A dual horizontal well SAGD recovery method and system

Abstract

The application provides a double horizontal well SAGD mining method and system, relates to the technical field of oil exploitation, and comprises the following steps: selecting a heavy oil reservoir; deploying a double horizontal well SAGD well group; establishing an underground electric heating system; establishing a new energy and industrial power grid coupling power supply system; sequentially injecting a liquid phase solvent slug, a water slug and a steam slug; continuously heating and warming by electric heating, keeping the wellbore temperature at 300 DEG C to 350 DEG C, realizing a solvent self-circulation process; starting electric heating assisted production; and repeatedly implementing the above process to realize multi-round mining. The application significantly improves the heat energy utilization rate and the solvent utilization rate, reduces heat loss, improves the recovery rate, is energy-saving and environment-friendly, has good economic benefits, and provides a new technical approach for clean and efficient development of super heavy oil resources.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil exploitation, in particular to a double horizontal well SAGD exploitation method and system. BACKGROUND

[0002] Heavy oil refers to crude oil with a viscosity of more than 50 mPa·s under the condition of 50℃ ground degassing. Due to its high viscosity and poor flowability, it is difficult to achieve economic and effective development by conventional exploitation methods. At present, heavy oil and super heavy oil reservoirs with 50℃ ground degassed crude oil viscosity less than 20000 mPa·s can be developed by conventional thermal recovery methods such as steam huff and puff, steam flooding, hot water flooding, and fire flooding. For super heavy oil reservoirs with continuous oil layer thickness of more than 10m, steam assisted gravity drainage (SAGD) is a relatively effective exploitation method.

[0003] SAGD technology was invented in 1978. Its principle is to deploy a pair of horizontally stacked wells in the same oil layer. High dryness steam is injected into the upper injection well. The steam, which has a much lower density than the crude oil, overlies the formation and forms a steam chamber. As the steam continues to be injected, the steam chamber expands upward and laterally, and exchanges heat with the crude oil in the oil layer. The heated crude oil, with reduced viscosity, flows downward under the action of gravity and is produced from the lower horizontal production well. This technology has been successfully applied in heavy oil reservoirs in the Canadian oil sand mine, the Liaohe oilfield, and the Xinjiang oilfield.

[0004] However, as the quality of heavy oil resources deteriorates, when the 50℃ degassed crude oil viscosity is greater than 100000 mPa·s, the traditional SAGD exploitation method faces serious challenges. At this time, the oil-steam ratio of the SAGD exploitation method decreases significantly from 0.25 to about 0.12, and the recovery efficiency decreases significantly. At the same time, the unit carbon emission reaches more than 1.2 tons of carbon per ton of oil, far exceeding environmental protection requirements. The internal rate of return also decreases to 6%-8%, close to the break-even point, and the development benefit risk gradually increases.

[0005] With the development of production demand, the problems of traditional SAGD technology are more prominent. First, there is a large heat loss at the steam injection end during SAGD development. The high-temperature steam produced by the ground boiler has significant heat loss during transportation to the bottom of the well, resulting in low heat energy utilization efficiency. Second, the ground needs to be equipped with a high-cost coal or gas boiler system, which not only has huge equipment investment, but also has high operating costs. In addition, traditional SAGD technology produces a large amount of carbon emissions, which is not environmentally friendly.

[0006] In recent years, with the substantial rise in natural gas prices, the efficiency of SAGD development will further decline, and even substantial losses may occur. The technical limitations and economic risks exposed by traditional SAGD technology in the development of super heavy oil reservoirs make it urgent for the industry to find more efficient, economic and environmentally friendly alternative technical solutions.

[0007] Chinese patent document CN104481483B discloses a heavy oil reservoir dual horizontal well SAGD mid-late stage exploitation method, which discloses a technical solution of deploying a horizontal well in the middle of adjacent dual horizontal SAGD wells and injecting a solvent and steam composition for synergistic exploitation, but still has the problems of relying on the ground steam system resulting in large heat loss, lack of clean energy application, mainly targeting the mid-late stage, and limited applicability for the development stage.

[0008] Chinese patent document CN119062295A discloses a circulating hot solvent extraction method for heavy oil reservoirs, which discloses a technical solution of using ground heating solvent combined with downhole electric heater for circulating hot solvent extraction, but still has the problems of solvent needing ground circulation treatment, complex equipment system and difficult maintenance, relying on traditional boiler heating resulting in heat loss, and low solvent utilization efficiency.

[0009] In addition, foreign existing technologies in the field of heavy oil development use solvent-assisted exploitation methods, but generally have the technical route of solvent ground heating vaporization and continuous injection all year round. This method not only has a high risk of leakage, but also has low solvent utilization efficiency, making it difficult to achieve large-scale industrial application. SUMMARY

[0010] The purpose of the present application is to provide a dual horizontal well SAGD exploitation technical solution that can significantly improve heat energy utilization and solvent utilization, reduce heat loss, improve recovery rate, save energy and protect the environment, and has good economic benefits.

[0011] To achieve the above-mentioned purpose, the present application realizes the following technical solution: a dual horizontal well SAGD exploitation method, comprising the following steps:

[0012] Step S1: selecting a heavy oil reservoir;

[0013] Step S2: deploying a dual horizontal well SAGD well group: lowering 1 long oil pipe and 1 short oil pipe into the SAGD steam injection horizontal well and the production horizontal well, respectively as the first long oil pipe, the second long oil pipe, the first short oil pipe and the second short oil pipe;

[0014] Step S3: Establishing downhole electric heating system: Lowering the first coiled tubing with the first temperature testing device into the first long oil pipe in the SAGD steam injection horizontal well shaft to the tail end of the steam injection horizontal well section, lowering the first short oil pipe into the heel of the steam injection horizontal well section, lowering the second coiled tubing with the first electric heating device into the first short oil pipe to the tail end of the steam injection horizontal well section; Lowering the third coiled tubing integrating the second electric heating device into the second temperature testing device into the second long oil pipe in the SAGD production horizontal well shaft to the tail end of the production horizontal well section, lowering the second short oil pipe into the heel of the production horizontal well section and connecting the oil production device;

[0015] Step S4: Establishing new energy and industrial power grid coupling power supply system: The new energy power generation device and the industrial power grid are connected with the first temperature testing device, the second temperature testing device, the first electric heating device and the second electric heating device through the ground intelligent control device respectively;

[0016] Step S5: Injecting liquid phase solvent slug: Injecting liquid phase solvent slug from the first long oil pipe and the second long oil pipe of the SAGD steam injection horizontal well and the production horizontal well respectively;

[0017] Step S6: Injecting clean water slug: Injecting clean water slug from the first long oil pipe, the second long oil pipe, the first short oil pipe, the second short oil pipe and the casing of the SAGD steam injection horizontal well and the production horizontal well at the same time, and displacing the liquid phase solvent into the oil layer;

[0018] Step S7: Injecting steam slug: Closing the casing of the SAGD steam injection horizontal well and the production horizontal well, and injecting steam slug from the first long oil pipe, the second long oil pipe, the first short oil pipe and the second short oil pipe of the SAGD steam injection horizontal well and the production horizontal well respectively;

[0019] Step S8: Carrying out continuous electric heating and temperature rising to realize solvent self-circulation oil discharge;

[0020] Step S9: Starting SAGD electric heating assisted production;

[0021] Step S10: Repeating steps S5-S9 until the investment and output ratio is 1, and stopping the exploitation.

[0022] Further: In step S1, the criteria for selecting heavy oil reservoirs are: the continuous oil layer thickness in the reservoir is 10m-100m; the reservoir is more than 50m away from edge water and bottom water, or is not affected by edge water and bottom water; the horizontal permeability is greater than 400mD, and the vertical permeability is greater than 300mD; the oil saturation is greater than 45%, and the surface degassed crude oil viscosity at 50℃ is 50000mPa·s-1000000mPa·s.

[0023] Further: In step S2, by using one or more of the following methods, including steam circulation start-up, downhole electric heating, and steam injection, a steam cavity is formed around the dual-horizontal well SAGD well group to achieve thermal connection between the steam injection horizontal well and the production horizontal well, with a thermal connection degree of more than 75%.

[0024] Furthermore: In step S2, both the SAGD steam injection horizontal well and the SAGD production horizontal well adopt screen pipe completion, and both the SAGD steam injection horizontal well and the SAGD production horizontal well adopt a double pipe structure.

[0025] Furthermore: In step S3, the entire well section of the second and third coiled tubing is insulated with magnesium oxide, and the power density of the electric heating device is 1000W / m-5000W / m.

[0026] Furthermore, in step S3, the first temperature testing device and the second temperature testing device can withstand high temperatures of 350°C or higher for extended periods.

[0027] Furthermore: In step S4, the ground intelligent control device, based on the power supply characteristics of the new energy power generation device, couples with the industrial power grid in real time to supply power to the underground electric heating device.

[0028] Further: In step S5, the injection volume of the liquid solvent slug is 50 tons / time to 600 tons / time, and the solvent component is C4-C9 alkanes, alkenes and / or aromatics, wherein the weight of C4-C7 hydrocarbon components is greater than 90%.

[0029] Further: In step S5, the liquid solvent slug injection frequency is twice a year, with each injection lasting 5-10 days.

[0030] Further: In step S6, the injection volume of the clean water slug is 40 tons / time to 50 tons / time, and the clean water salinity is less than 200 mg / L.

[0031] Further: In step S7, the steam slug injection volume of each SAGD steam injection horizontal well and production horizontal well is 500 tons / time to 1500 tons / time, the ratio of steam injection volume of long tubing to short tubing is 3:7, and the steam dryness at the wellhead is greater than 90%.

[0032] Furthermore: In step S7, the maximum steam injection pressure is less than 1.0 MPa of the target reservoir's direct caprock fracture pressure.

[0033] Further: In step S8, the specific method for continuous electric heating to achieve solvent self-circulation and oil drainage is as follows: turn on the downhole electric heating device of the SAGD steam injection horizontal well and the production horizontal well, and use full power mode to continuously heat up the temperature. When the highest temperature of the wellbore environment reaches 300℃-350℃, switch to constant temperature heating mode and continue heating for 30-40 days, keeping the temperature of the SAGD horizontal section at 300℃-350℃.

[0034] Further: In step S9, the specific steps for starting SAGD electric heating assisted production are as follows: start the SAGD steam injection horizontal well to inject steam, adjust the electric heating power of the SAGD production horizontal well, control the wellbore ambient temperature at 150℃-180℃, and start the oil production unit for continuous or intermittent production.

[0035] Further: In step S9, the steam injection method is steam injection through a short oil pipe, steam injection through a long oil pipe, or steam injection through both a short oil pipe and a long oil pipe simultaneously, with a steam injection rate of 24 tons / day to 72 tons / day.

[0036] Further: In step S9, during intermittent production, the downhole electric heating cable in the steam injection horizontal well is continuously electrically heated. After step S8, steam injection begins, and the downhole electric heating cable in the production horizontal well is continuously electrically heated. After step S8, the oil production unit is turned on to start production. When the water content of the produced fluid is greater than 85%, or the daily oil production is less than 5 tons / day, production is stopped, and step S10 is started.

[0037] Furthermore, in step S10, for each additional round, the injection volume of the solvent slug and vapor slug increases by 5%-10%, and the continuous electric heating time is extended by 10%.

[0038] Further: In step S10, under the condition of eliminating the risk of crude oil coking, the maximum wellbore ambient temperature is adjusted to 350°C.

[0039] A dual-horizontal-well SAGD production system includes: a dual-horizontal-well SAGD well group, a downhole electric heating system, a new energy and industrial power grid coupled power supply system, and an injection device;

[0040] The dual-horizontal-well SAGD well group includes a SAGD steam injection horizontal well and a SAGD production horizontal well. Both the wellbore of the SAGD steam injection horizontal well and the wellbore of the SAGD production horizontal well are equipped with one long oil pipe and one short oil pipe, namely the first long oil pipe, the second long oil pipe, the first short oil pipe and the second short oil pipe, respectively. The short oil pipe of the SAGD production horizontal well is connected to the oil production device.

[0041] The downhole electric heating system includes a first continuous tubing with a first temperature testing device installed in the long tubing of the SAGD steam injection horizontal well, a second continuous tubing with an electric heating device installed in the short tubing of the SAGD steam injection horizontal well, and a third continuous tubing with an integrated electric heating device and a second temperature testing device installed in the long tubing of the SAGD production horizontal well.

[0042] The new energy and industrial power grid coupled power supply system includes new energy power generation devices, industrial power grid and ground intelligent control devices. The ground intelligent control devices are electrically connected to the new energy power generation devices, industrial power grid and underground electric heating system respectively.

[0043] The injection device is connected to the long tubing, short tubing, and casing of the SAGD steam injection horizontal well and the production horizontal well, respectively.

[0044] Furthermore, the entire length of the second and third coiled tubing is insulated with magnesium oxide, and the power density of the electric heating device is 1000W / m-5000W / m.

[0045] The application of any one of the above-described dual-horizontal-well SAGD extraction methods in the crude oil industry for heavy oil reservoir extraction.

[0046] Compared with the prior art, the present invention has the following advantages:

[0047] I. This invention utilizes a downhole electric heater for direct heating, significantly reducing heat loss during re-injection after heating. Traditional technologies require surface boilers to generate high-temperature steam and transport it downhole, resulting in significant heat loss during transport. The downhole electric heating method of this invention avoids heat transfer losses from the surface to the well, significantly improving thermal energy utilization. Simultaneously, this invention innovatively achieves a self-circulation mechanism for the solvent within the reservoir. Through a self-circulation process of "downhole heating - gas phase diffusion - condensation and drainage - reheating - re-diffusion," the solvent can continuously exert a viscosity-reducing effect within the reservoir, lowering crude oil viscosity by over 90%, greatly improving solvent utilization efficiency. Compared to the traditional circulation method that requires solvent extraction to the surface for separation, compression, and reliquefaction, this reduces equipment complexity and operating costs.

[0048] Second, the present invention adopts a short-cycle slug injection method, which only requires injection twice a year, each time for only 5-10 days. This completely solves the leakage risk caused by the technical solution of continuous solvent injection 365 days a year used in the existing foreign technology. At the same time, it improves the safety of operation and the solvent recovery rate, which can reach 85%-88%.

[0049] Third, this invention achieves on-site consumption of clean energy and significantly reduces carbon emissions through intelligent coupling of new energy power generation devices with the industrial power grid. Compared to traditional SAGD technology, which requires coal / gas-fired boilers to generate high-temperature steam, this invention avoids carbon emissions during high-temperature steam production, making it more energy-efficient and environmentally friendly. The systematic coupling of electricity, agents, and steam solves the problem of limited applicability of traditional technologies. This invention is applicable to heavy oil reservoirs with continuous oil layer thickness of 10m-100m and crude oil viscosity of 50,000-1,000,000 mPa·s after degassing at 50℃, expanding the scope of application and providing an effective technical solution for the efficient development of extra-heavy oil reservoirs.

[0050] IV. This invention significantly improves the extraction efficiency of extra-heavy oil reservoirs. For extra-heavy oil reservoirs with a crude oil viscosity of over 100,000 mPa·s after degassing at 50℃, the recovery rate is increased by more than 15 percentage points compared to conventional SAGD development, daily oil production is increased by 6-8 tons, and steam consumption is reduced by 50%-60%, significantly improving the economic benefits of extraction. Attached Figure Description

[0051] Figure 1 A flowchart of a dual-horizontal-well SAGD mining method provided by the present invention;

[0052] Figure 2 This is a schematic diagram of a dual-horizontal-well SAGD electric heating structure provided by the present invention.

[0053] 1. Production horizontal well; 2. Steam injection horizontal well; 11. Heel of horizontal section of production horizontal well; 12. Tail end of horizontal section of production horizontal well; 21. Heel of horizontal section of steam injection horizontal well; 22. Tail end of horizontal section of steam injection horizontal well. Detailed Implementation

[0054] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] 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.

[0056] Example 1

[0057] like Figure 1 As shown, this invention provides a dual-horizontal-well SAGD mining method, which includes the following steps:

[0058] S1. Select a suitable heavy oil reservoir. The reservoir needs to meet specific geological conditions: a continuous oil layer thickness of 10m-100m, which ensures sufficient reserves and facilitates the deployment of horizontal wells and the formation of steam chambers; the reservoir is more than 50m away from edge water and bottom water, or has no edge water or bottom water influence, avoiding interference from edge water and bottom water during the extraction process; horizontal permeability is greater than 400mD and vertical permeability is greater than 300mD, ensuring good fluid flow in the reservoir; oil saturation is greater than 45%, ensuring the basic conditions for extraction; the viscosity of the degassed crude oil at 50℃ is in the range of 50000mPa·s-1000000mPa·s, which is the extra-heavy oil viscosity range that is particularly applicable to the technical solution of this invention.

[0059] S2 is a dual-horizontal-well SAGD well group. Both the SAGD steam injection horizontal well and the SAGD production horizontal well adopt the screen pipe completion method to ensure good oil and gas flow capacity. Each SAGD steam injection horizontal well and production horizontal well contains one long tubing and one short tubing, specifically the first long tubing, the second long tubing, the first short tubing, and the second short tubing. The first long tubing and the first short tubing are installed in the steam injection horizontal well, while the second long tubing and the second short tubing are installed in the production horizontal well. The first long tubing is longer than the first short tubing by a predetermined length, and the second long tubing is longer than the second short tubing by a predetermined length. Both wells employ a dual-tubing structure, meaning one long tubing and one short tubing are installed within the wellbore, providing channels for the injection of various fluids in subsequent processes. A steam chamber is formed around the SAGD wellbore of the dual horizontal well by means of steam circulation start-up, downhole electric heating or steam injection, so as to achieve thermal connection between the steam injection horizontal well and the production horizontal well. The degree of thermal connection needs to reach more than 75%, that is, to form an oil drainage channel of at least 75% of the horizontal section between the injection and production wells.

[0060] Steam circulation startup refers to the following: both the injection and production horizontal wells have dual tubing installed in their horizontal sections. The longer tubing continuously injects steam, while the shorter tubing drains fluid for production. The steam heats the oil layer, heating the layer between the injection and production horizontal wells, allowing for the extraction of internal crude oil and creating a condensate flow channel. Downhole electric heating refers to the following: both the injection and production horizontal wells have dual tubing installed in their horizontal sections. The longer tubing continuously injects water or steam, while the shorter tubing is equipped with electric heating devices distributed throughout the entire horizontal section. These devices continuously heat the water or steam, creating superheated steam that heats the oil layer. The superheated steam undergoes a hydrothermal cracking reaction with the heavy oil, replacing the S, N, and O elements in the heavy oil molecules with H elements, breaking them down into smaller molecules. Simultaneously, gases such as methane, ethane, butane, CO2, and H2S are produced. These gases mix with the heavy oil to form foamed oil, which is extracted from the ring between the short tubing and the electric heating cable. This process extracts crude oil from the layer between the injection and production horizontal wells, creating a condensate flow channel. Steam injection refers to the process where both injection and production horizontal wells use short-term steam injection, lasting 7-15 days. After shutting down the wellhead equipment and simmering the well for 48-72 hours, production begins. Once the water cut reaches over 90%, a second round is initiated, and this process is repeated to heat the oil layer between the injection and production horizontal wells, allowing the crude oil inside to be extracted and forming a condensate flow channel.

[0061] S3, Establish a downhole electric heating system. For example... Figure 2 As shown, in the SAGD steam injection horizontal well 2, a first continuous tubing equipped with a temperature testing device is run into the first long tubing, extending to the end 22 of the horizontal section of the steam injection horizontal well for real-time monitoring of wellbore temperature changes. A first short tubing is run into the foot 21 of the horizontal section of the steam injection horizontal well, and a second continuous tubing equipped with an electric heating device is run into the first short tubing to the end 22 of the horizontal section of the steam injection horizontal well. This configuration ensures uniform heating throughout the entire horizontal section. In the SAGD production horizontal well 1, a third continuous tubing with an integrated electric heating device and a temperature testing device is run into the second long tubing to the end 12 of the horizontal section of the production horizontal well, achieving integrated heating and monitoring. A second short tubing is run into the foot 22 of the horizontal section of the production horizontal well and connected to the production equipment, ensuring smooth delivery of production fluids. The second and third continuous tubing are insulated with magnesium oxide throughout the entire well section, exhibiting excellent high-temperature stability and insulation performance. The power density of the electric heating device is designed to be 1000W / m-5000W / m, ensuring sufficient heating capacity while avoiding equipment damage caused by overheating. The temperature testing device can withstand temperatures above 350℃ for extended periods, meeting the requirements for high-temperature operating environments.

[0062] S4 establishes a coupled power supply system between new energy sources and the industrial power grid. The new energy power generation unit and the industrial power grid are respectively connected to the ground-based intelligent control device, forming a flexible power supply network. The ground-based intelligent control device is electrically connected to the underground temperature testing device, electric heating device, and electric heating device with integrated temperature testing, enabling real-time monitoring and precise control. Based on the power supply characteristics of the new energy power generation unit, the ground-based intelligent control device couples with the industrial power grid in real time, outputting standard voltage and rated current power to supply the underground electric heating device, thus fully utilizing clean energy while ensuring power supply stability.

[0063] S5, liquid solvent slug injection, is the initial step in achieving solvent self-circulation. Liquid solvent slugs are injected into the long tubing of both the SAGD steam injection horizontal well and the production horizontal well, at injection volumes ranging from 50 to 600 tons per injection, with the specific volume determined based on reservoir size and characteristics. The solvent composition is a mixture of C4, C5, C6, C7, C8, and C9 alkanes, alkenes, or aromatics, with C4-C7 hydrocarbons comprising more than 90% by weight. This composition ensures both good solubility and suitable volatility. Liquid solvent slug injections are performed twice a year, with each injection lasting 5-10 days. This short-cycle slug injection method significantly reduces the risk of solvent leakage and improves operational safety.

[0064] S6, the purpose of injecting water slugs is to effectively displace the liquid solvent into the oil reservoir. Water slugs are injected simultaneously from the long tubing, short tubing, and casing of both the SAGD steam injection horizontal well and the production horizontal well. The amount of water slug is 40-50 tons per injection, and the water salinity is less than 200 mg / L. The low salinity of the water avoids adverse reactions with the solvent while ensuring a good displacement effect.

[0065] S7, the steam slug injection provides the necessary heat carrier for the subsequent electric heating process. After shutting off the casing of the SAGD steam injection horizontal well and the production horizontal well, steam slugs are injected from the long tubing and short tubing respectively, with a steam slug injection rate of 500-1500 tons / cycle per well. The steam injection ratio of the long tubing to the short tubing is designed to be 3:7, which ensures uniform steam distribution in the horizontal section. The steam dryness at the wellhead is greater than 90%, ensuring high-quality steam injection. The maximum steam injection pressure is controlled below the target reservoir's direct caprock fracture pressure minus 1.0 MPa, avoiding damage to the reservoir from fracturing.

[0066] S8 utilizes continuous electric heating to achieve solvent self-circulation and oil drainage. The downhole electric heating devices in the SAGD steam injection horizontal well and production horizontal well are activated, operating at full power for continuous heating. When the highest ambient temperature inside the wellbore reaches 300℃-350℃, a constant temperature heating mode is switched to continue heating for 30-40 days. Under the condition that the temperature in the SAGD horizontal section is maintained at 300℃-350℃, the liquid solvent continuously vaporizes, and the gaseous solvent rapidly diffuses into the steam chamber, forming a mixed chamber of steam and solvent. When the gaseous solvent diffuses to the edge of the mixed chamber, its temperature decreases through thermal conduction, causing it to condense into a liquid solvent. This liquid solvent undergoes a similar miscibility reaction with the crude oil, reducing the crude oil viscosity by more than 90%, forming an ultra-low viscosity mixed liquid. Under the influence of gravity, the mixed fluid seeps downward into the vicinity of the horizontal wellbore. Due to the continuous heating by the high-power electric heater in the horizontal well, the vicinity of the horizontal wellbore remains at a high temperature. The liquid solvent is heated and vaporized again, detaching from the mixed fluid and diffusing again into the vapor and solvent mixing cavity and its edge, realizing a self-circulating process of "downhole heating - vapor diffusion - condensation and oil drainage - reheating - re-diffusion".

[0067] S9. Start SAGD electric heating assisted production. Initiate steam injection in the SAGD steam injection horizontal well. The injection method can be short tubing steam injection, long tubing steam injection, or simultaneous short and long tubing steam injection. The steam injection rate is controlled at 24 tons / day to 72 tons / day, and the injection rate is matched with the total power of the downhole high-power heater to ensure that the downhole steam dryness in the horizontal section is greater than 95%. Adjust the electric heating power of the SAGD production horizontal well, control the wellbore ambient temperature at 150℃-180℃, and start the oil production unit for continuous or intermittent production.

[0068] In step S9, during intermittent production, the downhole electric heating cable in the steam injection horizontal well is continuously electrically heated. After S8, steam injection begins, and the downhole electric heating cable in the production horizontal well is continuously electrically heated. After S8, the oil production unit is turned on to start production. When the water content of the produced fluid is greater than 85%, or the daily oil production is less than 5 tons / day, production is stopped, and S10 is started.

[0069] S10: Achieve cyclical optimization of the process by repeating steps S5 to S9. For each additional cycle, the solvent slug and steam slug are increased by 5%-10%, and the continuous electric heating high-temperature time is extended by 10%. Under the condition of eliminating the risk of crude oil coking, the maximum wellbore ambient temperature is gradually adjusted towards 350℃ to continuously optimize the production parameters and improve the final recovery rate. When the input-output ratio of a certain cycle is 1, production is stopped.

[0070] The working principle of this method is as follows:

[0071] During operation, a high-temperature environment is first established through an underground electric heating system. The electric heating devices installed in the SAGD steam injection horizontal well and the production horizontal well operate continuously at a power density of 1000W / m-5000W / m, driven by a power supply system coupled with new energy and industrial power grids, precisely controlling the wellbore ambient temperature within the range of 300℃-350℃. This direct underground heating method completely avoids heat loss during the traditional process of transferring heat from surface boilers to the well, achieving highly efficient heating with zero heat loss.

[0072] Once the high-temperature environment is established, the system begins to execute a unique solvent self-circulation mechanism. The pre-injected liquid solvent in the reservoir rapidly vaporizes under the action of the downhole electric heater, forming a high-temperature gaseous solvent. Because the density of the gaseous solvent is much lower than that of crude oil, it rapidly diffuses upwards and spreads quickly within the vapor chamber, forming a mixed gas with the existing vapor. This diffusion process has extremely strong penetrating power, enabling it to reach reservoir areas that are difficult to cover with conventional steam.

[0073] As the gaseous solvent diffuses to the edge of the vapor chamber, its temperature gradually decreases due to its distance from the heat source. During this temperature reduction, the gaseous solvent releases heat through thermal conduction and convection, while simultaneously condensing into a liquid solvent. These liquid solvents undergo a similar miscibility reaction with the heavy oil in the reservoir. Due to the good compatibility between the solvent and crude oil, they can fully dissolve the heavy components in the crude oil, reducing its viscosity by more than 90% and forming an ultra-low viscosity solvent-crude oil mixture.

[0074] Under the influence of gravity, these ultra-low viscosity mixed fluids seep downwards, eventually converging near the wellbore of the SAGD production horizontal well. Due to the continuous operation of the high-power electric heaters within the production well, the area near the wellbore remains at a high temperature of 300°C-350°C. When the mixed fluid comes into contact with this high-temperature zone, the liquid solvent within it is reheated and vaporized, detaching from the mixed fluid and rising again under buoyancy, diffusing once more into the vapor chamber and its surrounding area.

[0075] This creates a complete self-circulating process of "downhole heating - vapor diffusion - condensation and drainage - reheating - re-diffusion". In this cycle, the solvent does not need to be extracted to the surface for processing, but is recycled entirely within the reservoir, greatly improving solvent utilization efficiency and reducing operational complexity and cost. Simultaneously, because the solvent continuously functions within the reservoir, it can continuously degrade the viscosity of heavy oil, increasing the frequency and efficiency of drainage.

[0076] After the solvent self-circulation has stabilized, the system enters the electrically assisted production stage. At this time, the SAGD steam injection horizontal well begins to inject steam at a rate of 24 tons / day to 72 tons / day. The steam injection rate is matched with the power of the downhole electric heater to ensure that the downhole steam dryness is greater than 95%. The production well adjusts the electric heating power to an appropriate level, and the wellbore temperature is controlled at 150℃-180℃, which ensures sufficient heating effect while avoiding energy waste caused by overheating.

[0077] Throughout the entire operation, the new energy and industrial power grid coupled power supply system played a crucial role. The ground-based intelligent control device, based on the power supply characteristics of the new energy power generation unit, coupled with the industrial power grid in real time, ensuring a stable and adjustable power output of standard voltage and rated current to the underground electric heating unit. This intelligent power allocation not only fully utilizes clean energy and reduces carbon emissions but also guarantees the stability and economy of the power supply.

[0078] Through real-time monitoring by the temperature testing device, the system can accurately grasp the temperature distribution and changing trend downhole, providing an accurate basis for adjusting the electric heating power. When the temperature reaches the set range, the system automatically switches from full-power heating mode to constant-temperature heating mode, achieving precise temperature control.

[0079] During production, the current production cycle ends when the water content of the produced fluid exceeds 85% and the daily oil production is less than 5 tons. At this point, the system repeats the solvent slug injection process, but optimizes and adjusts the injection parameters according to reservoir changes. The number of solvent and steam slugs increases by 5%-10% in each cycle, the continuous electric heating time is extended by 10%, and the maximum wellbore temperature is gradually adjusted towards 350℃ while eliminating the risk of crude oil coking, thus achieving dynamic optimization of production parameters.

[0080] The advantage of this working principle lies in achieving complete reservoir-internal circulation of the solvent, avoiding the complex process of solvent extraction to the surface for separation, compression, and reliquefaction as in traditional technologies. Simultaneously, direct downhole electric heating eliminates heat loss, the renewable energy power supply system reduces carbon emissions, and multiple rounds of optimization ensure maximum recovery. The synergistic operation of the entire system enables this invention to achieve significantly better extraction results than traditional SAGD technology in extra-heavy oil reservoirs, providing a novel technical solution for the efficient and clean development of heavy oil resources.

[0081] Example 2

[0082] This embodiment provides a dual-horizontal-well SAGD production system, including a dual-horizontal-well SAGD well group, a downhole electric heating system, a new energy and industrial power grid coupled power supply system, and an injection device.

[0083] The dual-horizontal-well SAGD well group serves as the foundation of the entire system, comprising two wells: a SAGD steam injection horizontal well and a SAGD production horizontal well. The SAGD steam injection horizontal well contains one long tubing and one short tubing within its wellbore; this dual-tubing structure provides a pathway for the subsequent injection of various slug fluids. Similarly, the SAGD production horizontal well also contains one long tubing and one short tubing within its wellbore. The short tubing in the SAGD production horizontal well connects to the production equipment, ensuring that production fluids can be transported from the reservoir to the surface.

[0084] The downhole electric heating system comprises three coiled tubing units. The first unit, equipped with a temperature monitoring device, is installed within the long tubing of the SAGD steam injection horizontal well. Its primary function is to monitor temperature changes within the injection well in real time, providing accurate data support for the overall system's temperature control. The second unit, also equipped with an electric heating device, is installed within the short tubing of the SAGD steam injection horizontal well. This unit provides the electric heating for the injection well, supplying a heat source for solvent vaporization and reservoir heating. The third unit, integrated with a temperature monitoring device, is installed within the long tubing of the SAGD production horizontal well. This unit combines electric heating and temperature monitoring functions, heating the production well and monitoring its temperature status in real time.

[0085] The renewable energy and industrial power grid coupled power supply system ensures the stability and cleanliness of the entire system's power supply. This system includes renewable energy power generation units, an industrial power grid, and a ground-based intelligent control unit. The renewable energy power generation units provide clean electricity, the industrial power grid serves as a backup and supplementary power source, and the ground-based intelligent control unit is the control center of the entire power supply system. The ground-based intelligent control unit is electrically connected to the renewable energy power generation units, the industrial power grid, and the underground electric heating system, and outputs power to the underground electric heating system through power dispatching.

[0086] The injection unit is responsible for injecting various working fluids downhole. This unit connects to the long tubing, short tubing, and casing of both SAGD steam injection horizontal wells and production horizontal wells. Through this comprehensive connection configuration, the injection unit can flexibly inject different types of working fluids, such as liquid solvents, water, and steam, into different pipelines and spaces according to process requirements, meeting the diverse injection needs of complex processes.

[0087] In the specific technical configuration of this system, the entire well section of both the second and third continuous tubing is insulated with magnesium oxide. Magnesium oxide insulation material possesses excellent high-temperature stability and electrical insulation properties, maintaining stable insulation performance over long periods in high-temperature operating environments, ensuring the safe and reliable operation of the electric heating device. The power density of the electric heating device is designed within the range of 1000W / m-5000W / m. This power density configuration ensures sufficient heating capacity, enabling the wellbore temperature to reach the required high-temperature range of 300℃-350℃, while avoiding energy waste and equipment damage risks caused by excessive power.

[0088] The entire system achieves synergistic effects of electric heating, solvent, and steam technologies through the coordinated operation of its various components. The dual-horizontal-well SAGD well group provides the basic platform for production, the downhole electric heating system provides an efficient heating method, the new energy and industrial power grid coupled power supply system ensures a clean and stable power supply, and the injection device ensures the precise injection of various working fluids. All system components support each other and work together to achieve efficient and clean production of heavy oil reservoirs.

[0089] Example 3

[0090] In this embodiment, an extra-heavy oil reservoir with a continuous oil layer thickness of 10m was selected. The viscosity of the degassed crude oil at 50℃ was 100,000 mPa·s, the horizontal permeability of the oil layer was 1500 mD, the vertical permeability was 800 mD, the original oil saturation was 67%, and the minimum fracture pressure of the oil layer was 7.5 MPa. The horizontal section of the SAGD was 400m long, the vertical distance between the steam injection well and the production well was 5m, and the power density of the downhole electric heater was 1000 W / m.

[0091] According to the method of this invention, a dual-horizontal-well SAGD well group and a downhole electric heating system are first established. A stable power supply is provided to the downhole electric heating device through a power supply system coupled with a new energy source and industrial power grid. 50 tons of C5-C9 mixed olefin solvent slug are injected into the wellbore, followed by 40 tons of water slug and 600 tons of steam slug until the bottomhole pressure reaches 6.5 MPa. The electric heater is then turned on and set to a constant temperature of 300°C. After 30 days of continuous heating, production begins. The steam injection rate is 40 tons / day. After 100 days of continuous production, if the daily oil production is less than 5 tons / day, the slug injection steps are repeated, with the solvent slug and steam slug increased by 5%.

[0092] After a complete extraction cycle, the final average daily oil production reached 20.0 tons, with a recovery rate of 58.1%. Compared to conventional SAGD development, daily oil production increased by 6 tons, the recovery rate increased by 15 percentage points, steam consumption decreased by 50%, and solvent recovery rate reached 85%.

[0093] Example 4

[0094] This embodiment selects an extra-heavy oil reservoir with a continuous oil layer thickness of 15m. The viscosity of the degassed crude oil at 50℃ is 80000mPa·s, the horizontal permeability of the oil layer is 1300mD, the vertical permeability is 600mD, the original oil saturation is 65%, and the minimum fracture pressure of the oil layer is 6.5MPa. The horizontal section of the SAGD is 400m long, the vertical distance between the steam injection well and the production well is 5m, and the power density of the downhole electric heater is 1000W / m.

[0095] Using a similar process, 60 tons of C5-C7 mixed olefin solvent slug are injected into the wellbore, followed by 50 tons of water slug and 800 tons of steam slug to bring the bottomhole pressure to 5.5 MPa. The electric heater is then set to a constant temperature of 300°C and heated continuously for 35 days before well production begins. Steam injection is carried out at a rate of 50 tons per day, and production continues for 200 days before the next round of extraction.

[0096] The final average daily oil production was 28.0 tons, with a recovery rate of 60.1%. Compared with conventional SAGD development, daily oil production increased by 8 tons, the recovery rate increased by 13 percentage points, steam consumption decreased by 60%, and solvent recovery rate reached 88%.

[0097] Examples 3 and 4 above demonstrate that the SAGD electro-solvent-vapor coupling extraction method for heavy oil reservoirs with dual horizontal wells of the present invention can significantly improve the extraction effect of extra-heavy oil reservoirs. Through the organic combination of solvent self-circulation mechanism and downhole electric heating technology, efficient, clean and economical heavy oil extraction is achieved, providing a new technical solution for the effective development of extra-heavy oil resources.

[0098] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A dual-horizontal-well SAGD mining method, characterized in that, Includes the following steps: Step S1: Select a heavy oil reservoir; Step S2: Deploy the dual horizontal well SAGD well group: Run one long tubing and one short tubing into both the SAGD steam injection horizontal well and the production horizontal well, namely the first long tubing, the second long tubing, the first short tubing, and the second short tubing, respectively. Step S3: Establish a downhole electric heating system: In the SAGD steam injection horizontal well, run a first continuous tubing with a first temperature testing device into the first long tubing to the end of the horizontal section of the steam injection horizontal well; run a first short tubing to the foot of the horizontal section of the steam injection horizontal well; run a second continuous tubing with a first electric heating device into the first short tubing to the end of the horizontal section of the steam injection horizontal well; in the SAGD production horizontal well, run a third continuous tubing integrating a second temperature testing device and a second electric heating device into the second long tubing to the end of the horizontal section of the production horizontal well; run a second short tubing to the foot of the horizontal section of the production horizontal well and connect it to the production equipment. Step S4: Establish a new energy and industrial power grid coupled power supply system: The new energy power generation device and the industrial power grid are respectively connected to the first temperature testing device, the second temperature testing device, the first electric heating device and the second electric heating device through ground intelligent control devices; Step S5: Injecting liquid solvent slugs: Inject liquid solvent slugs from the first and second long tubing of the SAGD steam injection horizontal well and the production horizontal well, respectively; Step S6: Inject water slugs: Simultaneously inject water slugs from the first long tubing, second long tubing, first short tubing, second short tubing, and casing of the SAGD steam injection horizontal well and the production horizontal well to displace the liquid solvent into the oil layer. In step S6, the injection volume of the clean water sluice is 40 tons / time to 50 tons / time, and the clean water salinity is less than 200 mg / L; Step S7: Inject steam slugs: Close the casing of the SAGD steam injection horizontal well and the production horizontal well, and inject steam slugs from the first long tubing, the second long tubing, the first short tubing, and the second short tubing of the SAGD steam injection horizontal well and the production horizontal well, respectively; Step S8: Continuous electric heating is performed to raise the temperature and achieve solvent self-circulation and oil draining; In step S8, the specific method for continuous electric heating to achieve solvent self-circulation and oil drainage is as follows: turn on the downhole electric heating device of the SAGD steam injection horizontal well and the production horizontal well, and use full power mode to continuously heat up the temperature. When the highest temperature of the wellbore environment reaches 300℃-350℃, switch to constant temperature heating mode and continue heating for 30-40 days, keeping the temperature of the SAGD horizontal section at 300℃-350℃. Step S9: Start SAGD electric heating auxiliary production; In step S9, the specific steps for starting SAGD electric heating assisted production are as follows: start the SAGD steam injection horizontal well to inject steam, adjust the electric heating power of the SAGD production horizontal well, control the wellbore ambient temperature at 150℃-180℃, and start the oil production unit for continuous or intermittent production. Step S10: Repeat steps S5 to S9 until the input-output ratio is 1, then stop mining.

2. The dual-horizontal-well SAGD mining method according to claim 1, characterized in that: In step S1, the criteria for selecting heavy oil reservoirs are as follows: the thickness of the continuous oil layer in the reservoir is 10m-100m; the reservoir is more than 50m away from the edge water and bottom water; the horizontal permeability is greater than 400mD and the vertical permeability is greater than 300mD; the oil saturation is greater than 45% and the viscosity of the degassed crude oil at the surface under 50℃ conditions is 50000mPa·s-1000000mPa·s.

3. The dual-horizontal-well SAGD mining method according to claim 1, characterized in that: In step S2, a steam chamber is formed around the dual-horizontal well SAGD well group by using one or more methods including steam circulation start-up, downhole electric heating, and steam injection, so as to achieve thermal connection between the steam injection horizontal well and the production horizontal well, with a thermal connection degree of more than 75%.

4. The dual-horizontal-well SAGD mining method according to claim 1, characterized in that: In step S2, both the SAGD steam injection horizontal well and the SAGD production horizontal well adopt screen pipe completion, and both adopt a double pipe structure.

5. The dual-horizontal-well SAGD mining method according to claim 1, characterized in that: In step S3, magnesium oxide is used to insulate the entire length of the second and third coiled tubing, and the power density of the electric heating device is 1000W / m-5000W / m.

6. The dual-horizontal-well SAGD mining method according to claim 1, characterized in that: In step S3, the first temperature testing device and the second temperature testing device can withstand high temperatures of 350°C or higher for a long time.

7. The dual-horizontal-well SAGD mining method according to claim 1, characterized in that: In step S4, the ground intelligent control device, based on the power supply characteristics of the new energy power generation device, couples with the industrial power grid in real time to supply power to the underground electric heating device.

8. The dual-horizontal-well SAGD mining method according to claim 1, characterized in that: In step S5, the injection volume of the liquid solvent slug is 50 tons / time to 600 tons / time, and the solvent component is C4-C9 alkanes, alkenes and / or aromatics, of which C4-C7 hydrocarbon components account for more than 90% by weight.

9. The dual-horizontal-well SAGD mining method according to claim 1, characterized in that: In step S5, the liquid solvent slug injection frequency is twice a year, with each injection lasting 5-10 days.

10. The dual-horizontal-well SAGD mining method according to claim 1, characterized in that: In step S7, the steam slug injection volume of each SAGD steam injection horizontal well and production horizontal well is 500 tons / time to 1500 tons / time, the ratio of steam injection volume of long tubing to short tubing is 3:7, and the steam dryness at the wellhead is greater than 90%.

11. The dual-horizontal-well SAGD mining method according to claim 1, characterized in that: In step S7, the maximum steam injection pressure is less than 1.0 MPa of the direct caprock fracture pressure of the target reservoir.

12. The dual-horizontal-well SAGD mining method according to claim 1, characterized in that: In step S9, the steam injection method is either short oil pipe steam injection, long oil pipe steam injection, or short oil pipe and long oil pipe steam injection simultaneously, and the steam injection rate is 24 tons / day to 72 tons / day.

13. The dual-horizontal-well SAGD mining method according to claim 1, characterized in that: In step S9, during intermittent production, the downhole electric heating cable in the steam injection horizontal well is continuously electrically heated. After step S8, steam injection begins, and the downhole electric heating cable in the production horizontal well is continuously electrically heated. After step S8, the oil production unit is turned on to start production. When the water content of the produced fluid is greater than 85%, or the daily oil production is less than 5 tons / day, production is stopped, and step S10 is started.

14. The dual-horizontal-well SAGD mining method according to claim 1, characterized in that: In step S10, for each additional round, the injection volume of the solvent slug and vapor slug increases by 5%-10%, and the continuous electric heating time is extended by 10%.

15. The dual-horizontal-well SAGD mining method according to claim 14, characterized in that: In step S10, under the condition of eliminating the risk of crude oil coking, the maximum wellbore ambient temperature is adjusted to 350°C.

16. The application of the dual-horizontal-well SAGD extraction method as described in any one of claims 1-15 in the crude oil industry for the extraction of heavy oil reservoirs.

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