A method for determining reasonable well spacing of a gas field in an overseas natural gas project

Abstract

The application discloses a kind of overseas natural gas project gas field reasonable well spacing determination method, including 1) determining reasonable technical well spacing, 2) determining economic well spacing, 3) best well spacing-comprehensive selection;In the application, technical well spacing is determined by using maximum recovery degree chart method, only need to establish typical well area chart, can be used in whole area or other same type gas field, with the characteristics of good universality, easy to use, improve work efficiency, save research cost, using the method, overseas natural gas project can obtain as many natural gas resources as possible at the end of project period, and obtain reasonable profit, innovation proposes the concept of tentative well spacing, deduces and solves to obtain the recovery degree and tentative well spacing relationship chart of different exploitation period series, forms the maximum recovery degree determination technical well spacing method, simultaneously, join product sharing proportion parameter in conventional economic well spacing calculation formula, obtain economic well spacing under product sharing contract mode, form reasonable profit economic technical well spacing method.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbonate rock oil and gas reservoir development, and particularly relates to a method for determining a reasonable well spacing of a gas field in an overseas natural gas project. BACKGROUND

[0002] A gas field development generally experiences a capacity construction stage, a natural stable production stage, a development adjustment and pressure boosting stable production stage, a decline stage, and is abandoned until the end. 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 pattern perfection and rolling extension. Reasonable use of accumulated dynamic and static data of the gas field for the layout of the gas wells in the gas field becomes a key to the development of the gas field to improve the recovery ratio and economic benefits of the gas field.

[0003] For a whole gas field with good connectivity and little difference in physical properties, the gas field capacity construction scale is determined according to the reserve scale and the gas production rate, and the required number of gas wells is calculated according to the single well production, so as to determine 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 formula (1) and formula (2) respectively.

[0004]

[0005]

[0006] The number of wells and well spacing calculated by formula (1) and formula (2) are appropriate at the initial stage of the gas field development, but other influencing factors such as contract period, gas well production decline and the like are not considered. Therefore, it is necessary to demonstrate the reasonable technical well spacing from the perspective of the whole project life cycle. The well spacing of the gas field has a great influence on the gas production rate and the stage recovery ratio, that is, the smaller the well spacing, the more the number of wells, and the higher the recovery ratio at the end of the production period. When the well spacing is small to a certain value, the recovery ratio in the contract period reaches the maximum recovery ratio, and timely reducing the well spacing will not increase the cumulative gas production. For an overseas oil and gas project, if it belongs to the product sharing contract (PSC) mode, the operator often hopes to obtain the maximum recovery ratio in the contract period.

[0007] The well pattern of the gas field development also considers the economic benefit index while considering the reasonable technical well spacing. First, the economic limit well spacing and the economic reasonable profit well spacing of the gas field are calculated according to the drilling, surface engineering, operation cost, natural gas price, tax and the like. The economic limit well spacing is generally used as the lower limit of the development well spacing, and the actual natural gas project often needs to consider a certain profit, that is, the economic reasonable profit, which can also be regarded as the minimum profit index. For an overseas product sharing contract, the project sharing ratio also needs to be considered.

[0008] Therefore, providing a method for determining a reasonable well spacing of a gas field of an overseas natural gas project to maximize the exploitation of natural gas within a remaining exploitation period and ensure reasonable profits is an urgent problem for those skilled in the art. SUMMARY

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

[0010] In order to achieve the above-mentioned application purposes, the technical solutions of the present application are as follows:

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

[0012] 1) determining a reasonable technical well spacing, comprising the following steps:

[0013] a. According to the exploitation characteristics of the gas field, dividing the entire exploitation life cycle into two stages of a stable production period and a decline period, assuming that the initial production of the gas well and the decline law are basically consistent, and obtaining a function expression 1 of the recovery degree, wherein the remaining exploitation period t is a variable,

[0014]

[0015] wherein: t is the remaining exploitation period, years; T s is the stable production time, years; L psd is the pseudo well spacing, years -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, using the numerical simulation software Eclipse or CMG, establishing a numerical simulation mechanism model of a typical well area, setting a series of exploitation scenarios of different well spacings, predicting the relationship between the future daily gas production and the cumulative gas production and time, and calculating the T s stable production time and D i initial decline rate in the mechanism model according to the relationship between the future daily gas production and the cumulative gas production and time, calculating the recovery degree according to the cumulative gas production and the geological reserves, drawing a relationship curve of the actual well spacing and the recovery degree under different remaining exploitation periods, and calculating the pseudo well spacing L psd according to the actual well spacing, and calculating the pseudo well spacing L psd and the recovery degree R(t) through the formula 1 in the above step a. psd Draw a theoretical chart of the pseudo well spacing L

[0017] c. In the above step b, the pseudo well spacing L psd is found in the theoretical chart of the recovery factor R(t) according to the remaining exploitation years of the gas reservoir, and the minimum pseudo well spacing L psd value corresponding to the maximum recovery factor is selected.

[0018] d. The minimum pseudo well spacing L psd value calculated in the above step c is used to calculate the corresponding real well spacing as the reasonable technical well spacing L t .

[0019] 2) Determine the economic well spacing, calculate the economic limit well spacing L min and the economic reasonable profit well spacing L a .

[0020] 3) After obtaining the reasonable technical well spacing L t , the economic limit well spacing L min and the reasonable profit well spacing L a according to the above steps 1) and 2), determine the optimal well spacing L opt .

[0021] a. When the reasonable technical well spacing L t is greater than the reasonable profit well spacing L a and the economic limit well spacing L min , select the reasonable technical well spacing L t as the optimal well spacing L opt .

[0022] b. When the reasonable technical well spacing L t is less than the reasonable profit well spacing L a and greater than the economic limit well spacing L min , select the reasonable profit well spacing L a as the optimal well spacing.

[0023] c. When the reasonable technical well spacing L t is less than the economic limit well spacing L min , select to abandon the gas field.

[0024] Further, the pseudo well spacing L psd in formula 1 in the above step 1) is defined as shown in formula 2:

[0025]

[0026] Wherein, L is the production well spacing, 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 well, decimal; q g is the average single well production, ×10 4 m 3 / d; B giThis is the original volume factor of natural gas, a decimal.

[0027] Furthermore, in step 1), step b involves calculating the proposed well spacing L based on the actual well spacing. psd The calculation method is as follows: input the parameters corresponding to the actual well spacing (L), the effective thickness of the reservoir in the specific well area, the natural gas compressibility coefficient, porosity, gas saturation, comprehensive utilization rate of gas wells, single-well production, and the original volume factor of natural gas into Equation 2, and calculate the proposed well spacing L. psd .

[0028] Furthermore, in step 1), step d, calculating the actual well spacing is used as the reasonable technical well spacing L. t The calculation method is as follows: input the minimum pseudo-well spacing L mentioned in step c of step 1) into Equation 2. psd The parameters, including the effective reservoir thickness in the specific well area, natural gas compressibility coefficient, porosity, gas saturation, comprehensive utilization rate of gas wells, single-well production, and original volume factor of natural gas, are used to calculate the corresponding actual well spacing L as the reasonable technical well spacing L. t .

[0029] Furthermore, step b in step 1) of establishing a numerical simulation mechanism model for a typical well area specifically involves: 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, relative permeability curves, and referencing the gas-water interface and pressure; 4) setting the gas well operating regime; and 5) calculating and predicting production results.

[0030] Furthermore, in step 2), the economically limited well spacing L of the gas field... min The calculation methods are shown in Equations 3 and 4.

[0031]

[0032]

[0033] Wherein: F min Economic limit well density, wells per m 2 E R Recovery rate, %; α, natural gas commercialization rate, %; G, geological reserves of the gas field, ×10 8 m 3 ;T a Gas tax rate, %; P, gas unit price, yuan / m³ 3 O, Operation fee, yuan / m 3 A, gas-bearing area, m 2 I, Total investment per well, in ten thousand yuan; R, Loan interest rate, %; T, Evaluation period, in years; L min Economic limit well spacing, m.

[0034] Further, the step 2) is the economic reasonable profit well spacing L a The calculation method is shown in formula 5 and formula 6.

[0035]

[0036]

[0037] Wherein: F a , economic reasonable profit well spacing, m 3 ; E R , recovery, %; alpha, natural gas commodity rate, %; G, geological reserves of the gas field, x10 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 of single well, ten thousand yuan; R, loan interest rate, %; T, evaluation period, years; P sc , project sharing ratio, %; beta, reasonable gross profit margin, generally greater than 0.2; L a , reasonable profit well spacing, years -1 .

[0038] Further, the gas reservoir is classified according to reservoir permeability, and for different types of gas reservoirs, the pseudo well spacing L psd and the theoretical chart of recovery degree R(t) are established according to reservoir types.

[0039] Further, the classification is that the gas reservoir with reservoir permeability greater than 50 mD is a high-permeability gas reservoir, the gas reservoir with reservoir permeability of 5-50 mD is a medium-permeability gas reservoir, the gas reservoir with reservoir permeability of 0.1-5 mD is a low-permeability gas reservoir, and the gas reservoir with reservoir permeability less than or equal to 0.1 mD is a tight gas reservoir.

[0040] Further, if the difference of effective thickness and porosity is large on the plane, the gas field is divided into high-position well area, wing well area and edge well area according to structure and gas column height, the effective thickness and porosity in the area are ensured to be close, and the pseudo well spacing L psd and the theoretical chart of recovery degree R(t) are established to calculate and determine the reasonable well spacing, and the pseudo well spacing L psd in formula 2 is representative.

[0041] The beneficial effects of the present application are as follows:

[0042] 1. The maximum recovery degree chart method is used to determine the technical well spacing in the application, only a typical well area chart needs to be established, and the method can be used in the whole area or other same type gas fields, has the characteristics of good universality and simple use, improves the work efficiency, saves the research cost, and using the method, the overseas natural gas project can obtain as much natural gas resources as possible at the end of the project period and reasonable profits.

[0043] 2. In the application, the concept of pseudo well spacing is proposed by comprehensively considering the reserve parameters and production capacity parameters, a recovery degree and pseudo well spacing relationship chart of different production years is derived and solved, and the maximum recovery degree determination technical well spacing method is formed. Meanwhile, the product sharing ratio parameter is added in the conventional economic well spacing calculation formula to obtain the economic well spacing under the product sharing contract mode, and the reasonable profit economic technical well spacing method is formed.

[0044] 3. In the application, the gas field development well pattern needs to consider the reasonable technical well spacing and economic benefit index. Firstly, the economic limit well spacing and economic reasonable profit well spacing are calculated according to the drilling, ground engineering, operation cost, natural gas price, tax and other parameters; if the input and output are balanced, the economic limit well pattern density and economic limit well spacing are obtained by using formula 3 and formula 4 respectively, and the economic limit well spacing is generally used as the lower limit of the development well spacing. The actual natural gas project often needs to consider a certain profit, that is, the economic reasonable profit, which can also be regarded as the minimum profit index. For the overseas product sharing contract, the project sharing ratio also needs to be considered, and the reasonable profit well pattern density and reasonable profit well spacing of the overseas natural gas project are obtained by using formula 5 and formula 6 respectively.

[0045] 4. In the application, when the reasonable technical well spacing L t is greater than the reasonable profit well spacing L a , it is obviously greater than the economic limit well spacing, and in this case, the reasonable technical well spacing L t is selected as the optimal well spacing L opt , that is, the maximum recovery degree can be obtained, and the economic profit is also greater; when the reasonable technical well spacing L t is less than the reasonable profit well spacing L a , the reasonable profit well spacing L a is selected as the optimal well spacing L opt , that is, the economic profit of the project is ensured, and a part of the recoverable reserves needs to be abandoned, and the optimal well spacing is comprehensively selected, and the reasonable profit economic technical well spacing method is formed. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 The future daily gas production and time relationship chart of the embodiment 1 of the application.

[0047] Figure 2 It is the pseudo well spacing and recovery degree relationship chart of the embodiment 1 of the application.

[0048] Figure 3 Economic and technical well spacing interval relationship diagram of the present application.

[0049] Figure 4 Partition diagram of high position well area, wing well area and edge well area of Example 1 of the present application.

[0050] Figure 5 Pseudo well spacing and recovery degree relationship chart of Examples 2 and 3 of the present application. DETAILED DESCRIPTION

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

[0052] Example 1

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

[0054] 1) determining reasonable technical well spacing, comprising the following steps,

[0055] a. According to the exploitation characteristics of the natural gas field, the entire development life cycle is divided into two stages of stable production period (stable production time T s ) and decline period. Assuming that the initial production of gas wells and the decline law are basically consistent, the function expression 1 of recovery degree can be obtained, wherein the remaining exploitation time t is the variable;

[0056]

[0057] The pseudo well spacing L psd in expression 1 is defined as expression 2:

[0058]

[0059] Wherein: t is the remaining exploitation time, years; T s is the stable production time, years; L psd is the pseudo well spacing, years -1 ; D i is the initial decline rate, decimal; L is the production well spacing, 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 and the physical properties of natural gas of the gas field, a numerical simulation mechanism model of a typical well area is established by using numerical simulation software Eclipse or CMG, a series of different well spacing exploitation scenarios are set, the future daily gas production and cumulative gas production and time relationship are predicted as shown in Figure 1 , and T s , stable production time and D i The initial decline rate is shown in Table 1, the recovery degree is calculated according to the cumulative gas production and the geological reserves, the relationship curves of the actual well spacing and the recovery degree under different remaining exploitation years are drawn, and the pseudo well spacing L psd is calculated according to the actual well spacing. psd The pseudo well spacing L psd and the recovery degree R(t) are calculated according to the above-mentioned formula 1. psd The theoretical chart of the pseudo well spacing L psd and the recovery degree R(t) is shown in Figure 2 .

[0061] The pseudo well spacing L psd is calculated according to the actual well spacing. psd The calculation method is that the corresponding actual well spacing is input as the true well spacing L, the parameters of the specific well area reservoir effective thickness, natural gas compressibility, porosity, gas saturation, gas well comprehensive utilization rate, single well production and natural gas original volume coefficient in formula 2, and the pseudo well spacing L psd is calculated.

[0062] The establishment of the numerical simulation mechanism model of the typical well area is specifically as follows: 1) establishing a grid model; 2) establishing an attribute field according to the porosity, effective thickness and permeability obtained from the geological results; 3) inputting PVT parameters and relative permeability curves, referring to the gas-water interface and pressure; 4) setting the gas well working system; 5) operating and predicting the production results.

[0063] Table 1 Yearly production decline rate of different well spacing schemes (unit, %)

[0064]

[0065]

[0066] c. In the theoretical chart of the pseudo well spacing L psd and the recovery degree R(t) described in step b above, according to the remaining exploitation years of the gas reservoir, the minimum pseudo well spacing L psd corresponding to the maximum recovery degree is found.

[0067] d. The minimum pseudo well spacing L psdThe parameters of the real well spacing L are calculated by back calculation according to the parameters of the real well spacing L, the specific well area reservoir effective thickness, the natural gas compression coefficient, the porosity, the gas saturation, the comprehensive utilization rate of the gas well, the single well production and the natural gas original volume coefficient t .

[0068] 2) Determining the economic well spacing, calculating the economic limit well spacing Lmin and the economic reasonable profit well spacing La according to the following formulas 3-6,

[0069]

[0070]

[0071]

[0072]

[0073] Wherein: F min , the economic limit well spacing density, well / m 2 ; E R , the recovery rate, %; a, the natural gas commodity rate, %; G, the geological reserves of the gas field, ×10 8 m 3 ; T a , the gas tax rate, %; P, the gas unit price, yuan / m 3 ; O, the operation fee, yuan / m 3 ; A, the gas-bearing area, m 2 ; I, the total investment of single well, ten thousand yuan; R, the loan interest rate, %; T, the evaluation period, years;

[0074] L min , the economic limit well spacing, m; F a , the economic reasonable profit well spacing density, well / m 3 ; P sc , the project proportion, %; β, the reasonable gross profit rate, usually greater than 0.2; L a , the reasonable profit well spacing, years -1 ;

[0075] 3) Determining the optimal well spacing, after the reasonable technical well spacing L t , the economic limit well spacing L min and the reasonable profit well spacing L a are obtained by the step 1) and the step 2), it is necessary to determine the optimal well spacing L opt of the gas field by comprehensive comparison and analysis; there are three cases for the size relationship between the reasonable technical well spacing and the reasonable profit well spacing:

[0076] a, when the reasonable technical well spacing L t is greater than the reasonable profit well spacing L aAt this time, it is obviously greater than the economic limit well spacing. In this case, a reasonable technical well spacing L should be selected. t As the optimal well spacing L opt This will allow for maximum extraction and also generate substantial economic profits.

[0077] b. When the reasonable technical well spacing L t Less than the reasonable profit well spacing L a At that time, select a reasonable profit well spacing L a As the optimal well spacing L opt To ensure that the project has a certain economic profit, it is necessary to give up a portion of recoverable reserves.

[0078] c. When the reasonable technical well spacing L t Less than the economic limit well spacing L min At that time, they chose to abandon the gas field.

[0079] In this embodiment, the BP gas field on the right bank of the Amu Darya River initially adopted a non-uniform well pattern development approach. Entering the mid-stage of development, the gas reservoir reserves were largely determined, and the development characteristics were better understood. To fully realize the gas field's development potential, it was necessary to optimize the existing well pattern. Research was conducted in the western well area of ​​the gas field on well pattern infill drilling potential evaluation, reasonable well spacing, infill well location deployment, and well type optimization.

[0080] Taking the western block of the gas field as the research object, for example Figure 4 As shown, the main geological and development parameters include: gas-bearing area A is 66.3 km². 2 The average effective thickness h of the gas layer is 57m, with 85m at the high point, 65m at the flanks, and 40m at the edges. The average porosity φ is 7.0%, and the average gas saturation S is... g The recovery rate is 60%, the permeability is 55 mD, and the oil recovery rate is E. R The volume factor of natural gas at its original pressure is 80%. gi The value is 0.0031. The contract type is a production sharing contract, and the remaining mining term of the operator's contract is 20 years. The average production per well is q. g 40×10 4 m 3 / d, where the high part is 50×10 4 m 3 / d, wing 45×10 4 m 3 / d, edge 30×10 4 m 3 / d, with a gas production rate of 3.7% in the gas reservoir engineering demonstration, and calculated based on 365 days per year, the comprehensive utilization rate η of gas wells is 0.93, and the production well spacing L is 1900m. The calculation results show that the technical well spacing of wells in the middle and high parts is 1638m, the technical well spacing of wells in the wing is 1777m, and the technical well spacing of wells in the edge is 1849m.

[0081] Based on the current well network status, formation pressure, remaining reserves, and water breakthrough risk assessment results, it is believed that the well network in the western block of this gas field has the potential for further improvement. Figure 1 The R(t)-Lpsd chart shown here corresponds to a series with a production life of 20 years, and the maximum simulated well spacing corresponding to the maximum recovery rate is 0.18 years. -1 Considering the reserve abundance and gas well productivity at different structural locations, the reasonable technical well spacing for the corresponding structural locations is calculated using the pseudo-well spacing formula, as shown in Table 1. Based on relevant economic parameters: the reasonable gross profit margin β is 0.25, and the project profit sharing ratio P... SC The percentage is 60%, and the unit price of gas, P, is 1.47 yuan / m³. 3 The gas tax rate Ta is 15%, the loan interest rate R is 6.5%, the natural gas commodity rate α is 0.96, the evaluation period is the remaining extraction years, the total investment per well I is 10.03 million yuan, and the operating fee O is 0.2 yuan / m³. 3 The economic limit well spacing was obtained, with the economic limit well spacing of high-position wells being 443m, the economic limit well spacing of wing wells being 507m, and the economic limit well spacing of edge wells being 646m. The economic reasonable profit well spacing was also obtained, with the economic reasonable profit well spacing of high-position wells being 736m, the economic reasonable profit well spacing of wing wells being 841m, and the economic reasonable profit well spacing of edge wells being 1072m.

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

[0083] Table 2 Summary of Optimal Well Spacing in Example 1

[0084]

[0085] Example 2:

[0086] This embodiment provides a method for determining the reasonable well spacing of gas fields in overseas natural gas projects, including the following steps:

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

[0088] a. Based on the characteristics of natural gas field extraction, the entire development life cycle is divided into a stable production period (stable production time T). s The recovery period consists of two stages: the initial production and the decline period. Assuming that the initial production and decline patterns of the gas well are basically consistent, we can obtain a functional expression 1 for the recovery rate, where the remaining production years t is a variable;

[0089]

[0090] The pseudo-well spacing L in Equation 1psd is defined as shown in formula 2:

[0091]

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

[0093] b. According to the average effective thickness, porosity and permeability parameters and the natural gas properties of the gas field, a numerical simulation mechanism model of a typical well area is established by using numerical simulation software Eclipse or CMG, a series of different well spacing exploitation scenarios are set, the future daily gas production and cumulative gas production and time relationship are predicted, and T s stable production time and D i initial decline rate are calculated according to the cumulative gas production and the geological reserves, the relationship curve of the actual well spacing and the recovery degree under the condition of different remaining exploitation life is drawn, and the pseudo well spacing L psd is calculated according to the actual well spacing psd and the recovery degree R(t), the theoretical graph of the pseudo well spacing L psd and the recovery degree R(t) is drawn as shown in Figure 5 ;

[0094] The pseudo well spacing L psd is calculated according to the actual well spacing, and the calculation method is that the corresponding actual well spacing is input as the true well spacing L, the parameters of the specific well area reservoir effective thickness, natural gas compressibility, porosity, gas saturation, gas well comprehensive utilization rate, single well production and natural gas original volume coefficient in formula 2, and the pseudo well spacing L psd is calculated

[0095] The establishment of the numerical simulation mechanism model of the typical well area is specifically as follows: 1) a grid model is established; 2) the porosity, effective thickness and permeability are obtained according to the geological results to establish the attribute field; 3) the PVT parameters and relative permeability curve are input, and the gas-water interface and pressure are referred; 4) the gas well working system is set; 5) the production result is calculated and predicted;

[0096] c. In the above step b, the pseudo-well spacing L psd In the theoretical chart of recovery factor R(t), the minimum pseudo-well spacing L psd corresponding to the maximum recovery factor is found according to the remaining recovery period of the gas reservoir

[0097] d. In formula 2, the minimum pseudo-well spacing L psd value in step c of step 1) in step 1), the effective reservoir thickness of the specific well area, the natural gas compressibility factor, the porosity, the gas saturation, the comprehensive utilization rate of the gas well, the single well production and the natural gas original volume factor are inputted, and the corresponding real well spacing L is calculated as the reasonable technical well spacing L t .

[0098] 2) Determine the economic well spacing, calculate the economic limit well spacing Lmin and the economic reasonable profit well spacing La according to the following formula 3- formula 6,

[0099]

[0100]

[0101]

[0102]

[0103]

[0104] Wherein: F min , economic limit well spacing, m 2 ; E R , recovery, %; 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 cost, yuan / m 3 ; A, gas-bearing area, m 2 ; I, total investment of single well, ten thousand yuan; R, loan interest rate, %; T, evaluation period, years;

[0105] L min , economic limit well spacing, m; F a , economic reasonable profit well spacing, well / m 3 ; P sc , project proportion, %;

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

[0107] 3) Determine the optimal well spacing. Steps 1) and 2) yield a reasonable technical well spacing L. t Economic limit well spacing L min and reasonable profit well spacing L a Afterwards, a comprehensive comparative analysis is needed to determine the optimal well spacing L for the gas field. opt There are three possible relationships between reasonable technical well spacing and reasonable profit well spacing:

[0108] a. When the reasonable technical well spacing L t Well spacing L greater than reasonable profit a At this time, it is obviously greater than the economic limit well spacing. In this case, a reasonable technical well spacing L should be selected. t As the optimal well spacing L opt This will allow for maximum extraction and also generate substantial economic profits.

[0109] b. When the reasonable technical well spacing L t Less than the reasonable profit well spacing L a At that time, select a reasonable profit well spacing L a As the optimal well spacing L opt To ensure that the project has a certain economic profit, it is necessary to give up a portion of recoverable reserves.

[0110] c. When the reasonable technical well spacing L t Less than the economic limit well spacing L min At that time, they chose to abandon the gas field.

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

[0112] In this embodiment, the reasonable well spacing of the gas field is determined using the same method as in Embodiment 1.

[0113] In such Figure 5 The R(t)-Lpsd chart shown here corresponds to a series with a production life of 7 years, and the maximum simulated well spacing corresponding to the maximum recovery rate is 0.032 years. -1 Using the pseudo-well spacing formula, a reverse calculation yielded a reasonable technical well spacing of 1097m for the corresponding structural location. Based on relevant economic parameters: a reasonable gross profit margin of 0.25%, a project profit sharing ratio of 60%, and a gas unit price of 1.47 yuan / m³. 3 The gas tax rate is 15%, the loan interest rate is 6.5%, the total investment for a single well is 10.03 million yuan, and the operating fee is 0.2 yuan / m³. 3 The economic limit well spacing was 745m and the economically reasonable profit well spacing was 1236m.

[0114] According to the principle of determining the optimal well spacing, such as Figure 3As shown in (b), the optimal well spacing for Example 2 is 1236m, as shown in Table 3.

[0115] Table 3 Summary of Optimal Well Spacing in Example 2

[0116]

[0117] Example 3:

[0118] This embodiment provides a method for determining the reasonable well spacing of gas fields in overseas natural gas projects. The difference from Embodiment 2 is that in this embodiment, the remaining mining years in Embodiment 2 are increased to 15 years through negotiation; and the reasonable well spacing of gas fields is determined in this embodiment using the same method as in Embodiment 2.

[0119] In such Figure 5 The R(t)-Lpsd chart shown here corresponds to a series with a production life of 15 years, and the maximum simulated well spacing corresponding to the maximum recovery rate is 0.096 years. -1 Using the pseudo-well spacing formula, the reasonable technical well spacing for the corresponding structural location was calculated to be 1899m. The economic limit well spacing was calculated to be 845m, and the economically reasonable profit well spacing was calculated to be 1401m.

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

[0121] Table 4 Summary of Optimal Well Spacing in Example 3

[0122]

[0123] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for determining a reasonable well spacing of a gas field in an overseas natural gas project, characterized in that: Comprising the following steps, 1) determining reasonable technical well spacing, comprising the following steps: a. According to the natural gas field development characteristics, the entire development life cycle is divided into stable production period and decline period two stages, assuming that the initial production and decline law of gas well is basically the same, the function expression 1 of recovery degree can be obtained, wherein the remaining exploitation time t is the variable, Formula 1 wherein: t is the remaining production life, years; T s is the stable production time, years; L psd is the pseudo well spacing, years -1 ; D i is the initial decline rate, decimal b. According to the average effective thickness, porosity and permeability parameters and natural gas properties of the gas field, a numerical simulation mechanism model of a typical well area is established by using numerical simulation software Eclipse or CMG, a series of different well spacing exploitation scenarios are set, the future daily gas production and cumulative gas production and time relationship are predicted, and T s stable production time and D i initial decline rate, the recovery degree is calculated according to the cumulative gas production and geological reserves, the relationship curve of actual well spacing and recovery degree under different remaining exploitation years is drawn, and the pseudo well spacing L is calculated according to the actual well spacing psd , and the pseudo well spacing L is calculated by formula 1 in step a psd and the recovery degree R(t) relationship, the theoretical graph of the pseudo well spacing L psd and the recovery degree R(t) is drawn; c. In the above step b said pseudo well spacing L psd Within the theoretical chart of recovery factor R(t), the minimum pseudo well spacing L corresponding to the maximum recovery factor is found according to the remaining exploitation period of the gas reservoir psd value; d. The minimum well spacing L is calculated according to step c above psd The corresponding true well spacing is calculated as the reasonable technical well spacing L t ; 2) Determine economic well spacing, calculate the economic limit of gas field well spacing L min and economic and reasonable profit well spacing L a ; 3) Reasonable technical well spacing L is obtained according to the step 1) and step 2) t , economic limit well spacing L min and reasonable profit well spacing After that, the optimal well spacing L opt is determined; a. When the reasonable technical well spacing L t is greater than the reasonable profit well spacing L a and the economic limit well spacing L min , the reasonable technical well spacing L t is selected as the optimal well spacing L opt ; b. When the reasonable technical well spacing L t is less than the reasonable profit well spacing L a and greater than the economic limit well spacing L min , the reasonable profit well spacing L a is selected as the optimal well spacing; c. When the reasonable technical well spacing L t is less than the economic limit well spacing L min , the gas field is selected to be abandoned.

2. The method of claim 1, wherein: The pseudo-aegean L in the formula 1 psd is defined as shown in formula 2: Formula 2 Wherein, L is the production well spacing, m; h is the effective thickness, m; is the porosity, decimal; S g is the gas saturation, decimal; η is the comprehensive utilization rate of gas well, 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.

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

4. The method of claim 2, wherein: The true well spacing is calculated as the reasonable technical well spacing L in step d of step 1 t The calculation method is to input the minimum fitting well spacing L in step c of step 1) in formula 2 psd The parameters of the value, the effective reservoir thickness of the specific well area, the natural gas compressibility factor, 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 are input, and the corresponding true well spacing L is calculated as the reasonable technical well spacing L t .

5. The method of claim 1, wherein: The step b in the step 1) establishes the numerical simulation mechanism model of the typical well area, specifically: 1) establishing a grid model; 2) obtaining porosity, effective thickness, permeability to establish attribute field according to geological results; 3) inputting PVT parameters and relative permeability curve, referring to gas-water interface and pressure; 4) setting gas well working system; 5) operating and predicting production results.

6. The method of claim 1, wherein: The calculation method of the economic limit well spacing Lmin of the gas field in the step 2) is shown as formula 3 and formula 4: Formula 3 Formula 4 Wherein: F min , economic limit well spacing density, m 2 ; E R , recovery efficiency, %; a, natural gas commodity rate, %; G, geological reserves of gas field is, ×10 8 m 3 ; T a , gas tax rate, %; , gas unit price, yuan / m 3 ; O, operating costs, yuan / m 3 ; , gas-bearing area, m 2 ; , total investment per well, ten thousand yuan; R, loan interest rate, %; T, evaluation period, years; L min , economic limit well spacing, m.

7. The method of claim 1, wherein: The step 2) in the gas field economic reasonable profit well spacing L a The calculation method is shown in formula 5 and formula 6: Formula 5 Formula 6 Wherein: F a , economic reasonable profit well spacing density, m 3 ; E R , recovery, %; α, natural gas commodity rate, %; G, gas field geological reserves for, ×10 8 m 3 ; T a , gas tax rate, %; P, gas unit price, yuan / m 3 ; O, operating costs, yuan / m 3 ; A, gas area, m 2 ; I, total investment per well, ten thousand yuan; R, loan interest rate, %; T, evaluation period, years; P sc , project proportion, %; β, reasonable gross profit margin, greater than 0.2; L a , reasonable profit well spacing, years -1 .

8. The method of claim 1, wherein: The gas reservoirs are classified according to the reservoir permeability, and for different types of gas reservoirs, the pseudo well spacing L is established according to the reservoir type psd with the theoretical chart of the recovery factor R(t).

9. The method of claim 8, wherein: The classification is specifically that the permeability of gas reservoir is > 50 mD for high permeability gas reservoir, 5-50 mD for medium permeability gas reservoir, 0.1-5 mD for low permeability gas reservoir, and ≤ 0.1 mD for tight gas reservoir.

10. The method of claim 2, wherein: 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, ensuring the effective thickness and porosity in the area, and respectively establishing the pseudo well spacing L psd The reasonable well spacing is determined by the theoretical chart calculation of the recovery degree R(t), ensuring the pseudo well spacing L in formula 2 psd is representative.

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