Method and device for accelerating preheating and starting of SAGD in heavy oil reservoir

Abstract

This invention discloses a method and apparatus for accelerating the preheating start-up of SAGD in heavy oil reservoirs. The method involves determining the required volume of a high thermal conductivity material dispersion based on the minimum fracture pressure of the target oil layer; injecting hot water into the cleaned steam injection wells and production wells to pressurize to the minimum fracture pressure of the oil layer and maintaining this pressure for a period of time; intermittently injecting the high thermal conductivity material dispersion into the steam injection wells and production wells until all the high thermal conductivity material dispersion is injected; and performing steam injection circulation preheating start-up on the steam injection wells and production wells containing the high thermal conductivity material dispersion. Through this method, this invention achieves significant improvement in the thermal conductivity coefficient of the formation near the wellbore by injecting a high thermal conductivity material into the microfractures formed by the super-fracture pressure without altering the original SAGD injection-production tubing structure, rapidly establishing a uniform oil drainage channel, reducing the start-up time by more than half compared to conventional steam injection preheating start-up methods, significantly reducing energy consumption, accelerating the transition to SAGD production, and increasing the oil production rate.

Description

Technical Field

[0001] This invention relates to the field of petroleum extraction technology, and in particular to a method and apparatus for accelerating the preheating and start-up of SAGD in heavy oil reservoirs. Background Technology

[0002] Steam Assisted Gravity Drainage (SAGD) was invented by Butler in Canada in 1978 and has been successfully applied in heavy oil reservoirs in Canadian oil sands, Liaohe Oilfield, and Xinjiang Oilfield in my country. The principle involves deploying horizontal well pairs stacked vertically within the same oil layer. High-dryness steam is injected into the upper steam injection well. Because the steam's density is much lower than that of crude oil, it rises and overlaps the formation, forming a steam cavity. As steam is continuously injected, the steam cavity expands upwards and laterally, exchanging heat with the crude oil in the oil layer. The heated crude oil's viscosity decreases, and it flows downwards with condensate under gravity, being extracted from the horizontal production wells in the lower part of the oil layer.

[0003] Relevant literature points out (Xi Changfeng, Ma Desheng, et al. "Optimization Study on SAGD Circulation Preheating Start-up of Dual-Horizontal Wells for Extra-Heavy Oil". Journal of Southwest Petroleum University (Natural Science Edition), 2010, 32(4).), SAGD mining is divided into two stages: SAGD start-up stage and SAGD production stage. In the SAGD start-up stage, there are currently two methods for SAGD start-up: huff and puff preheating start-up and steam injection circulation preheating start-up. Among them, huff and puff preheating start-up has high injection pressure and high temperature, which can easily damage the wellbore structure. Steam injection circulation preheating start-up heats evenly and starts smoothly. It is generally divided into three steps: (1) Steam circulates in the two wells, and the reservoir mainly transfers heat through heat conduction; (2) A pressure difference is formed between the two wells, and the pressure of the steam injection well is higher than that of the production well, so that the crude oil between the wells flows to the production well, preparing for the transition to full SAGD production; (3) The annulus of the upper steam injection well stops draining, and the lower production well stops injecting steam, transitioning to the full SAGD production stage.

[0004] Before SAGD production can commence, the well must undergo thermal cycling startup. The period from injecting steam into the production and injection wells to the start of SAGD production is called the startup phase or preheating phase. The goal of the preheating phase is to achieve uniform heating of the reservoir in the shortest possible time, ensuring uniform heating and connection between the injection and production wells, and establishing a drainage channel between them.

[0005] For conventional steam injection circulation preheating, a long tubing extending into the tip of the horizontal section and a short tubing extending into the heel of the horizontal section are installed in both the injection well and the production well. Steam is injected from the long tubing in the upper injection well and the lower production well, respectively, and then extracted from the short tubing in the same well. The oil layer between the injection well and the production well is heated by heat conduction and convection between the injected steam and the oil layer, reducing the crude oil viscosity to below 150 centipoise, thus improving its fluidity. This allows the crude oil to flow smoothly within the oil layer between the injection well and the production well during the SAGD production phase, forming a drainage channel that allows the steam chamber to continuously expand and the crude oil to be continuously extracted.

[0006] However, conventional SAGD production methods are affected by thermal properties such as reservoir thermal conductivity and thermal diffusivity, as well as tubing structure, on-site operating parameters, and process conditions. This can lead to excessively low temperatures at the toe and low utilization of the horizontal section, resulting in excessively long SAGD preheating time, high initial mining costs, and slow production growth.

[0007] In view of this, there is an urgent need to provide a method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs in order to solve the above problems. Summary of the Invention

[0008] The purpose of this invention is to provide a method for accelerating the preheating start-up of SAGD in heavy oil reservoirs, so as to reduce preheating time, save steam, and increase the size of the steam chamber.

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0010] A method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs, the method comprising:

[0011] The required volume of the high thermal conductivity material dispersion is determined based on the minimum fracture pressure of the target oil layer;

[0012] Hot water is injected into the cleaned steam injection wells and production wells to pressurize them to the minimum fracture pressure of the oil layer, and this process is continued for a period of time.

[0013] Intermittently pressurize and inject a high thermal conductivity material dispersion into the steam injection well and the production well until all of the high thermal conductivity material dispersion is injected into the steam injection well and the production well;

[0014] Steam injection circulation preheating is performed on the steam injection wells and production wells that have been injected with a dispersion of high thermal conductivity material.

[0015] As a further improvement of the present invention, the high thermal conductivity material dispersion is as follows:

[0016] A mixed solution of high thermal conductivity materials, hot water, and dispersants;

[0017] The high thermal conductivity material includes one or more of the following: nano-graphene, nano-graphite tube, nano-aluminum nitride, and boron nitride.

[0018] As a further improvement of the present invention, the mass concentration of the high thermal conductivity material dispersion includes 1‰-80‰.

[0019] As a further improvement of the present invention, the step of intermittently injecting a high thermal conductivity material dispersion into the steam injection well and the production well until all the high thermal conductivity material dispersion is injected into the steam injection well and the production well includes:

[0020] Inject high thermal conductivity material dispersion into the steam injection well and production well at a pressurization rate of 0.1 MPa, gradually increasing the injection pressure until the pressure at the bottom of both wells increases to more than 0.5 MPa above the minimum fracture pressure of the oil layer, at which point injection is stopped.

[0021] Once the pressure at the bottom of the two wells drops back to the minimum fracture pressure of the oil layer, the high thermal conductivity material dispersion is injected again by gradually increasing the pressure by 0.1 MPa until all the high thermal conductivity material dispersion is injected into the steam injection well and the production well.

[0022] As a further improvement of the present invention, the duration includes:

[0023] The duration is 24-48 hours.

[0024] As a further improvement of the present invention, the temperature of the hot water is 40℃-90℃.

[0025] As a further improvement of the present invention, the steam injection circulation preheating start-up of the steam injection well and production well into which the high thermal conductivity material dispersion is injected includes:

[0026] The steam injection rate of the long tubing in the steam injection well is controlled at 80-130 t / d, and the fluid production rate of the short tubing in the steam injection well is controlled at 80-110 t / d.

[0027] The steam injection rate for long tubing in production wells is 80-110 t / d, and the fluid production rate for short tubing in production wells is 80-120 t / d.

[0028] As a further improvement of the present invention, the steam injection circulation preheating start-up of the steam injection well and production well into which the high thermal conductivity material dispersion is injected includes:

[0029] The pressure at the bottom of the steam injection well should be 0.2-1.0 MPa higher than that at the bottom of the production well.

[0030] As a further improvement of the present invention, the method further includes:

[0031] During the steam injection cycle preheating start-up process, the temperature in the middle of the oil layer is monitored in real time by establishing a single-well group numerical model.

[0032] The present invention also provides a device for accelerating the preheating and start-up of SAGD in heavy oil reservoirs, the device comprising:

[0033] A determination unit is used to determine the volume of the required high thermal conductivity material dispersion based on the minimum fracture pressure of the target oil layer;

[0034] The hot water injection unit is used to inject hot water into the cleaned steam injection wells and production wells to pressurize the reservoir to the minimum fracture pressure and continue for a period of time.

[0035] A high thermal conductivity material injection unit is used to intermittently pressurize and inject a high thermal conductivity material dispersion into the steam injection well and the production well until all the high thermal conductivity material dispersion is injected into the steam injection well and the production well;

[0036] The circulating preheating start-up unit is used to perform steam injection circulation preheating start-up on steam injection wells and production wells that have been injected with high thermal conductivity material dispersion.

[0037] As a further improvement of the present invention, the high thermal conductivity material dispersion is a mixed solution of a high thermal conductivity material, hot water and a dispersant;

[0038] The high thermal conductivity material includes one or more of the following: nano-graphene, nano-graphite tube, nano-aluminum nitride, and boron nitride.

[0039] As a further improvement of the present invention, the mass concentration of the high thermal conductivity material dispersion includes 1‰-80‰.

[0040] As a further improvement of the present invention, the high thermal conductivity material injection unit includes:

[0041] The first injection module is used to inject a high thermal conductivity material dispersion into the steam injection well and the production well at a pressurization rate of 0.1 MPa, gradually increasing the injection pressure until the pressure at the bottom of both wells increases to more than 0.5 MPa above the minimum fracturing pressure of the oil layer, at which point the injection stops.

[0042] The pressure monitoring module is used to monitor the bottom pressure of the steam injection well and the production well. When the pressure at the bottom of the two wells drops back to the minimum fracture pressure of the oil layer, the high thermal conductivity material dispersion is injected again using the first injection module.

[0043] As a further improvement of the present invention, the cyclic preheating start-up unit includes:

[0044] The first control module is used to control the steam injection rate of the long tubing of the steam injection well to be 80-130 t / d, and the fluid production rate of the short tubing of the steam injection well to be 80-110 t / d; the steam injection rate of the long tubing of the production well to be 80-110 t / d, and the fluid production rate of the short tubing of the production well to be 80-120 t / d.

[0045] The pressure control module is used to control the pressure at the bottom of the steam injection well to be 0.2-1.0 MPa higher than the pressure at the bottom of the production well.

[0046] As a further improvement of the present invention, the device further includes:

[0047] The monitoring unit is used to monitor the temperature in the middle of the oil layer in real time during the steam injection cycle preheating start-up process.

[0048] The beneficial effects of this invention are:

[0049] The present invention provides a method and apparatus for accelerating the preheating and start-up of SAGD in heavy oil reservoirs. The method involves determining the required volume of a high thermal conductivity material dispersion based on the minimum fracture pressure of the target oil layer; injecting hot water into the cleaned steam injection wells and production wells to pressurize to the minimum fracture pressure of the oil layer and maintaining this pressure for a period of time; intermittently injecting the high thermal conductivity material dispersion into the steam injection wells and production wells until all the high thermal conductivity material dispersion is injected; and performing steam injection circulation preheating and start-up on the steam injection wells and production wells containing the high thermal conductivity material dispersion. Through these methods, the present invention achieves significant improvement in the thermal conductivity coefficient of the formation near the wellbore by injecting a high thermal conductivity material into the microfractures formed by the super-fracture pressure without altering the original SAGD injection-production tubing structure, thereby rapidly establishing a uniform oil drainage channel. This reduces the time by more than half compared to conventional steam injection preheating and start-up methods, significantly reduces energy consumption, accelerates the transition to SAGD production, and increases the oil production rate.

[0050] The present invention provides a method and apparatus for accelerating the preheating and start-up of SAGD in heavy oil reservoirs. By injecting a high thermal conductivity material dispersion into the oil layer, nano-strips are formed within the oil layer. This significantly increases the thermal conductivity of the reservoir surrounding the SAGD wellbore in a short period of time, enabling rapid transfer of the heat energy released by saturated steam to the interior of the oil layer, accelerating the formation of the steam chamber, and significantly increasing the volume of the steam chamber. This results in a noticeable decrease in the temperature of the produced fluid, reducing or even eliminating flash evaporation, making the production system more stable, and providing a solid foundation for switching to SAGD production. Furthermore, reservoir numerical simulation software shows that the method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs provided by the present invention can increase the inter-well temperature from 80–90°C to 150–160°C.

[0051] 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 may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0052] Figure 1 This is a schematic flowchart of the method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs according to the present invention;

[0053] Figure 2 This is a schematic diagram of the high thermal conductivity strip in the microcracks of the oil layer according to the present invention. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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] The present invention provides a method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs, such as... Figure 1 As shown, the main steps include: determining the required volume of high thermal conductivity material dispersion based on the minimum fracture pressure of the target oil layer; injecting hot water into the cleaned steam injection wells and production wells to pressurize to the minimum fracture pressure of the oil layer and continuing for a period of time; intermittently injecting high thermal conductivity material dispersion into the steam injection wells and production wells until all of the high thermal conductivity material dispersion is injected into the steam injection wells and production wells; and performing steam injection circulation preheating start-up on the steam injection wells and production wells that have been injected with the high thermal conductivity material dispersion.

[0056] The details are as follows:

[0057] (a) Determine the minimum fracturing pressure of the oil reservoir and calculate the volume of microfractures and fracturing fluid;

[0058] Specifically, during the preparation phase, at least two horizontal wells with horizontal sections on the same vertical plane and stacked one above the other should be set up in the oil layer to form a SAGD well group; 2-4 pressure measurement points and 6-12 thermocouple temperature measurement points or fiber optic continuous pressure and temperature measurement cables can be tied to the outside of the long oil tubing of the injection well and the production well, and connected to the ground control system.

[0059] Next, the minimum fracturing pressure of the oil layer is determined by methods including but not limited to indoor experiments or empirical formulas, and then the microfracture volume and the required fracturing fluid volume of the oil layer can be calculated.

[0060] (ii) Cleaning steam injection wells and production wells;

[0061] Hot water is injected into the long tubing of the steam injection well and the production well, and then drained through the short tubing for 7-14 days of wellbore cleaning. Of course, the cleaning time depends on the specific situation. At the same time, to ensure the cleaning effect, the hot water temperature should be controlled between 40℃ and 90℃.

[0062] (III) Preparatory work before fracturing;

[0063] To ensure the desired fracturing effect is achieved and to save on fracturing fluid usage, hot water at a temperature of 40℃-90℃ can be injected into the cleaned injection wells and production wells to pressurize them to the minimum fracturing pressure of the oil layer and continue to act for a period of time, typically 24-48 hours.

[0064] (iv) Oil layer fracturing:

[0065] This invention uses a mixed solution of hot water, dispersant, and high thermal conductivity material (high thermal conductivity material dispersion) as the fracturing fluid. The purpose is to enable it to form high thermal conductivity nanoribbons within the fracturing fracture after entering the oil reservoir. Figure 2 As shown, this allows the heat energy released by the saturated steam to be rapidly conducted into the oil layer, significantly increasing the volume of the steam chamber, causing a noticeable drop in the temperature of the produced liquid, reducing or even eliminating flash evaporation, and thus making the production system more stable, providing a solid foundation for switching to SAGD production.

[0066] Specifically, high thermal conductivity materials include, but are not limited to, one or more combinations of nano-graphene, nano-graphite tubes, nano-aluminum nitride, and boron nitride, as long as they achieve the aforementioned effects. Furthermore, to ensure good thermal conductivity while minimizing costs, the mass concentration of high thermal conductivity materials in the prepared mixed fluid (fracturing fluid) can be between 1‰ and 80‰. Of course, those skilled in the art will readily recognize that a higher amount of high thermal conductivity nanomaterials in the fracturing fluid will improve the corresponding thermal conductivity, but excessively high amounts will be detrimental to cost control. Therefore, any adjustments to the amount of high thermal conductivity materials made without departing from the inventive concept should fall within the scope of protection of this invention.

[0067] Furthermore, fracturing of the oil layer can be achieved by intermittently injecting a high thermal conductivity material dispersion into the injection and production wells until all the high thermal conductivity material dispersion is injected into the injection and production wells. Specifically, a mixture of hot water, dispersant, and high thermal conductivity material should be injected into the long tubing of the injection and production wells, and the fluid should first be drained from the short tubing of the injection and production wells for approximately 6-12 hours. The purpose is to squeeze out the hot water previously injected into the two wells. Next, the fluid composition at the wellhead of the short tubing of the injection and production wells should be monitored in real time. Once the high thermal conductivity material component is detected, the wellhead of the short tubing of the injection and production wells should be immediately closed. Subsequently, the high thermal conductivity material dispersion should be injected into the long tubing of the two wells at a pressurization rate of 0.1 MPa, gradually increasing the injection pressure until the pressure at the bottom of both wells increases to more than 0.5 MPa above the minimum fracturing pressure of the oil layer, at which point injection should be stopped to prevent the fracture size generated during the fracturing process from being too large. Furthermore, the surface pressure monitoring system monitors the pressure changes at the bottom of the two wells in real time. Once the pressure at the bottom of the two wells drops back to the minimum fracturing pressure of the oil layer, the high thermal conductivity material dispersion is injected into the wells in a gradually increasing manner using the same method described above. This cycle is repeated until all the prepared high thermal conductivity material dispersion (fracturing fluid) is injected into the steam injection well and the production well, thus completing the fracturing process. This process usually needs to be carried out intermittently for about 1-3 days, depending on the actual downhole operating environment.

[0068] (v) Steam circulation preheating;

[0069] Steam is injected into the long tubing of the fractured steam injection well and production well, while fluid is drained from the short tubing of the production well, thus initiating a steam injection cycle for preheating. Specifically, to save on steam injection costs during the preheating cycle, the preferred steam injection rate is controlled at 90-120 t / d for the long tubing of the steam injection well and 80-100 t / d for the short tubing; the steam injection rate for the long tubing of the production well is 80-110 t / d, and the fluid production rate for the short tubing is 90-120 t / d. At this point, the bottom hole pressure of the steam injection well is 0.2-1.0 MPa higher than that of the production well. This injection-production rate is maintained for 120-150 days of preheating. Experience has shown that this preheating cycle reduces the time by more than half compared to the traditional steam injection cycle preheating method, thereby significantly reducing energy consumption, accelerating the transition to SAGD production, and ultimately increasing oil production rate.

[0070] During this period, a numerical model of a single well group can be established to track and predict the temperature between injection and production wells, thereby determining the temperature in the middle of the oil layer and monitoring the preheating effect in real time. That is, the faster and higher the temperature rises in the middle of the oil layer, the more heat is retained in the oil layer during steam injection, the faster the oil can reach its melting temperature, and the shorter the required preheating time, which is beneficial for a rapid transition to the SAGD production stage.

[0071] Specifically, the numerical model of a single well group is preferably established using reservoir numerical simulation software; the preferred reservoir numerical simulation software includes, but is not limited to, STARS from CMG Corporation (Canada), Eclipse from Schlumberger Corporation (USA), and tNavigator from RFD Corporation (Russia). Reservoir numerical simulation software shows that the method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs provided by this invention can increase the inter-well temperature from 80–90°C to 150–160°C.

[0072] (vi) SAGD production;

[0073] Before officially transitioning to the SAGD production stage, methods such as numerical simulation, temperature testing, and interference well testing can be used to assess the thermal connectivity between injection and production wells. Once thermal connectivity is confirmed, the transition to the SAGD production stage can begin. Specifically, the long pipe of the production well is shut off, steam is injected simultaneously into both the long and short pipes of the steam injection well, and the production well is drained of fluid, thus entering the SAGD production stage.

[0074] The following describes in detail the effectiveness of the method for accelerating the SAGD preheating start-up of heavy oil reservoirs according to the present invention, using three specific embodiments.

[0075] Example 1

[0076] The method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs provided in this embodiment involves running a long tubing extending into the tip of the horizontal section and a short tubing extending into the heel of the horizontal section, parallel to the long tubing, into both the SAGD injection well and the production well. The method includes the following specific steps:

[0077] (1) In the SAGD well group at a depth of 400m and a reservoir depth of 350m, the minimum fracturing pressure of the oil layer was determined by triaxial rock stress tests, and the volume of microfractures and fracturing fluid was calculated, including 400m of 50℃ hot clean water. 3 A 100m solution of hot water with high thermal conductivity, dispersant, and nano-graphene. 3 The mass concentration of nano-graphene is 5.0‰.

[0078] (2) Inject hot water into the long tubing of the steam injection well and production well. The hot water temperature is 40℃-90℃. Drain the fluid through the short tubing and clean the wellbore for 10 days.

[0079] (3) Inject hot water into the steam injection well and production well to increase the pressure to the minimum fracture pressure of the oil layer, and continue for 24 hours.

[0080] (4) Inject a mixture of hot water, dispersant and high thermal conductivity material into the long tubing of the steam injection well and the production well, and drain the fluid through the short tubing of the steam injection well and the production well for 8 hours.

[0081] (5) High thermal conductivity material was detected at the short tubing wellheads of the steam injection well and production well, and the short tubing wellheads of the steam injection well and production well were closed.

[0082] (6) The injection well and the production well continue to inject a mixture of hot water, dispersant and high thermal conductivity material into the long tubing. When the bottom pressure is greater than the formation rupture pressure by 0.5 MPa, the injection stops. This process takes 2 days.

[0083] (7) Monitor the pressure drop to the minimum fracturing pressure, repeat (6) until all fracturing fluid is injected.

[0084] (8) Steam injection is performed in the long tubing of the steam injection well at a rate of 85 t / d. Fluid is drained from the short tubing of the steam injection well at a production rate of 82 t / d. Steam injection is also performed in the long tubing of the production well at a rate of 82 t / d. Fluid is drained from the short tubing of the production well at a production rate of 80 t / d. The bottom pressure of the steam injection well is 0.4 MPa higher than that of the production well. The well is preheated for 120 days and then switched to SAGD production. The long tubing of the production well is closed, and steam injection is performed simultaneously in both the long and short tubing of the steam injection well. Fluid is drained from the production well, and the SAGD production stage begins.

[0085] Compared with the conventional steam injection cycle preheating start-up method used in adjacent SAGD well pairs, the total preheating time in this embodiment is only 100 days, which is about half the time of the conventional preheating start-up method (conventional method: 180 days). This greatly improves the thermal energy utilization rate, enables rapid preheating start-up of SAGD, and speeds up the production rate of SAGD.

[0086] Example 2

[0087] The method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs provided in this embodiment involves running a long tubing extending into the tip of the horizontal section and a short tubing extending into the heel of the horizontal section, parallel to the long tubing, into both the SAGD injection well and the production well. The method includes the following specific steps:

[0088] (1) In the SAGD well group at a depth of 600m and a reservoir depth of 450m, the minimum fracturing pressure of the oil layer was determined by triaxial rock stress tests, and the volume of microfractures and fracturing fluid was calculated, including 650m of 50℃ hot clean water. 3 130m of mixed solution of hot water with high thermal conductivity, dispersant, and nano-graphene. 3 The mass concentration of nano-graphene is 8.0‰.

[0089] (2) Inject hot water into the long tubing of the steam injection well and production well. The hot water temperature is 40℃-90℃. Drain the fluid through the short tubing and clean the wellbore for 12 days.

[0090] (3) Inject 50°C hot water into the steam injection well and production well to increase the pressure to the minimum fracture pressure of the oil layer, and continue for 36 hours.

[0091] (4) Inject a mixture of hot water, dispersant and high thermal conductivity material into the long tubing of the steam injection well and the production well, and drain the fluid through the short tubing of the steam injection well and the production well for 10 hours.

[0092] (5) High thermal conductivity material was detected at the short tubing wellheads of the steam injection well and production well, and the short tubing wellheads of the steam injection well and production well were closed.

[0093] (6) Continue to inject a mixture of hot water, dispersant and high thermal conductivity material into the long tubing of the steam injection well and the production well. Stop injection when the bottom pressure is greater than the formation rupture pressure by 0.5 MPa. The injection time is 3 days.

[0094] (7) Monitor the pressure drop to the minimum fracturing pressure, repeat (6) until all fracturing fluid is injected.

[0095] (8) Steam injection is performed in the long tubing of the steam injection well at a rate of 110 t / d. Fluid is drained from the short tubing of the steam injection well at a production rate of 100 t / d. Steam injection is also performed in the long tubing of the production well at a rate of 100 t / d. Fluid is drained from the short tubing of the production well at a production rate of 95 t / d. The bottom pressure of the steam injection well is 0.6 MPa higher than that of the production well. The well is preheated for 160 days and then switched to SAGD production. The long tubing of the production well is closed, and steam injection is performed simultaneously in both the long and short tubing of the steam injection well. Fluid is drained from the production well, and the SAGD production stage begins.

[0096] Compared with the conventional steam injection cycle preheating start-up method used for adjacent SAGD well pairs, the total preheating time in this embodiment is only 160 days, which is more than half less than the conventional preheating start-up method (conventional method: 340 days). This greatly improves the thermal energy utilization rate, enables rapid preheating start-up of SAGD, and accelerates the production speed of SAGD.

[0097] Example 3

[0098] The method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs provided in this embodiment involves running a long tubing extending into the tip of the horizontal section and a short tubing extending into the heel of the horizontal section, parallel to the long tubing, into both the SAGD injection well and the production well. The method includes the following specific steps:

[0099] (1) In the SAGD well group at a depth of 800m and a reservoir depth of 470m, the minimum fracturing pressure of the oil layer was determined by triaxial rock stress tests, and the volume of microfractures and fracturing fluid was calculated, including 750m of 50℃ hot clean water. 3 150m of a mixed solution of hot water with high thermal conductivity, dispersant, and nano-graphene. 3 The mass concentration of nano-graphene is 6.0‰.

[0100] (2) Inject hot water into the long tubing of the steam injection well and production well. The hot water temperature is 40℃-90℃. Drain the fluid through the short tubing and clean the wellbore for 12 days.

[0101] (3) Inject 50°C hot water into the steam injection well and production well to increase the pressure to the minimum fracture pressure of the oil layer, and continue for 36 hours.

[0102] (4) Inject a mixture of hot water, dispersant and high thermal conductivity material into the long tubing of the steam injection well and the production well, and drain the fluid through the short tubing of the steam injection well and the production well for 10 hours.

[0103] (5) High thermal conductivity material was detected at the short tubing wellheads of the steam injection well and production well, and the short tubing wellheads of the steam injection well and production well were closed.

[0104] (6) Continue to inject a mixture of hot water, dispersant and high thermal conductivity material into the long tubing of the steam injection well and the production well. Stop injection when the bottom pressure is greater than the formation rupture pressure by 0.5 MPa. The injection time is 3 days.

[0105] (7) Monitor the pressure drop to the minimum fracturing pressure, repeat (6) until all fracturing fluid is injected.

[0106] (8) Steam injection is performed in the long tubing of the steam injection well at a rate of 130 t / d. Fluid is drained from the short tubing of the steam injection well at a production rate of 110 t / d. Steam injection is also performed in the long tubing of the production well at a rate of 110 t / d. Fluid is drained from the short tubing of the production well at a production rate of 100 t / d. The bottom pressure of the steam injection well is 0.6 MPa higher than that of the production well. The well is preheated for 185 days and then switched to SAGD production. The long tubing of the production well is closed, and steam injection is performed simultaneously in both the long and short tubing of the steam injection well. Fluid is drained from the production well, and the SAGD production stage begins.

[0107] Compared with the conventional steam injection cycle preheating start-up method used in adjacent SAGD well pairs, the total preheating time in this embodiment is only 185 days, which is more than half less than the conventional preheating start-up method (conventional method: 380 days). This greatly improves the thermal energy utilization rate, enables rapid preheating start-up of SAGD, and accelerates the production speed of SAGD.

[0108] In summary, the method and apparatus for accelerating SAGD preheating startup in heavy oil reservoirs provided by this invention have undergone comprehensive theoretical and numerical simulation studies, and relevant parameters have been fully verified. The technology is highly mature and can significantly increase the thermal conductivity of the reservoir surrounding the SAGD wellbore in a short time, accelerating the formation of a large-scale steam chamber. Nano-graphene (or a combination of materials), dispersant, and hot water are mixed and injected into the oil layer to form nano-strips, thereby rapidly transferring the heat energy released by saturated steam to the interior of the oil layer. This significantly increases the volume of the steam chamber, noticeably reduces the temperature of the produced fluid, reduces or even eliminates flash evaporation, and makes the production system more stable, providing a solid foundation for transitioning to SAGD production. Reservoir numerical simulation software shows that this technology can increase the inter-well temperature from 80–90℃ to 150–160℃, resulting in significant cost reduction and efficiency improvement.

[0109] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs, the method comprising: The required volume of the high thermal conductivity material dispersion is determined based on the minimum fracture pressure of the target oil layer; Hot water is injected into the cleaned steam injection wells and production wells to pressurize them to the minimum fracture pressure of the oil layer, and this process is continued for a period of time. Intermittently pressurize and inject a high thermal conductivity material dispersion into the steam injection well and the production well until all of the high thermal conductivity material dispersion is injected into the steam injection well and the production well; The process of intermittently injecting a high thermal conductivity material dispersion into the steam injection well and the production well until all of the high thermal conductivity material dispersion has been injected into the steam injection well and the production well includes: A high thermal conductivity material dispersion was injected into the steam injection well and production well at a pressurization rate of 0.1 MPa, gradually increasing the injection pressure. Injection was stopped when the pressure at the bottom of both wells increased to 0.5 MPa above the minimum fracture pressure of the oil layer. Once the pressure at the bottom of the two wells drops back to the minimum fracture pressure of the oil layer, the high thermal conductivity material dispersion is injected again by gradually increasing the pressure by 0.1 MPa until all the high thermal conductivity material dispersion is injected into the steam injection well and the production well. Steam injection circulation preheating is performed on steam injection wells and production wells that have been injected with high thermal conductivity material dispersion. The steam injection circulation preheating start-up of the injection well and production well for injecting the high thermal conductivity material dispersion includes: The steam injection rate of the long tubing in the steam injection well is controlled at 80-130 t / d, and the fluid production rate of the short tubing in the steam injection well is controlled at 80-110 t / d. The steam injection rate for long tubing in production wells is 80-110 t / d, and the fluid production rate for short tubing in production wells is 80-120 t / d.

2. The method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs according to claim 1, wherein, The high thermal conductivity material dispersion is: A mixed solution of high thermal conductivity materials, hot water, and dispersants; The high thermal conductivity material includes one or more of the following: nano-graphene, nano-graphite tube, nano-aluminum nitride, and boron nitride.

3. The method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs according to claim 2, wherein, The mass concentration of the high thermal conductivity material dispersion ranges from 1‰ to 80‰.

4. The method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs according to claim 1, wherein, The duration includes: The duration is 24-48 hours.

5. The method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs according to claim 1, wherein, The temperature of the hot water is 40℃-90℃.

6. The method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs according to claim 1, wherein, The steam injection circulation preheating start-up of the injection well and production well for injecting the high thermal conductivity material dispersion includes: The pressure at the bottom of the steam injection well should be 0.2-1.0 MPa higher than that at the bottom of the production well.

7. The method for accelerating the preheating and start-up of SAGD in heavy oil reservoirs according to claim 1, wherein, The method further includes: During the steam injection cycle preheating start-up process, the temperature in the middle of the oil layer is monitored in real time by establishing a single-well group numerical model.

8. An apparatus for accelerating the SAGD preheating start-up method for heavy oil reservoirs according to any one of claims 1-7, the apparatus comprising: A determination unit is used to determine the volume of the required high thermal conductivity material dispersion based on the minimum fracture pressure of the target oil layer; The hot water injection unit is used to inject hot water into the cleaned steam injection wells and production wells to pressurize the reservoir to the minimum fracture pressure and continue for a period of time. A high thermal conductivity material injection unit is used to intermittently pressurize and inject a high thermal conductivity material dispersion into the steam injection well and the production well until all the high thermal conductivity material dispersion is injected into the steam injection well and the production well; The high thermal conductivity material injection unit includes: The first injection module is used to inject a high thermal conductivity material dispersion into the steam injection well and the production well at a pressurization rate of 0.1 MPa, gradually increasing the injection pressure until the pressure at the bottom of both wells increases to more than 0.5 MPa above the minimum fracturing pressure of the oil layer, at which point the injection stops. The pressure monitoring module is used to monitor the bottom pressure of the steam injection well and the production well. When the pressure at the bottom of the two wells drops back to the minimum fracture pressure of the oil layer, the high thermal conductivity material dispersion is injected again using the first injection module. The circulating preheating start-up unit is used to perform steam injection circulation preheating start-up on steam injection wells and production wells that have been injected with high thermal conductivity material dispersion. The cyclic preheating start-up unit includes: The first control module is used to control the steam injection rate of the long tubing of the steam injection well to be 80-130 t / d and the fluid production rate of the short tubing of the steam injection well to be 80-110 t / d. The steam injection rate for long tubing in production wells is 80-110 t / d, and the fluid production rate for short tubing in production wells is 80-120 t / d.

9. The apparatus for accelerating the SAGD preheating start-up method in heavy oil reservoirs according to claim 8, wherein, The high thermal conductivity material dispersion is a mixed solution of high thermal conductivity material, hot water, and dispersant. The high thermal conductivity material includes one or more of the following: nano-graphene, nano-graphite tube, nano-aluminum nitride, and boron nitride.

10. The apparatus for accelerating the SAGD preheating start-up method in heavy oil reservoirs according to claim 8, wherein, The mass concentration of the high thermal conductivity material dispersion ranges from 1‰ to 80‰.

11. The apparatus for accelerating the SAGD preheating start-up method in heavy oil reservoirs according to claim 8, wherein, The pressure control module is used to control the pressure at the bottom of the steam injection well to be 0.2-1.0 MPa higher than the pressure at the bottom of the production well.

12. The apparatus for accelerating the SAGD preheating start-up method in heavy oil reservoirs according to claim 8, wherein, The device further includes: The monitoring unit is used to monitor the temperature in the middle of the oil layer in real time during the steam injection cycle preheating start-up process.

Images