A method for characterizing interwell displacement degree under non-uniform well spacing in offshore oil fields

Abstract

The present invention relates to the technical field of offshore oilfield exploitation, and specifically to a method for characterizing the degree of displacement between wells under non-uniform well spacing in offshore oilfields. The method comprises the following steps: applying the DTW algorithm, analyzing the distance between the time series of changes in injected water and the time series of changes in liquid production in the injection and production wells, and calculating the degree of connectivity between the injection and production wells; establishing a typical well group geological model according to the degree of connectivity between the wells, and obtaining the flow field distribution through streamline simulation calculation; calculating the streamline density and streamline intensity between the injection and production wells; calculating the coefficient of characterization of the degree of displacement between wells; and determining the optimal injection and production volume of a single well. The method of the present invention solves the problem that it is difficult to characterize the degree of displacement between injection and production wells in different well groups at sea under the influence of multiple factors, provides a basis for balanced displacement of offshore oilfields, and can greatly improve the recovery rate of offshore oilfields.

Description

Technical Field

[0001] The invention relates to the technical field of offshore oilfield exploitation, and in particular to a method for characterizing the degree of inter-well displacement under non-uniform well spacing in an offshore oilfield. Background Art

[0002] Shengli Offshore Chengdao Oilfield is the first oilfield with an annual production of one million tons to be developed and constructed in my country's extremely shallow sea areas. The oilfield was put into development in 1993. By the end of 2019, a total of 423 million tons of proven geological reserves and 58 million tons of cumulative oil production had been reported, making an important contribution to ensuring national energy security.

[0003] However, as the development progresses, the water content increases year by year, and the comprehensive water content has reached 84%, and the oil field has entered a high water content period. Limited by the environment, construction capacity, and liquid processing capacity, the contradiction between the low oil production rate of the oil field and the limited platform life is becoming increasingly obvious. "How to maximize the oil field recovery rate within the effective period and make full use of underground resources" has become the main problem facing Chengdao Oilfield.

[0004] Effective liquid extraction to achieve balanced displacement is an effective way to improve the recovery rate of offshore oilfield platforms during their effective period, and determining the displacement degree between injection and production wells is the key to achieving balanced displacement, improving the sweep coefficient of injected water, and avoiding the rapid rise of water content. Only by determining the displacement degree between injection and production wells, flow field adjustment, injection and production allocation and other adjustment measures can be targeted. However, at present, the displacement degree between wells is mostly characterized by a single parameter through numerical simulation of residual oil saturation, without considering the influence of multiple factors such as non-uniform well spacing, well-to-well connectivity, flow field sweep degree, and flow field intensity between wells in offshore oilfields.

[0005] Chinese invention patent CN105626007B discloses a method for calculating the water flow rate of different parts of a core-scale reservoir, which includes: step 1, deriving the streamline equation of a five-point homogeneous model to obtain the streamline distribution of different parts; step 2, establishing a flow distribution method between streamlines between injection and production wells to obtain the flow distribution of different parts; step 3, calculating the water flow rate of different parts along the streamline based on a core-scale one-dimensional homogeneous model; and step 4, calculating the water flow rate of different parts along the streamline of a five-point homogeneous model. This method makes full use of the rich data of indoor experiments to accurately describe the water flow rate of different parts of the reservoir, quantitatively characterize the displacement degree of different parts of the reservoir, and lay a solid foundation for formulating technical measures for mine development and adjustment.

[0006] However, there is no solution to the problem of characterizing the displacement degree between wells under non-uniform well spacing in offshore oil fields. Therefore, it is very necessary to provide a more accurate method for characterizing the displacement degree between wells. Summary of the invention

[0007] The main purpose of the present invention is to provide a method for characterizing the displacement degree between wells under non-uniform well spacing in offshore oil fields. The method of the present invention solves the problem that the displacement degree between injection and production wells of different well groups at sea is difficult to characterize under the influence of multiple factors, provides a basis for balanced displacement of offshore oil fields, and can greatly improve the recovery rate of offshore oil fields.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for characterizing the displacement degree between wells under non-uniform well spacing in an offshore oil field, which comprises the following steps:

[0010] 1) Apply the DTW algorithm to analyze the distance between the time series of injection water changes and the time series of liquid production changes in the injection and production wells, and calculate the degree of connectivity between the injection and production wells;

[0011] 2) According to the degree of inter-well connectivity, a typical well group geological model is established, and the flow field distribution is obtained by streamline simulation calculation;

[0012] 3) Calculate the flow line density and flow field intensity between injection and production wells;

[0013] 4) Calculate the coefficient of characterization of inter-well displacement degree;

[0014] 5) Determine the optimal injection and production volume for a single well.

[0015] Furthermore, in step 1), the optimal regularized path between the injection and production sequences is calculated in sequence according to the DTW algorithm. The greater the distance between the time series of the injection water change and the time series of the liquid production change of the corresponding injection and production wells, the worse the connectivity between the injection well and the corresponding production well, and vice versa. The corresponding well-to-well connectivity relationship diagram is drawn according to the distance.

[0016] Furthermore, in step 3), the characteristic data is analyzed, and the density of streamlines and the flow field intensity between the injection and production wells are obtained by cluster calculation, so as to obtain a flow field intensity distribution map reflecting the influence of the historical flow field on the reservoir.

[0017] Furthermore, the characteristic data includes the position, number and saturation of inter-well streamlines.

[0018] Furthermore, step 3) also includes counting the streamline density in different regions of the inter-well flow field to obtain a flow field density distribution diagram reflecting the flow field's ability to displace fluids.

[0019] Furthermore, in step 4), the inter-well displacement degree characterization coefficient is obtained by comprehensive calculation based on parameters such as the degree of connectivity between injection and production wells, well spacing, streamline density, flow field intensity, etc.:

[0020]

[0021] in: The degree of well connectivity and well spacing reflect the connectivity capacity and distance between wells; The inter-well flow field density reflects the inter-well displacement capacity and sweep degree; E i The intensity of the flow field between wells reflects the potential of remaining oil between wells; M i Inter-well connectivity, L i Injection-production well spacing, D i Interwell streamline density, S i The extent of flow field between wells, E i Interwell flow field intensity, F i Coefficient characterizing the degree of interwell displacement.

[0022] Furthermore, in step 5), the specific method for determining the optimal injection and production volume of a single well includes: optimizing the objective function based on streamline density and flow field intensity; generating a new injection and production volume by mutating cross-shift operations; and obtaining the optimal injection and production volume.

[0023] Furthermore, the objective function is to minimize the difference in displacement degree coefficients among wells.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The method of the present invention fully considers the influence of multiple factors such as uneven well spacing, well connectivity, flow field sweep, and well flow field intensity in offshore oil fields, and proposes for the first time to characterize the inter-well displacement degree coefficient Fi, providing a new method for balanced displacement of offshore oil fields. The method of the present invention has simple steps and is easy to use, providing technical support for significantly improving the recovery rate of offshore oil fields during the high water content period. The method has been widely used in Chengdao Oilfield, and a total of 31 well groups have been adjusted for injection and production. Through the calculation and analysis of the inter-well displacement degree, it is believed that there is an injection-production contradiction in 23 of the well groups. In view of the injection-production contradiction, the optimization algorithm is repeatedly optimized to obtain the optimal production and injection allocation of a single well with the minimization of the difference in the inter-well displacement degree coefficient Fi as the objective function. After the allocation is implemented, the displacement contradiction is effectively alleviated, and the adjustment has achieved good results. The daily liquid of the single well increased by 67t / d, the water content decreased by 7.2%, and the average daily oil increase was 16t / d. So far, the cumulative oil increase has reached 73,000 tons, and the recovery rate is expected to increase by 6% during the evaluation period. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0027] Figure 1 It is a distance diagram between the time series of water injection change and the time series of liquid production change of the offshore 22F well group DTW calculation injection and production wells according to a specific embodiment of the present invention;

[0028] Figure 2A connectivity diagram of injection and production wells centered on 22FC-3 according to a specific embodiment of the present invention;

[0029] Figure 3 A flow field distribution diagram of a typical well group streamline simulation according to a specific embodiment of the present invention;

[0030] Figure 4 A flow field intensity distribution diagram reflecting the influence of the historical flow field on the oil reservoir according to a specific embodiment of the present invention;

[0031] Figure 5 This is a schematic diagram of flow field density calculation reflecting the displacement capability of a flow field on a fluid according to a specific embodiment of the present invention;

[0032] Figure 6 This is a flow chart for optimizing the optimal injection and production volume of a single well according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0033] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0034] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0035] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0036] Example 1

[0037] A method for characterizing the displacement degree between wells under non-uniform well spacing in an offshore oil field comprises the following steps:

[0038] 1) Apply the DTW algorithm to analyze the distance between the time series of injection water changes and the time series of liquid production changes in the injection and production wells, and calculate the degree of connectivity between the injection and production wells; calculate the optimal regularized path between the injection and production sequences in turn according to the DTW algorithm. The greater the distance between the time series of injection water changes and the time series of liquid production changes in the corresponding injection and production wells, the worse the connectivity between the injection well and the corresponding production well, and vice versa. Draw the corresponding well connectivity relationship diagram according to the distance.

[0039] 2) According to the degree of inter-well connectivity, a typical well group geological model is established, and the flow field distribution is obtained by streamline simulation calculation;

[0040] 3) Calculate the density of streamlines and flow field intensity between injection and production wells; analyze the characteristic data including the position, number, saturation and other characteristic data of streamlines between wells, and obtain the density of streamlines and flow field intensity between injection and production wells by cluster calculation, and obtain the flow field intensity distribution map reflecting the impact of the historical flow field on the reservoir.

[0041] It also includes statistical analysis of streamline densities in different areas of the inter-well flow field to obtain a flow field density distribution diagram that reflects the flow field's ability to displace fluids.

[0042] 4) Calculate the inter-well displacement degree characterization coefficient:

[0043] According to the parameters such as the degree of connectivity between injection and production wells, well spacing, streamline density, flow field intensity, etc., the inter-well displacement degree characterization coefficient is obtained by comprehensive calculation:

[0044]

[0045] in: The degree of well connectivity and well spacing reflect the connectivity capacity and distance between wells; The inter-well flow field density reflects the inter-well displacement capacity and sweep degree; E i The intensity of the flow field between wells reflects the remaining oil potential between wells;

[0046] M i Inter-well connectivity, L i Injection-production well spacing, D i Interwell streamline density, S i The extent of flow field between wells, E i Interwell flow field intensity, F i Coefficient characterizing the degree of interwell displacement.

[0047] 5) Determine the optimal injection and production volume for a single well.

[0048] The specific method for determining the optimal injection and production volume of a single well includes: minimizing the difference in displacement degree coefficients between wells as the objective function; optimizing the objective function based on streamline density and flow field intensity; generating new injection and production volumes through mutated cross-shift operations; and obtaining the optimal injection and production volume.

[0049] Example 2

[0050] Taking Chengdao Oilfield as an example, the characterization method of interwell displacement degree under non-uniform well spacing includes the following steps:

[0051] (1) According to the DTW algorithm, the optimal regularized path between the injection and production sequences is calculated in sequence. The greater the distance between the time series of the injection water change and the time series of the liquid production change of the corresponding injection and production wells, the worse the connectivity between the injection well and the corresponding production well, and vice versa. The corresponding well-to-well connectivity relationship diagram is drawn according to the distance. Figure 1 , Figure 2 shown.

[0052] (2) According to the inter-well connectivity, a typical well group geological model is established, and streamline simulation is carried out to obtain the flow field distribution, such as Figure 3 shown.

[0053] (3) Based on the flow field simulation results, the characteristic data such as the position, number, and saturation of the inter-well streamlines are analyzed to obtain the flow field intensity distribution map reflecting the impact of the historical flow field on the reservoir, such as Figure 4 shown.

[0054] (4) Statistical flow line density in different areas of the inter-well flow field is used to calculate the flow field density distribution diagram that reflects the flow field's ability to displace fluids, such as Figure 5 shown.

[0055] Flow field density calculation disclosure:

[0056]

[0057] D0---streamline density in region 0

[0058] D1---Streamline density in the first area

[0059] D2---Streamline density in the second area

[0060] ---Average flow line density between injection and production wells

[0061] (5) Taking the minimization of the difference in displacement coefficient Fi between wells as the objective function, the optimal injection and production flow chart for a single well is optimized, as shown in Figure 6 shown.

[0062] A total of 31 well groups were adjusted for injection and production. Through calculation and analysis of the displacement degree between wells, it was found that there were injection-production conflicts in 23 of the well groups. To address the injection-production conflicts, the optimization algorithm was used to repeatedly optimize the optimal production and injection allocation for a single well, with the minimization of the difference in the displacement degree coefficient Fi between wells as the objective function. After the adjustment was implemented, the displacement conflict was effectively alleviated, and the adjustment achieved good results. The daily liquid output of each well increased by 67t / d, the water cut decreased by 7.2%, and the average daily oil production increased by 16t / d. So far, the cumulative oil production has increased by 73,000 tons, and the recovery rate is expected to increase by 6% during the evaluation period.

[0063] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for characterizing the displacement degree between wells under non-uniform well spacing in an offshore oil field, characterized in that: It includes the following steps: 1) Apply the DTW algorithm to analyze the distance between the time series of injection water changes and the time series of liquid production changes in the injection and production wells, and calculate the degree of connectivity between the injection and production wells; 2) According to the degree of inter-well connectivity, a typical well group geological model is established, and the flow field distribution is obtained by streamline simulation calculation; 3) Calculate the flow line density and flow field intensity between injection and production wells; 4) Calculate the coefficient of characterization of inter-well displacement degree; 5) Determine the optimal injection and production volume for a single well; In step 3), the characteristic data is analyzed, and the density of streamlines and the flow field intensity between the injection and production wells are obtained by cluster calculation, and a flow field intensity distribution map reflecting the impact of the historical flow field on the reservoir is obtained; The characteristic data include the position, number and saturation of inter-well flow lines; In step 4), the inter-well displacement degree characterization coefficient is obtained by comprehensive calculation based on the degree of connectivity between injection and production wells, well spacing, streamline density, and flow field intensity parameters: in: The degree of well connectivity and well spacing reflect the connectivity capacity and distance between wells; The inter-well flow field density reflects the inter-well displacement capacity and sweep degree; E i The intensity of the flow field between wells reflects the potential of remaining oil between wells; M i Inter-well connectivity, L i Injection-production well spacing, D i Interwell streamline density, S i The extent of flow field between wells, F i Characterization coefficient of interwell displacement degree; In step 5), the specific method for determining the optimal injection and production volume of a single well includes: optimizing the objective function based on streamline density and flow field intensity; generating new injection and production volumes by mutating cross-shift operations; and obtaining the optimal injection and production volume.

2. The method according to claim 1, characterized in that: In step 1), the optimal regularized path between the injection and production sequences is calculated in sequence according to the DTW algorithm. The greater the distance between the time series of the injection water change and the time series of the liquid production change of the corresponding injection and production wells, the worse the connectivity between the injection well and the corresponding production well, and vice versa. The corresponding well-to-well connectivity relationship diagram is drawn according to the distance.

3. The method according to claim 1, characterized in that: Step 3) also includes counting the streamline densities in different regions of the inter-well flow field to obtain a flow field density distribution diagram reflecting the flow field's ability to displace fluids.

4. The method according to claim 1, characterized in that: The objective function is to minimize the difference in displacement coefficients among wells.

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