Method for improving SAGD development effect through double horizontal wells and composite solvent

Abstract

The invention discloses a method for improving the SAGD development effect through double horizontal wells and a composite solvent. The method comprises the following steps: a circulating preheating stage: injecting steam and a composite solvent containing dimethyl ether and alcohol through long pipes of a horizontal injection well and a horizontal production well, and producing liquid through short pipes of the horizontal injection well and the horizontal production well; in the SAGD production stage, after the injection and production wells are in thermal communication, steam and the composite solvent are injected through the long pipe and the short pipe of the horizontal injection well, and production is conducted from the short pipe through an underground pump of the horizontal production well. Wherein the horizontal injection well and the horizontal production well are double horizontal well sets, the horizontal injection well is located on the upper portion, the horizontal production well is located on the lower portion, the horizontal injection well and the horizontal production well are transversely arranged in a staggered mode, and horizontal sections are drilled oppositely. According to the method, composite solvent viscosity reduction and transverse dislocation double horizontal wells are combined, the triple advantages of differential pressure compensation, gravity oil drainage and solvent viscosity reduction are brought into full play, the reserve utilization degree of strong heterogeneity thin-layer super heavy oil is increased, and meanwhile the oil yield and the oil-gas ratio are increased.

Description

Technical Field

[0001] The invention relates to the technical field of heavy oil exploitation in oil field development, and in particular to a method for improving SAGD development effect using a double horizontal well and a composite solvent. Background Art

[0002] The viscosity of crude oil in super-heavy oil reservoirs is high, and the viscosity of degassed crude oil is greater than 50,000 mPa.s at reservoir temperature. Steam-assisted gravity drainage technology is an effective development technology for the exploitation of heavy oil and super-heavy oil. At present, super-heavy oil reservoirs at home and abroad are generally developed using dual horizontal well steam-assisted gravity drainage technology (SAGD). This technology was proposed by Butler of Canada and was initially successful in the UTF test in Canada. It has been widely used in Canada, Venezuela, China, Russia and other countries, and has achieved remarkable application results. This process uses steam as a heat source and relies on the gravity of the crude oil itself after viscosity reduction to exploit heavy oil. The SAGD development method combines the advantages of horizontal wells and gravity-stabilized drainage, and has the characteristics of high production and high recovery rate (up to 50-75%). It is currently an effective technology for the development of super-heavy oil. Summary of the invention

[0003] In order to enrich the process routes and increase the selection space, the embodiment of the present invention provides a method for improving the SAGD development effect by using a dual horizontal well and a composite solvent, which combines the viscosity reduction of the composite solvent and the lateral dislocation of the dual horizontal well to improve the reserve utilization of the highly heterogeneous thin layer ultra-heavy oil, while improving the oil production and the oil-gas ratio.

[0004] In a first aspect, an embodiment of the present invention provides a dual horizontal well, comprising an upper horizontal injection well and a lower horizontal production well;

[0005] The horizontal injection wells and the horizontal production wells are arranged in a staggered manner in the transverse direction;

[0006] The horizontal sections of the horizontal injection well and the horizontal production well are drilled towards each other.

[0007] In some embodiments, the vertical distance between the horizontal injection well and the horizontal production well is 3 to 5 m, the lateral distance is 3 to 5 m, and the inclined distance is 4 to 6 m.

[0008] In some embodiments, the lateral distance between the dual horizontal well and an adjacent dual horizontal well in the drilled oil layer is 70-110 m.

[0009] In some embodiments, the thickness of the oil layer drilled by the dual horizontal wells is 8 to 15 m, and the oil layer is an extra heavy oil layer.

[0010] In some embodiments, the horizontal production well is 1 to 2 meters away from the bottom of the oil layer.

[0011] In a second aspect, an embodiment of the present invention provides a method for improving the SAGD development effect using a composite solvent, comprising using the above-mentioned dual horizontal well to perform the following steps:

[0012] In the circulation preheating stage, steam and a composite solvent containing dimethyl ether and alcohols are injected through the long tube of the horizontal injection well and the long tube of the horizontal production well, and liquid is produced through the short tube of the horizontal injection well and the short tube of the horizontal production well;

[0013] During the SAGD production phase, after the injection and production wells are thermally connected, steam and the composite solvent are injected through the long pipe and short pipe of the horizontal injection well, and produced from the short pipe through the downhole pump of the horizontal production well.

[0014] In some embodiments, the concentration of dimethyl ether and alcohol in the mixture of the injected steam and the composite solvent containing dimethyl ether and alcohol is 8-20 vol%.

[0015] In some embodiments, it also includes:

[0016] During the SAGD production stage, the pressure difference between the injection and production wells is maintained at 0.2-0.8 MPa, the production-injection ratio is maintained at 1.1-1.3, and the temperature difference between the injection and production wells is controlled at 0-15°C.

[0017] In some embodiments, it also includes:

[0018] In the circulation preheating stage, dimethyl ether and alcohols are separated from the produced fluid for circulation injection.

[0019] In some embodiments, it also includes:

[0020] In the SAGD production stage, after the set conditions are reached, the injection of the composite solvent is stopped and the non-condensable gas is injected instead.

[0021] In some embodiments, the non-condensable gas includes natural gas, N2, CO2 and flue gas.

[0022] In some embodiments, the injecting non-condensable gas further comprises:

[0023] The initial surface volume ratio of injected non-condensable gas to steam is controlled at 10 to 30, and the proportion of steam is reduced year by year according to the set ratio until the end of the SAGD production stage.

[0024] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0025] (1) When conventional steam stimulation or SAGD development is used for thin-layer ultra-heavy oil, the oil layer is thin and the production decreases rapidly. The double horizontal wells provided in the embodiments of the present invention are applied to SAGD development with high production and long stable production period: the double horizontal wells are arranged in a horizontally staggered manner to reduce the vertical displacement between the injection and production wells, increase the steam cavity height above the steam injection well, and utilize the effects of gravity oil drainage and lateral displacement to achieve high production and long stable production period.

[0026] (2) The dual horizontal well provided in the embodiment of the present invention has a high oil-gas ratio and high economic benefits: there is a large lateral offset displacement between the injection and production wells, which makes steam channeling less likely to occur, reducing heat loss, and in the production stage, it can reduce steam consumption while increasing oil production. Therefore, the oil-gas ratio is high and the economic benefits are high.

[0027] (3) The double horizontal well provided in the embodiment of the present invention has a high utilization rate of the horizontal wellbore: the horizontal injection well and the horizontal production well are arranged in opposite directions to each other, which can compensate for the problems of pressure drop from the heel to the toe of the steam injection well and the large heel pressure difference, small toe pressure difference and low utilization rate of the horizontal section caused by insufficient pump penetration of the production well when the conventional double horizontal wells are arranged in the same direction; at the same time, the injection well and the production well are arranged in opposite directions to balance the pressure difference between the injection and production wells and improve the uniformity of the horizontal section utilization of the production well; in addition, due to the lateral displacement of the injection and production wells, when there is an interlayer between the wells, the injection pressure can be appropriately increased to force the interlayer to break through, thereby improving the vertical utilization rate of the reservoir.

[0028] (4) The method for improving the SAGD development effect by using a composite solvent provided in an embodiment of the present invention, wherein the injected fluid is a composite solvent and steam, and the viscosity reduction effect and thermal effect of the solvent can be utilized simultaneously. Dimethyl ether in the composite solvent has a strong viscosity reduction effect, that is, it is soluble in both oil and water, and can quickly transfer mass in the reservoir to achieve rapid viscosity reduction; the latent heat (kJ / kg) of the alcohol solvent in the composite solvent is more than 3 times that of conventional hydrocarbon solvents (e.g., n-hexane), so its thermal effect is relatively high, so the injected composite solvent has a strong viscosity reduction effect and a strong heat carrying capacity, and can be transported to the front edge of the steam chamber together with steam to achieve the effect of rapid oil drainage; in addition, the price of alcohol solvents is lower than that of n-hexane, and the price of alcohol solvents is less affected by oil price fluctuations, so the economic benefits are better when injecting alcohol solvents. Conventional alcohols (e.g., methanol, ethanol) have a higher vapor pressure than water, so a lower temperature can be achieved at the same operating pressure, thereby achieving the effect of reducing heat loss (especially for thin-layer reservoirs).

[0029] (5) The method for improving the SAGD development effect by using a composite solvent provided in an embodiment of the present invention combines the composite solvent viscosity reduction and the lateral dislocation of the double horizontal wells to improve the reserve utilization of the highly heterogeneous thin layer of ultra-heavy oil, and at the same time improve the oil production and oil-gas ratio. Compared with the huff-and-puff reservoir, the utilization range is large and the recovery rate is high; compared with conventional SAGD, the production is high and the oil-gas ratio is high.

[0030] (6) The method for improving the SAGD development effect by using a composite solvent provided in an embodiment of the present invention is applicable to thin-layer ultra-heavy oil reservoirs with underground degassed crude oil viscosity greater than 50,000 cp and oil layer thickness greater than 8 m, thereby broadening the technical boundaries of steam-assisted gravity drainage.

[0031] (7) The method for improving the SAGD development effect by using a composite solvent provided in an embodiment of the present invention separates dimethyl ether and alcohols from the output fluid during the circulation stage for circulation injection. The dimethyl ether and alcohol solvents in the output fluid are easy to separate and can be achieved through a simple pressure reduction operation, thereby saving costs.

[0032] (8) The method for improving the SAGD development effect by using a composite solvent provided in an embodiment of the present invention stops injecting the composite solvent after the set conditions are reached in the SAGD production stage, and injects non-condensable gas instead. The non-condensable gas can displace the composite solvent in the wellbore and formation, so that the composite solvent can be recycled, thereby increasing economic benefits.

[0033] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0034] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0036] Figure 1 A three-dimensional schematic diagram of the double horizontal well arrangement in the first embodiment of the present invention;

[0037] Figure 2 A schematic diagram of a vertical section of a double horizontal well in Embodiment 1 of the present invention;

[0038] Figure 3 This is a flow chart of the method for improving the SAGD development effect with a composite solvent in Example 2 of the present invention;

[0039] Figure 4 It is a schematic diagram of the cross section of the horizontal wellbore along the staggered and opposite double horizontal wells in the production stage of the second embodiment of the present invention. DETAILED DESCRIPTION

[0040] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0041] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0042] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which the invention belongs. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0043] In the description of the present invention, it should be noted that the terms "include", "including", "have", "contain" and the like are open terms, meaning including but not limited to.

[0044] The inventor found in the work that the current conventional dual horizontal well SAGD well pattern mode is greatly limited by the thickness of the oil layer. The thickness of the oil layer directly affects the steam chamber oil leakage height. The greater the oil leakage height, the higher the production, the lower the heat loss of steam in the cap rock, and the better the production effect. If the dual horizontal well wants to obtain a good production effect, the thickness of the oil layer must be greater than 15m. When the thickness of the continuous oil layer is less than 15m, considering that the oil leakage spacing between the injection and production wells is 5m, the actual steam chamber oil leakage height is less than 10m. Although SAGD development can be implemented technically, the production and oil-gas ratio are relatively low, and the economic benefits are poor. In addition, considering that the reservoir has poor physical properties, severe heterogeneity, more developed interlayers, and thin thickness, the steam-assisted development effect is worse, which is characterized by low oil production and low oil-gas ratio. At present, for this type of reservoir, oil fields generally use horizontal well steam throughput to produce. However, compared with SAGD, the steam throughput heating range is small, the recovery rate is low, and the reserve utilization degree is low. There are large reserves of highly heterogeneous thin-layer ultra-heavy oil reservoirs in Canada and China. How to improve the reserve utilization, production and oil-gas ratio of such reservoirs is an urgent problem to be solved in this field.

[0045] There have been many studies on solvent-assisted steam gravity drainage. The commonly used hydrocarbon solvents are C3, C4 or C6-C10, which are injected with steam to exert the synergistic effect of solvent viscosity reduction and steam viscosity reduction, thereby increasing production and oil-gas ratio. C3 and C4 are lighter hydrocarbon solvents, which mainly reduce viscosity outside the steam chamber, but have weak heat carrying capacity, and their effect on improving steam-assisted gravity drainage development is limited. C6-C9 are heavier hydrocarbon solvents, which are more difficult to migrate outside the steam chamber. They mainly reduce viscosity near the wellbore, have weak heat carrying capacity, and have limited improvement in development effect. Moreover, heavier hydrocarbon solvents are often more expensive, so their economic benefits are poor and they are not suitable for long-term use. For example, a solvent-assisted horizontal well-to-well connection method proposed in 201510171051.5 mainly uses heavy hydrocarbon solvents, which mainly act in a small range between injection and production wells. In addition, 201510324029.X proposed a single horizontal well solvent-assisted production method, in which the injected solvent is a composite gas solvent of C1-C4 organic compounds and CO2, and the well pattern adopted is a single horizontal well, which has low cost per well, low drilling technology requirements, water-free process and low energy consumption. However, the solvent used in this method has poor heat carrying capacity, and the oil production technology that relies solely on solvent mass diffusion and viscosity reduction usually has low oil production. 201310553419.5 proposed a method and well pattern structure for solvent-assisted steam-assisted gravity drainage to produce heavy oil reservoirs. This well pattern can improve the gravity drainage effect of thick heterogeneous reservoirs, but it requires the assistance of multiple branch wells and / or vertical wells, and the drilling cost is high and the drilling difficulty is relatively large. 202210375485.7 proposed a method for solvent-assisted low-temperature oxidation air injection and huff-and-puff to recover heavy oil. This method extracts light components from the heavy oil by injecting solvent (mainly C4-C10), causing it to undergo a low-temperature oxidation reaction with oxygen. When the oxygen is fully consumed, the viscosity of the heavy oil is reduced, the quality of the heavy oil is improved, and the flowability of the heavy oil is enhanced. However, this method has a limited range of reservoir mobilization, similar to steam injection in horizontal wells, and has a limited range for improving recovery. 202010809783.3 proposed a composite development method for solvent-assisted flooding of shallow and thin layers of weak bottom water heavy oil. This method injects steam and solvent near the bottom water layer, which can easily cause steam and solvent to enter the water layer, resulting in large losses.

[0046] There is currently no economical and effective development method for highly heterogeneous thin-layer ultra-heavy oil reservoirs. An embodiment of the present invention provides a method for improving the SAGD development effect by using a dual horizontal well and a composite solvent, which combines the composite solvent viscosity reduction and the lateral dislocation of the dual horizontal well to improve the reserve utilization of the highly heterogeneous thin-layer ultra-heavy oil, while also improving the oil production and the oil-gas ratio.

[0047] Definitions of Abbreviations and Key Terms:

[0048] Extra heavy oil: Crude oil with a degassed viscosity greater than 50,000 mPa.s at reservoir temperature.

[0049] Steam Assisted Gravity Drainage, referred to as SAGD, consists of a pair of parallel horizontal wells. The upper horizontal well is injected with high-dryness, high-temperature, high-pressure steam, and the heated crude oil and condensate flow to the lower horizontal well under the action of gravity for production. Usually, the vertical distance between the steam injection well and the horizontal well is 5m.

[0050] Composite solvent: refers to the solvent injected during the development of oil and gas fields, which is composed of two or more solvents.

[0051] Oil-steam ratio: the volume ratio of oil production to injected steam. It includes instantaneous oil-steam ratio and cumulative oil-steam ratio. The instantaneous oil-steam ratio is the ratio of daily oil production to daily injected steam; the cumulative oil-steam ratio is the ratio of cumulative oil production to cumulative injected steam.

[0052] Thin layer extra-heavy oil reservoir: an extra-heavy oil reservoir with an effective oil layer thickness of 8 to 15 m.

[0053] Heterogeneous reservoir: a reservoir whose physical properties vary greatly in the horizontal and vertical directions.

[0054] Embodiment 1

[0055] Embodiment 1 of the present invention provides a dual horizontal well for SAGD development, referring to Figure 1 As shown, the dual horizontal well includes an upper horizontal injection well 1 and a lower horizontal production well 2.

[0056] The horizontal injection well 1 and the horizontal production well 2 are deployed in a staggered manner in the lateral direction, and the horizontal sections of the horizontal injection well 1 and the horizontal production well 2 are drilled toward each other.

[0057] The horizontal section lengths of the horizontal injection well 1 and the horizontal production well 2 are both 300 to 800 m.

[0058] The horizontal production well 2 is 1 to 2 meters away from the bottom of the oil layer.

[0059] When conventional steam stimulation or SAGD development is used for thin-layer ultra-heavy oil, the oil layer is thin and the production decreases rapidly. The double horizontal wells provided in the embodiment of the present invention are used for SAGD development with high production and long stable production period: the double horizontal wells are arranged in a horizontally staggered manner to reduce the vertical displacement between the injection and production wells, increase the steam cavity height above the steam injection well, and utilize the effects of gravity oil drainage and lateral displacement to achieve high production and long stable production period.

[0060] The double horizontal well provided in the embodiment of the present invention has a high oil-gas ratio and high economic benefits: there is a large offset displacement between the injection and production wells, steam channeling is not easy to occur, heat loss is reduced, and in the production stage, the steam consumption can be reduced while the oil production is increased. Therefore, the oil-gas ratio is high and the economic benefits are high.

[0061] The double horizontal well provided by the embodiment of the present invention has a high utilization degree of the horizontal wellbore: the horizontal injection well and the horizontal production well are arranged in opposite directions to each other, which can compensate for the problems of pressure drop from the heel to the toe of the steam injection well and insufficient pump descent depth of the production well, resulting in large heel pressure difference, small toe pressure difference and low utilization degree of the horizontal section when the conventional double horizontal wells are arranged in the same direction; at the same time, the injection well and the production well are arranged in opposite directions, which can balance the pressure difference between the injection and production wells and improve the uniformity of the horizontal section utilization of the production well; in addition, due to the lateral displacement of the injection and production wells, when there is an interlayer between the wells, the injection pressure can be appropriately increased to force the interlayer to break through, thereby improving the vertical utilization degree of the reservoir.

[0062] In some embodiments, reference Figure 2 As shown, the vertical distance between the horizontal injection well and the horizontal production well is 3 to 5 m, the lateral distance is 3 to 5 m, and the inclined distance is 4 to 6 m.

[0063] The slope distance between the horizontal injection well and the horizontal production well is basically consistent with the vertical distance of the conventional SAGD double horizontal wells. Preferably, the slope distance between the horizontal injection well and the horizontal production well is 5m.

[0064] The thickness of the oil layer drilled by the double horizontal wells is 8 to 15 meters, and the oil layer is an ultra-heavy oil layer.

[0065] The lateral distance between the double horizontal well and the adjacent double horizontal well in the drilled oil layer is 70 to 110 m.

[0066] The dual horizontal well in the embodiment of the present invention is particularly suitable for thin-layer extra-heavy oil reservoirs; it is still applicable to extra-heavy oil reservoirs with a thickness greater than 15 m, but its advantages over conventional SAGD dual horizontal wells are not as prominent as those in thin-layer extra-heavy oil reservoirs.

[0067] Embodiment 2

[0068] Embodiment 2 of the present invention provides a method for improving the SAGD development effect with a composite solvent, see Figure 3 As shown, using the above-mentioned dual horizontal well, perform the following steps:

[0069] Step S31: In the circulation preheating stage, steam and a composite solvent containing dimethyl ether and alcohols are injected through the long pipe of the horizontal injection well and the long pipe of the horizontal production well, and liquid is produced through the short pipe of the horizontal injection well and the short pipe of the horizontal production well.

[0070] The steam and composite solvent may be injected after mixing or by plug injection. The specific injection method may be selected according to the injection process conditions on site.

[0071] The horizontal injection well and the horizontal production well are simultaneously circulated and preheated by long-tube injection and short-tube production.

[0072] The concentration of dimethyl ether and alcohol in the mixture of the injected steam and the composite solvent containing dimethyl ether and alcohol is 8-20 vol%. The alcohol can be methanol and / or ethanol.

[0073] During the circulation preheating stage, dimethyl ether and alcohols are separated from the produced fluid for circulation injection.

[0074] Step S32: During the SAGD production phase, after the injection and production wells are thermally connected, steam and composite solvent are injected through the long pipe and short pipe of the horizontal injection well, and produced from the short pipe through the downhole pump of the horizontal production well.

[0075] After determining thermal connectivity according to the on-site thermal connectivity determination method, it was shown that connectivity between the injection and production wells was formed, and SAGD production was switched to maintain the pressure difference between the injection and production wells at 0.2-0.8 MPa, the production-injection ratio at 1.1-1.3, and the temperature difference between the injection and production wells at 0-15°C.

[0076] See also Figure 4 As shown, it is a schematic diagram of the cross-section of the staggered and opposite double horizontal wells along the horizontal wellbore during the SAGD production stage, wherein 11 is the screen pipe of the injection well, 12 is the long oil pipe of the injection well, 13 is the short oil pipe of the injection well, and 14 is the oil pipe coupling; 21 is the screen pipe of the production well, 22 is the temperature measuring pipeline of the production well, 23 is the downhole pump of the production well, that is, the oil production pump, and 24 is the short oil pipe of the production well.

[0077] During the SAGD production phase, when the set conditions are met, the injection of the composite solvent is stopped and non-condensable gas is injected instead.

[0078] Wherein, reaching the set condition may be determining that the steam chamber has expanded to the boundary of the double horizontal well group.

[0079] Non-condensable gases include natural gas, N2, CO2 and flue gas.

[0080] During the non-condensable gas injection and production process, the initial surface volume ratio of injected non-condensable gas to steam is controlled at 10-30, and the proportion of steam is reduced year by year according to the set ratio until the end of the SAGD production stage.

[0081] Specifically, the steam ratio may be reduced by 10 vol% each year, that is, the volume ratio of injected non-condensable gas to steam increases at a rate of 10 vol% each year until the development is completed.

[0082] During the SAGD production stage, when injecting non-condensate gas for production, the pressure difference between the injection and production wells still needs to be maintained at 0.2-0.8 MPa, the production-injection ratio needs to be maintained at 1.1-1.3, and the temperature difference between the injection and production wells needs to be controlled at 0-15°C.

[0083] The method for improving the SAGD development effect by using a composite solvent provided by an embodiment of the present invention, wherein the injected fluid is a composite solvent and steam, and the viscosity reduction effect and thermal effect of the solvent can be utilized simultaneously. The dimethyl ether in the composite solvent has a strong viscosity reduction effect, that is, it is soluble in both oil and water, and can quickly transfer mass in the oil reservoir to achieve rapid viscosity reduction; the latent heat (kJ / kg) of the alcohol solvent in the composite solvent is more than 3 times that of the conventional hydrocarbon solvent (e.g., n-hexane), so its thermal effect is relatively high, so the injected composite solvent has a strong viscosity reduction effect and a strong heat carrying capacity, and can be transported to the front edge of the steam chamber together with the steam to exert the effect of rapid oil drainage; in addition, the price of the alcohol solvent is lower than that of the n-hexane price, and the price of the alcohol solvent is less affected by the fluctuation of the oil price, so the economic benefit is better when the alcohol solvent is injected. The vapor pressure of conventional alcohols (e.g., methanol and ethanol) is higher than that of water, so a lower temperature can be achieved at the same operating pressure, thereby achieving the effect of reducing heat loss (especially for thin-layer oil reservoirs).

[0084] The method for improving the SAGD development effect by using a composite solvent provided in the embodiment of the present invention combines the composite solvent viscosity reduction and the lateral dislocation of the double horizontal wells to improve the reserve utilization of the highly heterogeneous thin layer of ultra-heavy oil, and at the same time improve the oil production and oil-gas ratio. Compared with the huff-and-puff oil reservoir, the utilization range is large and the recovery rate is high; compared with conventional SAGD, the production is high and the oil-gas ratio is high.

[0085] The method for improving the SAGD development effect by using a composite solvent provided in an embodiment of the present invention is applicable to thin-layer ultra-heavy oil reservoirs with underground degassed crude oil viscosity greater than 50,000 cp and oil layer thickness greater than 8 m, thereby broadening the technical boundaries of steam-assisted gravity drainage.

[0086] The method for improving the SAGD development effect by using a composite solvent provided in an embodiment of the present invention separates dimethyl ether and alcohols from the output fluid during the circulation stage for circulation injection. The dimethyl ether and alcohol solvents in the output fluid are easy to separate, which can be achieved by a simple pressure reduction operation, thereby saving costs.

[0087] The method for improving the SAGD development effect by using a composite solvent provided in an embodiment of the present invention stops injecting the composite solvent and injects non-condensable gas instead after the set conditions are reached in the SAGD production stage. The non-condensable gas can displace the composite solvent in the wellbore and formation, so that the composite solvent can be recycled, thereby increasing economic benefits.

[0088] Embodiment 3

[0089] Example 3 of the present invention provides an on-site exploitation implementation plan for a super-heavy oil reservoir, and predicts and compares the exploitation effect of this example with that of steam stimulation and conventional SAGD development.

[0090] (1) Reservoir parameters

[0091] Basic reservoir parameters: reservoir burial depth is 250m, reservoir temperature is 20℃, original reservoir pressure is 2MPa, porosity is 30%, oil saturation is 75%, permeability is 2000mD, reservoir thickness is 9m; crude oil degassing viscosity under reservoir conditions is 55000mPa.s.

[0092] (2) Well layout parameters

[0093] The offset horizontal well layout mode of embodiment 1 of the present invention is adopted, the length of the horizontal well section is 400m, the well group spacing is 100m, the injection well and the production well spacing are 4m in lateral displacement and 3m in vertical displacement, and the production horizontal well is arranged at 1m from the bottom of the oil layer.

[0094] (3) Injection and production parameters

[0095] 1) Circulation preheating stage: long pipe injection of steam and composite solvent, total ground injection speed 70m 3 / d, the steam bottom hole dryness is 75%, the preferred composite solvent injection concentration is 10vol% (5vol% dimethyl ether + 5vol% methanol), the maximum injection pressure is 3.5MPa, the short pipe minimum bottom hole flow pressure is 3.3MPa, and the maximum liquid production is 70t / d. After 120 days of circulation preheating, the upper and lower horizontal wells are connected, the well temperature reaches above 100℃, and the SAGD production stage is entered.

[0096] 2) SAGD production stage: Steam and composite solvent are injected into the long and short pipes of Well I (for the convenience of description, the horizontal injection well is referred to as Well I and the horizontal production well is referred to as Well P) at the same time, and the total surface injection rate is 70m 3 / d, the bottom hole steam dryness is 75%, the preferred concentration of the co-injected composite solvent is 15vol% (10vol% dimethyl ether + 5vol% methanol), and the maximum bottom hole injection pressure is 4MPa; take out the long section pipe from the P well, pump it down to 100m below point A, and switch to production, the production-injection ratio is controlled at about 1.2, and the temperature difference between wells is controlled within 0-15℃;

[0097] 3) When the oil production starts to decline, indicating that the steam chamber begins to decline, or when the temperature of the wells around the well group is observed to indicate that the steam chamber begins to decline, Well I stops injecting the composite solvent and switches to injecting natural gas (mainly CH4). The steam injection rate is reduced at a rate of 6 vol% / year, i.e., it starts at 63m 3 / d, 57m in the second year 3 / d, 51m in the third year 3 / d...; the preferred initial injection volume ratio of natural gas to steam is 15, and then increases by 10% each year, that is, the initial non-condensate injection rate is 945Sm 3 / d, 1040Sm in the second year 3 / d, 1143Sm in the third year 3 / d……), the temperature difference between production wells in P well is still controlled within 0-15℃ until the end of development.

[0098] As shown in Table 1, the production effects of this embodiment are compared with those of conventional steam stimulation and conventional SAGD development. During the 15-year development period, the recovery factor of steam stimulation is the lowest, only 20.82%, and the oil-gas ratio is low, only 0.07, and the average daily oil production is 4.7 t / d; the recovery factor of conventional SAGD development can reach 45.88%, but the oil-gas ratio is low, only 0.15, and the average daily oil production is 10.3 t / d; this embodiment can achieve the best development effect, with an average daily oil production of 12.3 t / d, and a recovery factor of 54.8%, which is more than 8 percentage points higher than conventional SAGD, and the oil-gas ratio is increased by 0.06.

[0099] Table 1

[0100] Technology Comparison Development time, years Cumulative oil-gas ratio Recovery rate, % Average daily oil production, t / d Steam intake 15 0.07 20.82 4.7 Conventional SAGD 15 0.15 45.88 10.3 This embodiment 15 0.21 54.80 12.3

[0101] Embodiment 4

[0102] Example 4 of the present invention provides another on-site implementation plan for an ultra-heavy oil reservoir, and predicts and compares the production effects of this example with those of conventional SAGD development.

[0103] (1) Reservoir parameters

[0104] Basic reservoir parameters: reservoir burial depth is 150m, reservoir temperature is 13℃, original reservoir pressure is 1.5MPa, porosity is 33%, oil saturation is 78%, permeability is 4000mD, reservoir thickness is 12m; crude oil degassing viscosity under reservoir conditions is 100000mPa.s.

[0105] (2) Well layout parameters

[0106] The offset horizontal well layout mode of the present invention is adopted, the length of the horizontal well section is 800m, the well group spacing is 80m, the injection well and the production well spacing are 3m in lateral displacement and 4m in vertical displacement, and the production horizontal well is arranged 1m from the bottom of the oil layer.

[0107] (3) Injection and production parameters

[0108] 1) Circulation preheating stage: long pipe injection of steam and composite solvent, total ground injection speed 120m 3 / d, steam bottom hole dryness is 75%, the preferred composite solvent injection concentration is 20vol% (12vol% dimethyl ether + 8vol% methanol), the maximum injection pressure is 2.5MPa, the short pipe minimum bottom hole flow pressure is 2.3MPa, and the maximum liquid production is 120t / d. After 90 days of circulation preheating, the upper and lower horizontal wells are connected, the well temperature reaches above 100℃, and the SAGD production stage is entered.

[0109] 2) SAGD production stage: Steam and composite solvent are injected into the long and short pipes of Well I at the same time, and the total injection rate on the ground is 150m 3 / d, the bottom hole steam dryness is 75%, the preferred concentration of the co-injected composite solvent is 20vol% (12vol% dimethyl ether + 8vol% methanol), and the maximum bottom hole injection pressure is 2.5MPa; take out the long section pipe from the P well, pump it down to 100m below point A, and switch to production, the production-injection ratio is controlled at about 1.2, and the temperature difference between wells is controlled within 0-15℃;

[0110] 3) When the oil production starts to decline, indicating that the steam chamber begins to decline, or when the temperature of the wells around the well group is observed to indicate that the steam chamber begins to decline, Well I stops injecting the composite solvent and switches to injecting natural gas (mainly CH4). The steam injection rate is reduced at a rate of 10 vol% / year, i.e., it starts at 135m 3 / d, 122m in the second year 3 / d, 109m in the third year 3 / d...; The preferred initial injection volume ratio of natural gas to steam is 20, which is then increased by 10% each year, i.e. the initial non-condensate injection rate is 2700Sm 3 / d, 2970Sm in the second year 3 / d, 3267Sm in the third year 3 / d……), the temperature difference between production wells in P well is still controlled within 0-15℃ until the end of development.

[0111] As shown in Table 2, the production effects of this embodiment and conventional SAGD development are compared. During the 15-year development period, the recovery factor of conventional SAGD development can reach 34.02%, with an average daily oil production of 16.8 t / d, but the oil-gas ratio is low, only 0.11; this embodiment can achieve a better development effect, with an average daily oil production of 28.4 t / d, a recovery factor of 57.38%, which is more than 23 percentage points higher than conventional SAGD, and the oil-gas ratio is increased by 0.11.

[0112] Table 2

[0113] Technology Comparison Development time, years Cumulative oil-gas ratio Recovery rate, % Average daily oil production, t / d Conventional SAGD 15 0.11 34.02 16.8 This embodiment 15 0.22 57.38 28.4

[0114] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of protection of the present disclosure. The attached method claims present the elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0115] In the above detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that the embodiments of the claimed subject matter require more features than are clearly stated in each claim. On the contrary, as reflected in the appended claims, the invention is in a state of having less than all the features of the disclosed individual embodiments. Therefore, the appended claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0116] The above description includes examples of one or more embodiments. Of course, it is impossible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it should be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is covered in a manner similar to the term "including", just as "including," is explained as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or".

Claims

1. A double horizontal well, characterized in that: It includes a horizontal injection well at the top and a horizontal production well at the bottom; The horizontal injection wells and the horizontal production wells are arranged in a staggered manner in the transverse direction; The horizontal sections of the horizontal injection well and the horizontal production well are drilled towards each other.

2. The dual horizontal well according to claim 1, characterized in that: The vertical distance between the horizontal injection well and the horizontal production well is 3 to 5 m, the lateral distance is 3 to 5 m, and the inclined distance is 4 to 6 m.

3. The dual horizontal well according to claim 1, characterized in that: The lateral distance between the double horizontal well and the adjacent double horizontal well in the drilled oil layer is 70-110 m.

4. The dual horizontal well according to claim 1, characterized in that: The thickness of the oil layer drilled by the double horizontal wells is 8-15 m, and the oil layer is an extra-heavy oil layer.

5. The dual horizontal well according to any one of claims 1 to 4, characterized in that: The horizontal production well is 1 to 2 meters away from the bottom of the oil layer.

6. A method for improving SAGD development effect by using a composite solvent, characterized in that: The method comprises utilizing the dual horizontal well according to any one of claims 1 to 5 to perform the following steps: In the circulation preheating stage, steam and a composite solvent containing dimethyl ether and alcohols are injected through the long tube of the horizontal injection well and the long tube of the horizontal production well, and liquid is produced through the short tube of the horizontal injection well and the short tube of the horizontal production well; During the SAGD production phase, after the injection and production wells are thermally connected, steam and the composite solvent are injected through the long pipe and short pipe of the horizontal injection well, and produced from the short pipe through the downhole pump of the horizontal production well.

7. The method according to claim 6, characterized in that The concentration of dimethyl ether and alcohol in the mixture of the injected steam and the composite solvent containing dimethyl ether and alcohol is 8-20 vol%.

8. The method according to claim 6, characterized in that Also includes: During the SAGD production stage, the pressure difference between the injection and production wells is maintained at 0.2-0.8 MPa, the production-injection ratio is maintained at 1.1-1.3, and the temperature difference between the injection and production wells is controlled at 0-15°C.

9. The method according to claim 6, characterized in that Also includes: In the circulation preheating stage, dimethyl ether and alcohols are separated from the produced fluid for circulation injection.

10. The method according to claim 6, characterized in that Also includes: In the SAGD production stage, after the set conditions are reached, the injection of the composite solvent is stopped and the non-condensable gas is injected instead.

11. The method according to claim 10, characterized in that The non-condensable gas includes natural gas, N2, CO2 and flue gas.

12. The method according to claim 10, characterized in that The non-condensable gas injection further comprises: The initial surface volume ratio of injected non-condensable gas to steam is controlled at 10 to 30, and the proportion of steam is reduced year by year according to the set ratio until the end of the SAGD production stage.

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