseudo well spacing formula yields a reasonable technical well spacing of 1899m for the corresponding structural position, an economic limit well spacing of 845m, and an economically reasonable profit well spacing of 1401m.

[0120] According to the optimal well spacing determination principle, Figure 3 As shown in (a), the optimal well spacing for Example 3 is 1899 m as shown in Table 4.

[0121] Table 4 Summary of optimal well spacing in Example 3

[0122]

[0123] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A method for determining reasonable well spacing of gas fields in overseas natural gas projects, characterized by: The following steps are included: 1) Determine the reasonable technical well spacing, including the following steps: a. According to the exploitation characteristics of natural gas fields, the entire development life cycle is divided into two stages: the stable production period and the decline period. Assuming that the initial production and decline rules of the gas well are basically the same, the functional expression of the recovery degree can be obtained as 1, where the remaining exploitation life t is a variable, Where: t is the remaining mining life, years; T s is the stable production time, year; L psd is the simulated well spacing, year -1 ;D i is the initial decline rate, a decimal; b. According to the average effective thickness, porosity and permeability parameters of the gas field and the physical properties of natural gas, the numerical simulation mechanism model of the typical well area is established using the numerical simulation software Eclipse or CMG, and a series of production scenarios with different well spacings are set to predict the relationship between the future daily gas production and the cumulative gas production and time. Based on the relationship between the future daily gas production and the cumulative gas production and time, T is calculated in the mechanism model. s Stable production time and D i Initial decline rate, calculate the recovery degree according to the cumulative gas production and geological reserves, draw the relationship curve between the actual well spacing and the recovery degree under different remaining mining years, and calculate the simulated well spacing L according to the actual well spacing psd , and calculate the pseudo well spacing L by formula 1 described in step a above psd The relationship between the recovery rate R(t) and the simulated well spacing L is plotted. psd Theoretical diagram of the recovery degree R(t); c. In the above step b, the simulated well spacing L psd In the theoretical diagram of the recovery degree R(t), according to the remaining exploitation years of the gas reservoir, find the minimum pseudo-well spacing L corresponding to the maximum recovery degree psd value; d. According to the minimum simulated well spacing L described in step c above psd The corresponding actual well spacing is calculated as the reasonable technical well spacing L t ; 2) Determine the economic well spacing, calculate the economic limit well spacing Lmin and the economically reasonable profit well spacing L a ; 3) According to the steps 1) and 2), the reasonable technical well spacing L is obtained. t , Economic limit well spacing L min and reasonable profit well spacing L a Then, determine the optimal well spacing L opt ; a. When reasonable technical well spacing L t Greater than reasonable profit well spacing L a Time and economic limit well spacing L min , select reasonable technical well spacing L t As the optimal well spacing L opt ; b. When the reasonable technical well spacing L t Less than reasonable profit well spacing L a , greater than the economic limit well spacing L min When selecting a reasonable profit well spacing L a As the optimal well spacing; c. When the reasonable technical well spacing L t Less than the economic limit well spacing L min When the gas field is abandoned, 2. The determination method according to claim 1, characterized in that: The pseudo well spacing L in formula 1 psd Defined as Equation 2 Where L is the distance between production wells, m; h is the effective thickness, m; φ is the porosity, decimal; S g is the gas saturation, decimal; η is the comprehensive utilization rate of gas wells, decimal; q g is the average single well production, ×10 4 m 3 / d; B gi is the original volume coefficient of natural gas, a decimal.

3. The determination method according to claim 2, characterized in that: In step 1), the pseudo well spacing L is calculated according to the actual well spacing in step b. psd The calculation method is to input the corresponding actual well spacing as the actual well spacing L, the effective thickness of the reservoir in the specific well area, the natural gas compressibility coefficient, the porosity, the gas saturation, the comprehensive utilization rate of the gas well, the single well production and the original volume coefficient of the natural gas in Formula 2 to calculate the simulated well spacing L psd .

4. The determination method according to claim 2, characterized in that: In step 1), the actual well spacing is calculated as the reasonable technical well spacing L in step d. t The calculation method is to enter the minimum simulated well spacing L described in step c of step 1) into formula 2 psd The corresponding actual well spacing L is calculated based on the parameters of the effective reservoir thickness, natural gas compressibility, porosity, gas saturation, comprehensive utilization rate of gas wells, single well production and original volume coefficient of natural gas, as the reasonable technical well spacing L. t .

5. The determination method according to claim 1, characterized in that: Step b in step 1) of establishing a numerical simulation mechanism model for a typical well area is specifically as follows: 1) establishing a grid model; 2) obtaining porosity, effective thickness, and permeability based on geological results to establish an attribute field; 3) inputting PVT parameters and relative permeability curves, and referring to the gas-water interface and pressure; 4) setting a gas well working system; and 5) calculating and predicting production results.

6. The determination method according to claim 1, characterized in that: The calculation method of the economic limit well spacing Lmin of the gas field in step 2) is shown in Formula 3 and Formula 4: Among them: F min , Economic limit well pattern density, mouth / m 2 ; E R , recovery rate, %; α, natural gas commodity rate, %; G, geological reserves of the gas field, ×10 8 m 3 ; T a , gas tax rate, %; P, gas unit price, yuan / m 3 ; O, operation fee, yuan / m 3 ; A, gas-bearing area, m 2 ; I, total investment per well, 10,000 yuan; R, loan interest rate, %; T, evaluation period, years; L min , economic limit well spacing, m.

7. The determination method according to claim 1, characterized in that: The method for calculating the economically reasonable profit well spacing La of the gas field in step 2) is shown in Formulas 5 and 6. Among them: F a , Economically reasonable profit well pattern density, mouth / m 3 ; E R , recovery rate, %; α, natural gas commodity rate, %; G, geological reserves of the gas field, ×10 8 m 3 ; T a , gas tax rate, %; P, gas unit price, yuan / m 3 ; O, operation fee, yuan / m 3 ; A, gas-bearing area, m 2 ; I, total investment per well, 10,000 yuan; R, loan interest rate, %; T, evaluation period, years; P sc , project sharing ratio, %; β, reasonable gross profit margin, usually greater than 0.2; L a , reasonable profit well spacing, year -1 .

8. The determination method according to claim 1, characterized in that: Gas reservoirs are classified according to reservoir permeability. For different types of gas reservoirs, the pseudo-well spacing L is established according to reservoir type. psd Theoretical graph of recovery rate R(t).

9. The determination method according to claim 8, characterized in that: The classification is specifically that gas reservoirs with a permeability of more than 50 mD are high permeability gas reservoirs, those with a permeability of 5 to 50 mD are medium permeability gas reservoirs, those with a permeability of 0.1 to 5 mD are low permeability gas reservoirs, and those with a permeability of ≤0.1 mD are tight gas reservoirs.

10. The determination method according to claim 1, characterized in that: According to the structure and gas column height, the gas field is divided into high-position well area, wing well area and edge well area to ensure that the effective thickness and porosity in the area are close. Each well area is established with a simulated well spacing L psd The theoretical plate calculation of the recovery degree R(t) determines the reasonable well spacing to ensure the pseudo well spacing L in formula 2 psd Representative.

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