Thermal internal drive enhanced recovery of low grade reservoirs

Abstract

The present application relates to the technical field of enhanced oil recovery, and is a method for improving the recovery ratio of low-grade oil reservoirs by thermal internal drive, which utilizes an existing circular well pattern, optimally selects a well at a high position of a structure, side-drills and transforms the central well, establishes a communication passage with a neighboring one-line gas injection well, then side-drills a branch central well for high-temperature ignition and gas injection, after the bottom hole temperature of the gas injection well reaches a certain temperature, the gas injection well is used for gas injection, when the fire line is pushed outward from the first circle of well groups to the second circle of well groups, the second row of gas injection wells are ignited by using the method of wind transfer and fire connection, one well group is pushed outward each time, and the remaining gas injection wells are synchronously injected with gas. The present application firstly utilizes thermal internal drive to generate heat in situ, heats the reservoir skeleton and fluid through heat conduction and heat convection, promotes the fluid in the pores which is difficult to be displaced, and after being heated, the fluid is self-displaced and flows to the production well by expansion or vaporization, which can further tap the remaining oil in low-permeability oil reservoirs and improve the recovery ratio of low-permeability reservoirs.

Description

Technical Field

[0001] This invention relates to the field of enhanced oil recovery technology, and is a method for improving the recovery rate of low-grade oil reservoirs through thermal internal drive. Background Technology

[0002] China possesses abundant low-permeability oil and gas resources with significant exploration and development potential. The need to increase the utilization of low-permeability reserves and improve the development efficiency of low-permeability oilfields is becoming increasingly urgent. After primary recovery of low-permeability reservoirs, waterflooding is the primary development method, replenishing formation energy through water injection. However, with the continued development of waterflooding, especially in the high water-cut, high-extraction stages, a large amount of injected water is ineffectively recycled, leading to a gradual decline in oilfield production and a deterioration in development efficiency, failing to meet the demands of economical waterflooding development.

[0003] Studies have found that during waterflooding in low-porosity, low-permeability reservoirs, water advances along relatively high-permeability paths, leaving large untouched areas outside the flow channels where residual oil remains abundant. Macroscopically, large-scale residual oil is almost completely exhausted, and the remaining oil is highly dispersed. Microscopically, water-washed inspection well analysis indicates that a significant amount of residual oil remains within the water-flooded layer, primarily in the form of…

[0004] The distribution is either "banded" or "comb-like". Reservoir characteristics of remaining oil distribution include two types: small radii and stuck sections (see...). Figure 1 The characteristics of residual oil make it difficult for waterflooding to achieve effective displacement.

[0005] Existing methods for enhancing oil recovery, such as modulating flooding, surfactant flooding, microbial flooding, and gas flooding, are unlikely to significantly improve the recovery rate of low-permeability, light oil reservoirs in the "high-permeability and high-oil-density" stage. This is because modulating flooding agents / surfactants still operate through the waterflood channel, displacing only a small amount of oil droplets or films that waterflooding cannot remove, thus improving the efficiency of oil washing, but the reduction in residual oil is limited. Although gas flooding can improve development results, it still needs to overcome the seepage resistance of small pores to displace crude oil. In addition, the large difference in mobility between the displacing phase and the displaced phase can easily lead to gas channeling, thus limiting the improvement in recovery rate.

[0006] Therefore, a new method is proposed to improve the recovery rate of low-permeability light oil reservoirs after they enter the "high-permeability and high-growth" stage. This method promotes the discharge of residual oil in small pores and pore structures, further taps the potential of residual oil, and improves the recovery rate of low-permeability light oil reservoirs. Summary of the Invention

[0007] This invention provides a method for improving the recovery rate of low-grade oil reservoirs through thermal internal drive, which overcomes the shortcomings of the prior art and can effectively improve the recovery rate of low-permeability light oil reservoirs.

[0008] The technical solution of this invention is achieved through the following measures: a method for improving the recovery rate of low-grade oil reservoirs via thermal internal drive, comprising:

[0009] Utilizing the existing area well network design to form a circular well network, firstly, wells in high structural positions are selected, and the central well is sidetracked to form a sidetracked branch center well. The sidetracked branch center well is connected to multiple adjacent gas injection wells. Then, the sidetracked branch center well is ignited and injected with high-temperature gas, injecting a certain volume of mixed gas into the first circular area reservoir of the circular well network to improve the oil saturation and temperature field near the injection well. While the sidetracked branch center well is injecting gas, the adjacent first-line injection wells begin production. After the bottom temperature of the injection wells reaches a certain temperature, the injection wells begin injecting gas. When the ignition line is pushed outward from the first ring of well groups to the second ring of well groups, the second row of injection wells is ignited by moving air to connect the ignition. Each time one well group is pushed outward, the remaining injection wells inject gas simultaneously. After pushing out three rings, for each new ring of injection wells, one old ring of injection wells is removed.

[0010] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0011] The aforementioned methods for improving the recovery rate of low-grade oil reservoirs through thermal internal drive specifically include:

[0012] Utilizing the existing area well network design to form a circular well network, firstly, five wells in the high-position area are selected, and the central well is modified by side-drilling to form a side-drilled branch center well. The side-drilled branch center well is connected to the four adjacent gas injection wells. Then, the side-drilled branch center well is ignited and injected with high-temperature gas, injecting mixed gas with a volume of 1 to 2 times the pore volume of the first circular area oil reservoir in the circular well network, thereby increasing the oil saturation and temperature field near the gas injection well. At the same time as the side-drilled branch center well is injecting gas, the four adjacent gas injection wells begin production. After the bottom temperature of the gas injection well reaches 150°C, the gas injection well begins to inject gas. When the ignition line is pushed outward from the first circle of well groups to the second circle of well groups, the second row of gas injection wells is ignited by moving the air to connect the ignition. One well group is pushed outward each time, and the remaining gas injection wells inject gas simultaneously. After pushing out three circles, one circle of old gas injection wells is removed for each new circle of gas injection wells.

[0013] The horizontal section of the aforementioned side-drilled center well is located in the middle of the reservoir, and its length is two-thirds of the distance between the center gas injection well and the first ring of gas injection wells. The distance between the first ring of gas injection wells and the side-drilled branch center well is 100m to 150m. The distance between the second ring of gas injection wells and the subsequent adjacent gas injection wells is 300m to 400m. The vertical well is divided into two perforation sections: the production section is located at the bottom of the oil layer, and the gas injection section is located at the top of the oil layer.

[0014] The specific method for high-temperature ignition and gas injection into the side-drilled branch center well is as follows: First, inject unheated air into the reservoir of the side-drilled branch center well for 7 to 14 days to establish a gas-liquid flow communication channel. The unheated air injection intensity is 100 standard cubic meters per meter of oil layer. After the unheated air injection time reaches the required time, inject the designed amount of crude oil into the reservoir. After the crude oil injection is completed, ignite the reservoir. First, inject room temperature oxygen-enriched air for 3 to 5 days, then inject hot air at a temperature of 150°C to 200°C into the reservoir. The injection intensity of air-1 is 800 standard cubic meters per meter of oil layer. The injection time of hot air-1 is 5 to 7 days, which causes the reservoir to expand due to heat, squeezing out the oil and gas in the pores. The oil and gas mix with hot air-1 and oxygen-enriched air-1, and quickly reach the ignition conditions. Then, hot oxygen-enriched air-2 at 250°C to 300°C is injected into the oil layer to establish a thermal internal drive cavity zone. The injection intensity of oxygen-enriched air-2 is 1000 standard cubic meters per meter of oil layer, and the injection time of oxygen-enriched air-2 is 45 to 75 days, thereby establishing a gas / vapor phase zone in the reservoir. Then, unheated air is injected to achieve injection-production balance.

[0015] The reservoir conditions described above are: porosity less than 15% and permeability less than 50 × 10⁻⁶. -3 μm, oil layer thickness 5m to 25m, crude oil viscosity less than 10mPa·s, reservoir temperature greater than 70℃.

[0016] In the process of establishing injection-production balance described above, unheated air is injected into the reservoir. The injection intensity of the unheated air is M.

[0017]

[0018] Where M is the unheated air injection intensity, m 3 , / (d·m); R is the combustion radius, m; n is the total number of injection wells; A is the air consumption required to burn a unit volume of core and reach 400℃, m3 / m3; ω is the air utilization rate, %; φ is the porosity, %; δ is the reservoir utilization rate, %; P is the reservoir pressure, MPa; Z is the air compressibility factor; α is the thermal internal drive reservoir constant, which is 2 to 3.

[0019] The above crude oil injection design volume is calculated as shown in equation (1).

[0020] q=(Q-Q0) / (42705000*60%) (1)

[0021] In formula (1), q represents the design amount of crude oil injection, Q represents the total heat required for ignition, 42705000 represents the unit heat of crude oil, 60% represents the utilization coefficient of injected oil, and Q0 is one-quarter to one-third of Q.

[0022] The total heat required for ignition is calculated as shown in equation (2).

[0023] Q = π(r) e 2 -r w 2 )HρC(T-Ti) (2)

[0024] In equation (2), Q represents the total heat required for ignition, and r e The ignition radius, r w The values ​​represent the wellbore radius, H represents the reservoir thickness (m), ρ represents the reservoir density, C represents the reservoir specific heat capacity, T represents the temperature at which the reservoir expands due to heat and squeezes out crude oil, and Ti represents the initial temperature of the reservoir. All units are in the International System of Units (SI).

[0025] The product of the oil layer density and the oil layer specific heat capacity is calculated as shown in equation (3).

[0026]

[0027] In equation (3), ρ represents the oil layer density, and C represents the oil layer specific heat capacity. ρ represents porosity. s C represents the density of rock. s ρ represents the specific heat capacity of rocks. o C represents the density of the injected oil. o S represents the specific heat capacity of the injected oil. wc ρ represents the degree of bound water saturation. w C represents the density of water. w This indicates the specific heat capacity of water.

[0028] This invention first utilizes thermal internal drive to generate heat in situ. Through heat conduction and heat convection, the reservoir framework and fluids are heated, which causes the fluids in the pores that are difficult to be discharged to be discharged to the production well by expanding or vaporizing after being heated. This can further tap the remaining oil in low-permeability reservoirs and improve the recovery rate of low-permeability reservoirs. Attached Figure Description

[0029] Appendix Figure 1 This represents the reservoir characteristics for the distribution of remaining oil.

[0030] Appendix Figure 2 This refers to the well pattern layout of a circular well network.

[0031] Appendix Figure 3 The internal drive zone is divided.

[0032] Appendix Figure 4 The mole fraction of the liquid phase at different temperatures and pressures (crude oil / air = 0.7).

[0033] Appendix Figure 5 The mole fraction of the gas phase at different temperatures and pressures (crude oil / air = 0.7).

[0034] Appendix Figure 1In the diagram, (a) represents the residual oil with a small radius of the grate, (b) represents the residual oil with a jamming effect, and (c) represents the residual oil with a jamming effect.

[0035] Appendix Figure 2 In the diagram, 1 is the production well, 2 is the gas injection well, and 3 is the side-drilled branch center well.

[0036] Appendix Figure 3 In the middle, the gas / vapor phase region is around 400℃; the oil-rich region is around 150℃; and the aqueous phase region is around 150℃. Detailed Implementation

[0037] This invention is not limited to the following embodiments; specific implementation methods can be determined according to the technical solution and actual conditions of this invention. In this invention, room temperature generally refers to a temperature between 15°C and 25°C.

[0038] The present invention will be further described below with reference to embodiments:

[0039] Example 1: As shown in the attached document Figure 2 As shown, this method for enhancing the recovery rate of low-grade oil reservoirs through thermal internal drive includes:

[0040] Utilizing the existing area well network design to form a circular well network, firstly, five wells in the high-position area are selected, and the central well is modified by side-drilling to form a side-drilled branch center well 3. The side-drilled branch center well 3 establishes a connection channel with the four adjacent gas injection wells 2. Then, the side-drilled branch center well 3 is ignited and injected with high-temperature gas, injecting mixed gas with an area of ​​1 to 2 times the pore volume of the reservoir in the first circle of the circular well network (the circular well network closest to the side-drilled branch center well 3), thereby increasing the oil saturation and temperature field near the gas injection well 2. At the same time as the side-drilled branch center well 3 is injecting gas, the four adjacent gas injection wells 2 begin production. After the bottom temperature of the gas injection well 2 reaches 150℃, the gas injection well 2 begins to inject gas. When the ignition line is pushed outward from the first circle (the circular well network closest to the side-drilled branch center well 3) to the second circle, the second row of gas injection wells is ignited by moving the air to connect the ignition. One well group is pushed outward each time, and the remaining gas injection wells inject gas simultaneously. After pushing out three circles, one circle of old gas injection wells is removed for each new circle of gas injection wells.

[0041] Example 2: As an optimization of the above example, the horizontal section of the sidetracked center well 3 is located in the middle of the reservoir, and its length is two-thirds of the distance between the center gas injection well (sidetracked center well 3) and the first ring of gas injection wells. The distance between the first ring of gas injection wells 2 and the sidetracked branch center well 3 is 100m to 150m. The distance between the second ring of gas injection wells and the subsequent adjacent gas injection wells is 300m to 400m. The vertical well is divided into two perforation sections, with the production section located at the bottom of the oil layer and the gas injection section located at the top of the oil layer.

[0042] Example 3: As an optimization of the above example, the method for high-temperature ignition gas injection into the side-drilled branch center well is as follows: First, inject unheated air into the reservoir of the side-drilled branch center well for 7 to 14 days to establish a gas-liquid flow communication channel. The unheated air injection intensity is 100 standard cubic meters per meter of oil layer. After the unheated air injection time reaches the required time, inject the designed amount of crude oil into the reservoir. After the crude oil injection is completed, ignite the reservoir by first injecting room temperature oxygen-enriched air for 3 to 5 days, followed by injecting hot air at a temperature of 150°C to 200°C into the reservoir. First, the injection intensity of both oxygen-enriched gas 1 and hot air 1 is 800 standard cubic meters per meter of oil layer. The injection time of hot air 1 is 5 to 7 days, which causes the reservoir to expand due to heat, squeezing out the oil and gas in the pores. The oil and gas mix with hot air 1 and oxygen-enriched gas 1, quickly reaching the ignition conditions. Then, hot oxygen-enriched gas 2 at 250°C to 300°C is injected into the oil layer to establish a thermal internal drive cavity zone. The injection intensity of oxygen-enriched gas 2 is 1000 standard cubic meters per meter of oil layer, and the injection time of oxygen-enriched gas 2 is 45 to 75 days, thereby establishing a gas / vapor phase zone in the reservoir. Then, unheated air is injected to achieve injection-production balance.

[0043] As is known to those skilled in the art, in water-driven oil reservoir development, the near-wellbore high water cut means that the amount of fuel available for combustion is very small, making it difficult to establish a high-temperature "gas / vapor phase zone". In oil reservoirs with low porosity and low permeability, the amount of fuel per unit volume of oil sands is small, making it difficult to initially form a high-temperature "gas / vapor phase zone". The above-mentioned methods can enable the reservoir to safely and quickly reach high-temperature oxidation combustion and successfully establish a high-temperature "gas / vapor phase zone".

[0044] The reservoir conditions are: porosity less than 15%, permeability less than 50 × 10⁻⁶. -3 μm, oil layer thickness 5m to 25m, crude oil viscosity less than 10mPa·s, reservoir temperature greater than 70℃.

[0045] The principle of the method described in this invention:

[0046] The reservoir characteristics of this invention are: the crude oil is light oil with a viscosity of less than 50 mPa·s (50℃, degassed crude oil), the density of the crude oil is less than the density of water, and it is a low-porosity, low-permeability reservoir.

[0047] Internal drive characteristics: Taking advantage of the lightness of light oil fractions and their easy vaporization after heating, the reservoir is heated, and the crude oil vaporizes / expands and flows out automatically from the rock pores, and is further driven to the production well.

[0048] Internal drive establishment method: Injecting hot air and / or oxygen-enriched fluid, the hot fluid heats the reservoir, and the crude oil in the reservoir expands and flows out, mixing with hot oxygen for oxidation and combustion, releasing heat in situ. Light oil fractions are light, and their oxidation and combustion generate a large amount of heat, while producing a small amount of coke and a large amount of flue gas, forming a thermal drive displacement zone.

[0049] Internal drive replacement zone division: As the thermal drive replacement zone advances, it is affected by the high pressure properties of crude oil ( Figure 4 , Figure 5 Four driving zones gradually form in the reservoir (see...) Figure 3 ).like Figure 3 As shown, the first phase zone is the "gas / vapor phase zone", which provides heat for internal drive to displace crude oil in the pores and displace the displaced crude oil; the second phase zone is the "condensate phase zone", which is the crude oil and steam condensed and heated water displaced by internal drive. Crude oil is mainly distributed in the upper part of the reservoir, and water is mainly distributed in the lower part; the third phase zone is the "new cold oil zone", which is simultaneously driven by gas from the top flue and water from the bottom.

[0050] Example 4: As an optimization of the above examples, during the injection-production balance process, unheated air is injected into the reservoir, and the injection intensity of the unheated air is M.

[0051]

[0052] Where M is the unheated air injection intensity, m 3 , / (d·m); R is the combustion radius, m; n is the total number of injection wells; A is the air consumption required to burn a unit volume of core and reach 400℃, m3 / m3; ω is the air utilization rate, %; φ is the porosity, %; δ is the reservoir utilization rate, %; P is the reservoir pressure, MPa; Z is the air compressibility factor; α is the thermal internal drive reservoir constant, which is 2 to 3.

[0053] For reservoirs with low porosity and permeability, the amount of fuel per unit volume of oil sands is small, and the continuous control of the high-temperature "gas / vapor phase zone" is difficult. By injecting unheated air of the specified intensity, the combustion effect can be improved, gas channeling can be reduced (without the need for large amounts of useless nitrogen), the width and stability of the "gas / vapor phase zone" can be increased, and an injection-production balance can be established.

[0054] Example 5: As an optimization of the above examples, the crude oil injection design volume is calculated as shown in equation (1).

[0055] q=(Q-Q0) / (42705000*60%) (1)

[0056] In formula (1), q represents the design amount of crude oil injection, Q represents the total heat required for ignition, 42705000 represents the unit heat of crude oil, 60% represents the utilization coefficient of injected oil, and Q0 is one-quarter to one-third of Q.

[0057] Example 6: As an optimization of the above examples, the total heat required for ignition is calculated as shown in equation (2).

[0058] Q = π(r) e 2 -r w 2 )HρC(T-Ti) (2)

[0059] In equation (2), Q represents the total heat required for ignition, and r e The ignition radius, r w The values ​​represent the wellbore radius, H represents the reservoir thickness (m), ρ represents the reservoir density, C represents the reservoir specific heat capacity, T represents the temperature at which the reservoir expands due to heat and squeezes out crude oil, and Ti represents the initial temperature of the reservoir. All units are in the International System of Units (SI).

[0060] Example 7: As an optimization of Example 5 above, the product of oil layer density and oil layer specific heat capacity is calculated as shown in equation (3).

[0061] In equation (3), ρ represents the oil layer density, and C represents the oil layer specific heat capacity. ρ represents porosity. s C represents the density of rock. s ρ represents the specific heat capacity of rocks. o C represents the density of the injected oil. o S represents the specific heat capacity of the injected oil. wc ρ represents the degree of bound water saturation. w C represents the density of water. w This indicates the specific heat capacity of water.

[0062] The following application examples illustrate this.

[0063] Application Case 1: An oilfield block with reservoir conditions of 12% porosity and 42×10⁻⁶ permeability. -3 μm, oil layer thickness 23m, crude oil viscosity 7mPa·s, reservoir temperature 94℃.

[0064] The method for improving the recovery rate of low-grade oil reservoirs through thermal internal drive includes:

[0065] Utilizing the existing area well network design to form a circular well network, firstly, five wells in the high-position area are selected, and the central well is sidetracked to form a sidetracked branch center well 3. The sidetracked branch center well 3 establishes a connection with four adjacent gas injection wells 2. Then, the sidetracked branch center well 3 undergoes high-temperature ignition and gas injection, injecting a mixed gas volume 1 to 2 times the pore volume of the reservoir in the first circle of the circular well network (the circle network closest to the sidetracked branch center well 3), increasing the oil saturation and temperature field near the gas injection wells 2. Simultaneously with gas injection in the sidetracked branch center well 3, the four adjacent gas injection wells 2 begin production. Once the bottom temperature of the gas injection wells 2 reaches 150℃, gas injection begins in the gas injection wells 2, and the ignition line moves from the first circle (the circle network closest to the sidetracked branch center well 3) to the next circle. When pushing the well group (the closest circular well network to the branch center well 3) outwards to the second ring of well groups, the second row of gas injection wells is ignited using a method of air transfer and ignition. One well group is pushed outwards at a time, with the remaining gas injection wells injecting gas simultaneously. After three rings of outwards, for each new ring of gas injection wells, one ring of old gas injection wells is removed. The horizontal section of the sidetracked center well 3 is located in the middle of the reservoir, with a length two-thirds of the distance between the center gas injection well (sidetracked center well 3) and the first ring of gas injection wells. The distance between the first ring of gas injection wells 2 and the sidetracked branch center well 3 is 100m. The distance between the second ring of gas injection wells and subsequent adjacent gas injection wells is 300m. The vertical wells are divided into two perforation sections: the production section is located at the bottom of the oil layer, and the gas injection section is located in the upper part of the oil layer.

[0066] The specific method for high-temperature ignition gas injection into the side-drilled branch center well is as follows: First, inject unheated air into the reservoir of the side-drilled branch center well for 12 days to establish a gas-liquid fluid flow communication channel. The unheated air injection intensity is 100 standard cubic meters per meter of oil layer. After the unheated air injection time reaches the required time, inject the designed amount of crude oil into the reservoir. The designed amount of crude oil injection is calculated according to the above formulas (1) to (3). After the crude oil injection is completed, ignite the reservoir. First, inject room temperature oxygen-enriched gas for 3 days, and then inject hot air at a temperature of 180℃ into the reservoir. The injection of oxygen-enriched gas and hot air is carried out in a tandem. The injection intensity was 800 standard cubic meters per meter of oil layer. Hot air injection (Type 1) was carried out over 7 days, causing the reservoir to expand due to heat, squeezing out oil and gas from the pores. The oil and gas mixed with hot air and oxygen-enriched air (Type 1), rapidly reaching ignition conditions. Subsequently, 250°C hot oxygen-enriched air (Type 2) was injected into the oil layer to establish a thermal internal drive zone. The injection intensity of oxygen-enriched air (Type 2) was 1000 standard cubic meters per meter of oil layer, and the injection time was 65 days, thereby establishing a gas / vapor phase zone in the reservoir. Then, unheated air was injected to achieve injection-production balance. During the establishment of injection-production balance, unheated air was injected into the reservoir at the same intensity as in Example 4. The crude oil recovery rate in Application Case 1 was 40%.

[0067] Application Case 2: An oilfield block with reservoir conditions of 10% porosity and 37×10⁻⁶ permeability. -3 μm, oil layer thickness 18m, crude oil viscosity 8mPa·s, reservoir temperature 80℃.

[0068] The method for improving the recovery rate of low-grade oil reservoirs through thermal internal drive includes:

[0069] Utilizing the existing area well network design to form a circular well network, firstly, five wells in the high-position area are selected, and the central well is sidetracked to form a sidetracked branch center well 3. The sidetracked branch center well 3 establishes a connection with four adjacent gas injection wells 2. Then, the sidetracked branch center well 3 undergoes high-temperature ignition and gas injection, injecting a mixed gas volume 1 to 2 times the pore volume of the reservoir in the first circle of the circular well network (the circle network closest to the sidetracked branch center well 3), increasing the oil saturation and temperature field near the gas injection wells 2. Simultaneously with gas injection in the sidetracked branch center well 3, the four adjacent gas injection wells 2 begin production. Once the bottom temperature of the gas injection wells 2 reaches 150℃, gas injection begins in the gas injection wells 2, and the ignition line moves from the first circle (the circle network closest to the sidetracked branch center well 3) to the next circle. When pushing the well group (the closest circular well network to the branch center well 3) outwards to the second ring of well groups, the second row of gas injection wells is ignited using a method of air transfer and ignition. One well group is pushed outwards at a time, with the remaining gas injection wells injecting gas simultaneously. After three rings of outwards, for each new ring of gas injection wells, one ring of old gas injection wells is removed. The horizontal section of the sidetracked center well 3 is located in the middle of the reservoir, with a length two-thirds of the distance between the center gas injection well (sidetracked center well 3) and the first ring of gas injection wells. The distance between the first ring of gas injection wells 2 and the sidetracked branch center well 3 is 150m. The distance between the second ring of gas injection wells and subsequent adjacent gas injection wells is 400m. The vertical wells are divided into two perforation sections: the production section is located at the bottom of the oil layer, and the gas injection section is located in the upper part of the oil layer.

[0070] The specific method for high-temperature ignition gas injection into the side-drilled branch center well is as follows: First, inject unheated air into the reservoir of the side-drilled branch center well for 10 days to establish a gas-liquid flow communication channel. The unheated air injection intensity is 100 standard cubic meters per meter of oil layer. After the unheated air injection time reaches the required time, inject the designed amount of crude oil into the reservoir. The designed amount of crude oil injection is calculated according to the above formulas (1) to (3). After the crude oil injection is completed, ignite the reservoir. First, inject room temperature oxygen-enriched gas for 5 days, and then inject hot air at a temperature of 200℃ into the reservoir. The injection of oxygen-enriched gas and hot air is carried out in a tandem. The injection intensity was 800 standard cubic meters per meter of oil layer. Hot air injection (Type 1) was carried out over 5 days, causing the reservoir to expand due to heat, squeezing out oil and gas from the pores. The oil and gas mixed with hot air and oxygen-enriched air (Type 1) to quickly reach ignition conditions. Subsequently, hot oxygen-enriched air (Type 2) at 290°C was injected into the oil layer to establish a thermal internal drive zone. The injection intensity of oxygen-enriched air (Type 2) was 1000 standard cubic meters per meter of oil layer, and the injection time was 45 days, thereby establishing a gas / vapor phase zone in the reservoir. Then, unheated air was injected to achieve injection-production balance. During the establishment of injection-production balance, unheated air was injected into the reservoir at the same intensity as in Example 4. The crude oil recovery rate in Application Case 2 was 38%.

[0071] Application Case 3: An oilfield block with reservoir conditions of 9% porosity and less than 45 × 10⁻⁶. -3μm, oil layer thickness 14m, crude oil viscosity 10mPa·s, reservoir temperature 76℃.

[0072] The method for improving the recovery rate of low-grade oil reservoirs through thermal internal drive includes:

[0073] Utilizing the existing area well network design to form a circular well network, firstly, five wells in the high-position area are selected, and the central well is sidetracked to form a sidetracked branch center well 3. The sidetracked branch center well 3 establishes a connection with four adjacent gas injection wells 2. Then, the sidetracked branch center well 3 undergoes high-temperature ignition and gas injection, injecting a mixed gas volume 1 to 2 times the pore volume of the reservoir in the first circle of the circular well network (the circle network closest to the sidetracked branch center well 3), increasing the oil saturation and temperature field near the gas injection wells 2. Simultaneously with gas injection in the sidetracked branch center well 3, the four adjacent gas injection wells 2 begin production. Once the bottom temperature of the gas injection wells 2 reaches 150℃, gas injection begins in the gas injection wells 2, and the ignition line moves from the first circle (the circle network closest to the sidetracked branch center well 3) to the next circle. When pushing the well group (the closest circular well network to the branch center well 3) outwards to the second ring of well groups, the second row of gas injection wells is ignited using a method of air transfer and ignition. One well group is pushed outwards at a time, with the remaining gas injection wells injecting gas simultaneously. After three rings of outwards, for each new ring of gas injection wells, one ring of old gas injection wells is removed. The horizontal section of the sidetracked center well 3 is located in the middle of the reservoir, with a length two-thirds of the distance between the center gas injection well (sidetracked center well 3) and the first ring of gas injection wells. The distance between the first ring of gas injection wells 2 and the sidetracked branch center well 3 is 120m. The distance between the second ring of gas injection wells and subsequent adjacent gas injection wells is 360m. The vertical well is divided into two perforation sections: the production section is located at the bottom of the oil layer, and the gas injection section is located in the upper part of the oil layer.

[0074] The specific method for high-temperature ignition gas injection into the side-drilled branch center well is as follows: First, inject unheated air into the reservoir of the side-drilled branch center well for 9 days to establish a gas-liquid flow communication channel. The unheated air injection intensity is 100 standard cubic meters per meter of oil layer. After the unheated air injection time reaches the required time, inject the designed amount of crude oil into the reservoir. The designed amount of crude oil injection is calculated according to the above formulas (1) to (3). After the crude oil injection is completed, ignite the reservoir. First, inject room temperature oxygen-enriched air for 3 days, and then inject hot air at a temperature of 180℃ into the reservoir. The injection intensity of oxygen-enriched air and hot air is... The temperature of the reservoir was 800 standard cubic meters per meter of oil layer. Hot air injection (type 1) was carried out over 6 days, causing the reservoir to expand due to heat, squeezing out oil and gas from the pores. The oil and gas mixed with hot air and oxygen-enriched air (type 1) to quickly reach ignition conditions. Subsequently, hot oxygen-enriched air (type 2) at 300°C was injected into the reservoir to establish a thermal internal driving zone. The injection intensity of oxygen-enriched air (type 2) was 1000 standard cubic meters per meter of oil layer, and the injection time was 50 days, thereby establishing a gas / vapor phase zone in the reservoir. Then, unheated air was injected to achieve injection-production balance. During the establishment of injection-production balance, unheated air was injected into the reservoir at the same intensity as in Example 4. The crude oil recovery rate in Application Case 3 was 32%.

[0075] The thermal internal drive method for improving the recovery rate of low-grade oil reservoirs according to the present invention does not require changes to the well network structure. By utilizing the existing well network structure in conjunction with the ignition and gas injection methods, it can improve the recovery rate of low-permeability light oil reservoirs, achieving a recovery rate of 30% to 40%. For reservoirs with similar reservoir conditions, the recovery rate of conventional oil production methods is far lower than that of the present invention, typically ranging from 3% to 5%.

[0076] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for improving the recovery rate of low-grade oil reservoirs through thermal internal drive, characterized in that... include: Utilizing the existing area well network design to form a circular well network, firstly, wells in structurally high locations are selected, and the central well is sidetracked to create a sidetracked branch center well. This branch center well is then connected to several adjacent gas injection wells. Next, the branch center well undergoes high-temperature ignition and gas injection, injecting a certain volume of mixed gas into the first circular area reservoir of the circular well network to increase the oil saturation and temperature field near the injection well. Simultaneously with gas injection from the branch center well, adjacent first-line injection wells begin production. Once the bottom-hole temperature of the injection wells reaches a certain level, gas injection begins. When the ignition line is pushed outward from the first ring of wells to the second ring, the second row of injection wells is ignited using a transfer-air-ignition method. One well group is pushed outward each time, with the remaining injection wells injecting gas simultaneously. After three rings, for each new ring of injection wells, one old ring of injection wells is removed. Specific details include... The process involves: utilizing existing area well networks to create a circular well network; firstly, selecting five wells in high-altitude areas and modifying the central well to form a side-drilled branch center well; establishing a connection between the side-drilled branch center well and four adjacent gas injection wells; then, high-temperature ignition and gas injection are performed on the side-drilled branch center well, injecting a mixed gas volume of 1 to 2 times the pore volume of the first circular area reservoir in the circular well network to increase the oil saturation and temperature field near the gas injection well; simultaneously, the four adjacent gas injection wells begin production; once the bottom temperature of the gas injection wells reaches 150℃, gas injection begins; when the ignition line is pushed outward from the first ring of well groups to the second ring of well groups, the second row of gas injection wells is ignited using a method of air transfer and ignition connection, pushing out one well group at a time, with the remaining gas injection wells injecting gas simultaneously; after pushing out three rings, for each new ring of gas injection wells added, one old ring of gas injection wells is removed.

2. The method for improving the recovery rate of low-grade oil reservoirs by thermal internal drive according to claim 1, characterized in that... The horizontal section of the side-drilled center well is located in the middle of the reservoir, and its length is two-thirds of the distance between the center gas injection well and the first ring of gas injection wells. The distance between the first ring of gas injection wells and the side-drilled branch center well is 100m to 150m. The distance between the second ring of gas injection wells and the subsequent adjacent gas injection wells is 300m to 400m. The vertical well is divided into two perforation sections: the production section is located at the bottom of the oil layer, and the gas injection section is located at the top of the oil layer.

3. The method for improving the recovery rate of low-grade oil reservoirs by thermal internal drive according to claim 1 or 2, characterized in that... The specific method for high-temperature ignition gas injection into the side-drilled branch center well is as follows: First, inject unheated air into the reservoir of the side-drilled branch center well for 7 to 14 days to establish a gas-liquid flow communication channel. The unheated air injection intensity is 100 standard cubic meters per meter of oil layer. After the unheated air injection time reaches the required duration, the designed amount of crude oil is injected into the reservoir. After the crude oil injection is completed, the reservoir is ignited. First, oxygen-enriched air at room temperature is injected for 3 to 5 days. Then, hot air at a temperature of 150°C to 200°C is injected into the reservoir. The injection intensity of both oxygen-enriched air and hot air is 800 standard cubic meters per meter of oil layer. The injection time of hot air is 5 to 7 days, which causes the reservoir to expand due to heat, squeezing out the oil and gas in the pores. The oil and gas mix with hot air and oxygen-enriched air to quickly reach the ignition conditions. Subsequently, hot oxygen-enriched air at 250°C to 300°C is injected into the oil layer to establish a thermal internal drive zone. The injection intensity of oxygen-enriched air is 1000 standard cubic meters per meter of oil layer. The injection time of oxygen-enriched air is 45 to 75 days, thereby establishing a gas / vapor phase zone in the reservoir. Then, unheated air is injected to achieve injection-production balance.

4. The method for improving the recovery rate of low-grade oil reservoirs by thermal internal drive according to claim 3, characterized in that... The reservoir conditions are: porosity less than 15% and permeability less than 50 × 10⁻⁶. -3 μm, oil layer thickness 5m to 25m, crude oil viscosity less than 10mPa·s, reservoir temperature greater than 70℃.

5. The method for improving the recovery rate of low-grade oil reservoirs by thermal internal drive according to claim 4, characterized in that... During the injection-production balance process, unheated air is injected into the reservoir at an injection intensity of [value missing]. M , ,in M For the intensity of unheated air injection, m 3 , / (d·m); R is the combustion radius, m; n is the total number of injection wells; A is the air consumption required to burn a unit volume of core and reach 400℃, m 3 / m 3 ; For air utilization rate, % φ represents porosity, % denoted as reservoir utilization rate (%), P as reservoir pressure (MPa), Z as air compressibility factor, and α as the thermal internal drive reservoir constant (2 to 3).

6. The method for improving the recovery rate of low-grade oil reservoirs by thermal internal drive according to claim 5, characterized in that... The crude oil injection design volume is calculated as shown in equation (1). q=(Q-Q0) / (42705000*60%) (1) In formula (1), q represents the design amount of crude oil injection, Q represents the total heat required for ignition, 42705000 represents the unit heat of crude oil, 60% represents the utilization coefficient of injected oil, and Q0 is one-quarter to one-third of Q.

7. The method for improving the recovery rate of low-grade oil reservoirs by thermal internal drive according to claim 6, characterized in that... The total heat required for ignition is calculated as shown in equation (2). Q=π(r e 2 -r w 2 (HρC(T-Ti) (2) In equation (2), Q represents the total heat required for ignition, and r e The ignition radius, r w The values ​​represent the wellbore radius, H represents the reservoir thickness (m), ρ represents the reservoir density, C represents the reservoir specific heat capacity, T represents the temperature at which the reservoir expands due to heat and squeezes out crude oil, and Ti represents the initial temperature of the reservoir. All units are in the International System of Units (SI).

8. The method for improving the recovery rate of low-grade oil reservoirs by thermal internal drive according to claim 7, characterized in that... The product of oil layer density and oil layer specific heat capacity is calculated as shown in equation (3). ρC=(1-φ)ρ s C s +fr o C o (1-S) wc )+fr w C w S wc (3) In equation (3), ρ represents the oil layer density, C represents the oil layer specific heat capacity, φ represents porosity, and ρ s C represents the density of rock. s ρ represents the specific heat capacity of rocks. o C represents the density of the injected oil. o S represents the specific heat capacity of the injected oil. wc ρ represents the degree of bound water saturation. w C represents the density of water. w This indicates the specific heat capacity of water.

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