A shale oil fracturing exploitation device and method

Abstract

The application provides a shale oil fracturing exploitation device and method, and belongs to the field of petroleum engineering.The device comprises: a conductive and heat-conductive layer arranged in a fracture zone formed in a fracturing process; a heating device arranged in a heating well; two electrodes arranged in a production well and the heating well respectively, and the two electrodes are connected through an electrode cable.The innovation of the application lies in that the electrodes and the heating device are heated and work simultaneously with the reservoir proppant conductive self-heating, the formation and the fracturing fracture are heated at the same time, the formation heating temperature is increased from 15 DEG C per month to 30 DEG C, the temperature heating time required for heating to 250-300 DEG C is 8-10 months, and the heating efficiency is increased by about 2 times; the single well oil production is increased from 3.2-8.0 m 3 / d to 15-20.0 m 3 / d, and the yield is increased by 3-5 times.

Description

Technical Field

[0001] This invention belongs to the field of petroleum engineering, specifically relating to a shale oil fracturing extraction device and method. Background Technology

[0002] my country possesses 70-90 billion tons of medium- to low-maturity (Ro: 0.5-0.9%) shale oil resources, but currently lacks mature engineering technologies for economically utilizing these resources. Internationally, related experiments are underway, primarily involving drilling production wells and heating wells within the formation. In the heating wells, the formation temperature is raised to 350-400°C via electric heating, causing the solid organic matter in the rock to decompose and generate liquid shale oil and hydrocarbon gases that can flow through formation pores and fractures, which are then produced from the production wells.

[0003] Chinese patent publication CN112901130A discloses an in-situ steam injection and circulation heating method for shale reservoir exploitation. The method involves a structure including a roof insulation layer, a floor insulation layer, an outer pipe of a multi-point injection double-layer pipe, an inner pipe of a multi-point injection double-layer pipe, a steam generator, a heater, a circulating heater, insulation material, thermally conductive material, a heat energy conversion device, and a product collection device. The output of the steam generator is connected to the heater to heat the steam to the required temperature; the output of the heater is connected to the multi-point injection double-layer pipe. In this method, the hot steam circulates in the inner pipe of the multi-point injection double-layer pipe, heating the mixed fluid flowing into the annular space between the inner and outer pipes, thus solving the problem of condensation during the transport of the mixed fluid.

[0004] Chinese patent publication CN111561303A discloses a device for heating coal reservoirs to increase the yield of low-rank coalbed methane. The device includes a truck, a flow meter, a first gas booster, a second gas booster, a mixed gas separator, a methane storage tank, a water collection tank, and a control system. A U-shaped well and several production wells are drilled into the coal reservoir from the ground. The U-shaped well consists of a first vertical section, a horizontal section, and a second vertical section. A fuel cell air heat exchange system is installed on the truck. The outlet of the fuel cell air heat exchange system is connected to the inlet of the first gas booster. The outlet of the first gas booster is connected to the wellhead of the first vertical section, the wellhead of the second vertical section is connected to the inlet of the second gas booster, and the outlet of the second gas booster is connected to the inlet of the mixed gas separator. Each production well is connected to an extraction device. This invention can effectively remove moisture from low-rank coal reservoirs, promote the desorption of methane molecules, and thus increase the yield of low-rank coalbed methane.

[0005] Chinese patent publication CN110593835A discloses a method for in-situ extraction of shale oil from shale oil reservoirs using electric field heating. The method comprises the following steps: ① Selecting shale oil reservoirs with relatively large thickness, moderate organic matter maturity, high abundance, and a type predominantly oil-generating; ② Drilling a series of vertical or horizontal wells with appropriate well spacing for the shale oil reservoir; ③ Adding an insulating layer between the metal casing in the shale oil reservoir and the metal casing in the non-shale oil reservoir, and lowering cables along the wellhead and connecting them to the metal casing in the shale oil reservoir; ④ Connecting power to these wellhead cables, ensuring that the positive and negative terminals of the metal casings connected to the power supply in the shale oil reservoir are adjacent; ⑤ Using the shale oil reservoir as a resistive element, heating the shale oil reservoir using an electric field, thus overcoming the bottleneck of shale oil extraction technology and achieving in-situ upgrading and extraction of shale oil.

[0006] Chinese patent publication CN107345480A discloses a method for heating an oil shale reservoir. The method involves constructing production wells and heating wells in the oil shale region of the target reservoir; injecting a heating medium into a gas compressor via a gas generator to pressurize the heating medium; injecting the pressurized heating medium into a medium heater to heat the heating medium to a predetermined temperature; injecting the heated medium through the heating well into the oil shale region to heat the oil shale within the region; pyrolyzing the oil shale through the heating medium to generate pyrolysis products, which flow into the production well and are extracted to the surface; separating the pyrolysis products extracted from the production well to generate hydrocarbon gases capable of heating the heating medium and heating medium that can be sequentially passed through the gas compressor and medium heater and then reinjected into the heating well for recycling.

[0007] The Chinese public literature "Numerical Simulation Study on Microwave In-situ Heating for Heavy Oil Extraction in Low Permeability" (Special Oil and Gas Reservoirs 2020, 27(6): 120-126) discloses the study of microwave heating for heavy oil extraction using numerical simulation. After microwave heating, the heavy oil reservoir can be divided into three regions: electromagnetic penetration zone, porous medium conduction zone, and unheated zone. The optimal radiation frequency is 2450MHz. Increasing the power can rapidly increase the formation temperature. In order to avoid overheating near the wellbore, a stepped heating mode with reduced power should be adopted. Hydraulic fracturing can effectively improve the seepage channels of low permeability reservoirs and can be used in conjunction with microwave heating for heavy oil extraction.

[0008] The Chinese publicly available paper, "Feasibility of Electric Heating-Assisted Huff and Puff in Horizontal Wells and Well Process Design" (first published online in the *Journal of Xi'an Petroleum University (Natural Science Edition)*, August 2021), addresses the low oil production and recovery rates of horizontal sections in conventional heavy oil well huff and puff areas in China. It conducts a feasibility study on electric heating-assisted horizontal well huff and puff and optimizes the heating process design. The paper optimizes the tubing structure for electric heating wells and predicts production effects using typical well groups. The prediction results show that adopting electric heating significantly improves the recovery rate of horizontal huff and puff wells, establishing key technological reserves.

[0009] The Chinese publicly available literature, "Analysis of Temperature Distribution and Influencing Factors in Heavy Oil Reservoirs under High-Frequency Electromagnetic Heating" (Petroleum Drilling Technology, 2020, 48(1): 90-97), mainly analyzes the factors affecting the temperature distribution of heavy oil reservoirs during high-frequency electromagnetic heating. A mathematical model describing the dynamic changes in reservoir properties was established, and a comparative method was used to analyze the influence of different factors on temperature distribution. The results show that reservoir properties, electromagnetic wave power, and frequency have a significant impact on the temperature distribution of the reservoir. The established mathematical model considering the dynamic changes in reservoir properties provides a theoretical basis for the field application of high-frequency electromagnetic heating technology for heavy oil. This paper focuses on the theoretical analysis of temperature distribution and influencing factors based on the heating effect theory.

[0010] This type of technology is simplistic and has low heating efficiency, only able to heat the formation by 15°C per month. It would take approximately 23 to 27 months to heat the formation to 350–400°C. Even after heating, production capacity is low, with a single well producing only about 3.2–8.0 m³ of oil per day. 3 / d does not meet the requirements for economical mining.

[0011] The publicly available Chinese document, "Pyrolysis Kinetics and Formation Permeability of Low-Maturity Shale Oil under Heating and Upgrading," discloses the use of a gold tube experimental setup to study the pyrolysis patterns and component kinetics of organic matter during shale heating, and the application of a triaxial high-temperature permeability testing device to test the dynamic changes in permeability under high-temperature conditions. However, it does not address the technical methods for fracturing and heating shale oil to improve production and recovery.

[0012] Chinese patent publication CN 206668238U discloses a downhole combined heating device, which includes an electromagnetic wave heat energy generator, an electrothermal film heating mechanism, etc. The electromagnetic wave heat energy generator heating section includes a magnetic rod and a resistance rod. Copper wire is wound around the magnetic rod, and a first tungsten wire is wound around the resistance rod. The electrothermal film heating mechanism is connected to a continuous tube and has an electric heating tube and a second tungsten wire wound around the electric heating tube. An electric heating film shell is sealed to the outside of the electric heating tube. The second tungsten wire is located inside the electric heating film shell, and a heating cavity is formed between the electric heating film shell and the electric heating tube. The heating cavity is filled with inert gas. The electromagnetic wave heat energy generator is located inside the continuous tube and below the electrothermal film heating mechanism. The heating section cable of the encapsulated cable is connected to the first tungsten wire, the superconducting pulse cable is connected to the copper wire, and the electrothermal film cable is connected to the second tungsten wire. Summary of the Invention

[0013] The purpose of this invention is to solve the problems existing in the prior art and provide a shale oil fracturing extraction device and method. The device involves multiple and multidirectional heating of the formation and fracturing fractures in the heating well and the fracturing fractures, respectively. The temperature at which the catalytic cracking agent decomposes organic matter into light hydrocarbons is significantly reduced. The simultaneous heating in the wellbore and the fracturing fractures greatly improves the heating efficiency. This not only reduces the viscosity of high-viscosity retained hydrocarbons in the rock, but also transforms unconverted organic matter in situ into flowable light hydrocarbons, thereby significantly increasing the oil production per well and the final recovery rate.

[0014] This invention is achieved through the following technical solution:

[0015] A first aspect of the present invention provides a shale oil fracturing extraction apparatus, the apparatus comprising:

[0016] A conductive and thermally conductive layer is placed within the fracture zone formed during the fracturing process;

[0017] The heating device is installed inside the heating well;

[0018] Two electrodes are installed in the production well and the heating well, respectively, and the two electrodes are connected by an electrode cable.

[0019] A further improvement of the present invention is that:

[0020] The conductive and thermally conductive layer is a proppant that is continuously laid in the crack area using a sand-addition method.

[0021] A further improvement of the present invention is that:

[0022] The proppant is quartz sand with a surface coated with a conductive and thermally conductive material.

[0023] A further improvement of the present invention is that:

[0024] The heating device is an electric heating rod.

[0025] In a second aspect, the present invention provides a shale oil fracturing extraction method, wherein the above-mentioned shale oil fracturing extraction device is used to fracture and extract shale oil.

[0026] A further improvement of the present invention is that:

[0027] The method includes the following steps:

[0028] Step 1: Drill two wells in the shale oil formation, one as a production well and the other as a heating well;

[0029] Step 2: Fracturing the production well;

[0030] Step 3: Production well backflow and production;

[0031] Step 4: After the production well is shut down, flush the well and use electrodes and heating devices in the production well and heating well to heat the formation and fracturing fractures simultaneously.

[0032] Step 5: When the production well produces light hydrocarbons, continue production while the proppant in the fracture zone and the heating well remain heated.

[0033] A further improvement of the present invention is that:

[0034] In the first step, two wells are drilled in the shale oil formation. The specific operation is as follows:

[0035] In shale oil formations, two wells are drilled along the azimuth of the maximum principal stress. One well is a vertical well, which serves as a production well, and the other well, whose vertical and horizontal sections are connected, serves as a heating well. The distance between the wellheads of the vertical sections of the production well and the heating well is 200m, and the horizontal section of the heating well is located at the bottom of the oil layer of the production well.

[0036] A further improvement of the present invention is that:

[0037] In the second step, a fracture zone is formed in the formation during the fracturing process. The fracture zone is set vertically and located in the middle of the oil layer of the production well. Propane is laid in the fracture zone by continuous sand addition to form a conductive and thermally conductive layer.

[0038] A further improvement of the present invention is that:

[0039] The proppant is quartz sand with a surface coated with a conductive and thermally conductive material.

[0040] A further improvement of the present invention is that:

[0041] The electrode consists of two electrodes, which are respectively located in the production well and the heating well, and are connected by an electrode cable.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] (1) The innovation of this invention is that the electrode, heating device and reservoir proppant work simultaneously to heat the formation and fracturing fractures at the same time, thereby improving heating efficiency.

[0044] (2) The temperature at which the catalytic cracking agent converts organic matter into light hydrocarbons is reduced from 350-400℃ to 250-300℃;

[0045] (3) Combining wellbore heating with heat conduction within fracturing fractures, the formation heating temperature is increased from 15℃ to 30℃ per month. It takes 8 to 10 months to heat the temperature to 250-300℃, and the heating efficiency is increased by about 2 times.

[0046] (4) Oil production per well ranges from 3.2 to 8.0 m³. 3 / d increased to 15-20.0m 3 / d, yield increases by 3 to 5 times. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the structure of a shale oil fracturing extraction device according to the present invention.

[0048] In the diagram, 1 is the conductive and heat-conducting layer, 2 is the crack zone, 3 is the heating device, 4 is the electrode, 5 is the electrode cable, 6 is the production well, and 7 is the heating well. Detailed Implementation

[0049] The present invention will now be described in further detail with reference to the accompanying drawings:

[0050] This invention targets medium- and low-maturity shale oil. First, fracturing technology is used to break up the target formation in the production well. During fracturing, a catalytic cracking agent is added to the proppant, and a conductive and thermally conductive proppant is used. The proppant is continuously added to the fracture to form a conductive and thermally conductive layer. Then, the formation and fractures are heated in a heating well. The temperature at which the catalytic cracking agent decomposes organic matter into light hydrocarbons is significantly reduced. Heating occurs simultaneously in the wellbore and the fracturing fractures, greatly improving heating efficiency. This not only reduces the viscosity of high-viscosity retained hydrocarbons in the rock but also transforms unconverted organic matter in situ into flowable light hydrocarbons, thereby significantly increasing single-well oil production and ultimate recovery rate, creating conditions for the economic development of medium- and low-maturity shale oil resources with vast reserves.

[0051] This invention provides a shale oil fracturing extraction device, and embodiments of the device are as follows:

[0052]

Example 1

[0053] like Figure 1 As shown, the device includes:

[0054] A conductive and thermally conductive layer 1 is disposed within the fracture zone 2 formed during the fracturing process;

[0055] Heating device 3 is installed inside heating well 7;

[0056] Two electrodes 4 are respectively installed in the production well 6 and the heating well 7, and the two electrodes 4 are connected by an electrode cable 5.

[0057] In one embodiment of the present invention, the conductive and thermally conductive layer 1 is a proppant that is continuously added to the fracture zone 2. The proppant is quartz sand coated with conductive and thermally conductive material. The proppant has two functions: first, to support the fracture, and second, to conduct electricity and heat, transferring heat from the fracture to the formation.

[0058] In one embodiment of the present invention, the heating device 3 is installed in the heating well 7. The heating device 3 can be any existing device with heating function, preferably an electric heating rod, for heating the formation and the fracturing fractures at the same time.

[0059] The device of this invention operates simultaneously with the heating of the electrode 4 and the heating device 3, and the conductive self-heating of the reservoir proppant, thereby achieving simultaneous heating of the formation and the fracturing fractures and improving heating efficiency.

[0060] This invention also provides a shale oil fracturing extraction method, which uses the above-mentioned shale oil fracturing extraction device to extract shale oil through fracturing. An embodiment of the method is as follows:

[0061]

Example 2

[0062] The method includes the following steps:

[0063] Step 1: In the shale oil formation, drill two wells along the direction of maximum principal stress. One of them is a vertical well as a production well, which is completed with perforated screen pipes. The other well, which connects the vertical and horizontal sections, is a heating well, which is also completed with perforated screen pipes. The distance between the wellheads of the vertical sections of the production well and the heating well is 200m. The horizontal section of the heating well is located at the bottom of the oil layer of the production well.

[0064] Step 2: Fracturing the production well

[0065] During fracturing, a catalytic cracking agent is added to the sand-carrying fluid. The main component of the catalytic cracking agent is aluminum silicate, including silica sol or aluminum sol catalytic cracking agents. The composition of the cracking catalyst is existing technology and will not be elaborated here. The role of the catalytic cracking agent is to lower the temperature at which organic matter is cracked into light hydrocarbons.

[0066] During fracturing, fracture zones are formed in the formation. These fracture zones are vertically positioned in the middle of the production well's oil layer. Propionate is laid within the fracture zones. The proppant is a conductive and thermally conductive proppant, which is laid in the fracture zones by continuous sand addition to form a conductive and thermally conductive layer.

[0067] In the prior art, proppant is an insulating material that prevents heat transfer. In this invention, the proppant is quartz sand coated with a thermally and electrically conductive material. The proppant has two functions: first, to support the fracture; and second, to conduct electricity and heat, transferring heat from the fracture to the formation.

[0068] The fracturing process of production wells is a very mature technology and will not be elaborated on here.

[0069] Step 3: Production well backflow.

[0070] Control the nozzle to allow fracturing fluid to flow back from the production well.

[0071] Step 4: Production well production.

[0072] After the fracturing fluid backflow is completed, production resumes according to the work schedule.

[0073] Production well backflow and production are well-established and mature technologies, and will not be elaborated upon here.

[0074] Step 5: Heating.

[0075] After the production well is shut down, the well is flushed, and electrodes and heating devices are used in both the production well and the heating well to heat the formation and fracturing fractures simultaneously.

[0076] Electrodes are placed in the production well and the heating well, respectively, and the two electrodes are connected by an electrode cable. The electrodes are used to heat the formation and the fracturing fractures simultaneously.

[0077] The heating device is installed in the heating well. Any existing device with heating function can be used, preferably an electric heating rod, to heat the formation and fracturing fractures simultaneously.

[0078] Step 6: Monitor changes in temperature, fluid type, flow rate, and pressure in the production well. Monitor the wellhead temperature, pressure, and the type and flow rate of the produced fluid at the wellhead.

[0079] Monitoring the temperature in the production well is to observe the heating effect; monitoring the fluid type is mainly to see if light hydrocarbons are produced; monitoring the flow rate and pressure is mainly to detect production capacity. Light hydrocarbons are generally produced at temperatures between 250 and 300°C, and there are no specific pressure requirements.

[0080] Step 7: Production well production.

[0081] When light hydrocarbons are produced in the production well, the nozzle is controlled to maintain stable production, and the heating well continues to be heated. In other words, when light hydrocarbons are detected in the production well in step six, production continues, while the proppant in the fracture and the heating well remain heated.

[0082] The invention will be further illustrated below with an application example.

[0083]

Example 3

[0084] (1) In a certain shale oil block, a vertical well with a depth of 1000m was drilled as a production well. The oil layer was located at 920-950m. A horizontal well was drilled 200m away from the vertical well as a heating well. The horizontal section was 160m long and 50m away from the oil layer.

[0085] (2) Fracturing the production well, with a construction flow rate of 4-5 cubic meters / day, pumping in 300 cubic meters of fracturing fluid containing catalytic cracking agent, adding 36 cubic meters of 20-40 mesh conductive and thermally conductive proppant, and draining the fluid after construction is completed;

[0086] (3) After the initial discharge, the daily oil production was 3.5 cubic meters / day. Production was suspended for 112 days, and the cumulative crude oil production was 270 tons.

[0087] (4) Heating rods are lowered into the production well and the heating well to heat the formation and fractures simultaneously;

[0088] (5) After heating for 260 days, the pressure of the production well gradually increased and crude oil was produced. The bottom temperature of the well was tested at 270℃. After heating to 300℃, the crude oil production reached 16.5 cubic meters / day. Heating continued and the production well continued to produce.

[0089] (6) Production lasted 680 days, with a cumulative production of 10,600 tons of crude oil, before production ceased.

[0090] The beneficial effects of this invention are:

[0091] (1) The innovation of this invention is that the electrode, heating device and reservoir proppant work simultaneously to heat the formation and fracturing fractures at the same time, thereby improving heating efficiency.

[0092] (2) The temperature at which the catalytic cracking agent converts organic matter into light hydrocarbons is reduced from 350-400℃ to 250-300℃;

[0093] (3) Combining wellbore heating with heat conduction within fracturing fractures, the formation heating temperature is increased from 15℃ to 30℃ per month. It takes 8 to 10 months to heat the temperature to 250-300℃, and the heating efficiency is increased by about 2 times.

[0094] (4) Oil production per well ranges from 3.2 to 8.0 m³. 3 / d increased to 15-20.0m 3 / d, yield increases by 3 to 5 times.

[0095] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0096] In the description of this invention, unless otherwise stated, the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0097] Finally, it should be noted that the above technical solution is only one embodiment of the present invention. For those skilled in the art, based on the application methods and principles disclosed in the present invention, it is easy to make various types of improvements or modifications, and not limited to the methods described in the above specific embodiments of the present invention. Therefore, the methods described above are only preferred and have no limiting significance.

Claims

1. A method for fracturing and extracting shale oil, characterized in that, The method includes the following steps: Step 1: Drill two wells in the shale oil formation, one vertical well as a production well and the other a heating well. The heating well includes a connected vertical section and a horizontal section, with the horizontal section of the heating well located at the bottom of the oil layer of the production well. The second step is to perform fracturing on the production well. During the fracturing process, a catalytic cracking agent is added, and a quartz sand proppant coated with a conductive and thermally conductive material is laid in the fracture zone to form a conductive and thermally conductive layer by continuously adding sand. Step 3: Production well backflow and production; Step 4: After the production well is shut down, flush the well and install electrodes in both the production well and the heating well. The two electrodes are connected by an electrode cable. At the same time, a heating device is installed in the heating well. Then, the heating device is started simultaneously, and power is supplied to the conductive and heat-conducting layer through the electrodes to heat the formation. Meanwhile, the conductive and heat-conducting layer generates resistance heat under the action of the current to heat the inside of the fracture zone, forming a three-dimensional heating of the formation and the fracturing fracture. Step 5: Monitor the production of light hydrocarbons in the production well. When light hydrocarbons are produced, continue production while maintaining the heating status of the heating device and the conductive and heat-conducting layer.

2. The method according to claim 1, characterized in that, In the first step, two wells are drilled in the shale oil formation. The specific operation is as follows: In the shale oil formation, two wells are drilled along the azimuth of the maximum principal stress, with the wellhead distance between the production well and the heating well being 200m in the vertical section.

3. The method according to claim 2, characterized in that, In the second step, the fracture zone is set vertically and located in the middle of the production well's oil layer.

4. The method according to claim 2, characterized in that, The heating device is a heating rod.

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