A method for quantitatively characterizing remaining oil in an injection-production well group in an extra-low permeability reservoir

Abstract

The present invention belongs to the technical field of oil and gas field development, and discloses a method for quantitatively characterizing remaining oil in an injection-production well group in an extra-low permeability reservoir, including: S1. Centering on the injection well, dividing the well group into injection-production units, and obtaining physical property parameters such as the average porosity, permeability, water cut, water saturation, and effective thickness of each unit; S2. Calculating the effective distances of the water-washed zone, two-phase zone, and swept zone corresponding to each unit respectively, and sequentially determining the control ranges of the above different zones; S3. Calculating the remaining oil saturations within the control ranges of the water-washed zone, two-phase zone, and swept zone corresponding to each unit respectively; S4. Drawing a remaining oil saturation distribution map of the injection-production well group to obtain the remaining oil distribution pattern of the well group in the extra-low permeability reservoir. The method of the present invention involves less difficulty in obtaining data, can quantitatively and intuitively describe the distribution law of remaining oil between wells, and points out the potential tapping directions of the well group under different remaining oil distribution patterns, providing a decision-making basis for improving the development effect of the extra-low permeability reservoir.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field development, and particularly relates to a method for quantitatively characterizing remaining oil in an injection-production well group in an extra-low permeability reservoir. Background Art

[0002] With the deepening of oil and gas exploration, many extra-low permeability reservoirs have been gradually discovered. In recent years, low-permeability to extra-low permeability reserves account for more than 68% of the newly discovered reserves. Therefore, extra-low permeability reservoirs play a very important role in China's oil and gas industry. Limited by the prominent characteristics of poor physical properties, strong heterogeneity, and developed fractures in such reservoirs, the development contradictions are constantly emerging, mainly manifested as the unclear connectivity of oil layers, the complex water drive and seepage laws between injection and production wells, and the unclear distribution of remaining oil, resulting in the lack of effective theoretical support for reservoir development adjustment and restricting the further exertion of oil well potential.

[0003] For a long time, many scholars have carried out a large number of research works on the distribution of remaining oil in extra-low permeability reservoirs, which can be mainly divided into two types: microscopic remaining oil characterization and macroscopic remaining oil characterization. Microscopic remaining oil mainly studies the occurrence state and distribution characteristics of remaining oil by means of core displacement and microscopic physical models; macroscopic remaining oil research mainly includes remaining oil logging and reservoir numerical simulation technology. Among them, reservoir numerical simulation is the remaining oil characterization method with the highest reliability and the widest application at present. However, due to the small research scale, microscopic remaining oil characterization can only be used as a qualitative mechanism research method; in the macroscopic remaining oil characterization method, remaining oil logging requires logging data acquisition of actual oil wells, and the construction cost is high; reservoir numerical simulation depends on a large amount of basic data and reservoir geological modeling, and the simulation process requires a large amount of computer time. In addition, as the smallest injection-production unit, only by focusing on the well group to carry out remaining oil characterization can it more directly and effectively provide a basis for remaining oil potential tapping and treatment. Obviously, the research scale of the existing methods is not very applicable to the description of remaining oil in well groups. Summary of the Invention

[0004] Aiming at the above deficiencies of the existing technology, the purpose of the present invention is to provide a method for quantitatively characterizing remaining oil in an injection-production well group in an extra-low permeability reservoir. During the process, only the physical properties and production data of injection and production wells are required. Its calculation process is relatively simple, and the data is easy to obtain. It can carry out the calculation of remaining oil between wells and quantitatively describe the distribution of remaining oil saturation, accurately and real-time providing theoretical support for the development adjustment of extra-low permeability reservoirs.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A method for quantitatively characterizing remaining oil in an injection-production well group in an extra-low permeability reservoir, comprising the following steps:

[0007] S1. Centering on the injection well, divide the injection-production unit of the well group, and calculate the average porosity, permeability, water cut, and water saturation of each unit;

[0008] S2. Calculate the effective distances of the water-washed zone, two-phase zone, and swept zone corresponding to each unit respectively, and determine the control ranges of the above different zones in turn;

[0009] S3. Calculate the remaining oil saturation within the control ranges of the water-washed zone, two-phase zone, and swept zone corresponding to each unit respectively;

[0010] S4. Draw the remaining oil saturation distribution map of the injection-production well group to obtain the remaining oil distribution pattern of the well group in the extra-low permeability reservoir.

[0011] Preferably, in step S1, the calculation methods of the average porosity, permeability, and water saturation are to conduct weighted averaging on the measured values of the injection-production wells.

[0012] Preferably, in step S1, the calculation method of the water cut is the average of the water cuts of the production wells in the past three months.

[0013] Preferably, in step S2, the calculation of the effective distance of the water-washed zone is divided into two cases: pore-type reservoir and fracture-type reservoir;

[0014] The calculation formula for the effective distance of the water-washed zone in the pore-type reservoir is:

[0015]

[0016] In the formula: r wr is the effective distance of the water-washed zone, m; S or is the residual oil saturation, %; is the derivative of the water cut vs. water saturation curve; φ is the average porosity, decimal; h is the effective thickness, m; q w is the water production of the production well, m 3 / d; t d is the water breakthrough time of the oil well, d, t is the production time;

[0017] The calculation formula for the effective distance of the water-washed zone in the fracture-type reservoir is:

[0018]

[0019] In the formula: K t is the average permeability of the water-washed zone, mD; μ is the formation water viscosity, mPa·s; C t is the comprehensive formation compressibility, MPa -1 ; φ is the average porosity, decimal.

[0020] Preferably, in step S2, the calculation of the effective distance in the two-phase region is also divided into two cases: porous reservoirs and fractured reservoirs;

[0021] The calculation formula for the effective distance in the two-phase region of the porous reservoir is:

[0022]

[0023] In the formula: r f is the effective distance in the two-phase region, m; R is the recovery factor of the crude oil in the well group, %; A, B, and C are constants related to the starting pressure gradient, mobility, and injection-production pressure difference respectively;

[0024] For the fractured reservoir, the two-phase region is elliptical, and the calculation formulas for the effective distances in the short-axis and long-axis directions are respectively:

[0025]

[0026]

[0027] In the formula: r af and r bf are the effective distances in the short-axis and long-axis directions respectively, m; L is the half-length of the fracture, m.

[0028] Preferably, in step S2, the calculation formula for the effective distance in the swept region is:

[0029]

[0030] In the formula: r is the effective distance in the swept region, m; r w is the wellbore radius; S w is the water saturation, %; t is the production time, d; is the derivative of the water cut vs. water saturation curve; φ is the average porosity, in decimals; h is the effective thickness, m; q w is the water production of the oil production well, m 3 / d.

[0031] Preferably, in step S3, the remaining oil saturation in the water-washed zone is the residual oil saturation.

[0032] Preferably, in step S3, the remaining oil saturation in the two-phase region is the average oil saturation in the two-phase region, and the calculation method is:

[0033]

[0034] In the formula: is the average oil saturation in the two-phase region, %; φ is the average porosity, in decimals; h is the effective thickness, m; q w is the water production of the oil production well, m 3 / d; r f is the effective distance in the two-phase zone, m; r wr is the effective distance in the water washing zone, m; t is the production time, d.

[0035] Preferably, in step S3, the remaining oil saturation in the swept zone is the average oil saturation in the swept zone, and the calculation method is:

[0036]

[0037] In the formula: S od is the average oil saturation in the swept zone, %; S oi is the initial oil saturation, %; A wr 、A tp 、A od 、A d respectively represent the areas of the water washing zone, the two-phase zone, the swept zone and the well group; S or is the residual oil saturation, %; is the average oil saturation in the two-phase zone, %.

[0038] Preferably, in step S4, the remaining oil distribution patterns in the well groups of ultra-low permeability reservoirs include moderately waterflooded uniformly affected type, unidirectional waterflooded directionally affected type, multi-directional waterflooded directionally affected type, locally weakly exploited directionally affected type and insufficient displacement weakly affected type.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The characterization method of the present invention can quantitatively and intuitively describe the distribution law of inter-well remaining oil, and point out the potential tapping directions of well groups under different remaining oil distribution patterns, providing a decision-making basis for improving the development effect of ultra-low permeability reservoirs;

[0041] (2) The present invention only requires physical property data such as porosity, permeability, effective thickness, and oil saturation of injection and production wells, as well as basic parameters such as production dynamic data. The data involved are few and easy to obtain;

[0042] (3) The present invention is mainly based on the two-phase seepage theory in reservoir engineering, and the calculation process is relatively simple and operable. Compared with traditional methods such as reservoir numerical simulation, it avoids a large amount of waste of computer time and saves a large amount of time and labor costs;

[0043] (4) Compared with the actual dynamic monitoring and analysis results, the calculation results of the present invention have a high degree of conformity, can meet the engineering needs, and can be widely applied in ultra-low permeability reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Other features, objectives, and advantages of the present invention will become more apparent by reading the following detailed description of non - restrictive embodiments with reference to the accompanying drawings:

[0045] Figure 1 This is a flow chart of the method for quantitatively characterizing the remaining oil in the injection - production well group of extra - low - permeability reservoirs of the present invention.

[0046] Figure 2 This is a schematic diagram of the division of the injection - production unit and different exploited areas provided by the present invention; among them, Figure 2 a is the division of the injection - production unit of the well group, Figure 2 b is a schematic diagram of the distribution of the water - flooded area, two - phase area, swept area, and unexploited area within the well group.

[0047] Figure 3 This is an application example of the comparison between the saturation distribution of the well group and the monitoring results of the water - flooding front completed according to the present invention; among them, Figure 3 a is the remaining - oil saturation distribution map of the injection - production well group, Figure 3 b is the monitoring result of the water - flooding front of the injection - production well group. Detailed Embodiment

[0048] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made. These all belong to the protection scope of the present invention.

[0049] Embodiment 1

[0050] As Figure 1 shown, a method for quantitatively characterizing the remaining oil in the injection - production well group of extra - low - permeability reservoirs includes the following steps:

[0051] S1. Taking the injection well as the center, divide the well group into injection - production units, and obtain physical property parameters such as the average porosity, permeability, water cut, and water saturation of each unit; among them, the calculation methods of the average porosity, permeability, and water saturation are to perform weighted averaging on the measured values of the injection - production wells; the calculation method of the average water cut is the average value of the water cut of the production wells in the past three months.

[0052] Well group Ping 39-31 is located in a ultra-low permeability reservoir. This well group has a rhombic inverted nine-spot well pattern. The average oil layer thickness (effective thickness) of the well group is 14.7 m, the average porosity and permeability are 9.72% and 0.46 mD respectively, and the initial oil saturation and residual oil saturation are 56.3% and 27.4% respectively. Currently, the production time of the well group is 7.4 years, and the average water cut of the well group has reached 62.8%. Geological and dynamic monitoring studies show that there are no fractures developed in this well group, and it is a pore-type reservoir. The specific reservoir physical properties and production data of production wells and injection wells are shown in Table 1; in addition, the wellbore radius of all single wells is 0.1 m, and other relevant constants can be referred to the classic literature in this industry.

[0053] Table 1 Statistical table of physical property parameters and production data of single wells in Well Group Ping 38-31

[0054]

[0055] The production performance data that need to be collected include: porosity, permeability, effective thickness, initial oil saturation and remaining oil saturation, oil production / water production of production wells, formation water viscosity, formation comprehensive compressibility, fracture half-length, water breakthrough time of oil wells, production time, oil recovery of the well group, constants related to starting pressure gradient, mobility and injection-production pressure difference, and wellbore radius. Collect according to the demand according to whether the reservoir type is pore-type reservoir or fracture-type reservoir.

[0056] S2. Calculate the effective distances of the water-washed zone, two-phase zone and swept zone corresponding to each unit respectively, and determine the control ranges of the above different zones in turn;

[0057] The calculation formula for the effective distance of the water-washed zone of the pore-type reservoir is:

[0058]

[0059] In the formula: r wr is the effective distance of the water-washed zone, m; S or is the residual oil saturation, %; is the derivative of the water cut vs. water saturation curve; φ is the average porosity, decimal; h is the effective thickness, m; q w is the water production of the production well, m 3 / d; t d is the water breakthrough time of the oil well, d, t is the production time;

[0060] The calculation formula for the effective distance of the two-phase zone of the pore-type reservoir is:

[0061]

[0062] In the formula: r fis the effective distance of the two-phase zone, m; R is the recovery factor of the crude oil in the well group, %; A, B, and C are constants related to the starting pressure gradient, mobility, and injection-production pressure difference, respectively.

[0063] The calculation formula for the effective distance of the swept zone is:

[0064]

[0065] In the formula: r is the effective distance of the swept zone, m; r w is the wellbore radius; S w is the water saturation, %; t is the production time, d; is the derivative of the water cut vs. water saturation curve; φ is the porosity, decimal; h is the effective thickness, m; q w is the water production of the oil production well, m 3 / d.

[0066] Taking the rhombic inverted nine-spot well pattern shown by this well group as an example, the division method of the injection-production unit of the well group is given (Appendix Figure 2 a) and the schematic diagrams of the distributions of the water-washed zone, two-phase zone, swept zone, and produced zone within the well group (Appendix Figure 2 b).

[0067] S3. Calculate the remaining oil saturation within the control ranges of the corresponding water-washed zone, two-phase zone, and swept zone in each unit;

[0068] The remaining oil saturation in the water-washed zone is the residual oil saturation.

[0069] The remaining oil saturation in the two-phase zone is the average oil saturation in the two-phase zone, and the calculation method is:

[0070]

[0071] In the formula: is the average oil saturation in the two-phase zone, %; φ is the porosity, decimal; h is the effective thickness, m; q w is the water production of the oil production well, m 3 / d; r f is the effective distance of the two-phase zone, m; r wr is the effective distance of the water-washed zone, m; t is the production time, d.

[0072] The remaining oil saturation in the swept zone is the average oil saturation in the swept zone, and the calculation method is:

[0073]

[0074] In the formula: S od is the average oil saturation in the swept zone, %; S oi is the initial oil saturation, %; A wr, A tp , A od , A d represent the areas of the water washing zone, two-phase zone, swept zone, and well pattern respectively; S or is the residual oil saturation, %; is the average oil saturation in the two-phase zone, %.

[0075] Based on the known parameters of the well pattern, using the characterization method described in the present invention, the effective distances and corresponding oil saturations of the water washing zone, two-phase zone, and swept zone are calculated respectively, and the specific results are shown in Table 2.

[0076] Table 2 Calculation results of the remaining oil quantitative characterization parameters of Well Pattern Ping 38-31

[0077]

[0078] Using the above calculation results, the remaining oil saturation distribution map of the injection-production well pattern is drawn ( Figure 3 a); at the same time, comparing the calculation results with the monitoring results of the water drive front of the well pattern ( Figure 3 b), it can be found that the calculation results are highly consistent with the actual monitoring, indicating the scientificity and reliability of the characterization method described in the present invention.

[0079] S4. Draw the remaining oil saturation distribution map of the injection-production well pattern to obtain the remaining oil distribution pattern of the well pattern in the extra-low permeability reservoir. The remaining oil distribution pattern of the well pattern in the extra-low permeability reservoir includes the moderately water-driven uniformly affected type, the unidirectional waterflooding directionally affected type, the multi-directional waterflooding directionally affected type, the locally weakly mobilized directionally affected type, and the insufficient displacement weakly affected type.

[0080] Using the drawn remaining oil distribution map between wells, the distribution law of the remaining oil between wells and the distribution characteristics of the unproduced oil reserves between wells can be very intuitively described, so as to facilitate the fine adjustment of the injection-production technical policy of the well pattern in a timely manner.

[0081] Example 2

[0082] According to the calculation process described in Example 1, the characterization of the remaining oil distribution of 53 well patterns in the reservoir where it is located is completed, five typical remaining oil distribution patterns existing in the extra-low permeability reservoir are proposed, and the corresponding remaining oil occurrence characteristics are summarized; on this basis, the remaining oil potential tapping directions of the well patterns under different patterns are given, providing a decision-making basis for effectively tapping the remaining oil of the well patterns and improving the development effect of the extra-low permeability reservoir (see Table 3).

[0083] Table 3 Remaining oil distribution patterns and potential tapping directions of well patterns in extra-low permeability reservoirs

[0084]

[0085] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for quantitatively characterizing the remaining oil in an injection-production well group in an ultra-low permeability reservoir, characterized in that, It includes the following steps: S1. Centering on the injection well, divide the injection-production unit of the well group, and obtain the average porosity, permeability, water cut and water saturation of each unit; S2. Calculate the effective distances of the water-washed zone, two-phase zone and swept zone corresponding to each unit respectively, and determine the control ranges of different zones in turn; The calculation of the effective distance of the water-washed zone is divided into two cases: porous reservoir and fractured reservoir; The calculation formula for the effective distance of the water-washed zone of the porous reservoir is: ， where: r wr is the effective distance of the water washing zone, m; S or is the residual oil saturation, %; is the derivative of the water cut vs. water saturation curve; φ is the average porosity, in decimals; h is the effective thickness, in m; q w is the water production of the oil production well, in m 3 / d; t d is the water breakthrough time of the oil well, in d, and t is the production time; The calculation formula for the effective distance of the water-washed zone of the fractured reservoir is: ， Where: K t is the average permeability in the water washing area, mD; μ is the viscosity of formation water, mPa·s; C t is the comprehensive compressibility of the formation, MPa -1 ; φ is the average porosity, decimal; The calculation of the effective distance of the two-phase zone is also divided into two cases: porous reservoir and fractured reservoir; The calculation formula for the effective distance of the two-phase zone of the porous reservoir is: ， where: r f is the effective distance in the two-phase zone, m; R is the oil recovery factor of the well group, %; A, B, and C are constants related to the starting pressure gradient, mobility, and injection-production pressure difference, respectively; For the fractured reservoir, the two-phase zone is elliptical, and the calculation formulas for the effective distances in the short-axis and long-axis directions are respectively: ， ， where: r af and r bf are the effective distances in the minor axis and major axis directions, respectively, in m; L is the half-length of the crack, in m; The calculation formula for the effective distance of the swept zone is: ， where: r is the effective distance of the affected area, m; r w is the wellbore radius; S w is the water saturation, %; t is the production time, d; is the derivative of the water content vs. water saturation curve; φ is the average porosity, in decimals; h is the effective thickness, in m; q w is the water production of the oil production well, in m 3 / d; S3. Calculate the remaining oil saturation within the control ranges of the water-washed zone, two-phase zone and swept zone corresponding to each unit respectively, The remaining oil saturation in the water-washed zone is the residual oil saturation; The remaining oil saturation in the two-phase zone is the average oil saturation in the two-phase zone, and the calculation method is: ， Where: is the average oil saturation in the two-phase zone, %; φ is the average porosity, in decimals; h is the effective thickness, in m; q w is the water production of the oil production well, in m 3 / d; r f is the effective distance of the two-phase zone, in m; r wr is the effective distance of the water-washed zone, in m; t is the production time, in d; The remaining oil saturation in the swept zone is the average oil saturation in the swept zone, and the calculation method is: ， Where: S od is the average oil saturation in the affected area, %; S oi is the initial oil saturation, %; A wr , A tp , A od , A d respectively represent the areas of the water-washed zone, two-phase zone, affected area and well group; S or is the residual oil saturation, %; is the average oil saturation in the two-phase zone, %; S4. Draw the remaining oil saturation distribution map of the injection-production well group to obtain the remaining oil distribution pattern of the well group in the extra-low permeability oil reservoir.

2. The method for quantitatively characterizing the remaining oil in an injection-production well group in an extra-low permeability reservoir according to claim 1, wherein In step S1, the calculation methods for the average porosity, permeability and water saturation are to perform weighted averaging on the measured values of the injection-production wells.

3. A method for quantitatively characterizing the remaining oil in an injection-production well group in an extra-low permeability reservoir according to claim 1, characterized in that, In step S1, the calculation method for the water cut is the average value of the water cuts of the production wells in the past three months.

4. A method for quantitatively characterizing remaining oil in an injection-production well group in an ultra-low permeability reservoir according to claim 1, characterized in that In step S4, the remaining oil distribution patterns of the well group in the extra-low permeability oil reservoir include the moderately water-flooded and uniformly affected type, the unidirectional water-flooded and directionally affected type, the multi-directional water-flooded and directionally affected type, the locally weakly mobilized and directionally affected type, and the insufficient displacement and weakly affected type.

Images