A composite double-well fire flooding method for low permeability difference oil layer

Abstract

A composite double well fire flooding method for low permeability difference oil layer belongs to the technical field of artificial auxiliary viscosity reduction technology in tertiary oil recovery process. The composite double well low permeability reservoir development process is as follows: two wells are drilled at all well sites in the oil production core area, one is a composite oil production well, and the other is a fire flooding air injection well. All the drilled wells at the outer edge of the reservoir are single oil production wells. The fire flooding air injection well in the well pattern supplements the high production layer and is ignited by physical and chemical methods. Any oil production well in the well pattern cannot supplement the fire flooding layer. The present application has the following characteristics: the composite double well fire flooding technology absorbs the advantages of steam huff and puff development, steam flooding, fire flooding and other development methods, has low cost, good effect, reduces labor intensity and saves human resources.

Description

Technical Field

[0001] This invention belongs to the field of artificially assisted viscosity reduction technology in tertiary oil recovery processes, specifically involving a composite dual-well fire flooding method for low-permeability, poor-permeability oil reservoirs. Background Technology

[0002] Heavy oil reserves account for approximately 60% of the total reserves in Liaohe Oilfield, primarily developed using steam injection and steam drive. Currently, some fault-block oilfields have poorly developed heavy oil blocks with numerous thin interbedded layers. Heavy oil extraction is in the mid-to-late stages of steam injection, exhibiting drawbacks such as high recovery rates, high injection cycles, low formation pressure, and low economic oil-gas ratio. With increasing extraction costs year by year, continuing steam injection will likely yield limited economic benefits. For example, in a well area of ​​a Liaohe Oilfield production plant, the current average formation pressure is 2.02 MPa, with a total pressure differential reaching 7.97 MPa, indicating extremely high formation depletion. The wells have entered a stage where an effective driving pressure differential cannot be established, resulting in poor huff and puff performance, edge water intrusion, and recovery rates as high as 56.8% in some well areas. The remaining oil in the available geological reserves is very limited, and the huff and puff effect is extremely unsatisfactory. The huff and puff cycle for a single well is distributed between 17 and 23 cycles, with an average daily production of only 0.6-0.8 t / d. Continuing to use steam-driven, hot-water-driven, and flue gas-driven methods will hardly achieve good results, causing the operating cost per ton of oil in the entire block to rise sharply, resulting in very poor economic benefits. Therefore, using fire-driven oil recovery is the best option for heavy oil well production. Compared to steam flooding and steam huff and puff, fire-driven oil recovery has a significant advantage in its rapid oil displacement rate. During fire-driven recovery, the heavy components of the crude oil in the reservoir are used as fuel; combustion generates heat, driving the crude oil from the injected well into another production well and bringing it to the surface. Statistics show that current global fire-driven oil recovery is approximately 5000 tons per day, mainly concentrated in the United States, Canada, Romania, and Venezuela. Practice has proven that fire-driven recovery can extract large quantities of crude oil from light oil reservoirs that have undergone water flooding. Successful fire-driven recovery rates in oil-producing countries worldwide can reach 50%. Currently, fire-driven oil recovery is mainly used abroad for light oil wells at depths of 500-900 meters and for oil wells with low viscosity, as well as some oil wells with high formation permeability. Most oil well ignition methods use electric heating, liquefied gas, and chemical methods. In China, Xinjiang Oilfield and the Majiapumiao No. 5 Oilfield of Liaohe Oilfield use cable-connected heaters to be sent into the ignition layer in the well for ignition, and then air is sent into the well through a compressor. Because the heating temperature is not easy to control and the well conditions are complex, the heating cable is easily burned out, resulting in a certain failure rate.

[0003] Existing fire-flooding technologies are not ideal. Analysis of fire-flooding results in blocks such as Du66 and Miao5 in a certain oilfield in my country shows that fire-flooding faces difficulties in control. The underground combustion status and range cannot be effectively monitored, and surrounding wells are easily affected by combustion exhaust gases, leading to low fluid production or even production shutdowns due to low fluid yields. While chemical profile control agents have achieved some success in some well areas to address these problems, overall effectiveness has been minimal. Therefore, there is still a long way to go in exploring and developing fire-flooded reservoir development methods for heavy oil.

[0004] Currently, the common practice of tertiary oil recovery technology in the domestic and international oil industries is as follows:

[0005] There are various methods for oilfield development, such as flowing well production, mechanical oil recovery, steam injection, chemical recovery, and fire-driven oil recovery. However, for some heavy oil blocks with deep and thin, poor-quality layers, steam-driven oil recovery is no longer economical, and its effectiveness is gradually becoming unsatisfactory. Fire-driven oil recovery, on the other hand, has many advantages such as low cost and ease of implementation. However, both fire-driven and steam-driven thermal recovery methods have some unresolved problems.

[0006] 1. The disadvantages of traditional steam injection development, steam-driven development, and fire-driven development are:

[0007] (1) Since most heavy oil fields in China use steam injection for development, each well has fewer injection cycles, and the effect deteriorates with the increase of cycles.

[0008] (2) Traditional steam drive development increases costs and the effect will not vary depending on the selected area. There is a problem of excessive hydrogen sulfide, which poses a great safety hazard. The workload is heavy and human resources are wasted.

[0009] (3) Traditional fire-driven systems are inexpensive, easy to construct and simple to operate, but they waste a lot of pipelines and exhaust gas separation equipment, put great pressure on the environment, and have high costs for investment in equipment and pipeline replacement.

[0010] (4) The combustion of traditional fire-driven fire is difficult to control. In particular, as the fire-driven project progresses, the amount of exhaust gas increases and becomes more corrosive, making it more difficult to handle.

[0011] (5) Whether it is steam injection development, steam drive development or fire drive development, there is no effective way to deal with oil layers with poor interlayer heterogeneity and thin, poor permeability layers. Summary of the Invention

[0012] To address the aforementioned problems, this invention proposes a composite dual-well fire-flooding method for low-permeability, poor-permeability oil reservoirs. The composite dual-well low-permeability reservoir development process involves drilling two wells at all well sites in the core production area: one is a composite production well, and the other is a fire-flooding air injection well. All wells drilled at the outer edge of the reservoir are single production wells.

[0013] Furthermore, by burning within the oil layer, the generated heat and carbon dioxide reduce the viscosity of the crude oil, igniting the heavy oil in the oil layer and using the heavy components within the oil layer as fuel to continuously generate heat, heating the crude oil in the adjacent upper and lower oil layers. Combined with conventional steam injection for surface extraction, this composite dual-well low-permeability and low-production reservoir development obtains heat by burning the residual oil in the high-production oil layer. The heat is then conducted to the upper and lower low-permeability and low-production oil layers, raising the overall temperature of the oil layers above and below the combustion zone. The low-permeability and low-production oil layers are extracted using steam injection or steam drive methods. Energy is obtained by burning the residual oil and asphaltenes in the high-production oil layer to heat the thin, differential layers above and below the oil layer. The residual oil has a gum and asphaltenes content of 70%-80%. The heat and carbon dioxide generated by burning within the oil layer reduce the viscosity of the crude oil.

[0014] Furthermore, the fire-driven air injection wells in the well network are used to re-open high-production layers and ignite them using physicochemical methods. It is required that no oil production well in the well network can re-open fire-driven layers. After a period of fire-driven operation, based on the gas composition content in the oil layer and the leakage of tail gas from some marginal wells, several wells are concentrated in the highest part of the structure, accounting for 50-80% of the total fire-driven air injection wells. These wells are used for oil production and tail gas discharge. The purified carbon dioxide is re-injected into other oil layers, and the residual heat is recovered to heat and reduce the viscosity of crude oil in the pipeline network.

[0015] Furthermore, in the oil wells, non-fire-driven low-permeability and low-production oil layers in the oil layers on the electrical logging interpretation curve results table are supplemented. Fire-driven high-production layers that cannot be supplemented are not supplemented. In the initial stage of development, steam injection development is used for production wells. In the later stage, according to the changes in the development environment, steam-driven development is adopted. While supplementing low-permeability and low-production oil layers, some marginal wells 1-9 are supplemented with fire-driven layers.

[0016] Furthermore, based on the original well network and the well conditions with casing damage, the wells were transformed into monitoring wells to monitor temperature, pressure, and exhaust gas component content within the well network.

[0017] Furthermore, oil wells in the well network are used in conjunction with chemical profile control, packer plugging, and hydraulic fracturing to tap the potential of each thin, poor-quality oil layer.

[0018] Furthermore, in the early stage of layer replenishment ignition, air injection wells in the well network select layers for perforation and ignition based on the reservoir conditions, and regulate layer replenishment ignition.

[0019] Furthermore, the physical properties of the heavy oil are as follows: viscosity value of 5,000–100,000 mps, non-flowing at 75°C, and density of 0.95–1 g / m³. 3 Heavy oil pour point: ±10℃, gum content: 30-40% or more; high pour point oil pour point: 30-45℃, asphalt gum content: less than 10%, wax content: 35-50%.

[0020] The beneficial effects of this invention are as follows: This invention addresses the shortcomings of various development methods in heavy oil extraction. Fire flooding has low cost, but exhaust gas is difficult to treat and its effectiveness is poor; steam flooding has relatively good effect, but its cost remains high and it poses safety hazards such as hydrogen sulfide. Steam injection is suitable for heavy oil extraction, but its effectiveness gradually decreases with the increase of injection cycles. This invention combines the advantages of fire flooding (low cost), steam flooding (good effect), and simple injection operation, improving reservoir development level while reducing extraction costs. This invention has the following characteristics: The composite dual-well fire flooding technology combines the advantages of steam injection development, steam flooding, and fire flooding, and has low cost, good effect, reduced labor intensity, and saved human resources.

[0021] The test well exhibited a longer cycle time than conventional wells in terms of single-well huff and puff, with more stable daily oil production and a longer stable production period. The average well temperature was also slightly higher than that of conventional wells in the non-fire-driven well network. Good production capacity was achieved initially with only a small amount of steam injected. Analysis suggests this is because the combustion of the upper fire-driven oil layer generates heat that warms the lower oil layer, improving the huff and puff effect of the lower layer. Attached Figure Description

[0022] Figure 1 This is a well network planning and design diagram for the composite dual-well low-permeability and low-production technology method of the present invention;

[0023] Figure 2 This is a diagram illustrating the implementation of the composite dual-well low-permeability and low-production technology method of the present invention.

[0024] Figure 3 This is a three-dimensional design diagram of the well network planning for the composite dual-well low-permeability and low-production technology method of the present invention;

[0025] Figure 4 This is a design drawing of the tail gas emission well and the dual wells for the composite dual-well low-permeability and low-production technology method of the present invention. Detailed Implementation

[0026] A composite dual-well fire-flooding method for low-permeability, poor-permeability oil reservoirs is proposed. This invention optimizes the development well pattern and utilizes composite dual-well technology to conduct tertiary development of oil reservoirs in the middle and late stages of heavy oil development, thereby maximizing reservoir recovery.

[0027] Development process of composite dual-well low-permeability reservoirs: such as Figure 1 and Figure 3 As shown, two wells are drilled at each well site in the core oil production area: one is a combined oil production well and the other is a fire-driven air injection well. All oil wells drilled at the outer edge of the reservoir are single oil production wells and are not designed as combined dual wells. The purpose is to control edge water at the structural edge, prevent the displacement of internal oil layers from overflowing, and further enhance the effect.

[0028] Figure 1 Zhongjing.com mainly focuses on fire-driven air injection wells for re-opening. Figure 2 The high-yield formations in the oilfield are ignited using physicochemical methods. It is required that no production well within the well network can be used to initiate fire-driven formations. After a period of fire-driven operation, the gas composition content within the oil layer and the leakage of tail gas from some edge wells are considered. Figure 4 As shown, several wells are concentrated at the highest part of the structure, accounting for 50-80% of the total fire-driven air injection wells. These wells are used for oil production and exhaust gas discharge, facilitating centralized treatment of exhaust gas. The purified carbon dioxide is then reinjected into other oil layers, and the residual heat is recovered to heat and reduce the viscosity of crude oil in the pipeline network.

[0029] Figure 1 In the oil wells of the medium-sized oil production wells, the non-fire-driven low-permeability and low-production oil layers in the electrical logging interpretation results table are not fire-driven high-production layers. In the initial stage of development, steam injection development can be used for production wells. In the later stage, steam drive and other development methods can be adopted according to changes in the development environment. Figure 1 The marginal wells 1-9 can simultaneously open up low-permeability and low-production oil layers, and some wells can open up fire-driven layers.

[0030] The daily injection rate of air injection wells in the well network should be set in combination with the thickness of the oil layer displaced by fire flooding and the saturation of residual oil. It should not be set too high and should increase by 7%-15% per year. The purpose of small-volume, slow gas injection is to establish a slow and uniform combustion state in the oil layer, which is more conducive to the combustion of blocky and patchy residual oil in the layer.

[0031] In principle, air injection wells are not equipped in the outermost oil production wells of the well network. The water body at the edge of the reservoir has strong energy and low remaining oil content, which is not conducive to the combustion of the oil layer or to more uniform distributed combustion. The edge oil wells are mainly responsible for suppressing edge water, downdip effect, preventing energy leakage from the well network and causing unnecessary heat loss. At the same time, it is also conducive to better and more timely monitoring of the entire fire drive combustion and huff and puff development trend.

[0032] Among them, the original well network and wells with casing damage were transformed into monitoring wells to monitor temperature, pressure and exhaust gas composition within the well network.

[0033] Among them, oil wells in the well network combine chemical profile control, packer plugging, hydraulic fracturing to tap the potential of each thin oil layer, and conventional oil enhancement methods such as injecting water-absorbing and expanding resin into the bottom of the well are used for regulation.

[0034] Among them, air injection wells in the well network are selected for perforation and ignition based on the reservoir conditions in the early stage of layer replenishment ignition, and layer replenishment ignition is adjusted as the project progresses.

[0035] The physical properties of the heavy oil are as follows: viscosity of 5,000 to 100,000 mps, non-flowing at 75°C, and density of 0.95 to 1 g / m³. 3 Heavy oil pour point: ±10℃, gum content: 30-40% or more; high pour point oil pour point: 30-45℃, asphalt gum content: less than 10%, wax content: 35-50%.

[0036] Therefore, combustion within the oil layer effectively reduces the viscosity of crude oil by generating heat and carbon dioxide. By igniting the heavy oil within the layer and using the heavy components as fuel, heat is continuously generated, ultimately heating the crude oil in the adjacent upper and lower oil layers. Combined with conventional steam injection, this method solves the challenges of developing heavy oil, extra-heavy oil, and thin interbedded, low-yield oil layers. The development of this composite dual-well low-permeability, low-production reservoir primarily relies on generating heat through combustion of residual interlayer oil in high-production oil layers. This heat is then conducted to the upper and lower low-permeability, low-yield oil layers, increasing the overall temperature of the upper and lower oil layers in the combustion zone. Assisted steam injection or steam drive further facilitates the efficient development of low-permeability, low-production oil layers. This invention obtains energy to heat the thin, differential layers above and below the oil layer by burning the residual oil and asphalt in the high-yield oil layer. The content of gum and asphalt in this residual oil is mostly between 70% and 80%, which cannot be extracted by conventional steam injection. Even if it is extracted, its economic value is lower than that of conventional heavy oil. Moreover, the resources consumed to extract it using existing technologies are greater than the extraction. Therefore, by burning inside the oil layer, the heat and carbon dioxide generated reduce the viscosity of the crude oil.

[0037] The production wells in the well network can be adjusted in a targeted manner as the overall displacement changes. As needed, some air injection wells and production wells in the core well network can be used to open up fire-flooded layers for production, making full use of the displacement, viscosity reduction and oil increase capabilities of fire-flooding to achieve the best potential tapping effect.

[0038] The development of low-permeability and low-production oil reservoirs using a composite dual-well system mainly involves generating heat by burning the residual oil in the high-production oil layer. This heat is then conducted to the upper and lower low-permeability and low-production oil layers, increasing the overall temperature of the oil layers above and below the combustion zone. With the assistance of steam injection or steam drive, this approach is beneficial for the efficient development of low-permeability and low-production oil layers.

[0039] This invention obtains energy to heat the thin, differential layers above and below the high-yield oil layer by burning residual oil and asphaltenes within the oil layer. The residual oil contains 70%-80% or more of resin and asphaltenes, making it impossible to extract using conventional steam injection. Even if extracted, its economic value is lower than that of conventional heavy oil, and the resources consumed for extraction using existing technologies exceed the extraction yield. Therefore, combustion within the oil layer generates heat and carbon dioxide, which effectively reduce the viscosity of the crude oil. The heavy oil in the oil layer is ignited, using the heavy components within the layer as fuel and continuously generating heat, ultimately heating the adjacent upper and lower crude oil layers. This method heats the crude oil within the formation and combines it with conventional steam injection to bring it to the surface, thus solving the challenges of extracting heavy oil, extra-heavy oil, and thin interbedded, low-yield oil layers. Compared to steam injection for heavy oil extraction, this method offers higher thermal recovery efficiency, lower operating costs, and can rely on the oil layer's own fuel to provide heat, thereby improving the utilization rate of dead oil in the wellbore and reducing energy consumption. Furthermore, compared to conventional fire-driven methods, this invention provides excellent control over combustion exhaust gases, storing over 80% of them within the oil layer. This significantly reduces surface operation costs and mitigates problems such as decreased pump efficiency and reduced production caused by excessive gas output. The ignition method employed in this invention utilizes natural ignition, which can be achieved using existing gas injection equipment. In the initial ignition phase, it is best to use treated air with high oxygen content to improve the ignition success rate, thereby reducing the need for surface ignition equipment and overcoming the drawbacks of manual ignition failures due to unsuitable equipment structures. Because there are enough air injection wells throughout the reservoir, large-scale combustion can be established in the oil layer in a relatively short time. Therefore, the amount and rate of air injection required by the injection wells are relatively low, and there are no excessive requirements for air compressors and surface pipelines. The construction of the entire surface pipeline network can be adapted to local conditions and existing equipment can be modified.

[0040] Example 1

[0041] Examples of oil recovery using fire flooding:

[0042] The JinX block fire-drive pilot test area is located in the central part of an experimental fault block in the Liaohe Oilfield. It is sandwiched by multiple faults and has a monocline structure with a dip angle of approximately 8–13°. The oil-bearing area is 0.2 km², with a geological oil reserve of 125.6 × 10⁴ t. The fault block in Group I is a monocline structure with an average dip angle of 7.5°. Linear fire-drive was chosen to start from a higher position to fully utilize gravity and avoid secondary over-firing of oil wells. Considering the high viscosity of the crude oil in Group I, an initial design of a reverse nine-point area well pattern was adopted to effectively establish the fire line. After the initial fire line is established, the side wells will be converted into gas injection wells, thus forming a linear fire-drive well pattern. Currently, the well pattern in the test area is an 83m well spacing square well pattern, which is relatively complete and can meet the design requirements for converting area fire-drive to linear fire-drive. Furthermore, using the existing well pattern and well spacing can effectively reduce the initial investment in the test. Therefore, both test areas adopted an initial reverse nine-point area well pattern, which will be converted to a linear fire-drive well pattern later.

[0043] This well group contains 9 fire-driven gas injection wells, with a cumulative gas injection of 158.6413 million cubic meters; 22 production wells, 17 of which are currently in operation, producing 367.5 tons of fluid and 17.8 tons of oil per day, with a water cut of 95.0%, an annual oil production of 6,922 tons, a cumulative oil production of 3.75 × 10⁴ tons, and a cumulative air-to-oil ratio of 4021 Nm³. 3 / t.

[0044] However, this fire-driven well group also faces several major problems, including difficulties in fire-driven control, monitoring, control of fire-driven advance, and tail gas leakage. Two oil wells were selected within the well area. It was known that fire-driven testing was underway in the upper part of the oil layer to which these wells belonged. Furthermore, the presence of burnt coke at the end of the tubing during operations further confirmed good combustion conditions in the well area. By supplementing the conventional oil layer below the fire-driven layer with steam injection, good oil production was achieved initially, with an overall daily oil production of 5-8 tons, daily fluid production of 12-21 tons, and a cumulative increase in oil production of 1500-2200 tons, achieving good production capacity. The test wells showed a longer cycle time than conventional injection wells, with more stable daily oil production and a longer stable production period. The well temperature was slightly higher than that of conventional wells in the non-fire-driven well network. Good production capacity was achieved even with a small amount of steam injected initially. Analysis suggests that the heat generated by the combustion of the upper fire-driven oil layer heated the lower oil layer, improving the injection effect of the lower layer. Further research revealed that this phenomenon can be learned from our heavy oil fire-flooding development method. Through continuous advancement and summarization of fire-flooding experiments, we proposed optimization schemes for composite dual-well fire-flooding well networks and put forward reasonable suggestions. Based on actual field work, we finally proposed this invention.

[0045] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A composite dual-well fire flooding method for low-permeability, poor-permeability oil reservoirs, characterized in that... The development process of composite dual-well low-permeability reservoir: Two wells are drilled at all well sites in the core oil production area, one is a composite oil production well and the other is a fire-driven air injection well. All oil wells drilled at the outer edge of the reservoir are single oil production wells. By burning within the oil reservoir, the generated heat and carbon dioxide reduce the viscosity of the crude oil, igniting the heavy oil in the reservoir and using the heavy components within the reservoir as fuel to continuously generate heat. This heats the crude oil in the adjacent upper and lower oil layers. Combined with conventional steam injection for surface extraction, this composite dual-well low-permeability, low-production reservoir development obtains heat by burning the residual oil in the high-production oil layer. The heat is then conducted to the upper and lower low-permeability, low-production oil layers, raising the overall temperature of the oil layers above and below the combustion zone. The low-permeability, low-production oil layer is extracted using steam injection or steam drive. Energy is obtained by burning the residual oil and asphaltenes in the high-production oil layer to heat the thin, differential layers above and below the oil layer. The residual oil has a gum and asphaltenes content of 70%-80%. The heat and carbon dioxide generated by burning within the oil layer reduce the viscosity of the crude oil. In the well network, fire-driven air injection wells are used to re-open high-production layers and ignite them using physicochemical methods. It is required that no oil production well in the well network can re-open fire-driven layers. After a period of fire-driven operation, based on the gas composition content in the oil layer and the leakage of tail gas from some marginal wells, several wells are concentrated at the highest part of the structure, accounting for 50-80% of the total number of fire-driven air injection wells. These wells are used for oil production and tail gas discharge. The purified carbon dioxide is re-injected into other oil layers, and the residual heat is recovered to heat and reduce the viscosity of crude oil in the pipeline network.

2. The composite dual-well fire flooding method for low-permeability, poor-permeability oil reservoirs according to claim 1, characterized in that, In the oil wells, non-fire-driven low-permeability and low-production oil layers in the oil layer interpretation curve results table are not fire-driven high-production layers. In the initial stage of development, steam injection development is used for production wells. In the later stage, according to the changes in the development environment, steam-driven development is adopted. While re-exploding low-permeability and low-production oil layers, fire-driven layers are re-exploded in some marginal wells 1-9.

3. The composite dual-well fire flooding method for low-permeability, poor-permeability oil reservoirs according to claim 2, characterized in that, Based on the existing well network and the well conditions with casing damage, the wells were transformed into monitoring wells to monitor temperature, pressure, and exhaust gas composition within the well network.

4. The composite dual-well fire flooding method for low-permeability, poor-permeability oil reservoirs according to claim 3, characterized in that, The oil wells in the well network are used to tap the potential of each thin oil layer by combining chemical profile control, packer plugging, and hydraulic fracturing.

5. The composite dual-well fire flooding method for low-permeability, poor-permeability oil reservoirs according to claim 4, characterized in that, In the early stage of layer replenishment ignition, air injection wells in the well network select layers for perforation and ignition according to the reservoir conditions, and regulate layer replenishment ignition.

6. The composite dual-well fire flooding method for low-permeability, poor-permeability oil reservoirs according to claim 5, characterized in that, The physical properties of the heavy oil are as follows: viscosity 5,000–100,000 mps, non-flowing at 75°C, and density 0.95–1 g / m³. 3 Heavy oil pour point: ±10℃, gum content: 30-40% or more; high pour point oil pour point: 30-45℃, asphalt gum content: less than 10%, wax content: 35-50%.

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