Methods for enhancing oil recovery in the mid-to-late stages of SAGD in heterogeneous extra-heavy oil reservoirs and injection-production well patterns

Abstract

This invention proposes a method and injection-production well pattern for enhancing oil recovery in the mid-to-late stages of heterogeneous extra-heavy oil reservoirs (SAGD). The method includes: preheating the SAGD well pair through circulation, then injecting steam; preheating electrically heated horizontal wells using huff-and-puff methods, followed by conversion to long-tube steam injection and short-tube oil production; when the recovery rate is 30-35%, injecting a catalytic modifier into the electrically heated catalytic-modified branch wells; co-injecting non-condensable gas into the injection wells of the SAGD well pair; gradually reducing the steam injection volume while increasing the non-condensable gas injection volume according to a set ratio until the surface volume ratio of steam and non-condensable gas injection reaches a preset ratio; converting the electrically heated horizontal wells to continuous production and implementing electrically heated assisted production; when the recovery rate is 55-60%, reducing the preset mass of water equivalent steam and increasing the injection of non-condensable gas until conversion to gas drive; and in the gas injection oil production stage, continuously injecting non-condensable gas until the production reduction value of the SAGD well pair reaches the minimum production threshold.

Description

Technical Field

[0001] This invention relates to the field of thermal oil recovery technology, and in particular to a method for enhancing oil recovery in the mid-to-late stage of SAGD in heterogeneous extra-heavy oil reservoirs and an injection-production well pattern. Background Technology

[0002] Extra-heavy oil has a low content of light components and a high content of gums and asphaltenes, characterized by high viscosity, high density, and poor fluidity. my country has relatively abundant heavy oil resources, with currently proven reserves of 19.87 billion tons. The distribution of my country's heavy oil resources is controlled by the Alpine and Circum-Pacific tectonic domains, mainly distributed in the eastern and western regions. Most of my country's heavy oil resources are Mesozoic-Cenozoic terrestrial sediments, with a small amount being Paleozoic marine sediments. The reservoirs are mainly clastic rocks, characterized by high porosity, high permeability, and loose cementation. More than 70 heavy oil fields have been discovered in basins such as the Songliao Basin, Junggar Basin, Tarim Basin, and Turpan-Hami Basin. The Liaohe Oilfield in Northeast China has the largest heavy oil reserves, followed by the Shengli Oilfield in the east and the Karamay Oilfield in Xinjiang in the northwest. my country's heavy oil reservoirs exhibit terrestrial sedimentary characteristics, severe heterogeneity of oil layers, complex geological structures, and diverse reservoir types.

[0003] Extra-heavy oil plays a crucial role in high-end products, such as premium lubricants. In recent years, my country's dependence on imported oil has intensified, necessitating continuous improvement and increased production of domestic extra-heavy oil. The development technology of extra-heavy oil super-aggregate distillation (SAGD) has entered the industrialization stage, with many reservoirs already in their mid-to-late stages. How to achieve a safe, efficient, and significantly enhanced oil recovery rate in the mid-to-late stages of SAGD is one of the most pressing issues to be addressed in this field. Summary of the Invention

[0004] To improve the recovery rate of heterogeneous extra-heavy oil reservoirs during the mid-to-late stage of SAGD development, this invention proposes a method and injection-production well pattern for improving the recovery rate of heterogeneous extra-heavy oil reservoirs during the mid-to-late stage of SAGD.

[0005] To achieve the above objectives, the technical solution proposed by this invention is as follows:

[0006] In a first aspect, embodiments of the present invention provide a method for enhancing oil recovery in the mid-to-late stages of SAGD in heterogeneous extra-heavy oil reservoirs, comprising:

[0007] Deployment of injection-production well network: Densify electrically heated horizontal wells on both sides of the SAGD well, and densify catalytically modified multi-branch wells with electrical heating at the top of the SAGD well;

[0008] SAGD production stage: After circulating preheating of the SAGD well pair, steam injection is used to switch to the cavity expansion production stage. After huff and puff preheating and electric preheating, the electrically heated horizontal well is switched to long-tube steam injection and short-tube oil production.

[0009] GCEASAGD production stage: When the recovery rate is 30-35%, a catalytic modifier is injected into the electrically heated catalytic modification branch well, and non-condensable gas is injected into the injection well of the SAGD well pair. The water equivalent of steam is reduced by a preset mass within a unit cycle time. The steam injection volume is gradually reduced according to a set ratio while the non-condensable gas injection volume is increased until the surface volume ratio of the steam and non-condensable gas injection volume reaches the preset ratio.

[0010] When the steam chamber of the SAGD well pair is connected to the steam chamber of the electrically heated horizontal well, the electrically heated horizontal well is converted to continuous oil production and electrically heated assisted production is carried out; when the recovery rate is 55-60%, the steam equivalent of a preset mass of water is reduced within a unit cycle time, and the injection of non-condensable gas is increased, and the increase in the injection of non-condensable gas is controlled to be a preset multiple range of the reduction in steam, until it is converted to gas drive;

[0011] Gas injection recovery production stage: Non-condensable gas is continuously injected to utilize the residual heat of the steam chamber and the remaining oil in the steam chamber until the production reduction value of the SAGD well pair reaches the minimum production threshold, at which point production ends.

[0012] In one or more optional embodiments, the method of densifying electrically heated horizontal wells on both sides of the SAGD well and densifying one electrically heated catalytic reforming multi-branch well at the top of the SAGD well includes:

[0013] The electrically heated horizontal wells are densified at a predetermined distance range on the left and right sides of the SAGD well pair in the horizontal direction. The length of the electrically heated horizontal well is a first length range, and the distance between two electrically heated horizontal wells is a first distance range.

[0014] The electrically heated catalytic reforming multi-branch wells are densified at a second distance from the top of the oil layer at the top of the SAGD well pair. The branch length of the electrically heated catalytic reforming multi-branch wells is within the second length range, the branch direction is the four corners of the oil layer, and it can cover at least one of the SAGD well pairs.

[0015] In one or more alternative embodiments, the injection rate of the catalytic modifier into the electrically heated catalytic modifier branch well is 1% to 5% of the crude oil production rate.

[0016] In one or more optional embodiments, the catalytic modifier is:

[0017] Based on a total mass of 100 wt% of the catalyst fluid, the mixture contains 10 wt% to 50 wt% of toluenesulfonyl hydrazine and hydrazine hydrate, 10 wt% of at least one of tetrahydronaphthalene, tetrahydronaphthone, and decahydronaphthalene, 5 wt% of coking inhibitor, and the remainder is an oil phase solvent. The mass ratio of the catalyst fluid to water is 9:1.

[0018] In one or more optional embodiments, the coking inhibitor includes at least one of sulfur-containing compounds, phosphorus compounds, organosulfur-phosphorus compounds, organometallic compounds, inorganic metal salts or oxides, rare earth compounds, boron compounds, and organopolysiloxane sulfides.

[0019] In one or more optional embodiments, the heating temperature of the electrically heated catalytic reforming branch well is 240°C to 260°C.

[0020] In one or more optional embodiments, the electric heating power for electric heating-assisted production of the electrically heated horizontal well is 1000-1500 W / m.

[0021] In one or more alternative embodiments, when the recovery rate is 55-60%, the initial injection velocity of the non-condensate gas is 4000-8000 m / s. 3 / d.

[0022] In one or more optional embodiments, during the gas injection recovery production phase, the continuous injection rate of non-condensable gas is 15,000–35,000 m³ / h. 3 / d.

[0023] In one or more alternative embodiments, the non-condensable gas includes at least one of methane and nitrogen.

[0024] Secondly, embodiments of the present invention provide an injection-production well pattern for enhancing oil recovery in the mid-to-late stages of SAGD in heterogeneous extra-heavy oil reservoirs, comprising:

[0025] SAGD well pair, electrically heated horizontal wells located on both sides of the SAGD well pair, and electrically heated catalytic reforming multi-branch well located at the top of the SAGD well pair;

[0026] During the SAGD production stage, the SAGD well pair is used for circulating preheating, and then steam injection is used to switch to the cavity expansion production stage; the electrically heated horizontal well is used for huff and puff preheating and then switched to long-tube steam injection short-tube oil production.

[0027] During the GCEASAGD production stage: when the recovery rate is 30-35%, the electrically heated catalytic reforming branch well is used to inject catalytic reforming agent, and the injection well of the SAGD well pair is used to inject non-condensable gas. The steam equivalent of a preset mass is reduced within a unit cycle time. The steam injection volume is gradually reduced according to a set ratio while the non-condensable gas injection volume is increased until the surface volume ratio of the steam and non-condensable gas injection volume reaches the preset ratio.

[0028] When the steam chamber of the SAGD well pair is connected to the steam chamber of the electrically heated horizontal well, the electrically heated horizontal well is used to switch to continuous oil production and perform electrically heated assisted production; when the recovery rate is 55-60%, the injection well of the SAGD well pair is used to reduce the water equivalent of steam by a preset mass within a unit cycle time and increase the injection of non-condensable gas, controlling the increase of non-condensable gas injection to be a preset multiple range of the decrease of steam, until it switches to gas drive;

[0029] During the gas injection oil recovery production stage: the injection well of the SAGD well pair is used to continuously inject non-condensate gas to utilize the residual heat of the steam chamber and the remaining oil in the steam chamber until the production of the SAGD well pair reaches the minimum production threshold, at which point production ends.

[0030] In one or more optional embodiments, the electrically heated horizontal wells are respectively located at a predetermined distance range in the horizontal direction on the left and right sides of the SAGD well pair, the length of the electrically heated horizontal well is a first length range, and the well distance between the two electrically heated horizontal wells located on the left and right sides of the SAGD well pair is a first distance range.

[0031] The electrically heated catalytic reforming multi-branch well is located at a second distance from the top of the oil layer on the top of the SAGD well pair. The branch length of the electrically heated catalytic reforming multi-branch well is within the second length range, the branch direction is the four corners of the oil layer, and it can cover at least one of the SAGD well pairs.

[0032] Based on the above technical solution, the beneficial effects of the present invention compared with the prior art are as follows:

[0033] The present invention provides a method for enhancing oil recovery in the mid-to-late stages of SAGD in heterogeneous extra-heavy oil reservoirs. This method employs an improved SAGD well network containing infill electrically heated horizontal wells and electrically heated catalytic reforming branch wells. It provides a production operation method corresponding to three stages, highlighting the key operational points and transition timing for the three oil production stages: SAGD cavity expansion, GCEASAGD, and gas injection-enhanced oil production. Gradual transition between each stage is beneficial for the stability of the steam cavity. The method proposes the coordinated operation of gas-assisted cavity expansion, catalytic reforming branch wells, and electrically heated horizontal production wells, which helps accelerate steam cavity expansion, reduce heavy oil viscosity, and increase oil production rate. The later-stage gas injection effectively utilizes the residual heat of the steam cavity, achieving gas recycling, energy saving, carbon reduction, and cost savings, thus improving the overall production efficiency of the SAGD process.

[0034] The method for enhancing oil recovery in the mid-to-late stages of SAGD (Super-Aggressive Oil Depletion) in heterogeneous extra-heavy oil reservoirs provided in this invention employs an improved SAGD well network structure, which is beneficial for accelerating oil production in the mid-to-late stages while saving energy and reducing carbon dioxide emissions. An electrically heated horizontal well is densified on each side of the SAGD well pair, effectively utilizing residual oil at the edge and accelerating oil production, thereby increasing the controlled reserves of the well pair. An electrically heated catalytic reforming branch well is densified above the SAGD well pair, which helps reduce the residual oil saturation of the reservoir, improving the oil production rate and ultimate recovery rate. The simultaneous commissioning of the SAGD well pair, the electrically heated horizontal well, and the electrically heated catalytic reforming branch well reduces the risk of steam leakage from the branch wells in the mid-to-late stages. The combination of multiple enhanced oil production measures improves the oil production rate throughout the entire stage while also achieving carbon reduction and energy conservation. The placement of the catalytic reforming branch well conforms to the steam migration pattern, enhancing the utilization of heat from the steam chamber and reducing the viscosity of the extra-heavy oil.

[0035] The method for enhancing oil recovery in the mid-to-late stages of SAGD in heterogeneous extra-heavy oil reservoirs provided in this invention first accelerates the connection between two steam chambers (one large and one small) through steam injection and electric heating. During the mid-development phase, catalytically modified branch wells and gas-assisted SAGD further accelerate the extraction of extra-heavy oil. After the steam chambers extend to the top, the SAGD well pairs employ catalytic modifiers to assist production. After the steam chambers extend to the top boundary, non-condensable gas is used to assist production. The non-condensable gas reduces subcooling and accumulates at the top of the steam chambers to form an insulating layer, reducing heat loss during extraction and stabilizing the production rate while increasing the oil-to-steam ratio to some extent. Simultaneously, the catalytic modifier injected into the top catalytically modified branch wells, under the displacement and diffusion effects of the non-condensable gas and steam, fully reacts with the extra-heavy oil using the heat of the steam chambers, achieving in-situ modification and reducing crude oil viscosity, further increasing the oil production rate and effectively utilizing remaining oil. Heating horizontal wells to assist SAGD production can effectively extract remaining oil between wells, ultimately achieving an oil recovery rate of over 65%.

[0036] The method for enhancing oil recovery in the mid-to-late stages of SAGD (Super Aquatic Oil Depletion) in heterogeneous extra-heavy oil reservoirs provided in this invention utilizes the injection of catalyst modifiers during the mid-development stage and the use of infill electrically heated production wells. This effectively accelerates oil production, utilizes the remaining oil in the triangular zone at the edge of the steam chamber, and reduces residual oil saturation. The large-scale injection of gas in the late development stage fully utilizes the residual heat of the steam chamber, ensuring continuous production in the later stages of SAGD. This method is beneficial for improving oil production speed in the mid-to-late development stages while simultaneously increasing the final recovery rate.

[0037] The method for enhancing oil recovery in the mid-to-late stages of SAGD in heterogeneous extra-heavy oil reservoirs provided in this invention utilizes non-condensable gas, catalytic modifiers, and electric heating, reducing steam consumption by up to 20% and carbon dioxide emissions. The large-scale injection of gas in the later stages allows 80-90% of the gas to be recovered and reused, lowering the cost per ton of oil. This method is both low-carbon and environmentally friendly while reducing costs.

[0038] The method for enhancing oil recovery in the mid-to-late stage of SAGD in heterogeneous extra-heavy oil reservoirs provided in this invention uses a novel catalytic modifier. The catalytic modifier contains toluenesulfonyl hydrazine (TSH) and hydrazine hydrate (HH), which can accelerate the reaction rate at the same temperature and effectively achieve catalytic modification of extra-heavy oil.

[0039] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained in accordance with the structures particularly pointed out in the description, claims and drawings.

[0040] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0041] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0042] Figure 1 A schematic flowchart illustrating the method for enhancing oil recovery in the mid-to-late stages of SAGD in heterogeneous extra-heavy oil reservoirs provided in this embodiment of the invention;

[0043] Figure 2 This is a well pattern distribution map of SAGD improvement for heterogeneous extra-heavy oil reservoirs provided in an embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of the SAGD cavity expansion production stage assisted by electric heating in an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of the steam / gas chamber connection for an electrically heated horizontal well-assisted SAGD in an embodiment of the present invention;

[0046] Figure 5 This is a schematic diagram of the steam (gas) chamber in the GCEASAGD stage of this invention.

[0047] Figure 6 This is a schematic diagram of the gas chamber in the later stage of the gas injection phase in an embodiment of the present invention;

[0048] The reference numerals in the attached diagram are as follows: 1 is the production horizontal well of the SAGD well pair, 2 is the injection horizontal well of the SAGD well pair, 3 is the electrically heated horizontal well, and 4 is the electrically heated catalytic reforming branch well. Detailed Implementation

[0049] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0050] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of methods consistent with some aspects of the invention as detailed in the appended claims.

[0051] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0052] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0053] Definitions:

[0054] Heterogeneous extra-heavy oil reservoirs: crude oil viscosity at 50℃ greater than 50000 mPa·s, porosity greater than 0.28, permeability greater than 1000 mD, oil layer depth 150–1600 m, oil layer thickness greater than 10 m, heterogeneity coefficient less than 1.5.

[0055] SAGD: Injecting steam to reduce the viscosity of extra-heavy oil in the formation, and then extracting the flowable crude oil after viscosity reduction by gravity.

[0056] GCEASAGD: A technology for developing SAGD with the synergistic assistance of gas-catalyst-electric heating.

[0057] Subcool: refers to the difference between the saturated steam temperature corresponding to the bottom pressure of the horizontal production well and the fluid temperature at the bottom of the horizontal production well. It reflects the level of the gas-liquid interface between the injection and production wells and is an important parameter for measuring the development effect and control level of the SAGD injection-production well pair.

[0058] The inventors discovered that extra-heavy oil reservoirs face the following development challenges in the mid-to-late stages: ① The high viscosity of extra-heavy oil leads to high steam consumption and poor oil recovery efficiency using conventional thermal recovery techniques; ② Due to the high heterogeneity of the reservoir, heat loss in the steam chamber increases in the mid-to-late stages, resulting in a decrease in the oil-gas ratio and daily oil production, an increase in water cut, and a large amount of unrecovered oil between wells. To address these challenges, it is necessary to effectively reduce the viscosity of extra-heavy oil and increase its fluidity, while simultaneously improving the thermal utilization rate of steam to achieve "green and low-carbon recovery" in the mid-to-late stages of extra-heavy oil development. Conventional thermal recovery technologies for heterogeneous extra-heavy oil reservoirs suffer from low oil-gas ratios, rapid production decline, and limited effectiveness in improving oil recovery. Through further research and development, the inventors have developed a comprehensive enhanced oil recovery method and injection-production well network for heterogeneous extra-heavy oil reservoirs using SAGD in the mid-to-late stages. This method integrates electrically heated horizontal well technology, catalytic upgrading technology, branch well technology, and gas-assisted SAGD technology. It significantly improves oil recovery in the mid-to-late stages of extra-heavy oil development, effectively utilizing the remaining oil in the reservoir and improving steam dryness and steam-driven oil recovery efficiency. This comprehensive enhanced oil recovery method solves the problems of poor utilization and low utilization rate in heterogeneous extra-heavy oil reservoirs.

[0059] This invention provides a method for enhancing oil recovery in the mid-to-late stages of SAGD in heterogeneous extra-heavy oil reservoirs, referring to... Figure 1 As shown, the method includes:

[0060] S101: Deployment of injection-production well network: Infiltrate electrically heated horizontal wells on both sides of the SAGD well, and infiltrate electrically heated catalytic reforming multi-branch wells on the top of the SAGD well.

[0061] In step S101 above, the process of drilling electrically heated horizontal wells on both sides of the SAGD well and drilling an electrically heated catalytic reforming multi-branch well at the top of the SAGD well specifically includes:

[0062] The electrically heated horizontal wells are densified at a predetermined distance range on the left and right sides of the SAGD well pair in the horizontal direction. The length of the electrically heated horizontal well is a first length range, and the distance between two electrically heated horizontal wells is a first distance range.

[0063] The electrically heated catalytic reforming multi-branch wells are densified at a second distance from the top of the oil layer at the top of the SAGD well pair. The branch length of the electrically heated catalytic reforming multi-branch wells is within the second length range, the branch direction is the four corners of the oil layer, and it can cover at least one of the SAGD well pairs.

[0064] In one specific embodiment, the aforementioned preset range can be 40-50m, the aforementioned first length range can be 200-300 meters, the aforementioned first distance range can be 80-100 meters, and the aforementioned second length range can be 50-200m. (Refer to...) Figure 2 As shown, two electrically heated horizontal wells 3 are densified next to the SAGD well pair. The electrically heated horizontal wells 4 are parallel to the direction of the SAGD well pair and are 40-50m apart in the horizontal direction. The length of the electrically heated horizontal wells 3 is 200-300m and the well spacing is 80-100m. A electrically heated catalytic reforming multi-branch well 4 is densified above the SAGD well pair. The branch length is 50-200m and the branch direction is the four corners of the oil layer. The electric heating power is 1000-1500W / m. It is located 2-5 meters below the top of the oil layer and can cover one or more SAGD well pairs.

[0065] The method for enhancing oil recovery in the mid-to-late stage of SAGD in heterogeneous extra-heavy oil reservoirs provided in this invention has controllable safety risks. By deploying SAGD horizontal well pairs, denser electrically heated horizontal wells, and catalytic reforming branch wells in the early stage of oilfield development, the risk of steam and other gas leakage from the denser well network in the mid-to-late stage can be avoided.

[0066] S102: SAGD production stage: After circulating preheating of the SAGD well pair, steam injection is used to switch to the cavity expansion production stage. After huff and puff preheating and electric preheating, the electrically heated horizontal well is switched to long-tube steam injection and short-tube oil production.

[0067] S103: GCEASAGD production stage: When the recovery rate is 30-35%, a catalytic modifier is injected into the electrically heated catalytic modification branch well, and non-condensable gas is injected into the injection well of the SAGD well pair. The steam injection volume is gradually reduced while the non-condensable gas injection volume is increased according to the set ratio until the surface volume ratio of the steam and non-condensable gas injection volume reaches the preset ratio.

[0068] In this embodiment of the invention, the heated catalytic reforming branch well can be put into use when the recovery rate is 30-35%. During this stage, the daily oil production decreases, the oil-gas ratio decreases, the water cut increases, the steam chamber expands laterally to its maximum, and the process begins to enter the decline stage. Catalytic reforming agent is added through the catalytic reforming branch well. The injection rate of catalytic reforming agent is determined according to the rate of crude oil production. The injection rate of catalytic reforming agent into the electrically heated catalytic reforming branch well is 1%-5% of the crude oil production rate, that is, 10-50 kg of catalytic reforming agent is injected for every ton of crude oil produced.

[0069] In this embodiment of the invention, the catalyst modifier is: based on the total mass of the catalyst fluid as 100wt%, 10wt% to 50wt% of toluenesulfonyl hydrazine (TSH) and hydrazine hydrate (HH), 10wt% of at least one of tetrahydronaphthalene (THN), tetrahydronaphthone, and decahydronaphthalene, 5wt% of coking inhibitor, and the remainder is an oil phase solvent, with a mass ratio of catalyst fluid to water of 9:1.

[0070] In one specific embodiment, the coking inhibitor includes at least one of sulfur-containing compounds, phosphorus compounds, organosulfur-phosphorus compounds, organometallic compounds, inorganic metal salts or oxides, rare earth compounds, boron compounds, and organopolysiloxane sulfides.

[0071] In one specific embodiment, the heating temperature of the electrically heated catalytic reforming branch well is 240℃~260℃.

[0072] The catalytic reforming agents provided in this invention embodiment are as follows: ① The reason for using toluenesulfonyl hydrazine (TSH) and hydrazine hydrate (HH) to catalytically reform crude oil is that TSH and HH readily react with crude oil through a large amount of chemical reaction to produce diimine. As an intermediate molecule, diimine has a high tendency to attack double bonds and can effectively hydrogenate crude oil. Diimine can undergo hydrogenation under mild conditions of 240℃ to 260℃, which can be achieved in oil reservoirs. The light components generated after hydrogenation can dissolve and reduce viscosity of crude oil. ② Tetrahydronaphthalene (THN), tetrahydronaphthone, and decahydronaphthalene reduce the viscosity of extra-heavy oil and can also act as solvents to dilute hydrocarbon macromolecular free radicals, reduce the chance of free radical collisions, inhibit polymerization and coking, and effectively break the C-S bonds and long carbon chains of heavy components, so that the reaction proceeds in the direction of hydrodesulfurization, thereby reducing the molecular weight of heavy oil, decreasing the asphaltenes content, and reducing the viscosity of heavy oil. ③ Oil-soluble solvents can fully mix and react with the oil phase, effectively reducing crude oil viscosity, enhancing the displacement effect of extra-heavy oil from the top of the oil layer to the production well, and reducing residual oil saturation.

[0073] This invention innovatively proposes the use of branch wells with catalytic modifiers and introduces a novel catalytic modifier. A catalytic modifier branch well was added to the upper part of the SAGD well, near the top of the oil layer, effectively enhancing the catalytic modification effect on extra-heavy oil by utilizing steam migration patterns. The proposed novel catalytic modifier, toluenesulfonyl hydrazine (TSH), hydrazine hydrate (HH), and other additives work synergistically, exhibiting characteristics of low reaction temperature and easy generation through extensive chemical reactions, effectively reducing crude oil viscosity.

[0074] In this embodiment of the invention, the unit cycle time can be a day, and the preset mass of water equivalent can be 2 tons of water equivalent. After injecting non-condensate gas into the injection well of the SAGD well pair, the injection well of the SAGD well pair begins to enter the gas injection stage, gradually reducing the proportion of steam, reducing the steam by 2 tons of water equivalent per day, and simultaneously injecting a corresponding proportion of gas. Finally, the surface volume ratio of the injected steam and gas is about 1:25.

[0075] In one specific embodiment, the non-condensable gas includes at least one of methane and nitrogen.

[0076] In this embodiment of the invention, gas-assisted SAGD involves: ① Using a bare heat-insulating pipe or a bare oil pipe, while injecting steam into the pipe, gas is continuously or slug-type injected into the annular space of the casing and tubing. This provides insulation and reduces heat loss in the wellbore. Simultaneously, due to gravitational differentiation, the gas accumulates at the top of the steam chamber, reducing heat loss and increasing the steam's swept volume. ② Non-condensable gas has good expandability, which can replenish formation energy.

[0077] In this embodiment of the invention, the use of electric heating technology can reduce crude oil viscosity, improve crude oil fluidity, reduce injection pressure, and at the same time, increase the temperature of the catalytic modifier and accelerate the reaction rate with crude oil.

[0078] The extraction method provided by this invention first adopts SAGD development technology, and then achieves enhanced extraction in the mid-to-late stages. The synergistic effect of non-condensable gas, catalytic modifier, and infill electrically heated production wells in the mid-term reduces the well spacing between SAGD well pairs, increases the recoverable reserves of SAGD well pairs, and improves the oil production rate throughout the entire extraction process.

[0079] S104: When the steam chamber of the SAGD well pair is connected to the steam chamber of the electrically heated horizontal well, the electrically heated horizontal well is converted to continuous oil production and electrically heated assisted production is carried out; when the recovery rate is 55-60%, the steam equivalent of a preset mass of water is reduced within a unit cycle time, and the injection of non-condensable gas is increased, and the increase in the injection of non-condensable gas is controlled to be a preset multiple range of the decrease in steam, until it is converted to gas drive;

[0080] In this embodiment of the invention, when the steam chamber of the SAGD well pair is connected to the steam chamber of the electrically heated horizontal well 3, the electrically heated horizontal well 3 stops long-tube steam injection and short-tube oil production and switches to continuous oil production operation. At the same time, the electrically heated horizontal well 3 is subjected to electric heating to assist production, with an electric heating power of 1000-1500 W / m. When the recovery rate is 55-60%, the steam equivalent of 2t of water is reduced per day, and the initial velocity of the injected gas is 4000-8000 m / s. 3 / d, the amount of injected gas increases by 3 to 4 times the amount of reduced steam volume, and the amount of steam is gradually reduced to switch to gas drive.

[0081] The method for enhancing oil recovery in the mid-to-late stages of heterogeneous extra-heavy oil reservoirs under SAGD (Super Aquaculture Digestion) provided in this invention employs gas and electric heating to intensify production during the later stages of SAGD development. The large-scale injection of gas replenishes formation energy. Considering the characteristics of the steam chamber reaching its maximum development and high temperature in the later stages of SAGD, this measure fully utilizes the residual heat of the steam chamber while reducing heat loss, effectively displacing the extra-heavy oil, reducing the residual oil saturation in the pores to below 5%, increasing the available reserves, and reducing steam utilization while achieving cost reduction and energy conservation. Electric heating of the production well replenishes the heat near the production well zone, reduces the viscosity of the extra-heavy oil, and improves the flowability of the crude oil.

[0082] S105: Gas injection oil production stage: Non-condensable gas is continuously injected to utilize the residual heat of the steam chamber and the remaining oil in the steam chamber until the production reduction value of the SAGD well pair reaches the minimum production threshold, and production ends.

[0083] In one specific embodiment, in step S105 above, during the gas injection oil recovery production stage, the continuous non-condensable gas injection rate is 15,000 to 35,000 m³ / d.

[0084] In the gas injection recovery production stage, the densified electrically heated horizontal wells can continuously produce oil and carry out electrically heated assisted production. The electrically heated catalytic reforming branch wells can continuously inject catalytic reforming agents and carry out electrically heated assisted production to increase the utilization effect of the remaining oil.

[0085] In this embodiment of the invention, the final injection gas injection rate is 15000–35000 m / s. 3 With a production rate of 80-90% per day, 80-90% of the gas can be recovered and reused, utilizing the residual heat of the steam chamber. Two electrically heated infill horizontal wells are placed on either side of the injection-production horizontal well pair, in areas of residual oil that are difficult to reach through the steam chamber, increasing the fluidity of the untapped residual oil. Production ceases when the SAGD well pair's production drops to approximately 3 t / d, indicating a lack of economic viability.

[0086] The method provided by this invention employs a combination of multiple enhanced extraction methods during the SAGD (Super Aquaculture Distillation) process, effectively improving development results at different stages. It also provides transition markers for different stages, enabling a gradual transition between them. Catalytic modifiers assist SAGD in reducing the viscosity of extra-heavy oil, gas-assisted SAGD reduces heat loss and increases the oil-gas ratio, and horizontally electrically heated production wells assist SAGD in increasing the oil production rate and oil-gas ratio. This effectively reduces steam consumption, increases the use of green and environmentally friendly energy, lowers the overall extraction cost, and ultimately achieves a recovery rate of over 65%.

[0087] To provide a clearer explanation of the method for enhancing oil recovery in the mid-to-late stages of SAGD in heterogeneous extra-heavy oil reservoirs provided in this invention, and to verify the effectiveness of the method, the following detailed description uses an example of a field implementation plan in an oilfield and a comparison of the predicted SAGD production effects with those of the patented invention at all stages:

[0088] This embodiment discloses an on-site implementation plan for an oil field and compares the predicted effects of this invention patent with the full-stage SAGD mining results.

[0089] Basic reservoir parameters: reservoir depth 200m, porosity 32%, oil saturation 75%, horizontal permeability 1500mD, vertical permeability 1200mD, oil layer thickness 20m, temperature 20℃, viscosity under reservoir temperature conditions 2334000mPa·s.

[0090] First, deploy SAGD to enhance the oil well network:

[0091] Designing and deploying SAGD-enhanced well networks within the production area of ​​extra-heavy oil reservoirs, such as Figure 2 As shown, this well network has at least one SAGD well pair (i.e., injection horizontal well 1 and production horizontal well 2), two electrically heated horizontal wells 3, and one electrically heated catalytic reforming multi-branch well 4. Injection horizontal well 1 is deployed at the bottom of the oil layer, production horizontal well 2 is located on the same vertical plane as injection horizontal well 1, and is 4-6m apart vertically. The horizontal distance between production horizontal well 2 and the two electrically heated horizontal wells 3 is 45m. The electrically heated catalytic reforming multi-branch well 4 is deployed 2m from the top of the oil layer.

[0092] Next, in the early stages of development, the SAGD cavity expansion production phase will be carried out:

[0093] After the SAGD well achieves interconnection with the circulating preheating system, injection horizontal well 1 continuously injects steam with a wellhead dryness of 85%, an injection rate exceeding 100 t / d, and a bottomhole pressure of 3 MPa. Production horizontal well 2 continuously discharges fluid, and the pressure difference between injection horizontal well 1 and production horizontal well 2 is controlled between 0.2 and 0.6 MPa. After the electrically heated horizontal well 3 performs huff and puff and preheating, it switches to circulating production, employing continuous steam injection through a long pipe and continuous fluid discharge through a short pipe, while simultaneously using electric heating. The steam injection rate through the long pipe is controlled at 20 t / d, and the bottomhole pressure is controlled at 2.5 MPa.

[0094] The steam chambers entered the horizontal stage, and the average daily oil production reached its peak. After 5.5 years of production, the SAGD well achieved a daily oil production of 42 t / d, while the electrically heated horizontal well 3 achieved a daily oil production of 11 t / d. The expansion of the steam chambers in the SAGD and electrically heated horizontal wells 3 is shown in [the diagram]. Figure 3 .

[0095] Next, in the later stages of development, the GCEASAGD generation phase begins:

[0096] After 10 years of production, the steam chamber expanded to the edge of the oil layer, and daily oil production began to decline, transitioning to the GCEASAGD enhanced oil production stage. SAGD wells achieved a daily oil production of 50 tons / day, while electrically heated horizontal wells achieved 13 tons / day, increasing oil production by more than 10% and maintaining stable production for over 6 years. A schematic diagram of the connection between the steam / gas chamber and the electrically heated horizontal well in the SAGD auxiliary system is shown below. Figure 4 A schematic diagram of the steam / gas chamber during the SAGD generation stage in the mid-to-late stage of SAGD enhanced oil recovery methods using gas / catalytic reforming / electric heating assisted SAGD is shown below. Figure 5 .

[0097] Finally, in the later stages of development, the gas injection recovery production phase begins.

[0098] During this stage, the steam chamber is expanded to achieve a maximum recovery rate of 65%. Large-scale gas injection utilizes the residual heat of the steam chamber to supplement displacement energy, achieving stable production for approximately 550 days. After this stage, the final recovery rate reaches 71%. A schematic diagram of the gas chamber during the gas injection stage of the late-stage SAGD enhanced oil recovery method is shown below. Figure 6 .

[0099] Table 1 Production Forecast for this Implementation Plan

[0100] Technology Comparison Time (years) Recovery rate Oil-to-gas ratio SAGD 13 52.6 0.19 The mining method of the present invention 18 71 0.23

[0101] As shown in Table 1, from a production perspective, the effective production time using dual-horizontal-well SAGD is 13 years, with a final recovery rate of 52.6% and an oil-gas ratio of 0.19. In contrast, the economically effective production time using the extraction method provided in this embodiment of the invention is approximately 18 years, with a final recovery rate of 71%. Specifically, the recovery rate during the GCEASAGD generation stage is 30%, and the recovery rate during the gas injection production stage is 6%.

[0102] This invention provides a method for enhancing oil recovery in the mid-to-late stages of SAGD (Super Aquaculture Distillation) in heterogeneous extra-heavy oil reservoirs. It offers an improved SAGD well pattern, firstly by accelerating the connection between two steam chambers (one large and one small) through steam injection and electric heating assistance; secondly, by accelerating the extraction of extra-heavy oil through catalytic-modified branch wells and gas-assisted SAGD; and thirdly, by providing a production operation method under this new SAGD well pattern, divided into three stages: SAGD chamber expansion production, GCEASAGD generation stage, and gas injection-enhanced oil production, thus improving the overall production efficiency of the SAGD process. Gas injection reduces heat loss during extraction, catalytic modifiers lower the viscosity of extra-heavy oil, and heating horizontal wells to assist SAGD production effectively extracts remaining oil between wells, ultimately achieving an oil recovery rate of over 65%.

[0103] Based on the same inventive concept, this invention also provides an injection-production well pattern for enhancing oil recovery in the mid-to-late stages of SAGD in heterogeneous extra-heavy oil reservoirs, referring to... Figure 2 Shown, including:

[0104] SAGD well pair, electrically heated horizontal wells located on both sides of the SAGD well pair, and electrically heated catalytic reforming multi-branch well located at the top of the SAGD well pair;

[0105] During the SAGD production stage, the SAGD well pair is used for circulating preheating, and then steam injection is used to switch to the cavity expansion production stage; the electrically heated horizontal well is used for huff and puff preheating and then switched to long-tube steam injection short-tube oil production.

[0106] During the GCEASAGD production stage: when the recovery rate is 30-35%, the electrically heated catalytic reforming branch well is used to inject catalytic reforming agent, and the injection well of the SAGD well pair is used to inject non-condensable gas. The steam equivalent of a preset mass is reduced within a unit cycle time. The steam injection volume is gradually reduced according to a set ratio while the non-condensable gas injection volume is increased until the surface volume ratio of the steam and non-condensable gas injection volume reaches the preset ratio.

[0107] When the steam chamber of the SAGD well pair is connected to the steam chamber of the electrically heated horizontal well, the electrically heated horizontal well is used to switch to continuous oil production and perform electrically heated assisted production; when the recovery rate is 55-60%, the injection well of the SAGD well pair is used to reduce the water equivalent of steam by a preset mass within a unit cycle time and increase the injection of non-condensable gas, controlling the increase of non-condensable gas injection to be a preset multiple range of the decrease of steam, until it switches to gas drive;

[0108] During the gas injection oil recovery production stage: the injection well of the SAGD well pair is used to continuously inject non-condensate gas to utilize the residual heat of the steam chamber and the remaining oil in the steam chamber until the production of the SAGD well pair reaches the minimum production threshold, at which point production ends.

[0109] In one specific embodiment, the electrically heated horizontal wells are respectively located at a predetermined distance range in the horizontal direction on the left and right sides of the SAGD well pair, the length of the electrically heated horizontal well is a first length range, and the well distance between the two electrically heated horizontal wells located on the left and right sides of the SAGD well pair is a first distance range;

[0110] The electrically heated catalytic reforming multi-branch well is located at a second distance from the top of the oil layer on the top of the SAGD well pair. The branch length of the electrically heated catalytic reforming multi-branch well is within the second length range, the branch direction is the four corners of the oil layer, and it can cover at least one of the SAGD well pairs.

[0111] The specific implementation method of the injection-production well network for enhancing oil recovery in the mid-to-late stage of SAGD in heterogeneous extra-heavy oil reservoirs provided in this embodiment of the invention can be referred to the detailed description of the method for enhancing oil recovery in the mid-to-late stage of SAGD in heterogeneous extra-heavy oil reservoirs in Embodiment 1 above, and will not be repeated here.

[0112] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other. This invention is not limited to any single aspect, nor to any single embodiment, nor to any combination and / or substitution of these aspects and / or embodiments. Each aspect and / or embodiment of this invention can be used alone, or in combination with one or more other aspects and / or other embodiments.

[0113] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for enhancing oil recovery in the mid-to-late stages of SAGD in heterogeneous extra-heavy oil reservoirs, characterized in that, include: Deployment of injection-production well network: Densify electrically heated horizontal wells on both sides of the SAGD well, and densify catalytically modified multi-branch wells with electrical heating at the top of the SAGD well; SAGD production stage: After circulating preheating of the SAGD well pair, steam injection is used to switch to the cavity expansion production stage. After huff and puff preheating and electric preheating, the electrically heated horizontal well is switched to long-tube steam injection and short-tube oil production. GCEASAGD production stage: When the recovery rate is 30-35%, the catalytic modifier is injected into the injection well of the SAGD well pair through the electrically heated catalytic modifier multi-branch well. Non-condensable gas is injected into the injection well of the SAGD well pair. The water equivalent of steam is reduced by a preset mass within a unit cycle time. The steam injection volume is gradually reduced according to a set ratio while the non-condensable gas injection volume is increased until the surface volume ratio of the steam and non-condensable gas injection volume reaches the preset ratio. When the steam chamber of the SAGD well pair is connected to the steam chamber of the electrically heated horizontal well, the electrically heated horizontal well is converted to continuous oil production and electrically heated assisted production is carried out; when the recovery rate is 55~60%, the steam equivalent of a preset mass of water is reduced within a unit cycle time, and the injection of non-condensable gas is increased, and the increase in the injection of non-condensable gas is controlled to be a preset multiple range of the reduction in steam, until it is converted to gas drive; Gas injection recovery production stage: Non-condensable gas is continuously injected to utilize the residual heat of the steam chamber and the remaining oil in the steam chamber until the production reduction value of the SAGD well pair reaches the minimum production threshold, at which point production ends.

2. The method as described in claim 1, characterized in that, The method of densifying electrically heated horizontal wells on both sides of the SAGD well, and densifying one electrically heated catalytic reforming multi-branch well at the top of the SAGD well, includes: The electrically heated horizontal wells are densified at a predetermined distance range on the left and right sides of the SAGD well pair in the horizontal direction. The length of the electrically heated horizontal well is a first length range, and the distance between two electrically heated horizontal wells is a first distance range. The electrically heated catalytic reforming multi-branch wells are densified at a second distance from the top of the oil layer at the top of the SAGD well pair. The branch length of the electrically heated catalytic reforming multi-branch wells is within the second length range, the branch direction is the four corners of the oil layer, and it can cover at least one of the SAGD well pairs.

3. The method as described in claim 1, characterized in that, The injection rate of the catalytic modifier into the electrically heated catalytic-modified multi-branch well is 1% to 5% of the crude oil production rate.

4. The method as described in claim 1, characterized in that, The catalytic modifier is: Based on a total mass of 100 wt% of the catalyst fluid, the mixture contains 10 wt% to 50 wt% of toluenesulfonyl hydrazine and hydrazine hydrate, 10 wt% of at least one of tetrahydronaphthalene, tetrahydronaphthone, and decahydronaphthalene, 5 wt% of coking inhibitor, and the remainder is an oil phase solvent. The mass ratio of the catalyst fluid to water is 9:

1.

5. The method as described in claim 4, characterized in that, The coking inhibitors include at least one of sulfur-containing compounds, phosphorus compounds, organosulfur-phosphorus compounds, organometallic compounds, inorganic metal salts or oxides, rare earth compounds, boron compounds, and organopolysiloxane sulfides.

6. The method as described in claim 4, characterized in that, The heating temperature of the electrically heated catalytically modified multi-branch well is 240℃~260℃.

7. The method as described in claim 1, characterized in that, The electric heating power for the electric heating auxiliary production of the electric heating horizontal well is 1000~1500W / m.

8. The method as described in claim 1, characterized in that, When the recovery rate is 55-60%, the initial velocity of the injected non-condensate gas is 4000-8000 m / s. 3 / d.

9. The method as described in claim 1, characterized in that, During the gas injection recovery production phase, the continuous injection rate of non-condensable gas is 15,000~35,000 m / s. 3 / d.

10. The method as described in claim 1, characterized in that, The non-condensable gas includes at least one of methane and nitrogen.

11. A well pattern for enhancing oil recovery in the mid-to-late stages of SAGD in heterogeneous extra-heavy oil reservoirs, characterized in that, include: SAGD well pair, electrically heated horizontal wells located on both sides of the SAGD well pair, and electrically heated catalytic reforming multi-branch well located at the top of the SAGD well pair; During the SAGD production stage, the SAGD well pair is used for circulating preheating, and then steam injection is used to switch to the cavity expansion production stage; the electrically heated horizontal well is used for huff and puff preheating and then switched to long-tube steam injection short-tube oil production. During the GCEASAGD production stage: when the recovery rate is 30-35%, the electrically heated catalytic reforming multi-branch well is used to inject catalytic reforming agent, and the injection well of the SAGD well pair is used to inject non-condensable gas. The steam equivalent of a preset mass is reduced within a unit cycle time. The steam injection volume is gradually reduced according to a set ratio while the non-condensable gas injection volume is increased until the surface volume ratio of the steam and non-condensable gas injection volume reaches the preset ratio. When the steam chamber of the SAGD well pair is connected to the steam chamber of the electrically heated horizontal well, the electrically heated horizontal well is used to switch to continuous oil production and perform electrically heated assisted production; when the recovery rate is 55~60%, the injection well of the SAGD well pair is used to reduce the water equivalent of steam by a preset mass within a unit cycle time and increase the injection of non-condensable gas, controlling the increase of the injection of non-condensable gas to be a preset multiple range of the reduction of steam, until it switches to gas drive; During the gas injection oil recovery production stage: the injection well of the SAGD well pair is used to continuously inject non-condensate gas to utilize the residual heat of the steam chamber and the remaining oil in the steam chamber until the production of the SAGD well pair reaches the minimum production threshold, at which point production ends.

12. The well pattern as described in claim 11, characterized in that, The electrically heated horizontal wells are located at a predetermined distance range in the horizontal direction on the left and right sides of the SAGD well pair, respectively. The length of the electrically heated horizontal well is a first length range, and the distance between the two electrically heated horizontal wells located on the left and right sides of the SAGD well pair is a first distance range. The electrically heated catalytic reforming multi-branch well is located at a second distance from the top of the oil layer on the top of the SAGD well pair. The branch length of the electrically heated catalytic reforming multi-branch well is within the second length range, the branch direction is the four corners of the oil layer, and it can cover at least one of the SAGD well pairs.

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