A method for adjusting well pattern structure for chemical flooding development of conventional heavy oil reservoirs

Abstract

This invention provides a well pattern adjustment method for chemical flooding development of ordinary heavy oil reservoirs, applicable to improving the water flooding effect in reservoirs during the "high-yield and high-volume" development stage, maximizing production enhancement, and further improving recovery rate. The steps include: selecting reservoirs that meet the conditions for chemical flooding development; determining the oil-water movement patterns and main water flooding directions based on dynamic and static data obtained at each development stage; determining the remaining oil distribution type and accurately estimating the current remaining oil saturation of the reservoir and target layer; determining the principles for selecting test wells and optimizing the test area; determining a suitable well pattern and well spacing, using a five-point well pattern, with the well pattern in the chemical zone either perpendicular to the source direction or laterally displacing the source; based on the remaining oil saturation, using old wells for injection conversion, splitting and reorganizing the well pattern for adjustment; and conducting chemical flooding production based on the adjusted well pattern and injection-production parameters.

Description

Technical Field

[0001] This invention belongs to the field of reservoir development technology, and relates to the development of layered ordinary heavy oil reservoirs using water injection, specifically a well pattern adjustment method for chemical flooding development of ordinary heavy oil reservoirs. Background Technology

[0002] Crude oil viscosity is a measure of the frictional resistance of one part of crude oil flowing relative to another, and it is an important parameter for oil and gas field development. Currently, China classifies heavy oil based on the viscosity of degassed crude oil under reservoir temperature conditions: ordinary heavy oil has a viscosity of 50–10000 mPa·s; extra-heavy oil has a viscosity of 10000–50000 mPa·s; and super-heavy oil has a viscosity greater than 50000 mPa·s. Although ordinary heavy oil has a relatively low viscosity, it still faces problems such as poor flowability and high extraction difficulty.

[0003] Water injection development involves using water injection equipment to inject qualified water from injection wells into the oil reservoir to maintain reservoir pressure and displace crude oil. In heterogeneous multi-layered reservoirs, the differences in reservoir properties—interlayer, planar, and intralayer—lead to uneven water propagation in each layer, complicating the oil-water relationship. Furthermore, the high viscosity ratio of oil to water causes high-permeability channels to form in ordinary heavy oil reservoirs after long-term water injection, resulting in inefficient or ineffective water circulation and hindering effective crude oil displacement, thus impacting development outcomes.

[0004] Chemical flooding, also known as modified waterflooding, is an oil recovery method that involves adding chemical agents to the injection water to alter the physicochemical properties of the displacing fluid and the interfacial properties between the displacing fluid and crude oil and rock minerals, thereby improving crude oil production. Chemical flooding enhanced oil recovery technologies mainly include polymer flooding, polymer-surfactant composite flooding, and ternary composite flooding, with polymer flooding being the most mature. Polymer flooding involves adding high-molecular-weight polymers to the injection water to increase the viscosity of the displacing phase, adjust the water absorption profile of the oil reservoir, and expand the swept volume of the displacing phase, thereby improving oil recovery. Polymer-surfactant composite flooding refers to polymer-surfactant binary composite flooding technology, a tertiary oil recovery technology developed in recent years. Polymer-surfactant composite flooding combines the function of polymer flooding in increasing swept volume with the effect of ternary composite flooding in improving oil displacement efficiency. It is expected to increase oil recovery by more than 18%, approaching the recovery rate of ternary composite flooding. It is a tertiary oil recovery method with minimal reservoir damage, good input-output prospects, and development potential, showing promising application prospects.

[0005] Oryx Corporation of the United States conducted a pilot test of alkali-free binary composite flooding in the Ranger oilfield, recovering one-quarter of the total residual oil after waterflooding, achieving significant oil displacement results. In 2003, Sinopec Shengli Oilfield conducted a pilot test of alkali-free binary composite flooding technology in the Gudong oilfield. The reservoir had an average permeability of 1320 mD, a permeability variation coefficient of 0.58, a porosity of 34%, an initial oil saturation of 72.0%, a residual oil saturation of 45.5%, and a subsurface crude oil viscosity of 45 mPa·s. This is currently one of the more successful polymer-surfactant binary composite flooding tests in China, with a maximum daily oil production increase of 166 tons, a water cut decrease of 12.5%, and an enhanced oil recovery of over 12% in the test area. Compared with the unit with the best polymer flooding effect in the Gudong oilfield, the water cut decrease in the binary composite flooding pilot test area was greater than that of the single polymer flooding unit, and the oil production increase in the binary composite flooding pilot test area was also greater than that of the single polymer flooding unit. Since 2008, China National Petroleum Corporation (CNPC) has accelerated the pace of major development trials of polymer-surfactant binary composite flooding, deploying major development trials of polymer-surfactant binary composite flooding in five blocks, which has also achieved significant results.

[0006] Although polymer-surface composite flooding has achieved many results in laboratory research and field trials, it remains a blank in the field of ordinary heavy oil. For layered sandstone ordinary heavy oil reservoirs in the "high-yield and high-volume" development stage, especially after 10 years of modified flooding development, transitioning to polymer-surface composite flooding still faces the following challenges:

[0007] (1) After the implementation of deep-seated regulation and flooding in the reservoir, the distribution of remaining oil becomes more complex and scattered. The precise determination of remaining oil is the key design technology that determines whether the development can be economically and effectively transitioned to chemical flooding. In other words, the accurate estimation of the remaining oil at the current stage determines the final recovery rate and economic benefits.

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

[0009] To address the development challenges faced by ordinary heavy oil reservoirs transitioning to chemical flooding during the "high-yield and high-efficiency" development phase, this invention provides a well network structure adjustment method for chemical flooding development in ordinary heavy oil reservoirs. This method is suitable for improving the water flooding effect in reservoirs during the "high-yield and high-efficiency" development phase, maximizing production enhancement, and further improving recovery rate.

[0010] The technical solution adopted by this invention to solve its technical problem is as follows:

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

[0012] Select reservoirs that meet the conditions for chemical flooding development and carry out chemical flooding development;

[0013] Based on the dynamic and static data obtained at each stage of reservoir development, the oil-water movement patterns and the main water drive directions are determined.

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

[0015] Determine the principles for well selection in the experiment and optimize the experimental area;

[0016] Determine an appropriate well pattern and spacing. The well pattern adopts the five-point method. The well pattern in the chemical zone is based on displacement in the direction perpendicular to the source material or laterally.

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

[0018] Chemical flooding production will be carried out based on the adjusted well pattern design injection and production parameters.

[0019] Furthermore, the reservoirs selected for chemical flooding development meet the following conditions: layered sandstone reservoirs with no gas cap and bottom water, reservoir permeability > 50 md, effective oil layer thickness > 8 m, reservoir connectivity > 70%, remaining oil saturation > 35%, stable interlayers at the top and bottom of the target layer, capping capacity > 1 million tons, formation temperature < 80℃, underground crude oil viscosity < 100 mPa·s, formation water salinity < 10000 mg / L, reservoir water drive control degree > 70%, and significant effectiveness during water injection development.

[0020] Furthermore, the method for accurately estimating the remaining oil saturation of the reservoir and target layer at this stage is as follows:

[0021] Option 1: Calculate the current water saturation of the oilfield based on the pore volume occupied by injected water in the produced oil.

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

[0023] Option 3: Based on the statistical water absorption profile data, calculate the cumulative water absorption and water absorption radius of each sub-layer of the injection well. For injection wells without a water absorption profile, divide them according to their perforation thickness and cumulative water injection volume using the perforation thickness permeability (kh) value. Mark the calculated water absorption radius of each sub-layer of each injection well onto each sub-layer oil layer isopyrograph to draw the approximate water flooding range. Determine the approximate water cut of each sub-layer of each oil well and mark it onto each sub-layer oil layer isopyrograph to further determine the water absorption and water flooding of each oil well and sub-layer of each injection well, and draw the main oil layer water flooding map. Calculate the water cut of each sub-layer of each oil well using a weighted average based on the effective thickness of the oil layer to obtain the water cut of each sandstone group, the water cut of the oil layer group, and the water cut at the wellhead.

[0024] Based on the combined results of the three research schemes and numerical simulation predictions, the remaining oil saturation of the reservoir and the target layer at the current stage is finally obtained.

[0025] Furthermore, the calculation formula for the current water saturation of the oilfield based on the pore volume occupied by injected water in the produced oil is as follows:

[0026]

[0027] In equation (1), S oi The original oil saturation is expressed as a percentage (%); N represents the geological reserves of crude oil, expressed as units of 10⁻⁶. 4 t; N p This indicates cumulative oil production, in units of 10. 4 t; B or Indicates the current formation crude oil volume factor; B oi This represents the original formation crude oil volume factor.

[0028] Furthermore, the oil saturation of the C / O test is corrected using a standard relative permeability curve, as shown in the following formula:

[0029]

[0030] In equation (2), Sw represents the water saturation of the corrected C / O ratio, in %; Sw' represents the water saturation of the uncorrected C / O ratio, in %; Swi represents the bound water saturation in the standard phase permeability curve, in %; and Sor represents the residual oil saturation in the standard phase permeability curve, in %.

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

[0032]

[0033] In equation (3), V w This indicates the cumulative water absorption of each sub-layer in the injection well, in meters (m³). 3 Qw This indicates the cumulative injection volume of the injection well during the testing phase, in cubic meters (m³). 3 ;λ i This indicates the percentage of relative water absorption in the test water absorption profile layer, expressed as a decimal.

[0034] Furthermore, the water absorption radius of each sub-layer of the injection well is calculated using the following formula:

[0035]

[0036] In equation (4), R represents the water absorption radius centered on the injection well, in meters; V w This indicates the cumulative water absorption of each sub-layer in the injection well, in meters (m³). 3 V wo This represents the cumulative water production volume from each sub-layer of the injection well, in cubic meters (m³). 3 h represents the effective thickness of the oil layer, in meters; φ represents porosity, in decimals; S O S represents the initial oil saturation of the oil reservoir, in decimal form. WO This indicates the current oil saturation level of the oil layer, expressed as a decimal.

[0037] Furthermore, the determination of the water absorption and water flooding conditions of each injection well and each sub-layer of each oil well, as described in Scheme 3, is based on the cumulative water absorption and water absorption radius of each sub-layer of the injection well, the approximate water content of each sub-layer of each oil well, the isopyrograph of the sub-layer oil layer, the water flooding interpretation data of the adjustment wells in recent years, the isopyrograph of porosity, permeability, saturation, sedimentary facies diagram and connectivity diagram of each sub-layer.

[0038] The beneficial effects of this invention include:

[0039] This invention develops a method for adjusting the structure of chemical flooding well networks. During the later stages of waterflooding development in conventional heavy oil reservoirs, when converting development methods, this method adjusts the injection-production well network to improve the flow direction of the injected medium, effectively displacing remaining oil and increasing recovery. Unlike traditional well network adjustments, this method directly selects side-reverse wells in the original injection-production well group for conversion without deploying adjustment wells, thus reducing investment. It splits and reorganizes the original injection-production well network, breaking the dominant channels formed under waterflooding development and achieving fluid flow redirection. This method is particularly suitable for well groups that have already undergone adjustment and flooding in the later stages of waterflooding development in conventional heavy oil reservoirs. Specifically, this invention has the following advantages:

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

[0041] Reduce development costs: Based on the principles of well selection for testing and appropriate well spacing, the well network structure can be optimized. Existing wells can be fully utilized for injection conversion, and the well network can be split, reorganized, and adjusted, thereby avoiding the high cost of building new wells and reducing the overall development cost.

[0042] Increase production revenue: By rationally designing injection and production parameters and carrying out chemical flooding production based on the adjusted well pattern, the reservoir's production capacity and recovery rate can be effectively improved, thereby increasing production revenue.

[0043] In summary, this well pattern adjustment method can improve the effectiveness of chemical flooding, reduce development costs, and increase production revenue, thus having a positive impact on the development of ordinary heavy oil reservoirs. Attached Figure Description

[0044] Figure 1 This is a schematic diagram comparing the chemical flooding well network structure before and after the adjustment of the present invention;

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

[0046] Figure 3 This is a comparison chart of waterflood recovery rates under different displacement directions according to the present invention;

[0047] Figure 4 This is a graph showing the connectivity coefficient under different well spacings according to the present invention. Detailed Implementation

[0048] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] To address the development challenges faced by ordinary heavy oil reservoirs during the "high-yield and high-volume" development phase, this invention proposes a well network structure adjustment method for chemical flooding development of ordinary heavy oil reservoirs, employing lateral reverse injection and streamline conversion to improve water drive effectiveness. The method includes the following steps:

[0050] (1) Select reservoirs that meet the conditions for chemical flooding development and carry out chemical flooding development;

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

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

[0053] (4) Determine the principles for selecting test wells and optimize the test area;

[0054] (5) Determine a reasonable well network and well spacing;

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

[0056] (7) Chemical flooding production is carried out according to the adjusted well pattern design injection and production parameters.

[0057] Specifically, the selected reservoirs meet the following conditions: layered sandstone reservoirs with no gas cap and bottom water, reservoir permeability > 50 md (millidarcy), effective oil layer thickness > 8 m, reservoir connectivity > 70%, remaining oil saturation > 35%, stable interlayers at the top and bottom of the target layer, capping capacity > 1 million tons, formation temperature < 80℃, underground crude oil viscosity < 100 mPa·s (millipascals per second, viscosity unit), formation water salinity < 10000 mg / L, reservoir water drive control degree > 70%, and significant effectiveness during water injection development.

[0058] Preferably, a relatively regular reverse seven-point well pattern with a well spacing of 120-200m is used, and the oil reservoir has been developed through deep displacement, with the recovery rate reaching 7%-15% during the deep displacement stage.

[0059] Furthermore, the optimization and adjustment of the well network structure is related to the distribution of remaining oil and the appropriate well spacing. When using old wells for injection or splitting and reorganizing the well network, the type of well network and the size of the well spacing after adjustment should be given special consideration. The lateral reverse oil in the main water drive direction of the well group is relatively rich 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 lines can be achieved.

[0060] The specific steps are as follows:

[0061] Accurately estimate remaining oil:

[0062] ①Material balance method:

[0063] In oilfields developed by maintaining formation pressure through water injection, the water saturation of the oilfield is calculated by the volume of injected water occupying the pore volume of produced oil. This is the mass balance method used to calculate the current oil saturation, and the formula is as follows:

[0064]

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

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

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

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

[0069] B oi --Original formation crude oil volume coefficient.

[0070] ②C / O testing method:

[0071] Because the oil saturation interpreted from C / O logging differs significantly from the oil saturation measured in the core and the oil saturation values ​​analyzed from production dynamic data, the oil saturation from C / O testing is corrected using a standard relative 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 – Bound water saturation in the standard relative permeability curve, %;

[0076] Sor – Residual oil saturation in the standard relative permeability curve, %.

[0077] ③ Dynamic analysis method:

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

[0079]

[0080]

[0081] In the formula: V w —Cumulative water absorption of each sub-layer in the injection well, in m³ 3 ;

[0082] Q w —The cumulative injection volume of the injection well during the testing phase, in m 3 ;

[0083] λ i —The relative water absorption percentage of the sub-layer of the water absorption profile is measured as a decimal.

[0084] V wo —Cumulative produced water volume from each sub-layer of the injection well, m³ 3 ;

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

[0086] φ—porosity, decimal;

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

[0088] S WO —Current oil saturation level in the oil layer, decimal;

[0089] R—Water absorption radius centered on the injection well, in meters.

[0090] For injection wells without a water absorption profile, they are divided according to their perforation thickness and cumulative water injection volume, using the perforation thickness permeability (kh) value. The calculated water absorption radius of each sub-layer of each injection well is then marked on each sub-layer oil layer isothickness map to draw the approximate water flooding range.

[0091] Record the complete interpretation table for each oil well. Then, based on the water-blocking and various measures taken over the years, combined with the current and past production history, determine the approximate water content of each sub-layer of each oil well and mark it on each sub-layer oil layer isopyrograph.

[0092] Based on the above data and the water flooding interpretation data of adjustment wells in recent years, as well as the thickness maps of porosity, permeability, saturation, sedimentary facies maps and connectivity maps of each sub-layer, the water absorption of each oil well and the water flooding of each sub-layer are further determined, and the water flooding map of the main oil layer is drawn.

[0093] The water cut of each oil well and each sub-layer is weighted and averaged according to the effective thickness of the oil layer, which yields the water cut of each sandstone group, the water cut of the oil layer group, and the water cut at the wellhead.

[0094] Based on the combined results of the three methods and numerical simulation predictions, the remaining oil saturation of the reservoir and the target layer at the current stage is finally obtained.

[0095] Determine a reasonable and appropriate well pattern and well spacing

[0096] Based on numerical simulation and dynamic analysis, and combined with domestic and international experience in chemical flooding, the five-point well pattern is adopted, and lateral flooding perpendicular to the source direction is superior.

[0097] Numerical simulation and dynamic analysis studies have shown that a well spacing of 150–200 m can meet the development requirements of chemical flooding. Furthermore, drawing on the effectiveness of deep-flooding, the well spacing for chemical flooding is designed to be 150 m. Under this well spacing condition, the chemical flooding injection rate has a large adjustment margin (0.11–0.22 PV / a), and the connectivity coefficients along and perpendicular to the river channel, as well as the polymer flooding control degree, both reach over 80%.

[0098] Example 1

[0099] refer to Figure 1 As shown, Figure 1This is a schematic diagram illustrating the adjustment of the well network structure for chemical flooding in layered ordinary heavy oil reservoirs according to the present invention. Based on dynamic analysis and research, this method optimizes and adjusts the well network through a process of splitting and recombining, and includes the following steps:

[0100] (1) Specific details of the selected reservoir: It is a high-porosity and high-permeability reservoir, with the main sedimentary layers consisting of channel and sandbar deposits, and an average porosity of 31.3% and a permeability of 1109×10⁻⁶. -3 μm 2 The pore structure is mainly of medium-high permeability, with large pores and medium-fine throats, and is relatively uniform. The target layer has low clay mineral content, and the thickness of the upper and lower interlayers is greater than 2m, averaging about 6m. It has good sealing properties, formation water salinity 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 reservoir underwent two main development stages: waterflooding and variator flooding. During the deep variator flooding process, the stage recovery rate was 8.6%. During water injection development, the production wells showed significant effectiveness. Statistical analysis of 30 water injection well groups and 89 first-line oil wells showed an effectiveness rate of over 90%. In terms of well effectiveness types, the main types were increased fluid and oil production, stable fluid and oil production, and reduced decline, with increased fluid and oil production and stable fluid and oil production accounting for over 70%. In terms of the direction of well effect, the main types were unidirectional effect, bidirectional effect, and multidirectional effect, with bidirectional or higher effects accounting for over 70%. During the deep variator flooding process, 78% of the water absorption thickness was improved, the average water absorption thickness per well increased by 0.7m, inter-layer and planar contradictions were effectively improved, and the utilization rate increased by 3.2%. The water precipitation has a significant effect on increasing oil production, with 79% of the corresponding oil wells showing results. More than 40% of the wells in categories I and II are effective, mainly distributed in structurally high areas. The well spacing between injection and production is 150-180m. The smaller the well spacing, the more obvious the effect of water diversion and flow control.

[0102] (3) This method mainly uses reservoir engineering methods such as material balance method, C / O test method, dynamic analysis method, and numerical simulation to calculate the remaining oil saturation based on the geological characteristics and actual production situation of the reservoir. According to the actual parameters, the average remaining oil saturation of the reservoir is calculated to be 41.1%, of which the remaining oil saturation of the target layer for chemical flooding is 37.7%. Numerical simulation studies show that although the reservoir is generally severely water-flooded, due to the heterogeneity of the reservoir and the degree of injection and production perfection, the oil saturation in the local river edge, inter-channel, and front thin sand areas is above 40%. The four main remaining oil modes are inter-well retention type, thin layer poor mobilization type, local imperfect well network type, and fault control type. Among them, the inter-well retention type accounts for the highest proportion and is 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 water flooding to tap the potential. Chemical flooding is needed to improve the swept volume and oil washing efficiency.

[0103] (4) Vertically, the thickness of the chemical flooding section is controlled between 10 and 20 meters, with each section having a relatively uniform thickness. The sedimentary units within the same displacement section should be relatively concentrated, and the top and bottom of the displacement well section should have relatively stable interlayers, possessing a certain injection and production capacity to meet the production needs of chemical flooding. Horizontally, factors such as structure, connectivity, oil-water distribution, and production capacity are fully considered. The oil layer has a wide distribution range, a high reserve ratio, and a connectivity coefficient of over 85%.

[0104] (5) The injection-production well network directly determines the technical and economic benefits of chemical flooding and is a key factor in its success. Based on numerical simulations, dynamic analysis studies, and combined with domestic and international experience in chemical flooding, such as... Figure 2 , Figure 3 As shown, the well pattern in the chemical zone exhibits good displacement effects in the vertical direction of the source or laterally, such as... Figure 4 As shown, a well spacing of 150-200m can well meet the development requirements of chemical flooding. Furthermore, drawing on the effectiveness of this reservoir in the deep-seated flooding phase, the well spacing for chemical flooding is designed to be 150m. Under this well spacing condition, the chemical flooding injection rate has a large adjustment margin (0.11–0.22 PV / a), and the connectivity coefficients along and perpendicular to the river channel, as well as the polymer flooding control degree, all reach over 80%.

[0105] (6) Make full use of old wells. Based on the water drive direction and the distribution of remaining oil, prioritize the conversion of old wells to injection wells, split and reorganize the original injection-production well network, and adjust the injection-production well spacing. For example... Figure 1 As shown, B1 and B2 are water injection wells, A2 is a production well in the chemical flooding zone, and A1 and A3 are production wells in the non-chemical flooding zone. Long-term water injection development has resulted in a fixed flow line. When designing the chemical flooding well network, B1 and B2 are adjusted to water injection in the non-chemical flooding zone, while A1 and A3 are adjusted to the chemical flooding zone. Simultaneously, A2 and A3, located in the opposite direction to the original injection wells, are converted to injection wells, forming a new injection-production well network. The injection wells are basically located in the center of the well group, with a distance commensurate with each affected well, an average well spacing of 150m, and each injection well corresponds to 6-7 oil wells.

[0106] (7) Chemical flooding production is carried out according to the reset well pattern and the injection parameters designed according to the chemical flooding scheme.

[0107] Application Example 1

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

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

[0110] Based on this, by comprehensively applying dynamic and static data collected at different stages, the oil-water movement patterns were analyzed, concluding that water flooding was severe along the source direction, with relatively abundant residual oil in the lateral and retrograde directions, and low water drive sweep rate. Four test well groups were reconstructed by transferring old wells and splitting and reorganizing the well network.

[0111] By adjusting the injection and production well system, the wells are vertically aligned with the target layer and horizontally reorganized. The average injection and production well spacing is 150m. Production and injection are allocated according to an injection-production ratio of 1:1, and chemical flooding tests are conducted.

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

[0113] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for adjusting the well pattern structure for chemical flooding development of ordinary heavy oil reservoirs, characterized by the following steps: include: Select reservoirs that meet the conditions for chemical flooding development and carry out chemical flooding development; Based on the dynamic and static data obtained at each stage of reservoir development, the oil-water movement patterns and the main water drive directions are determined. Determine the distribution type of remaining oil and accurately estimate the remaining oil saturation of the reservoir and target layer at the current stage; Determine the principles for well selection in the experiment and optimize the experimental area; Determine an appropriate well pattern and spacing. The well pattern adopts the five-point method. The well pattern in the chemical zone is based on displacement in the direction perpendicular to the source material or laterally. Based on the remaining oil saturation, old wells are used for injection conversion, and the well network is split, reorganized and adjusted; Chemical flooding production will be carried out based on the adjusted well pattern design injection and production parameters; The method for accurately estimating the remaining oil saturation of the reservoir and target layer at the current stage is as follows: Option 1: Calculate the current water saturation of the oilfield based on the pore volume occupied by injected water in the produced oil. Option 2: Test the current water saturation of the oilfield using the C / O test method, and correct the oil saturation of the C / O test using a standard relative permeability curve; Option 3: Based on the statistical water absorption profile data, calculate the cumulative water absorption and water absorption radius of each sub-layer of the injection well. For injection wells without a water absorption profile, divide them according to their perforation thickness and cumulative water injection volume, using the perforation thickness permeability. Mark the calculated water absorption radius of each sub-layer of each injection well onto each sub-layer oil layer isopyrograph to draw the approximate water flooding range. Determine the approximate water cut of each sub-layer of each oil well and mark it onto each sub-layer oil layer isopyrograph to further determine the water absorption and water flooding of each oil well and sub-layer of each injection well, and draw the main oil layer water flooding map. Calculate the water cut of each sub-layer of each oil well using a weighted average based on the effective thickness of the oil layer to obtain the water cut of each sandstone group, the water cut of the oil layer group, and the water cut at the wellhead. Based on the combined results of the three research schemes and numerical simulation predictions, the remaining oil saturation of the reservoir and the target layer at the current stage is finally obtained.

2. The well pattern adjustment method for chemical flooding development of ordinary heavy oil reservoirs according to claim 1, characterized in that, The reservoirs selected for chemical flooding development meet the following conditions: layered sandstone reservoirs with no gas cap and bottom water, reservoir permeability > 50 md, effective oil layer thickness > 8 m, reservoir connectivity > 70%, remaining oil saturation > 35%, stable interlayers at the top and bottom of the target layer, capping capacity > 1 million tons, formation temperature < 80℃, underground crude oil viscosity < 100 mPa·s, formation water salinity < 10000 mg / L, reservoir water drive control degree > 70%, and significant effectiveness during water injection development.

3. The well pattern adjustment method for chemical flooding development of ordinary heavy oil reservoirs according to claim 1, characterized in that, The calculation formula for the current water saturation of the oilfield, which is based on the pore volume occupied by injected water in the produced oil, is as follows: In equation (1), S oi The original oil saturation is expressed as a percentage (%); N represents the geological reserves of crude oil, expressed as units of 10⁻⁶. 4 t; N p This indicates cumulative oil production, in units of 10. 4 t; B or Indicates the current formation crude oil volume factor; B oi This represents the original formation crude oil volume factor.

4. The well pattern adjustment method for chemical flooding development of ordinary heavy oil reservoirs according to claim 1, characterized in that, The oil saturation of the C / O test is corrected using a standard relative permeability curve, as shown in the following formula: In equation (2), Sw represents the water saturation of the corrected C / O ratio, in %; Sw' represents the water saturation of the original C / O ratio, in %; Swi represents the bound water saturation in the standard phase permeability curve, in %; Sor represents the residual oil saturation of the standard phase permeation curve, in percentage.

5. The well pattern adjustment method for chemical flooding development of ordinary heavy oil reservoirs according to claim 1, characterized in that, The cumulative water absorption of each sub-layer of the injection well is calculated using the following formula: In equation (3), V w This indicates the cumulative water absorption of each sub-layer in the injection well, in meters (m³). 3 Q w This indicates the cumulative injection volume of the injection well during the testing phase, in cubic meters (m³). 3 ; λ i This indicates the percentage of relative water absorption in the test water absorption profile layer, expressed as a decimal.

6. A well pattern adjustment method for chemical flooding development of ordinary heavy oil reservoirs according to claim 5, characterized in that, The water absorption radius of each sub-layer in the injection well is calculated using the following formula: In equation (4), R represents the water absorption radius centered on the injection well, in meters; V w This indicates the cumulative water absorption of each sub-layer in the injection well, in meters (m³). 3 V wo This represents the cumulative water production volume from each sub-layer of the injection well, in cubic meters (m³). 3 h represents the effective thickness of the oil layer, in meters (m). S represents porosity, in decimal units; O S represents the initial oil saturation of the oil reservoir, in decimal form. WO This indicates the current remaining oil saturation level in the oil reservoir, expressed as a decimal.

7. The well pattern adjustment method for chemical flooding development of ordinary heavy oil reservoirs according to claim 1, characterized in that, The further determination of the water absorption and water flooding conditions of each injection well and each sub-layer of each oil well, as described in Scheme 3, is based on the cumulative water absorption and water absorption radius of each sub-layer of the injection well, the approximate water content of each sub-layer of each oil well, the isopyrograph of the sub-layer oil layer, the water flooding interpretation data of the adjustment wells in recent years, the isopyrograph of porosity, permeability, saturation, sedimentary facies diagram and connectivity diagram of each sub-layer.

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