CO2-driven variable-parameter perforation multi-layer long-span WAG mixed injection benefit injection method

Abstract

The invention discloses a CO2 flooding variable-parameter perforation multi-layer long-span WAG mixed injection benefit injection method, and relates to the technical field of CO2 flooding in a low-permeability oil and gas reservoir development technology, and the CO2 flooding variable-parameter perforation multi-layer long-span WAG mixed injection benefit injection method comprises the steps that reservoir differentiation adjustment is achieved through a variable-parameter differentiation perforation technology before displacement; dynamic optimization is carried out through a trapezoidal WAG water-gas alternation technology in the displacement process; the variable-parameter differential perforation technology comprises the steps of carrying out fine evaluation on a reservoir of a CO2 drive target oil reservoir and compiling a variable-parameter differential perforation scheme; according to the trapezoidal WAG water-gas alternation technology, slugs with different gas-water ratios are implemented in the area where the gas well is obviously seen and the area where the gas well is not obviously seen. And multi-reservoir long-span uniform air suction is guaranteed, and the purposes of low-cost multi-layer effective displacement and recovery efficiency improvement are achieved. Through the improvement of the design, the CO2 oil displacement injection process is simplified, the construction difficulty is reduced, and the construction cost and the testing and debugging cost are greatly saved.

Description

Technical Field

[0001] The present invention relates to the technical field of CO2 flooding in low permeability oil and gas reservoir development technology, and in particular to a CO2 flooding variable parameter perforation multi-layer long-range WAG mixed injection efficiency injection method. Background Art

[0002] CO2 flooding technology began abroad in the 1950s and became a mature technology by the 1980s. my country's research into this technology was relatively late, but after decades of continuous research, significant progress has been made in many areas. Waterflooding is a common oilfield technology. To mitigate the large differences in water absorption between layers caused by varying reservoir permeabilities, injection wells mostly use a stratified water injection process. Separating reservoirs with varying permeabilities with packers creates different injection zones. The permeability difference (maximum permeability divided by minimum permeability) between sub-layers within a given zone is generally no greater than 3, ensuring that each sub-layer can absorb water. By using different sized water nozzles between the sub-layers, it is usually possible to achieve three to five, and sometimes even seven to nine, sub-layers within the same wellbore. Each injection zone receives water at the required injection rate, achieving effective stratified waterflooding. Due to the special properties of CO2, such as its phase state and viscosity, even a small pressure change can cause large fluctuations in flow rate. If we imagine using isolation tools to separate different reservoirs with large permeabilities into multiple injection sections like water injection, a low-cost, mature and reliable CO2 stratified injection process has not yet been developed. The more prominent problem is the lack of corresponding mature CO2 drive testing and debugging technology. Even if the cost is not taken into account and the CO2 injection section is divided into multiple sections, the lack of corresponding mature and reliable testing methods means that multiple layers are actually mixed. Moreover, the insertion of multiple-stage isolation tools into the wellbore can easily cause accidents during the next well repair operation, and sometimes even cause the injection well operation to be scrapped. Currently, in actual production in mines, the more mature technology for stratified CO2 injection wells can only achieve two-section injection through double pipes on the ground, but the cost of this will be significantly higher than the mixed injection process. In terms of cost, it is not as effective and reliable as drilling a new well to inject two different layers separately.

[0003] For oil reservoirs developed using CO2 flooding to supplement energy, due to the lack of a low-cost, mature and reliable stratified injection process, the traditional water flooding multi-layer mixed injection technology is used. The permeabilities of each layer vary greatly, making it difficult to effectively displace low-permeability reservoirs, which is prone to gas channeling, and the effect of CO2 injection to improve oil recovery will be greatly reduced. If the CO2 flooding process is adopted layer by layer, it is difficult to implement in most oil reservoirs due to the limitations of reserve abundance and economic benefits. How to achieve low-cost and effective displacement of reservoirs with different permeabilities under mixed injection conditions with CO2 flooding poses a huge challenge to the design of reservoir engineering schemes. Summary of the Invention

[0004] The object of the present invention is to provide a CO2 flooding variable parameter perforation multi-layer long-span WAG mixed injection benefit injection method, which realizes uniform longitudinal and planar displacement of CO2 injection through low-cost fine design, and greatly improves the recovery rate.

[0005] To achieve the above object, the technical solution of the present application is: a CO2 flooding variable parameter perforation multi-layer long-span WAG mixed injection benefit injection method, including: realizing reservoir differential adjustment through variable parameter differential perforation technology before displacement; performing dynamic optimization through trapezoidal WAG water and gas alternating technology during displacement;

[0006] The variable parameter differential perforation technology includes fine evaluation of the reservoir of the CO2 flooding target oil reservoir and preparation of a variable parameter differential perforation plan;

[0007] The trapezoidal WAG water and gas alternating technology implements different gas-water ratio slugs in the obvious gas production well area and the non-obvious gas production well area.

[0008] Further, the fine evaluation of the reservoir of the CO2 flooding target oil reservoir includes establishing a logging interpretation model of the target oil reservoir, classifying and evaluating the single sand body reservoir, and finely dividing the single sand body of the injection well reservoir.

[0009] Further, establishing the logging interpretation model of the target oil reservoir is specifically as follows:

[0010] If the target oil reservoir implementing CO2 flooding development is located in a developed block, through the rich dynamic and static data of the target oil reservoir, the core analysis data, porosity model, and permeability model of this area are obtained;

[0011] If the target oil reservoir implementing CO2 flooding development is located in an undeveloped block, through the exploration evaluation stage and reserve report data of the block where the target oil reservoir is located and the dynamic and static data of the surrounding adjacent oil reservoirs or similar oil reservoirs, the core analysis data, porosity model, and permeability model of this area are obtained.

[0012] Further, classifying and evaluating the single sand body reservoir is specifically as follows: using the logging interpretation model to quantify the physical properties of the single sand body of the injection-production well, and combining the differences in the monitoring data of the gas absorption and water absorption profiles, the single sand body reservoir is divided into three categories: the permeability of the first type of single sand body reservoir > 5 md, and the characteristics of the corresponding layer section of the logging curve are that AC > 235 us / m; the permeability of the second type of single sand body reservoir is 0.2 - 5 md, and the characteristics of the corresponding layer section of the logging curve are that 215 us / m < AC ≤ 235 us / m; the permeability of the third type of single sand body reservoir is 0.06 - 0.2 md, and the characteristics of the corresponding layer section of the logging curve are that 206 us / m < AC ≤ 215 us / m.

[0013] Furthermore, the single sand bodies of the injection well reservoir are finely divided as follows: When a newly drilled injection well or an old well is used to perforate an unperforated reservoir, the longitudinal variation characteristics of the reservoir are effectively classified and identified first. Taking the single sand body as the basic unit, the response characteristics of the mudstone interbed are determined by using well logging data to complete the division of single sand bodies in each small layer and guide reservoir classification.

[0014] Furthermore, when finely dividing the single sand bodies of the injection well reservoir, the deep induction resistivity RILD, natural gamma GR, acoustic travel time AC, and spontaneous potential SP well logging curves are used as comparison curves that can reflect lithology-sensitive parameters.

[0015] Furthermore, when finely dividing the single sand bodies of the injection well reservoir, the response characteristics of the mudstone interbed in well logging data are identified by combining core data. Specifically, the gamma well logging curve shows a high value greater than 120 API, the spontaneous potential well logging curve is close to the baseline, the microelectrode well logging curve and the micro-amplitude well logging curve show a decrease in amplitude, and the amplitude difference between the two is zero or less than 2 Ω.m; compared with the adjacent layer, the decrease amplitude of the deep lateral resistivity well logging curve is less than 3 Ω.m; the neutron gamma well logging curve is less than 0.88 API; the acoustic travel time well logging curve shows a high value above 230 μS / m; the caliper well logging curve shows obvious hole enlargement.

[0016] Furthermore, a variable parameter differential perforation plan is compiled, specifically as follows:

[0017] 1) Determine the perforated reservoir according to the connectivity of the injection-production well reservoir, and finely divide the target perforated layer to the single sand body level;

[0018] 2) According to the single sand body division results, use the well logging curve response characteristics of each single sand body and the porosity model and permeability model of this block to obtain the physical property parameters of each single sand body;

[0019] 3) Divide each single sand body into Class I, Class II, and Class III according to the physical property parameters of each single sand body. Class I reservoir: K > 5 mD; Class II reservoir: 0.2 < K ≤ 5 mD; Class III reservoir: 0.06 < K ≤ 0.2 mD;

[0020] 4) Statistically analyze the division results of various single sand bodies, record the top and bottom depths of each single sand body, and obtain the specific thickness of each single sand body;

[0021] 5) Compile a variable parameter differential CO2 flooding perforation plan, and its differential parameters include main perforation process parameters such as perforation method, perforating gun type, perforation single type, and perforation density;

[0022] 6) Hand over the prepared variable parameter differential CO2 flooding perforation plan to the perforation construction department.

[0023] As a further step, a variable parameter differentiated CO2 flooding perforation scheme was developed. Specifically, for Class I reservoirs, conventional perforation with low perforation density was used; for Class II reservoirs, composite perforation with medium perforation density was used; and for Class III reservoirs, ultra-deep penetration perforation with high perforation density was used. Specific parameters are shown in the table below. This differentiated perforation approach ensures relatively uniform gas absorption capacity among the three reservoir types.

[0024] Differentiated perforation parameter list

[0025]

[0026] As a further step, the trapezoidal WAG water-gas alternation technology is to implement a 1:1 or 1:2 gas-water ratio slug in the high-yield gas well area, and a 3:1 or 2:1 gas-water ratio slug in the unproductive well area;

[0027] Injection wells with different gas-seeping types are classified and alternating slugs are designed: they are divided into three categories based on the gas-seeping time, daily gas production, and CO2 content of the wells, as shown in the following table. To effectively expand the CO2 swept volume, the water-gas alternating slug ratio for Category 1 gas-seeping wells is 3:1 or 2:1; for Category 2 gas-seeping wells, the water-gas alternating slug ratio is 1:1; and for Category 3 gas-seeping wells, the water-gas alternating slug ratio is 1:2 or 1:3.

[0028] Table 3 Oil well classification indicators

[0029] Oil well classification Time to see gas <![CDATA[Produced gas (m 3 )]]> <![CDATA[CO2 content (%)]]> Corresponding alternating slugs Type I gas well 0.02HCPV ＞1000 ＞50 3:1 or 2:1 Type II gas wells 0.06HCPV 400-600 10-50 1：1 Three types of gas wells 0.18HCPV ＜100 ＜10 1:2 or 1:3

[0030] By adopting the above technical solution, the present invention can achieve the following technical effects:

[0031] (1) The CO2 flooding variable parameter perforation multi-layer long-range WAG mixed injection efficiency injection method provided by the present invention has great practicality

[0032] It can effectively avoid the phenomenon that high permeability reservoirs have large gas absorption and serious gas channeling under the traditional perforation method; low permeability reservoirs have difficulty in gas absorption and poor oil displacement effect. This method helps to alleviate the contradiction of large gas absorption differences between layers due to large permeability differences in each reservoir, and can effectively promote relatively uniform gas absorption in each layer under multi-layer mixed injection conditions, thereby improving the uniform displacement effect of CO2 flooding in each small layer. This method can effectively control the contradiction of CO2 flooding plane fingering, slow down the occurrence of plane gas channeling, and increase the swept volume of CO2 flooding.

[0033] ㈡The CO2 flooding variable parameter perforation multi-layer long-scale WAG mixed injection efficiency injection method provided by the present invention has great economical

[0034] It simplifies the injection process of CO2 injection wells, greatly reduces the construction difficulty, greatly saves construction costs, avoids a large amount of testing and debugging costs, and effectively promotes the effectiveness of CO2-EOR work. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0036] Figure 1 This is the principle diagram of the CO2 flooding variable parameter perforation multi-layer long-width WAG mixed injection efficiency injection method;

[0037] Figure 2 This is the intersection diagram of the core well porosity and GR logging curve characteristics;

[0038] Figure 3 This is the intersection diagram of the core well porosity and AC logging curve characteristics;

[0039] Figure 4 This is the intersection diagram of porosity and permeability of the core well;

[0040] Figure 5 This is the logging curve response characteristic of the mud barrier in the first typical well;

[0041] Figure 6 This is the logging curve response characteristic diagram of the mud interlayer in the second typical well;

[0042] Figure 7 This is the connection diagram of the injection-production relationship between the Hei+79-12-12 oil well and the water injection well. DETAILED DESCRIPTION

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. 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 making creative efforts shall fall within the scope of protection of the present invention.

[0044] It should be noted that, unless there is any conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0045] It should also be noted that the terms used in this application are generally commonly used by those skilled in the art. If there is any discrepancy between the terms used in this application and the commonly used terms, the terms used in this application shall prevail. For those skilled in the art, the specific meanings of the terms in this application in the present invention can be understood based on the specific circumstances.

[0046] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. It should be understood that the terms used in this way can be interchanged under appropriate circumstances. This is merely a way of distinguishing objects of the same attributes when describing them in the embodiments of the present application. Moreover, the terms "include" and "comprise" include not only those elements, but also other elements that are not clearly listed, or elements that are inherent to such processes, methods, articles or equipment. In the absence of more restrictions, the elements limited by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or equipment that include the elements.

[0047] To address the problem of large differences in gas absorption in reservoirs with different permeabilities under mixed CO2 flooding conditions, which affects the effective displacement of low-permeability reservoirs, the present invention establishes a combined injection mode of differentiated perforation + trapezoidal WAG slugs (as the CO2 injection time increases, in order to improve the utilization rate of CO2, while ensuring that the formation pressure reaches a certain level, the injection rate of the gas slugs is gradually reduced and the injection rate of the water slugs is increased during the alternating water and gas injection process, fundamentally solving the problem of uniform and effective gas absorption in the vertical and horizontal directions of the reservoir. Before gas injection, the target layer is multi-stage sand body superimposed into small layers, the single sand body is subdivided, a porosity and permeability model is established, the physical properties of the single sand body in each small layer are identified, and the reservoir classification evaluation is completed; for reservoirs with different permeabilities, differentiated perforation technology is applied to complete the well, and the air absorption capacity of each small layer is transformed from the design source, so that the small layers with different innate permeabilities are transformed through artificial fine reservoirs, and the acquired air absorption capacity is relatively uniform, so as to achieve the purpose of reducing the vertical heterogeneity of the reservoir; during the gas injection process, the trapezoidal WAG segment plug design is applied to make the air absorption capacity of each small layer in the same injection section relatively uniform under the mixed injection condition, which solves the problem of large air absorption difference in reservoirs with different permeabilities under the mixed injection condition of CO2 flooding, so that the low permeability reservoir with the lowest permeability can also achieve effective oil recovery by CO2 flooding; in the process of multi-layer CO2 injection, through continuous Optimizing the design of injection parameters for the trapezoidal WAG plug can effectively control the fingering phenomenon on each plane, control unidirectional gas channeling, and achieve uniform displacement in the plane. In this way, through low-cost and sophisticated design, uniform vertical and planar displacement of CO2 injection can be achieved, significantly improving the recovery rate. Since the calibrated recovery rate of water flooding development in low-permeability oilfields is basically between 20% and 25%, and the continuous CO2 injection tests with small well spacing in the Daqingzijing oilfield have increased the recovery rate in the core evaluation area by 25.5 percentage points, the total recovery rate (water drive + gas drive) has reached 56.4%, which is equivalent to the discovery of another Daqingzijing oilfield (proven reserves of 170 million tons). Therefore, this technology will play a very important role in the domestic efficient implementation of industrial CO2 injection to improve recovery.

[0048] This invention primarily improves the perforation scheme for injection well reservoirs. By applying this scheme, the impact of extreme permeability differences is reduced. Incorporating trapezoidal WAG alternation during the injection process further mitigates the significant differences in gas absorption capacity caused by poor reservoir physical properties. This results in a technique that enables effective CO2 oil recovery even in reservoirs with the lowest permeability under multi-layer, combined injection wellbore conditions. It is particularly important to note that the core of this invention lies in the variable parameter perforation technique and the trapezoidal WAG water-gas alternation technique; in particular, the variable parameter perforation technique is not only applicable to this invention, but will also play a positive role in stratified water injection and stratified gas injection (N2, flue gas) in oilfield development.

[0049] like Figure 1As shown, a CO2 flooding variable parameter perforation multi-layer long-range WAG mixed injection efficiency injection method is characterized by: before the displacement, the variable parameter differentiated perforation technology is used to achieve reservoir differentiation adjustment; during the displacement process, the trapezoidal WAG water-gas alternation technology is used to perform dynamic optimization;

[0050] The variable parameter differential perforation technology includes A. performing a detailed evaluation of the reservoir of the CO2 flooding target reservoir and B. formulating a variable parameter differential perforation plan;

[0051] A. Conduct detailed reservoir evaluation of the target CO2 flooding reservoir, including:

[0052] A1 Establish a well logging interpretation model for the target reservoir:

[0053] For oil reservoirs that are developed using CO2 flooding, there will generally be relevant data on water flooding or other development methods in the early stages, and a wealth of dynamic and static data on the target reservoir will be collected, including reserve reports, core analysis data, well logging curves, remaining oil research data, and other dynamic and static data; especially the proven reserve report of the target reservoir, in which the core analysis data, porosity model, permeability model and other interpretation parameters of the area will be found; if the target reservoir is a new development block and there is not enough relevant data in the early stages, the exploration and evaluation stage of the block where the target reservoir is located, as well as the dynamic and static data of the surrounding adjacent or similar reservoirs, can be used to obtain core analysis data, porosity model, permeability model, etc. As the data continues to become richer after development, the relevant models can be revised to make them better conform to the actual situation of the area; the following takes the dynamic and static data of oil and water wells in the Hei 125 block of the Daqingzijing Oilfield during water flooding development as an example to illustrate how to establish the logging interpretation model of the Hei 125 block;

[0054] A11 porosity model: During the water flooding development of the Heilongjiang 125 block, it was shown that the porosity of the core wells had a good correlation with the gamma log curve and the acoustic time difference log curve. Based on this, a fitting formula for rock porosity and GR log was established, such as Figure 2 As shown in the figure, the AC logging fitting formula is as follows: Figure 3 The porosity model is: Por = 0.2182*AC-0.05924*GR-36.2034

[0055] A12 permeability model: Single correlation analysis of permeability and porosity shows that there is a high correlation between porosity and permeability. In order to explain the permeability more accurately, the relationship between porosity and permeability is divided into three sections, such as Figure 4 As shown, the porosity is less than <8%, 17%> porosity ≥8%, and porosity >17%.

[0056] The permeability model is:

[0057] ① Porosity ≥ 17% (effective layer): Perm = 5.5801 × exp(0.1062 × Por)

[0058] ② 17% ≥ Porosity ≥ 8% (effective layer): Perm = 0.0006 × exp(0.6537 × Por)

[0059] ③ Porosity < 8% (dry layer): Perm = 0.0052 × exp(0.2802 × Por)

[0060] Reliability analysis and evaluation of A13 interpretation model

[0061] In order to detect the reliability of the well logging interpretation model, the core analysis and laboratory tests of the core wells are compared with the well logging interpretation results, and the overall trends are consistent. When comparing by small layers according to fluid properties, as shown in Table 1, the fitting compliance rate of porosity in oil layers is 96%, the fitting compliance rate of porosity in dry layers is 84%, the fitting compliance rate of permeability in oil layers is 77%, and the fitting compliance rate of permeability in dry layers is 61%. The comparison results show that the interpretation models of parameters such as porosity and permeability established with core analysis data and well logging data have guiding significance for practice.

[0062] Table 1 Comparison table of well logging fitting and measured porosity and permeability of typical wells

[0063]

[0064] A2 Reservoir classification and evaluation:

[0065] Using the well logging interpretation model to quantify the physical property characteristics of single sand bodies in injection and production wells in the block, and combining with the differences in monitoring data such as the gas injection and water absorption profiles, the single sand body reservoirs are divided into three categories: for the first category of single sand body reservoirs, the permeability > 5 md, and the main characteristics of the corresponding well logging curve segments are AC > 235 (μs / m); for the second category of single sand body reservoirs, the permeability is 0.2 - 5 md, and the main characteristics of the corresponding well logging curve segments are (μs / m) 215 < AC ≤ 235 (μs / m); for the third category of single sand body reservoirs, the permeability is 0.06 - 0.2 md, and the main characteristics of the corresponding well logging curve segments are (μs / m) 206 < AC ≤ 215 (μs / m).

[0066] A3 Fine division of single sand bodies in injection well reservoirs:

[0067] For the reservoirs developed by CO2 flooding, when perforating the unperforated reservoirs for newly drilled injection wells or converting old wells for injection, first effectively classify and identify the longitudinal variation characteristics of the reservoirs, take the single sand body as the basic research unit, use well logging data to determine the response characteristics of mudstone interbeds, and accurately complete the division of single sand bodies in each small layer to guide reservoir classification.

[0068] A31 Optimized Well Logs: Single sand body delineation is primarily performed using well logs. Each well has multiple logs reflecting different parameter characteristics. To facilitate comparison, four well logs—reflecting lithologic-sensitive parameters—were selected based on three basic principles: high vertical resolution, distinct subtle contrast characteristics, stable log logs for wells drilled in different eras, and log commonality. These logs are Deep Induction Resistivity (RILD), Natural Gamma Ray (GR), Acoustic Travel (AC), and Spontaneous Potential (SP).

[0069] A32 interlayer division: Combined with the core data, the response characteristics of the mudstone interlayer in the logging data are identified. Specifically, the gamma log curve is high, generally greater than 120API, the natural potential log curve is close to the baseline, the microelectrode and microamplitude log curves have a significant decrease in amplitude, and the amplitude difference is almost zero or less than 2Ω.m; compared with the adjacent layer, the deep lateral resistivity log curve has a large decrease in amplitude, generally less than 3Ω.m; the neutron gamma log curve is stable and low, often less than 0.88API; the sonic time difference log curve shows a high value, generally above 230μS / m; the wellbore diameter is significantly expanded, such as Figure 5-6 shown.

[0070] B. Prepare a differentiated perforating plan with variable parameters;

[0071] The traditional conventional perforation plan is usually compiled as follows:

[0072] 1) Based on the connectivity of the oil well sub-layers, determine which sub-layers (not subdivided into single sand bodies) in the injection well require perforation and gas injection;

[0073] 2) Determine the specific depth and corresponding thickness of the top and bottom boundaries of each sub-layer that requires gas injection;

[0074] 3) Based on the specific depths and corresponding thicknesses of the top and bottom boundaries of each sub-layer that have been determined, a perforation plan is prepared, which mainly includes the main perforation process parameters such as perforation gun type, perforation unit type, perforation density and phase.

[0075] 4) The construction department shall strictly carry out construction work according to the requirements of the perforation plan.

[0076] The new perforation plan of the present invention is compiled as follows:

[0077] 1) Determine which reservoirs to perforate based on the reservoir connectivity between the injection and production wells. However, in the specific division process, the traditional practice of dividing the reservoir into small layers should be changed, and the target perforation layer should be further divided into the single sand body level;

[0078] 2) Based on the results of the single sand body division, the physical properties of each single sand body are obtained by using the logging curve response characteristics of each single sand body and the porosity and permeability model that has been established in this block;

[0079] 3) Classify each individual sand body into Class I, Class II, and Class III according to the physical property parameters of each individual sand body. Class I reservoir: K > 5 mD; Class II reservoir: 0.2 < K ≤ 5 mD; Class III reservoir: 0.06 < K ≤ 0.2 mD;

[0080] 4) Statistically analyze the classification results of various individual sand bodies, record the specific depths of the top and bottom boundaries of each individual sand body, and obtain the specific thickness of each individual sand body;

[0081] 5) Compile a variable parameter differential CO2 flooding perforation plan. The main differential parameters (Table 2) include main perforation process parameters such as perforation method, perforating gun type, perforation single type, and perforation density. For Class I reservoirs, use the conventional perforation method with a low perforation density; for Class II reservoirs, use the composite perforation method with a medium perforation density; for Class III reservoirs, use the ultra-deep penetration perforation method with a high perforation density. Through this differential perforation, the gas absorption capacity of the three types of reservoirs can reach relative uniformity.

[0082] Table 2 Detailed list of differential perforation parameters

[0083]

[0084]

[0085] 6) After the differential perforation plan is compiled, hand it over to the perforation construction department and strictly require construction according to the design.

[0086] The trapezoidal WAG water and gas alternating technology includes:

[0087] Due to the naturally formed heterogeneity of the reservoir, variable parameter differential perforation can alleviate this problem to a certain extent vertically. Horizontally, due to variations in sedimentary conditions along the provenance and the influence of possible natural fractures, the permeability of the same reservoir varies greatly in all directions. Even if a single CO2 injection regime is maintained for a relatively short period of time during the injection process, due to its strong permeability, the injected gas can easily flow along a high-permeability zone, forming a unidirectional finger-like flow. This can cause the CO2 to break through prematurely during injection and reduce the oil recovery effect. To expand the CO2 swept volume and promote uniform gas sweep, the Daqingzijing Mine has demonstrated that the most effective and economical technical countermeasure for controlling gas cross-flow is to implement a trapezoidal WAG injection method, i.e., alternating water and gas injection. Of course, to effectively apply this technology, a personalized WAG water-gas alternation scheme must be designed for each injection well. Based on previously established reservoir classification standards and the connectivity of specific inter-well sand bodies, a reservoir connectivity classification standard was established. Using component numerical simulation, targeted injection schemes were optimized. While maintaining a constant daily injection rate, slugs with gas-to-water ratios of 2:1, 1:1, and 1:2 were compared. This comparison determined that implementing slugs with gas-to-water ratios of 1:1 or 1:2 in areas with high gas production effectively controlled high gas production in the wells, while implementing slugs with gas-to-water ratios of 3:1 or 2:1 in areas with ineffective wells promoted production in the corresponding areas.

[0088] Oil wells with different gas-seeping types were classified and alternating slug designs were performed. Wells were divided into three categories based on their gas-seeping time, daily gas production, and CO2 content (Table 3). Modeling results showed that to effectively expand the CO2 swept volume, Category 1 gas-seeping wells required a water-gas alternating slug ratio of 3:1 or 2:1, Category 2 gas-seeping wells required a water-gas alternating slug ratio of 1:1, and Category 3 gas-seeping wells required a water-gas alternating slug ratio of 1:2 or 1:3.

[0089] Table 3 Oil well classification indicators

[0090] Oil well classification Time to see gas <![CDATA[Produced gas (m 3 )]]> <![CDATA[CO2 content (%)]]> Corresponding alternating slugs Type I gas well 0.02HCPV ＞1000 ＞50 3:1 or 2:1 Type II gas wells 0.06HCPV 400-600 10-50 1：1 Three types of gas wells 0.18HCPV ＜100 ＜10 1:2 or 1:3

[0091] Well Hei+79-12-12 is a new production well drilled during the transition from water flooding to CO2 flooding in the Hei 125 block of the Daqingzijing Oilfield. After nearly 20 years of water flooding development, the Hei 125 block has achieved a water-driven recovery rate of nearly 20%, essentially reaching the target recovery factor for the block's water flooding development plan. To improve development results, research has shown that it is suitable for a CO2 flooding conversion to further enhance recovery. To accommodate CO2 flooding development, the block implemented a well pattern intensification adjustment to meet the requirements of the water-to-CO2 conversion. Intensified drilling was performed on the original 160 x 480 m inverted nine-point water injection well pattern, converting it to a 160 x 240 m five-point CO2 flooding well pattern. A total of 24 new wells were drilled. Well logging data from new and old wells show that the vertical distance between the uppermost reservoir and the lowermost reservoir in the first section of Qing in this block is 150 to 180 meters; among the 24 newly drilled wells, only the Hei+79-12-12 well is used as an oil production well, and the other 23 new wells are all injection wells. After the completion of the drilling of the Hei+79-12-12 well, through the comparison and analysis of the logging curve with the old wells around the well, the drilling situation of each small layer is very consistent with the prediction of the plan. The 7th, 9th, 10th, 11th, 12th, and 14th layers of the first section of Qing in this well are relatively well developed. From the perspective of reservoir permeability analysis, they all belong to Class I and Class II reservoirs; however, the permeability of the No. 4 layer of the first section of Qing in this well is 0.06mD according to the well logging curve calculation, which obviously belongs to Class III reservoir; there are 3 newly drilled injection wells around this well. Figure 7As shown, the reservoir development and permeability encountered by each injection well are basically the same as those of each sub-layer of the oil well; each sub-layer of the injection well is perforated and transformed using differentiated perforation technology according to the reservoir classification and evaluation results, and then multi-layer mixed injection completion is implemented; CO2 injection development is started in this block. Although the 7th, 9th, 10th, 11th, 12th and 14th layers of the Hei+79-12-12 oil well are relatively well developed and the remaining oil saturation is relatively high, if we consider it from the perspective of high oil production, these layers should be used first. However, in order to identify the lower limit of the CO2 drive reservoir production, this well is put into production separately with the No. 4 layer. The purpose is to identify this layer that will not be put into production under water drive conditions. Under CO2 drive conditions, whether it can produce oil, how much oil can be produced, and Hei+79-12-12 oil well can produce oil. The No. 4 layer of well 2-12 was put into production by fracturing, with 13 cubic meters of sand and 160 cubic meters of fracturing fluid. Pumping began in the same month after fracturing, with an initial liquid production of 5.2 cubic meters / day and a water content of 100%. After that, the daily liquid production continued to decrease. After more than two months of continuous production, until the dynamic liquid level approached the pump hanger, the daily liquid production dropped to "0 tons" and then pumping was stopped for observation. During this period, the casing pressure of the well was always "0Mp", and the water content was monitored every day at 100%. Before stopping pumping, the cumulative liquid production was 149.4 tons, and the fracturing fluid of the layer was basically drained out without a drop of oil. This also proves that this layer cannot be used under water drive conditions, otherwise, there will be no oil at all. After the initial stop of pumping, pumping was resumed at regular intervals for a few days to monitor the production and water content at irregular intervals. Each time, pumping was stopped after no liquid was produced, and no oil was observed during this period. Data collected after a period of time showed that the casing pressure of the well had risen from the previous "0Mp" to 0.15Mp, and gas component monitoring showed that the CO2 content was 3% to 9%. After the oil well was started, the initial daily liquid production of a single well was 4.2 tons and the daily oil production was 0.3 tons. The highest daily liquid production was 5.7 tons and the daily oil production was 1.2 tons. Due to the overall low daily liquid production, the pump was stopped and restarted several times due to the dynamic liquid level approaching the pump. Statistics show that the cumulative oil production during this period was 53 tons. Comprehensive evaluation shows that after the CO2 flooding of the No. 4 layer of the well took effect, the stable daily oil production capacity was more than 0.15 tons, and the cumulative oil production capacity of CO2 flooding development is expected to reach 1,000 tons.The significance of this experiment is as follows: First, reservoirs like the No. 4 layer cannot be used under water drive conditions, because the water content remains at 100% for a long time after the initial fracturing and the water content remains at 100% until the fracturing fluid is completely drained; but they can be used under CO2 drive conditions and will make a certain contribution; second, the lower limit of CO2 drive reservoir production is clarified. In mine production, reservoirs with a permeability of more than 0.06 can be effectively used by CO2 drive; third, different reservoirs with a permeability difference of less than 70 can achieve multi-layer long-scale trapezoidal WAG mixed injection through variable parameter perforation to achieve effective CO2 drive in each small layer. If not In this way, layer 4 in the surrounding injection wells will not absorb gas, the casing pressure of layer 4 in the oil well will not rise and CO2 will not be produced, and the oil well should not produce oil as in the early stage of production; through the application of this technology, it is fully proved that in the oil reservoirs where CO2 flooding is implemented, multi-layer low-permeability oil reservoirs with an oil layer span of less than 180 meters and a permeability difference of less than 70 can achieve effective displacement of each layer through mixed injection, thereby avoiding the need for complex process design and exponential cost expenditure for the implementation of separate injection. The "variable parameter perforation multi-layer long-width WAG mixed injection efficiency injection method" technology will play a huge role in promoting the benefits of the industrial implementation of CO2 oil recovery in my country.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A CO2 flooding variable parameter perforation multi-layer long-range WAG mixed injection efficiency injection method, characterized in that: Including: Before displacement, differential reservoir adjustment is achieved through variable parameter differential perforation technology; During displacement, dynamic optimization is carried out through trapezoidal WAG (Water Alternating Gas) technology; The variable parameter differential perforation technology includes fine evaluation of the reservoir of the CO2 flooding target reservoir and preparation of a variable parameter differential perforation plan; The trapezoidal WAG technology implements different gas-water ratio slugs in the areas with obvious gas breakthrough wells and the areas without obvious gas breakthrough wells.

2. A CO2 flooding variable parameter perforation multi-layer long-range WAG mixed injection efficiency injection method according to claim 1, characterized in that: Fine evaluation of the reservoir of the CO2 flooding target reservoir includes establishing a logging interpretation model for the target reservoir, classifying and evaluating single sandbody reservoirs, and finely dividing single sandbodies of the injection well reservoir.

3. A CO2 flooding variable parameter perforation multi-layer long-range WAG mixed injection efficiency injection method according to claim 2, characterized in that: Establishing a logging interpretation model for the target reservoir is specifically as follows: If the target reservoir for CO2 flooding development is located in a developed block, through the rich dynamic and static data of the target reservoir, the core analysis data, porosity model, and permeability model of this area are obtained; If the target reservoir for CO2 flooding development is located in an undeveloped block, through the exploration evaluation stage and reserve report data of the block where the target reservoir is located and the dynamic and static data of surrounding adjacent reservoirs or similar reservoirs, the core analysis data, porosity model, and permeability model of this area are obtained.

4. A CO2 flooding variable parameter perforation multi-layer long-range WAG mixed injection efficiency injection method according to claim 2, characterized in that: Classifying and evaluating single sandbody reservoirs is specifically as follows: Using the logging interpretation model to quantify the physical property characteristics of single sandbodies in injection and production wells, and combining the differences in suction and water intake profile monitoring data, single sandbody reservoirs are divided into three categories: The permeability of the first category of single sandbody reservoirs > 5 md, and the corresponding characteristics of the logging curve segment are that AC > 235 μs / m; The permeability of the second category of single sandbody reservoirs is 0.2 - 5 md, and the corresponding characteristics of the logging curve segment are that 215 μs / m < AC ≤ 235 μs / m; The permeability of the third category of single sandbody reservoirs is 0.06 - 0.2 md, and the corresponding characteristics of the logging curve segment are that 206 μs / m < AC ≤ 215 μs / m.

5. A CO2 flooding variable parameter perforation multi-layer long-range WAG mixed injection efficiency injection method according to claim 2, characterized in that: Finely dividing single sandbodies of the injection well reservoir is specifically as follows: When perforating the unperforated reservoir of a newly drilled injection well or using an old well, first effectively classify and identify the longitudinal variation characteristics of the reservoir. Taking the single sandbody as the basic unit, use logging data to determine the response characteristics of shale interlayers, complete the division of single sandbodies in each small layer, and guide reservoir classification.

6. A CO2 flooding variable parameter perforation multi-layer long-range WAG mixed injection efficiency injection method according to claim 5, characterized in that: When finely dividing single sandbodies of the injection well reservoir, the deep induction resistivity RILD, natural gamma GR, acoustic travel time AC, and spontaneous potential SP logging curves are used as comparison curves that can reflect lithology sensitive parameters.

7. A CO2 flooding variable parameter perforation multi-layer long-range WAG mixed injection efficiency injection method according to claim 5, characterized in that: When finely dividing single sandbodies of the injection well reservoir, combined with core data to identify the response characteristics of shale interlayers in logging data, which are specifically manifested as the gamma logging curve being a high value greater than 120 API, the spontaneous potential logging curve being close to the baseline, the microelectrode logging curve and the micro-amplitude logging curve showing a decrease in amplitude, and the amplitude difference between the two being zero or less than 2 Ω.m; Compared with adjacent layers, the decrease amplitude of the deep lateral resistivity logging curve is less than 3 Ω.m; the neutron gamma logging curve is less than 0.88 API; the acoustic travel time logging curve shows a high value above 230 μS / m; the caliper logging curve shows hole enlargement.

8. The CO2 flooding variable parameter perforation multi-layer long-range WAG mixed injection efficiency injection method according to claim 1 is characterized in that: Preparing a variable parameter differential perforation plan is specifically as follows: 1) Determine the perforated reservoir according to the connectivity of the injection-production wells in the reservoir, and finely divide the target perforated layer to the single sand body level; 2) Based on the division results of the single sand bodies, use the logging curve response characteristics of each single sand body and the porosity model and permeability model of this block to obtain the physical property parameters of each single sand body; 3) Divide each single sand body into Class I, Class II, and Class III according to the physical property parameters of each single sand body. Class I reservoir: K > 5 mD; Class II reservoir: 0.2 < K ≤ 5 mD; Class III reservoir: 0.06 < K ≤ 0.2 mD; 4) Statistically analyze the division results of various types of single sand bodies, record the depths of the top and bottom boundaries of each single sand body, and obtain the specific thickness of each single sand body; 5) Compile a variable parameter differential CO2 flooding perforation plan, and its differential parameters include perforation method, perforating gun type, perforation single type, and perforation density; 6) Hand over the prepared variable parameter differential CO2 flooding perforation plan to the perforation construction department.

9. A CO2 flooding variable parameter perforation multi-layer long-range WAG mixed injection efficiency injection method according to claim 8, characterized in that: Compile a variable parameter differential CO2 flooding perforation plan, specifically: for Class I reservoirs, use the conventional perforation method with a low perforation density; for Class II reservoirs, use the composite perforation method with a medium perforation density; for Class III reservoirs, use the ultra-deep penetration perforation method with a high perforation density; the specific parameters are shown in the following table: Differential Perforation Parameter Details 10. The CO2 flooding variable parameter perforation multi-layer long-range WAG mixed injection efficiency injection method according to claim 1, characterized in that: The trapezoidal WAG water-gas alternating technology is: determine to implement a gas-water ratio slug of 1:1 or 1:2 in the high gas production well area, and implement a gas-water ratio slug of 3:1 or 2:1 in the area of wells that have not seen obvious effects; Classify the injection wells with different gas breakthrough types and design alternating slugs: divide them into three categories according to the gas breakthrough time, daily gas production, and CO2 content of the oil wells, as shown in the following table: To effectively expand the CO2 sweep volume, control the water-gas alternating slug of the first-class gas breakthrough wells to be 3:1 or 2:1, the second-class gas breakthrough wells to be 1:1, and the third-class gas breakthrough wells to be 1:2 or 1:3; Oil Well Classification Index 。

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