CN106056252B - A three-level optimization method for well group division in shale gas fields - Google Patents

Abstract

The invention discloses a three-level optimization method for well group division of a shale gas field. The technical scheme is that a hierarchical optimization and integration strategy is adopted to convert the well group optimization division problem into a three-level optimization problem: establishing gas collecting station site optimization models of different development years by taking the construction cost of the gas collecting pipe network system of each development year of the shale gas field as a target function; dividing the optimal gas gathering station site of each development year into a plurality of clustering clusters by adopting a hierarchical clustering method, and taking the clustering center of each cluster as the global optimal gas gathering station site; and establishing an optimization model of the membership relationship between the shale gas field global optimal gas gathering station and the well site by taking the shortest sum of the distances between the global optimal gas gathering stations and the well site as an objective function. The method considers the unconventional characteristics that the shale gas well has fast yield attenuation and is continuously put into production by new wells, provides a new method for determining the well group division scheme with the most economical gas collection pipe network construction cost in the whole life cycle of the shale gas field, and has important significance for reducing the construction cost of shale gas ground engineering.

Description

A three-level optimization method for well group division in shale gas fields

technical field

The invention relates to a well group division optimization method in a shale gas field, and belongs to the technical field of layout optimization of a gathering and transportation pipeline network system in a shale gas field.

Background technique

As an unconventional natural gas resource with great development value, shale gas accounts for an increasing proportion of the world's total natural gas resources year by year, and has attracted great attention from all over the world. However, due to the unconventional characteristics of shale gas wells, such as rapid production decay rate, long production time, and large-scale rolling development, resulting in high development costs and high investment risks, low-cost strategies must be implemented to achieve profitability. Optimizing the design of the shale gas surface gathering and transportation pipeline network system is one of the important ways to reduce the cost of shale gas development.

Shale gas formations are poorly permeable and require drilling a large number of production wells during development. In order to save development costs and reduce the impact on the environment, 4 to 20 slave wells are often drilled in the same well site. Well group division refers to determining the grouping plan for a large number of well sites in shale gas fields, that is, determining the number and location of gas gathering stations and their affiliation with well sites. At present, the division of well groups in shale gas fields generally adopts the method of scheme comparison or comprehensive evaluation. The basic idea is to establish several relatively reasonable well group division schemes based on engineering experience, and then compare them with each other, and select the best scheme as the final scheme. This method is simple and easy to implement, but it is closely related to the experience of engineers, and the optimization results are difficult to achieve global optimality. At present, scholars at home and abroad have made a lot of research results on the optimization of conventional gas fields, which have been widely used in engineering practice, and have certain reference significance for the optimization of well groups in shale gas fields. It usually adopts the method of establishing a mathematical model, that is, by constructing an objective function that reflects the relationship between the optimization objective and the variables, and under the constraint conditions, the extreme value of the objective function is solved to obtain the corresponding well group optimization division scheme. Common mathematical models are roughly divided into three categories, that is, the objective function is to choose the most economical pipeline construction cost, the shortest pipeline length, and the shortest pipeline production distance, and the selection of the gas gathering station site and the membership relationship between the well site and the gas gathering station are used as the decision variables. Under the constraints of the number of well sites and the radius of gathering and transportation under the control of the gas gathering station, an optimal division model of the corresponding well group is established. However, these models are based on the following assumptions: each well site is put into production at the same time: the production rate of each well site is constant and does not change with the development time. Therefore, the above models can only be used for conventional gas fields with long development cycles and stable production, and are not suitable for well group optimization in shale gas fields with significant unconventional characteristics such as rapid production decay rate, long production ramp-up time, and large-scale rolling development.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a well group optimization division method that adapts to the unconventional characteristics such as rapid production decline of shale gas wells and continuous production of new wells in view of the defects existing in the existing optimization methods. Provide the basis for the well group division plan with the most economical gas pipeline network construction cost, so as to reduce the construction cost of shale gas surface engineering.

Its technical solution includes the following steps:

Step a. According to the production performance curve of the exploratory well obtained by the pilot development test of the shale gas field, use the shale exponential decline method or the hyperbolic decline method to obtain the production attenuation characteristic curve of the single well in the corresponding block: according to the production plan of each single well and the output Attenuation characteristic curve, determine the production attenuation curve of each well site:

Step b. Take the most economical construction cost of the gas-gathering pipeline network system in each development year since the shale gas field was put into production as the objective function, and take the affiliation of the gas-gathering station site, the well site and the gas-gathering station as the decision variable: the affiliation at the well site Under the constraints of constraints, development time constraints, gas gathering station processing capacity constraints, the number of well sites under the gas gathering station’s jurisdiction, gathering and transportation radius constraints, and gas gathering station site constraints, the gas gathering capacity of shale gas fields in different development years is established. Site site optimization model:

Step c. Using the hierarchical clustering method, the optimal gas gathering station sites of each development year of the shale gas field are divided into several clusters, and the cluster center of each cluster is regarded as the globally optimal gas gathering station of the shale gas field. Site address:

Step d, take the shortest sum of distances between the shale gas field global optimal gas gathering station site and the well site as the objective function, and take the membership relationship between the well site and the gas gathering station as the decision variable; Under the constraints of the processing capacity of the gas-gathering station, the number of well sites under the gas-gathering station, and the radius of gathering and transportation, an optimization model of the membership relationship between the global optimal gas-gathering station and the well site in the shale gas field is established.

A three-level optimization method for well group division in a shale gas field, characterized in that the construction cost of the gas gathering pipe network system in the shale gas field described in step b includes the construction cost of gas gathering pipelines and gas gathering stations.

A three-level optimization method for well group division in a shale gas field, characterized in that the constraints described in steps b and d: the well site membership constraint means that for any well site, there is one and only one gas gathering station and its Connected: The development time constraint means that the well sites put into production in different development periods of the shale gas field are included in the corresponding optimization model; The total output of the well sites in each development year; the constraint on the number of well sites under the jurisdiction of the gas gathering station refers to the maximum number of well sites that a single gas gathering station can manage; the gathering and transportation radius constraint means that the length of the gas gathering pipeline should not exceed the economic gathering Gas radius: The site constraint of the gas gathering station means that the gas gathering station is located in the production center of the well group under its jurisdiction.

A three-level optimization method for well group division in a shale gas field, characterized in that the hierarchical clustering method described in step c adopts the single-linkage clustering method.

The beneficial effects of the present invention are: considering the characteristics of rapid production decline of shale gas wells and continuous production of new well sites, the strategy of hierarchical optimization and integration is adopted to transform the problem of shale gas well group division into a three-level optimization problem. By establishing the corresponding optimization model, the optimal gas gathering station site of shale gas field in different development years, the global optimal gas gathering station site of shale gas field and the best affiliation relationship with the well site are respectively determined. The invention provides a new idea for determining the well group division scheme with the most economical construction cost of the global gas gathering pipeline network of the shale gas field, and has great significance for reducing the construction cost of the surface engineering of the shale gas field.

Description of drawings

Fig. 1 shows the production decay curves of two typical wellsites in different blocks of a shale gas field

Fig. 2 shows the optimal well group division plan of a shale gas field in the sixth year of development

Figure 3 shows all the annual optimal gas gathering station sites in a shale gas field between 2014 and 2030

Figure 4 shows the globally optimal gas gathering station site for a shale gas field

Fig. 5 shows the optimal well group division scheme in the whole life cycle of a shale gas field

Fig. 6 is the flow chart of the three-level optimization method for well group division in shale gas fields

Detailed ways

Specific embodiment: take a domestic shale gas field as an example, and illustrate the content and realization principle of the present invention in conjunction with the accompanying drawings:

The technical scheme of the present invention is to adopt the hierarchical optimization and integration strategy to transform the well group optimization division problem into a three-level optimization problem: taking the most economical construction cost of the gas gathering pipeline network system in each development year of the shale gas field as the objective function, establish a Gas-gathering station site optimization model: Hierarchical clustering method is used to divide the optimal gas-gathering station sites in each development year into several clusters, and the cluster center of each cluster is used as the global optimal gas-gathering station site : Taking the shortest sum of the distances between each global optimal gas gathering station and the well site as the objective function, an optimization model of the membership relationship between the global optimal gas gathering station and the well site is established in the shale gas field. The specific process is as follows:

1. Basic overview of well site and prediction of production decay law

A shale gas field has completed the preliminary production test evaluation, which proves that the reservoir is thick and rich in resources. It is planned to deploy more than 1,050 wells and 86 well sites between 2014 and 2030, with a designed production capacity of 1,500×10 ⁴ m ³ /d in the stable production stage. According to the shale gas surface engineering construction plan, the shale gas field development and construction schedule is shown in Table 1. The well site distribution is shown in Figure 5.

Table 1 Development and construction schedule of a shale gas field

Based on some single well production performance curves obtained from pilot development tests of shale gas fields, the power-law exponential decline method and the hyperbolic decline method were used to fit the average production curves of all wells in each block, and the curve with a higher degree of fitting was selected. As the single well production decay curve of this block. Combined with the production schedule of each well site, the production decay curve of each well site is obtained by the superposition method, as shown in Figure 2.

2. Establishment of site optimization models for gas gathering stations in different development years of shale gas fields

Taking the most economical construction cost of the gas-gathering pipeline network system in each development year since the shale gas field was put into production as the objective function, the affiliation of the gas-gathering station site, the well site and the gas-gathering station was selected as the decision variables. Under the constraints of well site membership, development time, processing capacity of gas gathering stations, number of well sites under the jurisdiction of gas gathering stations, gathering and transportation radius constraints, and gas gathering station site constraints, the establishment of shale gas fields in different The site optimization model of the gas gathering station in the year of development. The specific steps include:

(1) Establish the objective function

The construction cost of the gas gathering pipeline network system in the shale gas field includes the construction cost of gas gathering pipelines and gas gathering stations. Among them, the construction cost of gas gathering pipeline is mainly related to parameters such as length, pipe diameter and wall thickness. However, the gathering and transportation pipelines in shale gas fields generally belong to the same pressure level, and the wall thickness of the pipelines is not much different. In addition, when the length of the gas collecting pipeline is certain, the pipeline flow is mainly related to the pipe diameter. Since each well site can only be connected to one gas gathering station, the flow rate of the gas gathering pipeline between the well site and the gas gathering station is the real-time gas production of the well site. Therefore, the construction cost of the gas gathering pipeline can be expressed as a function of length and well site gas production. At the same time, the construction cost of the gas gathering station is mainly related to its processing capacity. The functional relationship between the construction cost of the gas-gathering station and its processing capacity can be obtained by using the least squares regression method according to the previous design data. The scheme with the least construction cost of the gas gathering pipeline network system in each development year is the optimal well group division scheme in that year. Among them, the objective function of well group division in year t is:

km：K、γ均为系数，可根据以往的设计资料采用最小二乘回归等方法得到：Q_j为集气站j的日处理量，10⁴m³/d。where m _t and n _t are the number of well sites and the number of gas gathering stations in the t year of shale gas field development, respectively: C _ij is the construction cost of the gas gathering pipeline between well site i and gas gathering station j, yuan: c _j is the construction cost of gas-gathering station j, yuan: L _ij is the length of the gas-gathering pipeline between well site i and gas-gathering station j,

km: K and γ are coefficients, which can be obtained by using the least squares regression method according to the previous design data: Q _j is the daily processing capacity of gas gathering station j, 10 ⁴ m ³ /d.

(2) Establish constraints

Well site affiliation constraint: For any well site, there is one and only one gas gathering station connected to it: Development time constraint: The value of the development year of the shale gas field should be the year when the first batch of well sites is put into production and all well sites enter the stable production period Between years: the processing capacity constraint of the gas gathering station: the upper limit and lower limit of the processing capacity of any gas gathering station should meet the total production of the well sites under the control of the processing in each development year: the number of well sites under the jurisdiction of the gas gathering station: a single gas gathering station The maximum number of well sites under the jurisdiction of the gas station: Gathering and transportation radius constraint: The length of the gas gathering pipeline should not exceed the economic gas gathering radius: The gas gathering station site constraint: The gas gathering station is located in the production center of the well group under its jurisdiction, which can be expressed as :

In the formula: (x _i , y _i ), (x _j , y _j ) are the position coordinates of well site i and gas gathering station j, respectively: q _{i , t} represent the gas production of well site i in development year t: m _t is the number of well sites in the development year t: δ _ij is a 0-1 variable, indicating the affiliation between well site i and gas gathering station j, that is, when the value of δ _ij is 1, it means that the two are connected: when When the value of _δij is 0, it means that the two are not connected.

By solving the model, the number of gas-gathering stations corresponding to each development year of the shale gas field, their location and their affiliation with the well site can be obtained. The number of gas-gathering stations required in each development year is shown in Table 2, and the optimal gas-gathering station site and its affiliation with the well site in the sixth year of development of the shale gas field are shown in Figure 3. The obtained optimal gas gathering station sites for each year between 2014 and 2030 are summarized, as shown in Figure 4. As can be seen from Figure 4 and Table 2, the maximum number of gas gathering stations required by the shale gas field globally is 8, with a total of 99 annual optimal gas gathering stations.

Table 2 The number of gas gathering stations required in each development year of shale gas fields

3. Determination of the global optimal gas gathering station site for shale gas fields

According to the obtained maximum number of gas-gathering stations and 99 annual optimal gas-gathering station sites for shale gas fields, the 99 annual optimal gas-gathering station sites are divided into 8 clusters by hierarchical clustering method. The cluster center of each cluster is taken as the globally optimal gas gathering station site of the shale gas field. The specific steps are as follows:

(1) Establish an analysis sample set

The optimal gas gathering station sites in each development year of the shale gas field are used as the analysis sample set.

(2) Establish a distance matrix

First, each gas gathering station is regarded as a cluster. At this time, the distance between two clusters is the distance between two gas gathering stations, and the distance between any two clusters can be expressed as:

In the formula, d _k1 is the distance between the No. k gas gathering station and the No. 1 gas gathering station: (x _k , y _k ), (x ₁ , y ₁ ) are the coordinates of X _k and Y _k respectively, that is, The site of No. k and No. 1 gas gathering stations: k and l are the sample numbers respectively; N is the number of samples. The distance matrix between each gas gathering station is:

(3) Determine the globally optimal gas gathering station site for shale gas fields

The single-linkage clustering method is used to divide the optimal gas gathering stations in each development year of the shale gas field into 8 clusters, and the cluster center of each cluster is regarded as the globally optimal gas gathering station of the shale gas field. Site address, which can be expressed as:

为第j个簇的聚类中心的坐标，即为第j个簇的全局最优集气站站址：μ_kj为0-1变量，表示第k号集气站与第j个聚类簇之间的隶属关系，即当μ_kj的值取1时，表示第k号集气站隶属于第j个聚类簇；当δ_ij的值取0时，反之。因此，确定8个全局最优的集气站站址，如图5所示。where:

is the coordinate of the cluster center of the jth cluster, that is, the global optimal gas gathering station site of the jth cluster: μ _kj is a 0-1 variable, indicating the kth gas gathering station and the jth cluster cluster The membership relationship between , that is, when the value of μ _kj is 1, it means that the kth gas gathering station belongs to the jth cluster; when the value of δ _ij is 0, the opposite is true. Therefore, 8 globally optimal gas gathering station sites are determined, as shown in Figure 5.

4. Establishment of the optimization model of the membership relationship between the global optimal gas gathering station and the well site in the shale gas field

The objective function is to take the shortest sum of the distances between the global optimal gas gathering station site and the well site in the shale gas field, and the membership relationship between the well site and the gas gathering station is selected as the decision variable. Under the constraints of well site membership, gas gathering station processing capacity, number of well sites under the gas gathering station, and gathering and transportation radius constraints, the optimal gas gathering station and well site in the whole life cycle of a shale gas field are established. The membership optimization model. The specific steps are as follows:

(1) Establish the objective function

Based on the determined 8 globally optimal gas gathering station sites, combined with the positions of each well site, the objective function is to take the shortest sum of the distances between the optimal gas gathering station site and the well site as the objective function, which can be expressed as follows:

where m is the number of global gas gathering stations, and n is the total number of well sites in the shale gas field.

(2) Establish constraints

Well site affiliation constraint: For any well site, there is one and only one gas gathering station connected to it: Gas gathering station processing capacity constraint: The upper and lower limits of the processing capacity of any gas gathering station should meet the requirements of the wellsite under the shale treatment. The total production of the global gas: the number of well sites under the jurisdiction of the gas gathering station: the maximum number of well sites under the jurisdiction of a single gas gathering station: the radius of gathering and transportation: the length of the gas gathering pipeline should not exceed the economic gas gathering radius.

By solving the model, the optimal membership relationship between the global optimal gas gathering station and the well site in the shale gas field is obtained, as shown in Figure 5. The flow chart of the three-level optimization method for shale gas field well group division provided by the present invention is shown in FIG. 6 .

Claims (3)

1. a three-level optimization method for shale gas field well group division is characterized in that comprising the following steps: Step a: According to the production performance curve of the exploratory well obtained by the pilot development test of the shale gas field, the power-law exponential decline method or the hyperbolic decline method is used to obtain the production attenuation characteristic curve of the single well in the corresponding block; Attenuation characteristic curve, determine the production attenuation curve of each well site; Step b. Take the gas-gathering station site, the affiliation between the well site and the gas-gathering station as decision-making variables; the well-site membership constraints, development time constraints, gas-gathering station processing capacity constraints, and the number of well sites under the control of the gas-gathering station are constrained , gathering radius constraint, gas gathering station location constraint, among them, well site membership constraint: for any well site, there is one and only one gas gathering station connected to it; development time constraint: development year of shale gas field The value should be between the year when the first batch of well sites was put into production and the year when all well sites entered the stable production period; the processing capacity constraint of the gas gathering station: the upper and lower limits of the processing capacity of any gas gathering station should meet the requirements of The total output of each development year; the number of well sites under the jurisdiction of the gas gathering station: the maximum number of well sites under the jurisdiction of a single gas gathering station; the limitation of the gathering and transportation radius: the length of the gas gathering pipeline should not exceed the economic gas gathering radius; the gas gathering station Location constraints: The gas gathering station is located in the production center of the well group under its jurisdiction, which can be expressed as:

Establish the site optimization model of gas gathering stations for shale gas fields in different development years, solve the above shale gas field optimization models for gas gathering stations in different development years, and obtain the number of gas gathering stations corresponding to each development year of the shale gas field, The address of each gas gathering station and the affiliation between each gas gathering station and the well site; among them, the objective function of the optimization model of the gas gathering station site is

where m _t and n _t are the number of well sites and the number of gas gathering stations in the t year of shale gas field development, respectively; L _ij is the length of the gas gathering pipeline from well site i to gas gathering station j,

K and γ are coefficients, which are obtained by the least square regression method; Q _j is the daily processing capacity of gas gathering station j, (x _i , y _i ), (x _j , y _j ) are the wellsite i and gas gathering station, respectively The position coordinates of station j; q _{i, t} represent the gas production of well site i in development year t; m _t is the number of well sites in development year t; δ _ij is a 0-1 variable, representing the relationship between well site i The membership relationship of the gas station j, that is, when the value of δ _ij is 1, it means that the two are connected; when the value of δ _ij is 0, it means that the two are not connected; Step c. Using the hierarchical clustering method, the optimal gas gathering station sites of each development year of the shale gas field are divided into several clusters, and the cluster center of each cluster is regarded as the globally optimal gas gathering station of the shale gas field. site address; Step d, take the shortest sum of distances between the shale gas field global optimal gas gathering station site and the well site as the objective function, and take the membership relationship between the well site and the gas gathering station as the decision variable; Under the constraints of the processing capacity of the gas-gathering station, the number of well sites under the gas-gathering station, and the radius of gathering and transportation, an optimization model of the membership relationship between the global optimal gas-gathering station and the well site in the shale gas field is established. Solve the optimization model of the membership relationship between the global optimal gas gathering station and the well site in the shale gas field, and obtain the optimal membership relationship between the global optimal gas gathering station and the well site in the shale gas field; Step e: Output the optimal well group division in the whole life cycle of the shale gas field according to the globally optimal gas gathering station site of the shale gas field and the optimal membership relationship between the global optimal gas gathering station and the well site of the shale gas field According to the above-mentioned optimal well group division scheme in the whole life cycle of the shale gas field, the shale gas surface engineering is established. 2. a three-level optimization method for shale gas field well group division according to claim 1, characterized in that, the constraints described in step b and step d: the well site membership constraint refers to any well site , there is only one gas gathering station connected to it; the development time constraint means that the well sites put into production in different development periods of the shale gas field are included in the corresponding optimization model; the gas gathering station processing capacity constraint refers to the processing capacity of any gas gathering station The upper and lower limits of the gas gathering station should meet the full production of the well sites under its jurisdiction in each development year; the number of well sites under the jurisdiction of the gas gathering station refers to the maximum number of well sites that a single gas gathering station can manage; the gathering and transportation radius constraint refers to the collection and transportation radius constraint. The length of the gas pipeline should not exceed the economical gas gathering radius; the site constraint of the gas gathering station means that the gas gathering station is located in the production center of the well group under its jurisdiction. 3 . The three-level optimization method for shale gas field well group division according to claim 1 , wherein the hierarchical clustering method described in step c adopts the single-linkage clustering method. 4 .

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