Well pattern structure adjusting method for chemical flooding development of common heavy oil reservoir

Abstract

The invention provides a well pattern structure adjusting method for chemical flooding development of a common heavy oil reservoir, which is suitable for improving the water flooding effect of the reservoir in a'double-high 'development stage, maximizing the yield increasing effect and further improving the recovery efficiency. The method comprises the steps that an oil reservoir meeting chemical flooding development conditions is selected for chemical flooding development; determining an oil-water movement rule and a main water drive direction according to the dynamic and static data obtained in each development stage of the oil reservoir; determining the remaining oil distribution type, and accurately estimating the remaining oil saturation of the oil reservoir and the target layer at the current stage; determining a test well selection principle, and preferably selecting a test area; a proper well pattern and well spacing is determined, a five-point method well pattern is adopted as the well pattern form, and the well pattern of the chemical zone interval displaces in the direction perpendicular to the source or the lateral direction; according to the saturation degree of the remaining oil, an old well is used for transfer injection, and the well pattern is split and recombined for adjustment; and injection-production parameters are designed according to the adjusted well pattern, and chemical flooding production is conducted.

Description

Technical Field

[0001] The invention belongs to the technical field of oil reservoir development, and relates to the development of layered common heavy oil reservoirs for water injection development, and specifically to a well pattern structure adjustment method for chemical flooding development of common heavy oil reservoirs. Background Art

[0002] The viscosity of crude oil is a measure of the frictional resistance of one part of the crude oil relative to another part when it flows. It is an important parameter for oil and gas field development. At present, China's classification method for heavy oil is based on the viscosity of degassed crude oil under reservoir temperature conditions: ordinary heavy oil has a viscosity of 50 to 10,000 mPa·s; extra heavy oil has a viscosity of 10,000 to 50,000 mPa·s; and super heavy oil has a viscosity greater than 50,000 mPa·s. Although ordinary heavy oil has a relatively low viscosity, it also faces the problem of poor flowability and difficulty in extraction.

[0003] Water injection development is to use water injection equipment to inject water of the required quality from the water injection well into the oil layer to achieve the purpose of maintaining the oil layer pressure and displacing crude oil. In the process of water injection development of heterogeneous multi-layer reservoirs, due to the three major differences in the properties of the oil layers, the plane and the layer, the injected water is unevenly advanced in the direction of each oil layer, and the oil-water relationship is complicated. At the same time, affected by the large oil-water viscosity ratio, ordinary heavy oil reservoirs form high-permeability water channels after long-term water injection flushing, resulting in inefficient or ineffective circulation of a large amount of injected water, which cannot effectively displace crude oil and affects the development effect.

[0004] Chemical flooding, also known as modified water flooding chemical method, refers to adding chemical agents to the injected water to change the physical and chemical properties of the displacement fluid and the interface properties between the displacement fluid and crude oil and rock minerals, so as to facilitate crude oil production. Chemical flooding EOR technologies mainly include polymer flooding, polymer-surfactant composite flooding, ternary composite flooding, etc., among which polymer flooding is the most mature. Polymer flooding is to add high molecular polymers to the injected water to increase the viscosity of the displacement phase, adjust the water absorption profile of the oil layer, and expand the swept volume of the displacement phase, thereby improving the recovery rate. Polymer-surfactant composite flooding refers to polymer-surfactant binary composite flooding technology, which is an tertiary oil recovery technology developed in recent years. Polymer-surfactant composite flooding has the function of polymer flooding to increase the swept volume, and the function of ternary composite flooding to improve the oil recovery efficiency. It is expected to increase the recovery rate by more than 18%, which is close to the recovery rate increase of ternary composite flooding. It is a tertiary oil recovery method with little damage to the reservoir, good input-output prospects, and development potential, and has good application prospects.

[0005] Oryx Company of the United States conducted a pilot test of alkali-free binary composite flooding in Ranger Oilfield. The amount of oil produced accounted for one-fourth of the total amount of residual oil after water flooding, and achieved significant oil flooding effect. In 2003, Sinopec Shengli Oilfield conducted a pilot test of alkali-free binary composite flooding technology in Gudong Oilfield. The average reservoir permeability was 1320mD, the permeability variation coefficient was 0.58, the porosity was 34%, the original oil saturation was 72.0%, the residual oil saturation was 45.5%, and the underground crude oil viscosity was 45mPa·s; it is currently a relatively successful polymer-surfactant binary composite flooding test in China. The daily oil production increased by up to 166t, the water content decreased by 12.5%, and the test area increased the recovery rate by more than 12%. Compared with the unit with the best polymer flooding effect in Gudong Oilfield, the water content reduction in the pilot test area of ​​binary composite flooding was higher than that of the single polymer flooding unit, and the oil increase in the pilot test area of ​​binary composite flooding was also higher than that of single polymer flooding. Since 2008, PetroChina has accelerated the pace of major development tests of polymer-surfactant binary composite flooding, deployed major development tests of polymer-surfactant binary composite flooding in five blocks, and achieved significant results.

[0006] Although PSC flooding has achieved many results in laboratory research and field tests, it is still a blank in the field of ordinary heavy oil. For ordinary heavy oil reservoirs in the layered sandstone in the "double high" development stage, especially after 10 years of adjustment and flooding development, the transition to PSC flooding still faces the following challenges:

[0007] (1) After deep flooding of oil reservoirs, the distribution of remaining oil becomes more complex and scattered. Refining the remaining oil is a key design technology that determines whether it can be economically and effectively transferred to chemical flooding development. In other words, accurate estimation of the current remaining oil determines the final recovery rate and economic benefits.

[0008] (2) The impact of deep flooding on the injection effect of chemical flooding is still unclear. The adaptability of the well pattern and well spacing to chemical flooding needs further evaluation and research. Without deploying new wells, it is extremely important to optimize the well pattern and well spacing and improve the utilization rate of old wells. Summary of the invention

[0009] In order to improve the development contradictions faced by ordinary heavy oil reservoirs in the transition to polymer-surface composite flooding in the "double high" development stage, the present invention provides a well network structure adjustment method for chemical flooding development of ordinary heavy oil reservoirs, which is suitable for improving the water flooding effect of oil reservoirs in the "double high" development stage, maximizing the production increase effect, and further improving the recovery rate.

[0010] The technical solution adopted by the present invention to solve the technical problem is:

[0011] A method for adjusting a well pattern structure for chemical flooding development of a common heavy oil reservoir, comprising the following steps:

[0012] Select oil reservoirs that meet the chemical flooding development conditions for chemical flooding development;

[0013] Determine the law of oil-water movement and the main water drive direction based on the dynamic and static data obtained at each stage of reservoir development;

[0014] Determine the remaining oil distribution type and accurately estimate the remaining oil saturation of the current reservoir and target layer;

[0015] Determine the test well selection principles and select the best test area;

[0016] Determine the appropriate well spacing and well pattern. The well pattern adopts the five-point method. The well pattern of the chemical zone layer is in the vertical direction of the source or lateral displacement.

[0017] According to the remaining oil saturation, old wells are used for injection, and the well network is split, reorganized and adjusted;

[0018] The injection and production parameters are designed according to the adjusted well pattern, and chemical flooding production is carried out.

[0019] Furthermore, the oil reservoirs selected for chemical flooding development meet the following conditions: layered sandstone reservoirs without gas cap and bottom water, reservoir permeability>50md, effective oil layer thickness>8m, reservoir connectivity>70%, remaining oil saturation>35%, stable barriers at the top and bottom of the target layer, coverage>1 million tons, formation temperature<80℃, underground crude oil viscosity<100mPa·s, formation water mineralization<10000mg / L, reservoir water flooding control degree>70%, and obvious effect during water injection development.

[0020] Furthermore, the method for accurately estimating the remaining oil saturation of the current reservoir and target layer is:

[0021] Option 1: Calculate the current water saturation of the oil field by taking the pore volume of produced oil occupied by injected water;

[0022] Option 2: Test the current water saturation of the oil field through the C / O test method, and correct the C / O test oil saturation using the standard phase permeability curve;

[0023] Scheme 3: Based on the statistical water absorption profile data, calculate the cumulative water absorption and water absorption radius of each sublayer of the water injection well, and split the water injection wells without water absorption profile according to their perforation thickness and cumulative water injection volume with the perforation thickness permeability kh value; mark the calculated water absorption radius of each sublayer of each water injection well on each sublayer oil layer isopach map, and draw the approximate flooding range; judge the approximate water content of each sublayer of each oil well, and mark it on each sublayer oil layer isopach map, further determine the water absorption and oil well flooding of each sublayer of each oil well, and draw the main oil layer flooding map; weighted average the water content of each sublayer of each oil well according to the effective thickness of the oil layer, and obtain the water content of each sandstone group single well, oil layer group and wellhead water content;

[0024] Combining the research results of the above three schemes with numerical simulation prediction, the remaining oil saturation of the reservoir and target layer at this stage is finally obtained.

[0025] Furthermore, the current water saturation of the oil field is calculated by taking the pore volume of the produced oil occupied by the injected water, and the calculation formula is as follows:

[0026]

[0027] In formula (1), S oi It represents the original oil saturation, in %; N represents the crude oil geological reserves, in 10 4 t;N p Indicates the cumulative oil production, unit 10 4 t; B or Indicates the current formation crude oil volume coefficient; B oi Represents the volume coefficient of original formation crude oil.

[0028] Furthermore, the oil saturation of the C / O test is corrected using a standard phase permeability curve, and the formula is as follows:

[0029]

[0030] In formula (2), Sw represents the water saturation of C / O ratio after correction, unit %; Sw' represents the water saturation of C / O ratio before correction, unit %; Swi represents the irreducible water saturation in the standard phase permeability curve, unit %; Sor represents the residual oil saturation in the standard phase permeability curve, unit %.

[0031] Furthermore, the cumulative water absorption of each sublayer of the water injection well is calculated using the following formula:

[0032]

[0033] In formula (3), V w Indicates the cumulative water absorption of each sublayer of the injection well, unit: m 3 ;Qw Indicates the cumulative injection volume of the injection well during the test phase, in m 3 ; i It indicates the relative water absorption percentage of the small layer in the tested water absorption profile, in decimal units.

[0034] Furthermore, the water absorption radius of each small layer of the water injection well is calculated according to the following formula:

[0035]

[0036] In formula (4), R represents the water absorption radius centered on the injection well, in meters; V w Indicates the cumulative water absorption of each sublayer of the injection well, unit: m 3 ; V wo Indicates the cumulative water volume produced by each sublayer of the injection well, unit: m 3 ; h is the effective thickness of the oil layer, in m; φ is the porosity, in decimal; S O Indicates the original oil saturation of the oil layer, in decimal units; S WO Indicates the current remaining oil saturation of the oil layer, in decimal units.

[0037] Furthermore, the water absorption of each sub-layer of each oil well and the water flooding of the oil wells as described in Plan 3 are further determined based on the cumulative water absorption and water absorption radius of each sub-layer of the water injection wells, the approximate water content of each sub-layer of each oil well, the sub-layer oil layer isopach map, the interpretation data of well flooding adjustment in recent years, the porosity, permeability, saturation isopach map of each sub-layer, the sedimentary phase map and the connectivity map.

[0038] The beneficial effects of the present invention include:

[0039] The present invention develops a method for adjusting the chemical drive well network structure. In the process of converting the development mode in the later stage of water drive development of ordinary heavy oil reservoirs, the injection and production well network is adjusted to improve the seepage direction of the injected medium, effectively displace the remaining oil, and improve the recovery rate. This method is different from the traditional well network structure adjustment. Without deploying adjustment wells and reducing investment, the side reverse oil wells in the original injection and production well group are directly selected for injection, and the original injection and production well network is split and reorganized to break the dominant channel formed under the water injection development mode and realize the liquid flow diversion. This method is particularly suitable for well groups that have been adjusted and driven in the later stage of water injection development of ordinary heavy oil reservoirs. Specifically, the present invention has the following advantages:

[0040] Improve reservoir development results: By determining the oil-water movement law and the main water drive direction based on the dynamic and static data obtained at each stage of reservoir development, and accurately estimating the remaining oil saturation, the well network structure can be optimized in a targeted manner, thereby improving the effect of chemical flooding.

[0041] Reduce development costs: By optimizing the well network structure based on experimental well selection principles and appropriate well spacing, old wells can be fully utilized for injection, and the well network can be split, reorganized and adjusted, thereby avoiding the high cost of new wells and reducing the overall development cost.

[0042] Increase production revenue: By rationally designing injection and production parameters and conducting chemical flooding production according to the adjusted well pattern, the production capacity and recovery rate of the reservoir can be effectively improved, thereby increasing production revenue.

[0043] In general, this well pattern structure adjustment method can improve the chemical flooding development effect, reduce development costs, and increase production revenue, which has a positive impact on the development of ordinary heavy oil reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Schematic diagram of the comparison of the chemical flooding well pattern structure before and after adjustment of the present invention;

[0045] Figure 2 This is a schematic diagram of three-directional displacement of numerical simulation of the present invention;

[0046] Figure 3 This is a comparison diagram of water flooding recovery rates in different displacement directions of the present invention;

[0047] Figure 4 It is a curve diagram of connectivity coefficient under different well spacings of the present invention. DETAILED DESCRIPTION

[0048] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] In order to improve the development contradictions faced by ordinary heavy oil reservoirs in the "double high" development stage, the present invention proposes a well pattern structure adjustment method for chemical flooding development of ordinary heavy oil reservoirs using lateral reverse injection and flow line change to improve water flooding effect, comprising the following steps:

[0050] (1) Selecting oil reservoirs that meet the chemical flooding development conditions for chemical flooding development;

[0051] (2) Based on the dynamic and static data obtained at each development stage, study the laws of oil and water movement and analyze the main water drive directions;

[0052] (3) Combine multiple methods to study the distribution type of remaining oil and accurately estimate the remaining oil;

[0053] (4) Determine the test well selection principles and select the best test area;

[0054] (5) Determine the reasonable well pattern and spacing;

[0055] (6) Use old wells for re-injection and split, reorganize and adjust the well network;

[0056] (7) Design injection and production parameters according to the adjusted well pattern and carry out chemical flooding production.

[0057] Specifically, the selected oil reservoirs meet the following conditions: layered sandstone reservoirs without gas cap and bottom water, reservoir permeability>50md (millidarcy), effective oil layer thickness>8m, reservoir connectivity>70%, remaining oil saturation>35%, the top and bottom of the target layer have stable barriers, coverage scale>1 million tons, formation temperature<80℃, underground crude oil viscosity<100mPa·s (milliPascal·second, unit of viscosity), formation water mineralization<10000mg / L, reservoir water drive control degree>70%, and obvious effect in the water injection development process.

[0058] Preferably, a relatively regular inverted seven-spot well pattern with a well spacing of 120 to 200 m is used, and the oil reservoir has been developed by deep adjustment and flooding, and the recovery rate in the deep adjustment and flooding stage reaches 7% to 15%.

[0059] Furthermore, the optimization and adjustment of the well network structure is related to the distribution of remaining oil and the appropriate well network spacing; the use of old wells for injection and splitting and reorganizing the well network should focus on the adjusted well network type and well spacing; the lateral reverse remaining oil in the main water drive direction of the well group is relatively enriched and has not been effectively displaced in the previous development process. By injecting old wells in this area, the purpose of changing the established flow line can be achieved.

[0060] The specific steps are as follows:

[0061] Accurately estimate remaining oil:

[0062] ①Material balance method:

[0063] In oil fields developed by water injection to maintain formation pressure, the water saturation of the oil field is calculated by the pore volume of the produced oil occupied by the injected water, that is, the material balance method is used to calculate the current oil saturation. The formula is as follows:

[0064]

[0065] In the formula, S oi --Original oil saturation, %;

[0066] N--geological reserves of crude oil, 10 4 t;

[0067] N p --Cumulative oil production, 10 4 t;

[0068] B or--Current formation crude oil volume factor;

[0069] B oi --Volume coefficient of original formation crude oil.

[0070] ②C / O test method:

[0071] Because the oil saturation interpreted by C / O logging is quite different from the oil saturation measured by core and the oil saturation value analyzed by production dynamic data, the oil saturation tested by C / O is corrected using the standard phase permeability curve. The calculation formula is as follows:

[0072]

[0073] Where: Sw——corrected C / O ratio water saturation, %;

[0074] Sw'——C / O ratio water saturation before correction, %;

[0075] Swi——Immobile water saturation in standard relative permeability curve, %;

[0076] Sor——Residual oil saturation of standard phase permeability curve, %.

[0077] ③Dynamic analysis method:

[0078] First, according to the statistical water absorption profile data, the cumulative water absorption and water absorption radius of each small layer of the water injection well are calculated. The calculation formula is as follows:

[0079]

[0080]

[0081] Where: V w —Accumulative water absorption of each sublayer in the injection well, m 3 ;

[0082] Q w —Cumulative injection volume of water injection wells during the test phase, m 3 ;

[0083] λ i —Relative water absorption percentage of the small layer of the test water absorption profile, decimal;

[0084] V wo —Cumulative water volume produced from each layer of the injection well, m 3 ;

[0085] h—effective thickness of oil layer, m;

[0086] φ—porosity, decimal;

[0087] S O—Original oil saturation of the oil layer, decimal;

[0088] S WO —The current remaining oil saturation of the oil layer, decimal;

[0089] R—water absorption radius centered on the injection well, m.

[0090] For water injection wells without water absorption profiles, they are split according to their perforation thickness and cumulative water injection volume, using the permeability kh value of the perforation thickness. The calculated water absorption radius of each small layer of each water injection well is marked on each small layer oil layer isopach map to draw a rough flooding range.

[0091] The interpretation table of each oil well is recorded in full, and then based on the water detection and plugging measures in previous years and combined with the current and past production history, the approximate water content of each sublayer of each oil well is determined and marked on each sublayer oil layer isopach map.

[0092] Combining the above data with the interpretation data of well flooding adjustment in recent years, the porosity, permeability, saturation and other thickness maps of each sublayer, the sedimentary phase map and the connectivity map, we further determined the water absorption situation of each oil well and the flooding situation of each sublayer of the water injection well, and drew the flooding map of the main oil layer.

[0093] The water content of each small layer in each oil well is weighted averaged according to the effective thickness of the oil layer, and the water content of each sandstone group, the oil layer group and the wellhead can be obtained respectively.

[0094] Combining the research results of the above three methods with numerical simulation prediction, the remaining oil saturation of the reservoir and target layer at this stage is finally obtained.

[0095] Determine reasonable and appropriate well pattern and spacing

[0096] According to numerical simulation, dynamic analysis and research, combined with domestic and foreign experience in chemical flooding, a five-point well pattern is adopted, and lateral flooding in the direction perpendicular to the source is preferred.

[0097] Through numerical simulation, dynamic analysis and research, it is found that 150-200m well spacing can meet the development needs of chemical flooding. At the same time, drawing on the effectiveness of deep flooding, the chemical flooding well spacing is designed to be 150m. Under this well spacing condition, the chemical flooding injection rate has a large adjustment margin (0.11-0.22PV / a), and the connectivity coefficient of the downstream and vertical channels and the degree of polymer flooding control are all above 80%.

[0098] Example 1

[0099] refer to Figure 1 As shown, Figure 1This is a schematic diagram of the chemical flooding well pattern structure adjustment of layered common heavy oil reservoirs of the present invention. The method is based on dynamic analysis and research, and uses the method of splitting and reorganizing the well pattern for optimization and adjustment, including the following steps:

[0100] (1) Specific conditions of the selected reservoir: It is a high-porosity and high-permeability reservoir, with the main layer being mainly river channel and sand bar deposits, with an average porosity of 31.3% and a permeability of 1109×10 -3 μm 2 The pore structure type is mainly medium-high permeability large pores with medium-fine throats and relatively uniform type. The clay mineral content of the target layer is low. The thickness of the upper and lower barriers is greater than 2m, with an average of about 6m. The sealing property is good, the formation water mineralization is 2528mg / L, and the temperature of the target layer is 62-74℃, which is suitable for chemical flooding.

[0101] (2) The selected ordinary heavy oil reservoirs have gone through two main development stages: water flooding and adjustment and displacement. During the deep adjustment and displacement process, the stage recovery rate was 8.6%. During the water flooding development process, the oil wells showed obvious effects. According to the statistical analysis of the effects of 30 water injection well groups and 89 first-line oil wells, the effect rate reached more than 90%. From the perspective of the effect type of the oil wells, they mainly showed three types: increased liquid and oil, stable liquid and oil, and slowed decline. Among them, the proportion of increased liquid and oil, stable liquid and oil was more than 70%. From the perspective of the effect direction of the oil wells, they mainly showed three types: unidirectional effect, two-way effect and multi-directional effect. Among them, the proportion of two-way effect or more was more than 70%. During the deep adjustment and displacement process, 78% of the water absorption thickness was improved, the average single well water absorption thickness increased by 0.7m, the interlayer and plane contradictions were effectively improved, and the production degree increased by 3.2%. The effect of reducing water and increasing oil production is significant, with 79% of the corresponding oil wells showing results, of which Class I and Class II effective wells account for more than 40%, and are mainly distributed in high structural parts. The distance between injection and production wells is 150 to 180 meters. The smaller the well spacing, the more obvious the effect of regulation and drive.

[0102] (3) This method is mainly based on the geological characteristics and actual production situation of the reservoir, and uses reservoir engineering methods such as material balance method, C / O test method, dynamic analysis method, numerical simulation, etc. to calculate the remaining oil saturation. According to the actual parameters, the average remaining oil saturation of the reservoir is calculated to be 41.1%, among which the remaining oil saturation of the target layer of chemical flooding is 37.7%. The numerical modeling study shows that although the reservoir is severely flooded as a whole, the oil saturation of the local river channel edge, between river channels, and front thin sand area is above 40% due to the heterogeneity of the reservoir and the degree of injection and production perfection. The four main remaining oil modes are inter-well retention type, poor thin layer production type, local well network imperfect type, and fault control type. Among them, the inter-well retention type accounts for the highest proportion, mainly distributed in the original injection and production well network perfect area. The remaining oil distribution is scattered and complex, and it is difficult to continue to tap the potential of water flooding. Chemical flooding is needed to increase the swept volume and oil washing efficiency.

[0103] (4) The thickness of the chemical flooding layer is controlled between 10 and 20 meters in the vertical direction, and the thickness of each section is as balanced as possible. The sedimentary units in the same displacement layer should be relatively concentrated, and there should be relatively stable barriers at the top and bottom of the displacement well section, with a certain injection and production capacity to meet the production needs of chemical flooding. In the plane, the structure, connectivity, oil-water distribution, production capacity and other factors are fully considered. The oil layer has a wide distribution range, a high reserve ratio, and a connectivity coefficient of more than 85%.

[0104] (5) The injection-production well pattern directly determines the technical and economic benefits of chemical flooding and is the key factor in the success of chemical flooding. Based on numerical simulation, dynamic analysis and research, combined with domestic and foreign chemical flooding experience, such as Figure 2 , Figure 3 As shown in Figure 2, the well pattern in the chemical zone has a better displacement effect in the vertical direction of the source or lateral direction, such as Figure 4 As shown in the figure, when the well spacing is 150-200m, it can better meet the development needs of chemical flooding. At the same time, drawing on the effectiveness of the reservoir in the deep flooding stage, the chemical flooding well spacing is designed to be 150m. Under this well spacing condition, the chemical flooding injection rate has a large adjustment margin (0.11-0.22PV / a), and the connectivity coefficient of the downstream and vertical channels and the degree of polymer flooding control are all above 80%.

[0105] (6) Make full use of old wells, select old wells for injection according to the water drive direction and the distribution of remaining oil, split and reorganize the original injection-production well network, and adjust the injection-production well spacing. Figure 1 As shown in the figure, B1 and B2 are water injection wells, A2 is a chemical drive target layer oil production well, A1 and A3 are non-chemical drive layer oil production wells, and long-term water injection development forms a fixed flow line. When designing the chemical drive well network, B1 and B2 are adjusted to the non-chemical drive layer water injection, and A1 and A3 are adjusted to the chemical drive layer. At the same time, A2 and A3 located in the reverse direction of the original injection well side are transferred to form a new injection and production well network. The injection well is basically located in the center of the well group, and the distance from each effective well is equivalent. The average well spacing is 150m, and each injection well corresponds to 6 to 7 oil wells.

[0106] (7) Carry out chemical flooding production according to the reconfigured well pattern and the injection parameters designed according to the chemical flooding scheme.

[0107] Application Example 1

[0108] The test area adopts an irregular injection and production well pattern. The target layer reservoir is buried at a depth of -1680 to -1760 m, with an average effective oil layer thickness of 11.6 m. The top and bottom interlayers of the target layer are well developed, with an average porosity of 31.1%, an average permeability of 1109 md, and a surface crude oil viscosity of 1224 mPa·s at 50°C. It is a layered ordinary heavy oil reservoir.

[0109] First, the development effect of the test area was evaluated to clarify the distribution characteristics of the remaining oil and its development potential. Calculations using a variety of methods showed that the current oil saturation in the test area was 37.3%, which provides a material basis for chemical flooding.

[0110] On this basis, the dynamic and static data collected at different stages were comprehensively applied to analyze the law of oil and water movement, and it was found that the flooding was serious along the source direction, the residual oil was relatively enriched in the lateral and reverse directions, and the degree of water flooding was low. Four test well groups were reconstructed by transferring old wells and splitting and reorganizing the well network.

[0111] By adjusting the injection and production wells, they were relocated to the target layer vertically and reorganized in plane. The average injection and production distance was 150m. The production and injection were allocated according to the injection-production ratio of 1:1, and chemical flooding tests were carried out.

[0112] Field test results show that the average daily oil production of the variable flow line well group is 3.8 tons per well, and the water cut decreases by 16.3%. Numerical simulation results show that the variable flow line chemical flooding increases the recovery factor by 19.3%, which is 2.8% higher than the recovery factor of the original flow line chemical flooding.

[0113] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for adjusting the well pattern structure for chemical flooding development of ordinary heavy oil reservoirs, wherein the characteristic steps are include: Select oil reservoirs that meet the chemical flooding development conditions for chemical flooding development; Determine the law of oil-water movement and the main water drive direction based on the dynamic and static data obtained at each stage of reservoir development; Determine the remaining oil distribution type and accurately estimate the remaining oil saturation of the current reservoir and target layer; Determine the test well selection principles and select the best test area; Determine the appropriate well spacing and well pattern. The well pattern adopts the five-point method. The well pattern of the chemical zone layer is in the vertical direction of the source or lateral displacement. According to the remaining oil saturation, old wells are used for injection, and the well network is split, reorganized and adjusted; The injection and production parameters are designed according to the adjusted well pattern, and chemical flooding production is carried out.

2. The method for adjusting the well pattern structure for chemical flooding development of common heavy oil reservoirs according to claim 1, characterized in that: The oil reservoirs selected for chemical flooding development meet the following conditions: layered sandstone reservoirs without gas cap and bottom water, reservoir permeability>50md, effective oil layer thickness>8m, reservoir connectivity>70%, remaining oil saturation>35%, stable barriers at the top and bottom of the target layer, coverage>1 million tons, formation temperature<80℃, underground crude oil viscosity<100mPa·s, formation water mineralization<10000mg / L, reservoir water flooding control degree>70%, and obvious effect during water injection development.

3. The method for adjusting the well pattern structure for chemical flooding development of common heavy oil reservoirs according to claim 1, characterized in that: The method for accurately estimating the remaining oil saturation of the current reservoir and target layer is: Option 1: Calculate the current water saturation of the oil field by taking the pore volume of produced oil occupied by injected water; Option 2: Test the current water saturation of the oil field through the C / O test method, and correct the C / O test oil saturation using the standard phase permeability curve; Scheme 3: Based on the statistical water absorption profile data, calculate the cumulative water absorption and water absorption radius of each sublayer of the water injection well, and split the water injection wells without water absorption profile according to their perforation thickness and cumulative water injection volume with the perforation thickness permeability kh value; mark the calculated water absorption radius of each sublayer of each water injection well on each sublayer oil layer isopach map, and draw the approximate flooding range; judge the approximate water content of each sublayer of each oil well, and mark it on each sublayer oil layer isopach map, further determine the water absorption and oil well flooding of each sublayer of each oil well, and draw the main oil layer flooding map; weighted average the water content of each sublayer of each oil well according to the effective thickness of the oil layer, and obtain the water content of each sandstone group single well, oil layer group and wellhead water content; Combining the research results of the above three schemes with numerical simulation prediction, the remaining oil saturation of the reservoir and target layer at this stage is finally obtained.

4. The method for adjusting the well pattern structure for chemical flooding development of common heavy oil reservoirs according to claim 3, characterized in that: The current water saturation of the oil field is calculated by taking the pore volume of the produced oil occupied by the injected water, and the calculation formula is as follows: In formula (1), S oi It represents the original oil saturation, in %; N represents the crude oil geological reserves, in 10 4 t;N p Indicates the cumulative oil production, unit 10 4 t; B or Indicates the current formation crude oil volume coefficient; B oi Represents the volume coefficient of original formation crude oil.

5. The method for adjusting the well pattern structure for chemical flooding development of common heavy oil reservoirs according to claim 3, characterized in that: The oil saturation of the C / O test is corrected using the standard phase permeability curve, and the formula is as follows: In formula (2), Sw represents the water saturation of C / O ratio after correction, in %, Sw' represents the water saturation of C / O ratio before correction, in %. Swi represents the irreducible water saturation in the standard relative permeability curve, unit: %; Sor represents the residual oil saturation of the standard phase permeability curve, in %.

6. The method for adjusting the well pattern structure for chemical flooding development of common heavy oil reservoirs according to claim 3, characterized in that: The cumulative water absorption of each small layer of the water injection well is calculated by the following formula: In formula (3), V w Indicates the cumulative water absorption of each sublayer of the injection well, unit: m 3 ;Q w Indicates the cumulative injection volume of the injection well during the test phase, in m 3 ; λ i It indicates the relative water absorption percentage of the small layer in the tested water absorption profile, in decimal units.

7. The method for adjusting the well pattern structure for chemical flooding development of common heavy oil reservoirs according to claim 6, characterized in that: The water absorption radius of each small layer of the water injection well is calculated by the following formula: In formula (4), R represents the water absorption radius centered on the injection well, in meters; V w Indicates the cumulative water absorption of each sublayer of the injection well, unit: m 3 ; V wo Indicates the cumulative water volume produced by each sublayer of the injection well, unit: m 3 ; h is the effective thickness of the oil layer, in m; φ is the porosity, in decimal; S O Indicates the original oil saturation of the oil layer, in decimal units; S WO Indicates the current remaining oil saturation of the oil layer, in decimal units.

8. The method for adjusting the well pattern structure for chemical flooding development of common heavy oil reservoirs according to claim 3, characterized in that: The further determination of the water absorption and water flooding conditions of each oil well and each sub-layer of the water injection well as described in Plan 3 is based on the cumulative water absorption and water absorption radius of each sub-layer of the water injection well, the approximate water content of each sub-layer of each oil well, the sub-layer oil layer isopach map, the interpretation data of well flooding adjustment in recent years, the porosity, permeability, saturation isopach map of each sub-layer, the sedimentary phase map and the connectivity map.

Images