Method for treating shale oil crack wall surface by using carbon nanotubes to increase heat transfer capacity of reservoir

Abstract

The invention relates to a method for treating shale oil crack wall surfaces by using carbon nanotubes to increase the heat transfer capacity of a reservoir, a plurality of horizontal wells are drilled from the ground, the horizontal sections of the horizontal wells form three parallel well rows, the uppermost well row and the lowermost well row are heating wells, and the middle well row is a production well. The fracturing fluid carrying the proppant is injected into the heating well and the production well with the displacement greatly exceeding the stratum absorption capacity, the bottom hole pressure is larger than the stratum fracture pressure, hydraulic fracturing is carried out, a tensional fracture area and a communication well group are generated, and meanwhile it is guaranteed that fractures are not closed after the proppant is filled. Under the condition that the pressure is lower than the formation fracture pressure, a weak acid solution is slowly squeezed into the heating well and the production well, the well wall and the crack wall face are treated, and a large number of corrosion micropores are formed. And under the condition that the pressure is lower than the stratum fracture pressure, a weak acid solution added with the carbon nano tubes is squeezed into the heating well and the production well, so that the carbon nano tubes are adsorbed or filled in the corrosion micropores, and the micropores where the carbon nano tubes are attached are formed. And high-temperature steam is circularly introduced into the heating well and the production well to heat the oil shale stratum. After heating for a certain time, stopping steam injection of the production well, and changing into production; and continuously injecting steam into the heating well. The method is suitable for an oil shale underground in-situ conversion exploitation technology, and is also suitable for geothermal exploitation and heavy oil thermal exploitation.

Description

Technical Field

[0001] The present invention belongs to the technical field of unconventional oil and gas reservoir transformation and oil and gas development, and specifically relates to a method for increasing the heat transfer capacity of a reservoir by treating the walls of shale oil fractures with carbon nanotubes. Background Art

[0002] The underground in-situ conversion of shale oil is the most promising alternative energy source. Globally, technically recoverable shale oil resources are estimated to be approximately 1.4 trillion tons, nearly three times the total amount of conventional oil resources. Shale oil consists of converted hydrocarbons and unconverted organic matter, and is self-generated and self-reserved within the source. Underground in-situ conversion of oil shale utilizes horizontal well (electrical) heating to convert heavy oil, asphalt, and organic matter in shale at depths of 300-3000 meters into lighter oil and natural gas on a large scale. This process, often called an "underground refinery," offers significant advantages in terms of clean extraction, total production volume, and output quality.

[0003] The in-situ conversion process of shale oil underground enables clean production and a very high crude oil recovery rate. Artificial heating accelerates degradation to form light oil and natural gas, significantly reducing crude oil viscosity. To increase interwell thermal connectivity and the area for oil and gas drainage, hydraulic fracturing can be used before formal heating. Macroscopic horizontal fractures are created between the heated wells in the oil shale, and then the shale formation is heated by injecting high-temperature steam. This technology increases the heat transfer area of ​​the reservoir through planar heating, improving heating efficiency compared to the linear heat source of traditional technologies. However, due to the low permeability and slow thermal conductivity of the reservoir matrix, as well as the low thermal convection efficiency between the hot fluid and the wellbore wall, and between the hot fluid and the fractures, the heating and conversion process is extremely slow, increasing energy dissipation and severely impacting shale oil production.

[0004] The thermal convection coefficient at the solid-liquid interface is key to increasing the thermal convection capacity of the interface. Numerous factors influence the convection heat transfer coefficient, including the type and phase transition of the fluid, its physical properties, its temperature, its flow state, the cause of its flow, and the nature, size, and location of the heat transfer surface. To increase the efficiency of thermal convection between the hot fluid and the wellbore and fracture walls, the walls are treated with weak acids and nanoparticles. This significantly increases the contact area between the solid-liquid heat transfer surface and improves the fluid's physical properties by increasing its thermal conductivity. Weak acid treatment of the wellbore or fracture walls creates numerous corrosion micropores, increasing the heat transfer surface area. The subsequent adsorption of nanoparticles within these micropores further increases the heat transfer surface area. The addition of nanoparticles increases the thermal conductivity of the solid-liquid two-phase flow and improves the convection heat transfer coefficient between the hot fluid and the wellbore and fracture walls. This treatment method will enhance convective heat transfer, increase the heat transfer rate within the oil shale reservoir, and accelerate the conversion of medium and low maturity shale oil, thereby increasing speed, efficiency and production.

[0005] Walnut shells, a common solid waste in agriculture and forestry, are low-cost and widely available. Under specific conditions, they can be prepared into carbon nanotubes. This nanomaterial can be prepared into nanofluids with high thermal conductivity. Summary of the Invention

[0006] In order to overcome the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a method for increasing the heat transfer capacity of the reservoir by treating the walls of shale oil fractures with carbon nanotubes, which is applicable to underground in-situ conversion and mining technology of oil shale, and is also applicable to geothermal mining and heavy oil thermal recovery.

[0007] The technical solution provided by the present invention is:

[0008] A method for treating shale oil fracture walls using carbon nanotubes to increase reservoir heat transfer capacity, characterized by comprising the following steps:

[0009] Step 1: Drill multiple horizontal wells from the ground. The horizontal sections of the horizontal wells form three parallel well rows, of which the top and bottom well rows are heating wells, and the middle well row is a production well.

[0010] Step 2: Inject the fracturing fluid carrying proppant into the heating well and production well at a rate far exceeding the absorption capacity of the formation, so that the bottom hole pressure is greater than the formation fracture pressure, and hydraulic fracturing is carried out to produce a tensile fracture zone to connect the well group. At the same time, the proppant is filled to ensure that the fracture does not close.

[0011] Step 3: Under the condition of lower than the formation fracture pressure, slowly squeeze weak acid solution into the heating well and production well to treat the well wall and fracture wall to form a large number of dissolution micropores.

[0012] Step 4: Under the condition of lower than the formation fracture pressure, a weak acid solution with carbon nanotubes added is squeezed into the heating well and the production well, so that the carbon nanotubes are adsorbed or filled in the dissolution micropores, forming micropores to which the carbon nanotubes are attached.

[0013] Step 5: Circulate high-temperature steam into the heating well and production well to heat the oil shale formation.

[0014] Step 6: After heating for a certain period of time, stop injecting steam into the production well and switch to production; continue injecting steam into the heating well.

[0015] In step 1, the horizontal well is composed of a vertical well section, a deflection section and a horizontal section. The vertical well section passes through the stratum above the cap rock, the cap rock and part of the reservoir, and the deflection section and the vertical well section are completely in the reservoir section.

[0016] In step one, the distance between adjacent wells in the horizontal section of the upper heating well and the horizontal section of the lower heating well is L1, the distance between adjacent wells of the production well is L2, and L2 = n × L1 (n is an integer, 2≤n≤5).

[0017] In step one, the vertical distance between the upper heating well row and the lower heating well row is L3, the vertical distance between the middle production well row and the upper heating well row and the lower heating well row is L4 (i.e., L3 = 2 × L4), the vertical distance between the upper heating well row and the cap layer is L5, and the vertical distance between the lower heating well row and the bottom layer is L6.

[0018] In step one, the three parallel rows of wells formed in the horizontal section of the horizontal well have the following four modes: the characteristic of mode one is that the upper row of heating wells and the lower row of heating wells are not aligned, the production wells and the lower row of heating wells are aligned, and the production wells and the lower row of heating wells are located on the vertical bisector of the adjacent wells of the upper row of heating wells; the characteristic of mode two is that the upper row of heating wells and the lower row of heating wells are not aligned, the production wells and the upper row of heating wells are aligned, and the production wells and the upper row of heating wells are located on the vertical bisector of the adjacent wells of the lower row of heating wells; the characteristic of mode three is that the upper row of heating wells and the lower row of heating wells are aligned, and the production wells are located on the vertical bisector of the adjacent wells of the upper row of heating wells; the characteristic of mode four is that the upper row of heating wells, the lower row of heating wells and the production wells are aligned.

[0019] In step 1, the vertical well section of the horizontal wells of modes 1 and 2 only extends into one horizontal section, while the vertical well section of the horizontal wells of modes 3 and 4 can extend into two horizontal sections to form a multi-branch horizontal well or extend into one horizontal section.

[0020] In step one, the condition for the vertical well section of the horizontal well to extend into two horizontal sections is that the two horizontal sections are vertically aligned and both are heating wells.

[0021] In the second step, the open hole horizontal well fracturing completion technology is adopted to combine the fracturing transformation string and the completion string string into one trip and run them into the well for fracturing, without the need for casing and cementing.

[0022] In step 2, the calculation method of the formation fracture pressure is: the formation fracture pressure p f = formation fracture pressure gradient D × vertical depth H. The formation fracture pressure gradient D is obtained based on a large amount of fracturing practice data in this area.

[0023] In the step 3, the weak acid solution is a formic acid solution, an acetic acid solution, a carbonic acid solution or a hydrochloric acid solution with a relatively low concentration, or an earth acid solution.

[0024] In step three, the reason for using a weak acid solution to corrode the well wall and the crack wall is that when corroding pits of the same volume, the surface area of ​​the micropores formed by the weak acid on the well wall and the crack wall is much larger than the larger pores formed by the strong acid, which is beneficial to increase the contact area for heat convection and is conducive to the filling and attachment of nanoparticles.

[0025] In step 3, a weak acid solution is squeezed into the heating well and the production well in a progressive manner in four stages, gradually increasing the bottom hole pressure to the maximum bottom hole pressure p dmax , maximum acid squeezing pressure p dmax Specific formation fracture pressure p f 0.5MPa lower. The reservoir depth is H, and the hydrostatic column pressure p h =ρgH, where ρ is the density of the acid solution and g is 9.8m·s -2 Therefore, the maximum wellhead pressure p wmax =p dmax -p h The total acid squeezing time is T, which is divided into 4 stages: In the first stage, the wellhead pressure is increased to p within 1 hour. wmax / 4, and maintain it until T / 4; in the second stage, the wellhead pressure is increased to p within 1 hour. wmax / 2, and maintain it until T / 2; in the third stage, increase the wellhead pressure to 3p within 1 hour wmax / 4, and maintain it until 3T / 4; in the fourth stage, the wellhead pressure is increased to p within 1 hour. wmax , and maintain until time T, when the acid squeezing is completed.

[0026] In step 4, the wellhead pressure p is controlled wmax Keeping the same, a weak acid solution with carbon nanotubes added is squeezed into the heating well and the production well for a duration of T1.

[0027] In step 5, high-temperature steam is circulated into the heating well and the production well, which requires a special downhole pipe string. Two oil pipes are lowered into the wellbore at the same time, with a longer oil pipe extending from the wellhead to a point L away from the toe of the horizontal well. u The other shorter oil pipe extends from the wellhead to a position L below the horizontal well root. d During construction, gas is injected into the upper oil pipe, and the steam condenses and is circulated and discharged from the lower oil pipe.

[0028] In step 5, the maximum steam pressure at the bottom of the well is controlled at p dmax About, duration is T2.

[0029] In step six, after the steam injection into the production well is stopped, a pump is lowered to carry out production, and the bottom-hole steam pressure of the heating well remains unchanged or increases slightly.

[0030] The beneficial effects of the present invention are:

[0031] The present invention utilizes carbon nanotubes to treat the fracture wall to increase the heat transfer capacity of the reservoir, and is applicable to underground in-situ conversion and mining technology of oil shale, as well as geothermal mining, heavy oil thermal recovery and other technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Main steps of the method for treating the wall of oil shale fractures with carbon nanotubes to increase the heat transfer capacity of the reservoir

[0033] Figure 2 Cross-section of the horizontal section of the horizontal well in model 1 perpendicular to the wellbore direction

[0034] Figure 3 Cross-sectional view of the entire horizontal well section of Model 1 on sections 6 and 7

[0035] Figure 4 Cross-section of the horizontal section of the horizontal well in model 2 perpendicular to the wellbore direction

[0036] Figure 5 Cross-sectional view of the full well section of the horizontal well in model 2 on sections 8 and 9

[0037] Figure 6 Cross-section of the horizontal section of the model 3 horizontal well array perpendicular to the wellbore direction

[0038] Figure 7 Cross-sectional view of the single-branch horizontal heating well and production well arranged on sections 10 and 11 in mode 3

[0039] Figure 8 Cross-sectional view of model 3 double-branch horizontal heating wells and production wells arranged on sections 10 and 11

[0040] Figure 9 Cross-section of the horizontal section of the model 4 horizontal well in the direction perpendicular to the wellbore

[0041] Figure 10 Cross-sectional view of the single-branch horizontal heating well and production well arrangement on section 12 in mode 4

[0042] Figure 11 Cross-sectional view of the double-branch horizontal heating well and production well arrangement on section 12 in mode 4

[0043] Figure 12 Schematic diagram of the special downhole tubing required for circulating high-temperature steam in heating wells and production wells and the direction of fluid movement in the tubing

[0044] Figure 13 Schematic diagram of weak acid dissolution of micropores and attached carbon nanotubes

[0045] Among them, 1 is a production well, 2 is a heating well, 3 is an oil shale reservoir, 4 is a cap rock, 5 is a bottom layer, 6 is a vertical section through the horizontal section of the upper heating well in mode 1, 7 is a vertical section through the horizontal section of the middle production well and the lower heating well in mode 1, 8 is a vertical section through the horizontal section of the lower heating well in mode 2, 9 is a vertical section through the horizontal section of the upper heating well and the middle production well in mode 2, 10 is a vertical section through the horizontal section of the upper heating well and the lower heating well in mode 3, 11 is a vertical section through the horizontal section of the middle production well in mode 3, 12 is a vertical section through the horizontal section of the upper heating well, the middle production well and the lower heating well in mode 4, 13 is the toe of the horizontal section of the horizontal well, 14 is a long pipe, 15 is a short pipe, 16 is high-temperature steam, 17 is liquid water, 18 is the well wall or fracture wall, 19 is carbon nanotubes, and 20 is proppant particles. DETAILED DESCRIPTION

[0046] The present invention is further described below with reference to the embodiments and accompanying drawings.

[0047] Example 1:

[0048] like Figure 1 As shown, a method for treating the wall of oil shale fractures using carbon nanotubes to increase the heat transfer capacity of the reservoir is characterized by comprising the following steps:

[0049] Step 1: Figures 2 to 11 As shown, multiple horizontal wells are drilled from the ground, and the horizontal sections of the horizontal wells form three parallel well rows, of which the uppermost and lowermost well rows are heating wells, and the middle well row is a production well.

[0050] Step 2: Inject the fracturing fluid carrying proppant into the heating well and production well at a rate far exceeding the absorption capacity of the formation, so that the bottom hole pressure is greater than the formation fracture pressure, and perform hydraulic fracturing to generate tension fracture zones and connect the well groups. Figure 13 At the same time, the proppant is filled to ensure that the cracks do not close.

[0051] Step 3: Slowly squeeze a weak acid solution into the heating well and production well under the condition of lower than the formation fracture pressure to treat the well wall and fracture wall, such as Figure 13 As shown, a large number of dissolution micropores are formed.

[0052] Step 4: Under the condition of lower than the formation fracture pressure, squeeze the weak acid solution with carbon nanotubes into the heating well and the production well, such as Figure 13 As shown, carbon nanotubes are adsorbed or filled in the eroded micropores to form micropores to which carbon nanotubes are attached.

[0053] Step 5: Figure 12 As shown, high-temperature steam is circulated into the heating well and the production well to heat the oil shale formation.

[0054] Step 6: After heating for a certain period of time, stop injecting steam into the production well and switch to production; continue injecting steam into the heating well.

[0055] In step 1, the horizontal well is composed of a vertical well section, a deflection section and a horizontal section. The vertical well section passes through the stratum above the cap rock, the cap rock and part of the reservoir, and the deflection section and the vertical well section are completely in the reservoir section.

[0056] In step one, the distance between adjacent wells in the horizontal section of the upper heating well and the horizontal section of the lower heating well is L1, the distance between adjacent wells of the production well is L2, and L2 = n × L1 (n is an integer, 2≤n≤5).

[0057] In step one, the vertical distance between the upper heating well row and the lower heating well row is L3, the vertical distance between the middle production well row and the upper heating well row and the lower heating well row is L4 (i.e., L3 = 2 × L4), the vertical distance between the upper heating well row and the cap layer is L5, and the vertical distance between the lower heating well row and the bottom layer is L6.

[0058] In step one, the three parallel rows of wells formed in the horizontal section of the horizontal well have the following four modes: the characteristic of mode one is that the upper row of heating wells and the lower row of heating wells are not aligned, the production wells and the lower row of heating wells are aligned, and the production wells and the lower row of heating wells are located on the vertical bisector of the adjacent wells of the upper row of heating wells; the characteristic of mode two is that the upper row of heating wells and the lower row of heating wells are not aligned, the production wells and the upper row of heating wells are aligned, and the production wells and the upper row of heating wells are located on the vertical bisector of the adjacent wells of the lower row of heating wells; the characteristic of mode three is that the upper row of heating wells and the lower row of heating wells are aligned, and the production wells are located on the vertical bisector of the adjacent wells of the upper row of heating wells; the characteristic of mode four is that the upper row of heating wells, the lower row of heating wells and the production wells are aligned.

[0059] In step 1, the vertical well section of the horizontal wells of modes 1 and 2 only extends into one horizontal section, while the vertical well section of the horizontal wells of modes 3 and 4 can extend into two horizontal sections to form a multi-branch horizontal well or extend into one horizontal section.

[0060] In step one, the condition for the vertical well section of the horizontal well to extend into two horizontal sections is that the two horizontal sections are vertically aligned and both are heating wells.

[0061] In the second step, the open hole horizontal well fracturing completion technology is adopted to combine the fracturing transformation string and the completion string string into one trip and run them into the well for fracturing, without the need for casing and cementing.

[0062] In step 2, the calculation method of the formation fracture pressure is: the formation fracture pressure p f = formation fracture pressure gradient D × vertical depth H. The formation fracture pressure gradient D is obtained based on a large amount of fracturing practice data in this area.

[0063] In the step 3, the weak acid solution is a formic acid solution, an acetic acid solution, a carbonic acid solution or a hydrochloric acid solution with a relatively low concentration, or an earth acid solution.

[0064] In step three, the reason for using a weak acid solution to corrode the well wall and the crack wall is that when corroding pits of the same volume, the surface area of ​​the micropores formed by the weak acid on the well wall and the crack wall is much larger than the larger pores formed by the strong acid, which is beneficial to increase the contact area for heat convection and is beneficial to the filling and attachment of carbon nanotubes.

[0065] In step 3, a weak acid solution is squeezed into the heating well and the production well in a progressive manner in four stages, gradually increasing the bottom hole pressure to the maximum bottom hole pressure p dmax , maximum acid squeezing pressure p dmax Specific formation fracture pressure p f 0.5MPa lower. The reservoir depth is H, and the hydrostatic column pressure p h =ρgH, where ρ is the density of the acid solution and g is 9.8m·s -2 Therefore, the maximum wellhead pressure p wmax =p dmax -p h The total acid squeezing time is T, which is divided into 4 stages: In the first stage, the wellhead pressure is increased to p within 1 hour. wmax / 4, and maintain it until T / 4; in the second stage, the wellhead pressure is increased to p within 1 hour. wmax / 2, and maintain it until T / 2; in the third stage, increase the wellhead pressure to 3p within 1 hour wmax / 4, and maintain it until 3T / 4; in the fourth stage, the wellhead pressure is increased to p within 1 hour. wmax , and maintain until time T, when the acid squeezing is completed.

[0066] In step 4, the wellhead pressure p is controlled wmax Keeping the same, a weak acid solution with carbon nanotubes added is squeezed into the heating well and the production well for a duration of T1.

[0067] In step 5, high-temperature steam is circulated into the heating well and the production well, which requires a special downhole pipe string. Two oil pipes are lowered into the wellbore at the same time, with a longer oil pipe extending from the wellhead to a point L away from the toe of the horizontal well. u The other shorter oil pipe extends from the wellhead to a position L below the horizontal well root. d During construction, gas is injected into the upper oil pipe, and the steam condenses and is circulated and discharged from the lower oil pipe.

[0068] In step 5, the maximum steam pressure at the bottom of the well is controlled at p dmax About, duration is T2.

[0069] In step six, after the steam injection into the production well is stopped, a pump is lowered to carry out production, and the bottom-hole steam pressure of the heating well remains unchanged or increases slightly.

[0070] This example is the Fuyu shale oil reservoir. The overlying stratum of the oil shale is mudstone. The reservoir top is 470m deep, the reservoir thickness is 20m, the initial average reservoir pressure is 5MPa, and the initial average formation temperature is 10°C. According to a large amount of fracturing practice data in this area, the formation fracture pressure gradient D is 0.0196MPa / m, and the formation fracture pressure at the middle position of the reservoir is p f =0.0196MPa / m×480m=9.408MPa.

[0071] like Figures 1 and 2 As shown, this embodiment adopts mode 1 to deploy horizontal wells, and the horizontal section length of the horizontal well is designed to be 500m. The adjacent well spacing between the horizontal sections of the upper and lower heating wells is L1 = 50m, and the adjacent well spacing between production wells is L2 = 100m. The vertical spacing between the upper and lower heating well rows is L3 = 10m, the vertical distance between the middle production well row and the upper and lower heating well rows is L4 = 5m, the vertical distance between the upper heating well row and the caprock is L5 = 5m, and the vertical distance between the lower heating well row and the bottom layer is L6 = 5m.

[0072] In this embodiment, 10% acetic acid solution is used for extrusion, and the density of the acetic acid solution is 1.0125 g / cm 3 In 4 stages, a weak acid solution is squeezed into the heating well and the production well, and the bottom hole pressure is gradually increased to the maximum bottom hole acid squeezing pressure p dmax =p f -0.5MPa=8.908MPa. The middle depth of the reservoir is H=480m, and the static column pressure p h =0.00981×1.0125g / cm 3 × 480m = 4.768MPa. Therefore, the maximum wellhead pressure p wmax =p dmax -p h =8.908MPa-4.768MPa=4.14MPa. The total acid squeezing time is T=100h, which is divided into four stages: the first stage, the wellhead pressure is increased to 1.035MPa within 1h and maintained until the 25th hour; the second stage, the wellhead pressure is increased to 2.07MPa within 1h and maintained until the 50th hour; the third stage, the wellhead pressure is increased to 3.105MPa within 1h and maintained until the 75th hour; the fourth stage, the wellhead pressure is increased to 4.14MPa within 1h and maintained until the 100th hour, when the acid squeezing is completed.

[0073] In this embodiment, the wellhead pressure p is controlled wmax =4.14MPa remains unchanged, and a weak acid solution with carbon nanotubes added is squeezed into the heating well and the production well for a duration of T1=100h.

[0074] In this embodiment, 500℃ high temperature steam is circulated into the heating well and the production well. Two oil pipes are lowered into the wellbore at the same time. A longer oil pipe extends from the wellhead to a point L away from the toe of the horizontal well. u = 2m, located slightly above the wellbore; another shorter oil pipe extends from the wellhead to the horizontal well root L d =3m, located at the lower part of the wellbore.

[0075] In this embodiment, the maximum steam pressure at the bottom of the well is controlled at p dmax = about 8.908MPa, duration is T 2＝ 300 days later, steam injection into the production well was stopped and a pump was lowered to resume production. The bottomhole steam pressure of the heating well was increased to 9.208 MPa.

[0076] Example 2:

[0077] According to another embodiment of the method of using carbon nanotubes to treat the wall of oil shale fractures to increase the heat transfer capacity of the reservoir, the modification steps, working principles, and beneficial effects are the same as those of the first embodiment, except for the deployment of horizontal wells and the selection of weak acid solution: In this embodiment, according to Figures 3 and 4 Deploy horizontal wells and select saturated carbonate solution for fluid extrusion.

[0078] Example 3:

[0079] According to another embodiment of the method of using carbon nanotubes to treat the wall of oil shale fractures to increase the heat transfer capacity of the reservoir, the modification steps, working principles, and beneficial effects are the same as those of the first embodiment, except for the deployment of horizontal wells and the selection of nanoparticles: In this embodiment, according to Figure 5 and Figure 7 Deploy horizontal wells and select carbon nanotubes with added Al2O3 nanoparticles. This embodiment allows two horizontal sections to be drilled in the same vertical well section as dual-branch heating wells, saving drilling investment.

[0080] Example 4:

[0081] According to another embodiment of the method of using carbon nanotubes to treat the walls of oil shale fractures to increase the reservoir heat transfer capacity, the modification steps, working principles, and beneficial effects are the same as those of the first embodiment, with the difference being the matching relationship between the various parameters in the modification steps:

[0082] This example is the Jimusar oil shale reservoir, with a top depth of 344m, a bottom depth of 388m, and a reservoir thickness of 44m. According to a large amount of fracturing practice data in this area, the formation fracture pressure gradient D is 0.017MPa / m, and the formation fracture pressure at the middle position of the reservoir is p f =0.017MPa / m×366m=6.222MPa.

[0083] like Figures 1 and 2 As shown, this embodiment adopts mode 1 to deploy horizontal wells, and the horizontal section length of the horizontal well is designed to be 500m. The adjacent well spacing between the horizontal sections of the upper heating well and the lower heating well is L1 = 50m, and the adjacent well spacing between the production wells is L2 = 100m. The vertical spacing between the upper and lower heating well rows is L3 = 22m, the vertical distance between the middle production well row and the upper and lower heating well rows is L4 = 11m, the vertical distance between the upper heating well row and the caprock is L5 = 11m, and the vertical distance between the lower heating well row and the bottom layer is L6 = 11m.

[0084] In this embodiment, 10% acetic acid solution is used for extrusion, and the density of the acetic acid solution is 1.0125 g / cm 3 In 4 stages, a weak acid solution is squeezed into the heating well and the production well, and the bottom hole pressure is gradually increased to the maximum bottom hole acid squeezing pressure p dmax =p f -0.5MPa=5.722MPa. The middle depth of the reservoir is H=366m, and the static liquid column pressure p h =0.00981×1.0125g / cm 3 ×366m=3.635MPa. Therefore, the maximum wellhead pressure p wmax =p dmax -p h =5.722MPa-3.635MPa=2.087MPa. The total acid squeezing time is T=100h, which is divided into four stages: the first stage, the wellhead pressure is increased to 0.522MPa within 1h and maintained until the 25th hour; the second stage, the wellhead pressure is increased to 1.044MPa within 1h and maintained until the 50th hour; the third stage, the wellhead pressure is increased to 1.565MPa within 1h and maintained until the 75th hour; the fourth stage, the wellhead pressure is increased to 2.087MPa within 1h and maintained until the 100th hour, when the acid squeezing is completed.

[0085] In this embodiment, the wellhead pressure p is controlled wmax =2.087MPa remains unchanged, and a weak acid solution with added carbon nanoparticles is squeezed into the heating well and the production well for a duration of T1=100h.

[0086] In this embodiment, 500℃ high temperature steam is circulated into the heating well and the production well. Two oil pipes are lowered into the wellbore at the same time. A longer oil pipe extends from the wellhead to a point L away from the toe of the horizontal well. u = 2m, located slightly above the wellbore; another shorter oil pipe extends from the wellhead to the horizontal well root L d =3m, located at the lower part of the wellbore.

[0087] In this embodiment, the maximum steam pressure at the bottom of the well is controlled at p dmax = about 5.722MPa, duration is T 2＝ 300 days later, steam injection into the production well was stopped and a pump was lowered to resume production. The bottomhole steam pressure of the heating well was increased to 6.022 MPa.

Claims

1. A method for increasing the heat transfer capacity of a shale oil reservoir by treating the wall of a shale oil fracture with carbon nanotubes, characterized in that: The following steps are involved: Step 1: Drill multiple horizontal wells from the ground. The horizontal sections of the horizontal wells form three parallel well rows, of which the top and bottom well rows are heating wells, and the middle well row is the production well; The horizontal well consists of a vertical well section, a build-up section, and a horizontal section. The vertical well section passes through the strata above the caprock, the caprock, and part of the reservoir, while the build-up section and the vertical well section are completely within the reservoir section. The distance between adjacent wells in the horizontal section of the upper heater well and the horizontal section of the lower heater well is L1, and the distance between adjacent wells of the production well is L2, and L2 = n × L1 (n is an integer, 2≤n≤5); The vertical distance between the upper and lower heating well rows is L3, the vertical distance between the middle production well row and both the upper and lower heating well rows is L4 (i.e., L3 = 2 × L4), the vertical distance between the upper heating well row and the caprock is L5, and the vertical distance between the lower heating well row and the bottom layer is L6; Step 2: Inject the fracturing fluid carrying proppant into the heating well and production well at a rate far exceeding the absorption capacity of the formation, so that the bottom hole pressure is greater than the formation fracture pressure, and hydraulic fracturing is performed to generate tension fracture zones, connecting the well group, and at the same time, the fractures are ensured not to close after the proppant is filled; The open hole horizontal well fracturing completion technology is used to combine the fracturing string and the completion string into one trip to the well for fracturing, without the need for casing and cementing. The calculation method of the formation fracture pressure is: the formation fracture pressure p f = formation fracture pressure gradient D × vertical depth H. The formation fracture pressure gradient D is obtained based on a large amount of fracturing practice data in this area; Step 3: Slowly squeeze a weak acid solution into the heating well and production well under the condition of being lower than the formation fracture pressure to treat the well wall and fracture wall to form a large number of dissolution micropores; In four stages, a weak acid solution is squeezed into the heating well and the production well, and the bottom hole pressure is gradually increased to the maximum bottom hole pressure p dmax , maximum acid squeezing pressure p dmax Specific formation fracture pressure p f 0.5MPa lower. The reservoir depth is H, and the hydrostatic column pressure p h =ρgH, where ρ is the density of the acid solution and g is 9.8m·s -2 Therefore, the maximum wellhead pressure p wmax =p dmax -p h The total acid squeezing time is T, which is divided into 4 stages: In the first stage, the wellhead pressure is increased to p within 1 hour. wmax / 4, and maintain it until T / 4; in the second stage, the wellhead pressure is increased to p within 1 hour. wmax / 2, and maintain it until T / 2; in the third stage, increase the wellhead pressure to 3p within 1 hour wmax / 4, and maintain it until 3T / 4; in the fourth stage, the wellhead pressure is increased to p within 1 hour. wmax , and maintain until time T, when the acid extrusion ends; Step 4: Under conditions below the formation fracture pressure, a weak acid solution containing carbon nanotubes is squeezed into the heating well and the production well, so that the carbon nanotubes are adsorbed or filled in the dissolution micropores, forming micropores to which the carbon nanotubes are attached; Step 5: Circulate high-temperature steam into the heating well and the production well to heat the oil shale formation; Step 6: After heating for a certain period of time, stop injecting steam into the production well and switch to production; continue injecting steam into the heating well.

2. The method of increasing the heat transfer capacity of a shale oil reservoir by treating the wall of a shale oil fracture with carbon nanotubes according to claim 1, characterized in that: In the step one, the three parallel rows of wells formed in the horizontal section of the horizontal well have the following four modes: the characteristic of mode one is that the upper row of heating wells and the lower row of heating wells are not aligned, the production wells and the lower row of heating wells are aligned, and the production wells and the lower row of heating wells are located on the vertical bisector of the adjacent wells of the upper row of heating wells; the characteristic of mode two is that the upper row of heating wells and the lower row of heating wells are not aligned, the production wells and the upper row of heating wells are aligned, and the production wells and the upper row of heating wells are located on the vertical bisector of the adjacent wells of the lower row of heating wells; the characteristic of mode three is that the upper row of heating wells and the lower row of heating wells are aligned, and the production wells are located on the vertical bisector of the adjacent wells of the upper row of heating wells; the characteristic of mode four is that the upper row of heating wells, the lower row of heating wells and the production wells are aligned.

3. The method of increasing the heat transfer capacity of a reservoir by treating the wall of a shale oil fracture with carbon nanotubes according to claim 1, characterized in that: In step 1, the vertical well section of the horizontal wells of modes 1 and 2 only extends into one horizontal section, while the vertical well section of the horizontal wells of modes 3 and 4 can extend into two horizontal sections to form a multi-branch horizontal well or extend into one horizontal section.

4. The method of claim 1, wherein the method comprises: In step 1, the condition for the vertical well section of the horizontal well to extend into two horizontal sections is that the two horizontal sections are vertically aligned and both are heating wells.

5. The method of increasing reservoir heat transfer capacity by treating shale oil fracture walls with carbon nanotubes according to claim 1, characterized in that: In the step 3, the weak acid solution is a formic acid solution, an acetic acid solution, a carbonic acid solution or a hydrochloric acid solution or an earth acid solution with a relatively low concentration.

6. The method of claim 1 for treating shale oil fracture walls with carbon nanotubes to increase reservoir heat transfer capacity, characterized in that: In the fourth step, the wellhead pressure p is controlled wmax Keeping the same, a weak acid solution with carbon nanotubes added is squeezed into the heating well and the production well for a duration of T1.

7. The method of claim 1 for treating shale oil fracture walls with carbon nanotubes to increase reservoir heat transfer capacity, characterized in that: In step 5, high-temperature steam is circulated into the heating well and the production well, which requires a special downhole pipe string. Two oil pipes are lowered into the wellbore at the same time, and a longer oil pipe extends from the wellhead to the horizontal well toe L. u The other shorter oil pipe extends from the wellhead to a position L below the horizontal well root. d The position is located at the lower part of the wellbore. During construction, gas is injected into the upper oil pipe, and the steam is condensed and circulated and discharged from the lower oil pipe. The maximum steam pressure at the bottom of the well is controlled at p dmax About, duration is T2.

8. The method of increasing reservoir heat transfer capacity by treating shale oil fracture walls with carbon nanotubes according to claim 1, characterized in that: In the step six, after the steam injection into the production well is stopped, a pump is lowered to carry out production, and the bottom-hole steam pressure of the heating well remains unchanged or increases slightly.

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