CN112922577B - Shale reservoir multi-level radial horizontal well methane combustion and explosion fracturing method - Google Patents
Shale reservoir multi-level radial horizontal well methane combustion and explosion fracturing method Download PDFInfo
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 165
- 238000004880 explosion Methods 0.000 title claims abstract description 45
- 238000000034 method Methods 0.000 title claims abstract description 41
- 238000002485 combustion reaction Methods 0.000 title claims abstract description 24
- 239000012530 fluid Substances 0.000 claims abstract description 59
- 238000006073 displacement reaction Methods 0.000 claims abstract description 17
- 238000002347 injection Methods 0.000 claims description 45
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- 230000015572 biosynthetic process Effects 0.000 claims description 3
- 238000010892 electric spark Methods 0.000 claims description 3
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 13
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- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/30—Specific pattern of wells, e.g. optimising the spacing of wells
- E21B43/305—Specific pattern of wells, e.g. optimising the spacing of wells comprising at least one inclined or horizontal well
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- E21B43/14—Obtaining from a multiple-zone well
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- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/164—Injecting CO2 or carbonated water
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- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/24—Enhanced recovery methods for obtaining hydrocarbons using heat, e.g. steam injection
- E21B43/243—Combustion in situ
- E21B43/247—Combustion in situ in association with fracturing processes or crevice forming processes
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- E21B43/26—Methods for stimulating production by forming crevices or fractures
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- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/295—Gasification of minerals, e.g. for producing mixtures of combustible gases
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Abstract
The invention discloses a shale reservoir multi-level radial horizontal well methane explosion fracturing method, which is characterized in that existing methane of a shale reservoir is used as fuel, air injected from the ground is mixed with the shale reservoir methane in radial horizontal wells to form combustible mixed fluid and explode the combustible mixed fluid, and impact pressure generated by explosion is used for fracturing the reservoir, so that large-scale three-dimensional network fractures are formed in the shale reservoir. The invention combines the conventional explosive fracturing, radial horizontal well technology and supercritical CO2The method has the advantages that the displacement technology is combined, the shale reservoir is divided into different transformation areas by reasonably arranging the layer number, the branch number and the azimuth angle of the radial horizontal well, and methane combustion and explosion fracturing in the radial horizontal well is implemented in the corresponding areas, so that the traditional combustion and explosion fracturing operation area is expanded from a shaft to the deep part of the stratum, the methane combustion and explosion position and direction can be controlled, the purpose of improving the combustion and explosion fracturing efficiency of the reservoir is achieved, and the efficient development of shale gas resources is realized.
Description
Technical Field
The invention relates to the technical field of unconventional natural gas development and shale gas reservoir fracturing yield increase, in particular to a shale reservoir multi-level radial horizontal well methane combustion explosion fracturing method.
Background
At present, most of onshore main oil and gas fields in China enter the middle and later stages of development and exploitation stages, and the onshore main oil and gas fields show the characteristics of high remarkable extraction degree, high comprehensive water content, high rate of decline of development and production capacity and the like, so that oil field companies face a very nervous production stabilizing trend. In 2019, the external dependence of petroleum and natural gas in China is 70.8% and 43.4% respectively, and the safe supply of oil and gas faces huge challenges. Under such severe practical conditions, it is very important to find alternative energy sources for conventional oil and gas. At present, unconventional natural gas represented by shale gas becomes an important part of natural gas supply in the world, and the shale gas resource amount in China is about 134.42 multiplied by 1012m3The natural gas is 2.5 times of the conventional natural gas, the reserves are very rich, and the realization of the efficient development of shale gas resources has great strategic significance for guaranteeing the national energy safety.
The shale reservoir mainly takes nano pores as reservoir space and has the permeability of about (0.001-1) x 10-3And mD, the development difficulty is very high, wherein more than 90% of shale gas reservoirs need to form highly dense reticular fractures in a reservoir after hydraulic fracturing modification, so that artificial fractures and natural fractures are mutually staggered to form an artificial shale gas reservoir, and the industrial capacity can be obtained. In 2017, the U.S. horizontal well fracturing technology contributes up to 97% to the shale gas production, and becomes an 'absolute main force' for promoting the shale gas production to increase. Therefore, reservoir fracturing is the core technology of the efficient development of shale gas at present. With the continuous expansion of the fracturing scale, the hydraulic fracturing technology also brings a series of problems, which are firstly reflected in the gas reservoir damage caused by the retention of the fracturing fluid. For most shale gas reservoirs water is the wetting phase, invasion and retention of the water phase can cause severe water lock and water sensitivity damage to the reservoir, and the lower the permeability and water saturation of the reservoir, the more serious the damage. Therefore, how to eliminate or reduce the damage of water to the stratum to the maximum extent in the fracturing process is one of the keys of unconventional gas reservoir reconstruction such as shale gas. In addition, the shale gas reservoir in China has the common reservoir buried depth (2000-3500 m), the reservoir rock has strong plasticity and large horizontal stress difference of the stratum, and the conventional water power is adoptedThe fracturing method is not easy to form complex cracks and is difficult to meet the technical requirements of high-efficiency development of shale gas. The shale gas area features of China are various mountainous regions and hills, the area of a well site is narrow, traffic is blocked, and the application of a large-scale hydraulic fracturing technology is greatly influenced. Most of the north and the west with relatively mild topography face the problems of water resource shortage and serious water resource pollution, and the hydraulic fracturing technology which uses water to reach thousands of places frequently will undoubtedly further intensify the situation of water resource shortage in these areas.
In order to improve the fracture degree of reservoir rock, increase the fracture complexity and overcome the dependence of reservoir fracture on water resources, researchers adopt a shaft blasting fracture mode to fracture the stratum so as to form a complex fracture system near a shaft. Research shows that the combustible in the shaft can instantaneously generate high pressure of over 60MPa when being rapidly combusted, the crack expansion can break through the ground stress limitation, and a plurality of radial short cracks are formed along the shaft. In order to further improve the extension distance of the crack, researchers utilize different burning rate combinations of different gunpowder and control the burning rate of the fracturing gunpowder to form a plurality of continuously loaded pulse pressures in the stratum so as to increase the blasting time of a shaft and further achieve the effect of multistage blasting and fracturing. However, the method still adopts shaft blasting, and the fracture is difficult to extend to a far-end stratum and is difficult to form a large-range network fracture. Therefore, in the process of developing shale gas, the limitation of the framework in the prior art needs to be broken through, and a new fracturing process is developed to realize green and efficient development of shale gas resources.
Disclosure of Invention
The invention aims to provide a shale reservoir multi-level radial horizontal well methane combustion explosion fracturing method, which solves the problems that in the prior art, fracturing fractures of a shale reservoir are single in shape and complex fracture networks are not easy to form, and the like, so that efficient development of shale gas resources is realized.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a shale reservoir multi-level radial horizontal well methane combustion and explosion fracturing method comprises the following steps:
1) determining a fracturing layer section: according to the logging data of the shale gas main shaft and the geological characteristics of a drilled reservoir, dividing the shale reservoir into a plurality of fracturing operation intervals, wherein each interval is used as an independent working process;
2) sidetrack drilling of a radial horizontal well by using a coiled tubing: the method comprises the following steps of drilling a plurality of radial horizontal wells perpendicular to a main shaft on the inner side of a fracturing operation interval of a shale gas reservoir by adopting a coiled tubing sidetracking method, wherein the radial horizontal wells in each fracturing operation interval are arranged in an upper layer and a lower layer, the radial horizontal wells in the same fracturing operation interval are collectively called a construction well group, the radial horizontal well group on the lower layer is called an injection well group, and the radial horizontal well group on the upper layer is called a fracturing well group;
3) arranging downhole tools and surface equipment: after all the construction well groups are drilled, putting down a fracturing tool to the bottom of the well through the continuous oil pipe, and installing and connecting ground equipment; the fracturing tool comprises a first-stage ejector, a second-stage ejector, a first-stage packer, a second-stage packer and a third-stage packer, wherein the first-stage packer, the first-stage ejector, the second-stage packer, the second-stage ejector and the third-stage packer are sequentially connected, the first-stage ejector and the second-stage ejector are respectively provided with a switchable sliding sleeve for opening and closing a fluid outlet on the ejector, and an ignition electrode is further arranged in the second-stage ejector; the ground equipment comprises a fluid injection system, coiled tubing equipment, a ground ignition device and a switchable sliding sleeve controller, wherein a cable is arranged in the coiled tubing, the front end of the cable is respectively connected with an ignition electrode and a starting device of the switchable sliding sleeve, and the tail end of the cable is respectively connected with the ground ignition device and the switchable sliding sleeve controller;
in the initial stage, the fracturing tool is firstly put down to the lowest fracturing operation interval, and the specific arrangement scheme of the fracturing tool is as follows: the first-stage packer is positioned below an injection well group of the fracturing operation interval, the second-stage packer is positioned between the injection well group and a fracturing well group, the third-stage packer is positioned above the fracturing well group, and fluid outlets of the first-stage ejector and the second-stage ejector are respectively positioned at the same depth as inlets of the injection well group and the fracturing well group; before fracturing operation, the switchable sliding sleeves in the ejector are all in a closed state, and the internal space of the fracturing tool is not communicated with the shaft at the moment;
4) supercritical CO2And (3) displacement operation: opening the switchable sliding sleeve in the first-stage ejector, and injecting supercritical CO into the injection well group through the ground fluid injection system through the coiled tubing2Fluid, supercritical CO2After entering the bottom of the well, the fluid flows into an injection well group of the fracturing operation interval from a fluid outlet on the first-stage ejector, and a closed space is formed between the packer and a radial horizontal well hole of the injection well group under the sealing action of the first-stage packer and the second-stage packer; supercritical CO under the action of fluid pressure2Penetrating into a reservoir around a radial horizontal well of the injection well group; supercritical CO2Can displace methane adsorbed on shale during flowing in a reservoir and displace the methane into a free state along with supercritical CO2Continuously injecting, wherein free methane gas in the reservoir is gradually displaced to the periphery of the fracturing well group above the fracturing layer section, and further flows into the fracturing well group from the reservoir; in supercritical CO2Under the displacement action of the fracturing well group, a large amount of methane gas flows into the radial horizontal well holes of the fracturing well group, and a methane accumulation zone is formed in a reservoir layer around the radial horizontal well holes, so that the methane concentration in the zone is increased;
5) pumping air into the fracturing well group: closing the switchable sliding sleeve in the first-stage ejector, then opening the switchable sliding sleeve in the second-stage ejector, injecting air into the radial horizontal well holes of the fracturing well group through the ground fluid injection system through the continuous oil pipe, and mixing the air injected into the fracturing well group with methane existing in the radial horizontal well holes to form a methane-air mixed fluid;
6) and (3) methane combustion and explosion fracturing operation: starting a ground ignition device, igniting the methane-air mixed fluid in the radial horizontal well bore of the fracturing well group by using electric sparks released by an ignition electrode in the second-stage ejector, so that the methane-air mixed fluid is combusted and exploded, and impacting reservoir rock by using instant shock waves generated by methane combustion and explosion and high-temperature and high-pressure gas to form complex artificial cracks around the radial horizontal well bore, thereby realizing methane combustion and explosion fracturing of the shale reservoir;
7) lifting the fracturing tool: lifting the fracturing tool in the main shaft to the next fracturing operation interval in a continuous oil pipe recovery mode, wherein the arrangement scheme of the fracturing tool is the same as that in the step 3);
8) repeating the steps 4) to 7), and continuing to perform supercritical CO2And (4) performing displacement and methane combustion and explosion fracturing operation until the methane combustion and explosion fracturing of the shale reservoir of the whole main shaft is completed.
Preferably, in step 2), the number and the orientation of the radial horizontal wells of each layer in each fracturing operation interval are the same.
Preferably, in step 4), supercritical CO2Is above the formation pressure of the reservoir and below the reservoir fracture pressure or fracture extension pressure.
Further, in step 3), the fluid injection system comprises an air cylinder group and CO2Bottle group, air compressor, gas booster and heater, air bottle group and CO2The gas outlet of the bottle group is respectively connected with the inlet of the gas booster, the outlet of the air compressor is connected with the other inlet of the gas booster, the outlet of the gas booster is connected with the inlet of the heater, and the outlet of the heater is connected with the injection end of the continuous oil pipe.
The invention combines the conventional explosive fracturing, radial horizontal well technology and supercritical CO2The displacement technology is combined, the shale reservoir is divided into different transformation areas by reasonably arranging the layer number, the branch number and the azimuth angle of the radial horizontal well, and methane blasting fracturing in the radial horizontal well is implemented in the corresponding areas, so that the traditional blasting fracturing operation area is expanded from a shaft to the deep part of the stratum, the methane blasting position and direction can be controlled, and the purpose of improving the blasting fracturing efficiency of the reservoir is achieved. Due to supercritical CO2The surface tension is extremely low, the diffusivity is extremely strong, and the supercritical CO is adopted to enable the fluid to flow in a compact shale reservoir more easily than other fluids2The displacement mode is beneficial to improving the desorption efficiency of methane into the radial well hole. Furthermore, supercritical CO2The adsorption capacity of the shale is larger than that of methane molecules, so that the supercritical CO is adopted2And a part of methane in an adsorbed state can be replaced into a free state and further displaced into a radial horizontal well to be fractured.
The shale reservoir methane explosion fracturing method provided by the invention firstly utilizes the radial horizontal well technology to provide larger explosion space and farther explosion position for shale reservoir methane, expands the effective action range of conventional explosion fracturing from the periphery of the main shaft to the deep part of the reservoir, further forms complex artificial fractures in the reservoir, and effectively solves the limitation of insufficient fracture expansion range in the explosion fracturing. In addition, the instantaneous impact effect generated by methane explosion can overcome the limit of ground stress on the crack expansion direction, and the crack expansion and extension along a single direction can be avoided, so that a complex crack net can be formed in a reservoir.
Drawings
FIG. 1 is a schematic illustration of the distribution of a fracture job interval within a shale reservoir in accordance with the method of the present invention;
FIG. 2 is a schematic view of the radial horizontal well distribution in the process of the present invention;
FIG. 3 is a schematic representation of a downhole fracturing tool and surface equipment in the method of the present invention;
FIG. 4 is a schematic illustration of the closure of the sliding sleeve within the downhole fracturing tool in the method of the present invention;
FIG. 5 is a schematic view of the opening of the inner sliding sleeve of the downhole fracturing tool in the method of the present invention;
FIG. 6 shows supercritical CO in the process of the present invention2A displacement process schematic;
FIG. 7 is a schematic diagram of the pumping of air into a frac well string in the method of the present invention;
FIG. 8 is a schematic representation of methane deflagration fracturing within a radial horizontal well in the method of the present invention;
FIG. 9 is a schematic representation of the downhole fracturing tool being lifted in the method of the present invention;
FIG. 10 is a second supercritical CO stage of the process of the present invention2A displacement schematic;
FIG. 11 is a schematic representation of a second methane deflagration fracturing of a radial horizontal well in the method of the present invention;
FIG. 12 is a schematic representation of the overall fracturing reformation effect of a reservoir in the method of the present invention;
in the figure: 1. a main shaft 2, fracturing operation layer sections I and 3, fracturing operation layer sections II and 4, fracturing operation layer sections III, 5 a-5 f,Radial horizontal wells (injection well group), 6 a-6 f, radial horizontal wells (fracturing well group), 7, coiled tubing, 8a, a first-stage packer, 8b, a second-stage packer, 8c, a third-stage packer, 9a, a first-stage injector, 9b, a second-stage injector, 10, an injector fluid outlet, 11, an ignition electrode, 12, a cable, 13, a switchable sliding sleeve, 14, an ignition device, 15, a switchable sliding sleeve controller, 16, an air bottle group, 17, CO2A cylinder group, 18, a gas booster, 19, an air compressor, 20, a heater, 21, a coiled tubing operation vehicle, 22, a coiled tubing roller, 23, a coiled tubing injection head, 24, CO2Fluid, 25, supercritical CO2Fluid, 26, methane, 27, supercritical CO2Displacement zone, 28, supercritical CO2Methane mixing zone, 29, methane accumulation zone, 30, air, 31, high pressure air, 32, complex fissures.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples.
The invention provides a shale reservoir multi-level radial horizontal well methane blasting fracturing method, and aims to improve the control volume of a shale gas single well and form complex fractures in the reservoir. In the specific implementation, the existing methane of a shale reservoir is used as a fuel, the air injected from the ground is mixed with the methane of the shale reservoir to form a combustible mixed fluid, and then the combustible fluid is subjected to combustion and explosion in a radial horizontal well in a downhole ignition mode to generate impact pressure to fracture the reservoir, so that a large-range three-dimensional network fracture is formed, and the method specifically comprises the following steps:
1) a fractured interval of the shale reservoir is determined. And dividing the reservoir into a plurality of fracturing operation intervals according to the logging data of the shale gas main shaft and the geological characteristics of the reservoir drilled by the shale gas main shaft. In the embodiment shown in fig. 1, the reservoir encountered by shale gas main wellbore 1 is divided into three fracturing operation intervals: namely a fracturing operation interval I2, a fracturing operation interval II 3 and a fracturing operation interval III 4, wherein each operation interval is used as an independent working process;
2) and sidetrack drilling a radial horizontal well by using the coiled tubing. As shown in fig. 2, an upper radial horizontal well and a lower radial horizontal well which are perpendicular to the main shaft 1 are drilled in each fracturing operation interval by adopting a coiled tubing sidetracking method, the number and the direction of each radial horizontal well are the same, and the drilled radial horizontal wells are located in the well-divided fracturing operation intervals. In the embodiment shown in fig. 2, the radial horizontal wells at the same depth are arranged in a symmetrical double wing arrangement, and the borehole axis is parallel to the direction of minimum horizontal ground stress. The radial horizontal wells in the same fracturing operation interval are collectively called a construction well group, namely each construction well group comprises an upper layer of radial horizontal well group and a lower layer of radial horizontal well group, each group comprises a plurality of radial horizontal wells, the radial horizontal well group on the lower layer is called an injection well group, and the radial horizontal well group on the upper layer is called a fracturing well group. As shown in fig. 2, the set of construction wells in the first fracturing interval 2 includes radial horizontal wells 5a, 5b, 6a, and 6b, the set of construction wells in the second fracturing interval 3 includes radial horizontal wells 5c, 5d, 6c, and 6d, and the set of construction wells in the third fracturing interval 4 includes radial horizontal wells 5e, 5f, 6e, and 6 f. The radial horizontal wells 5a to 5f are injection well groups in corresponding fracturing operation intervals, and the radial horizontal wells 6e to 6f are fracturing well groups in corresponding fracturing operation intervals.
3) Downhole tools and surface equipment are deployed. After all the construction well groups are drilled, the fracturing tool is put down to the first fracturing operation interval 2 of the bottommost layer through the coiled tubing 7 in the mode shown in the figure 3, and ground equipment is installed and connected. The used fracturing tool consists of a first-stage packer 8a, a first-stage ejector 9a, a second-stage packer 8b, a second-stage ejector 9b and a third-stage packer 8c from bottom to top in sequence, namely the two-stage ejectors are respectively positioned between every two packers. The specific arrangement scheme of the fracturing tool is as follows: the first-stage packer 8a is located below an injection well group (radial horizontal wells 5 a-5 b) of the first fracturing operation interval 2, the second-stage packer is located between the injection well group (radial horizontal wells 5 a-5 b) and a fracturing well group (radial horizontal wells 6 a-6 b) of the first fracturing operation interval 2, the third-stage packer is located above the fracturing well group (radial horizontal wells 6 a-6 b), a fluid outlet 10 of the first-stage ejector 9a is aligned with inlets of the injection well group (radial horizontal wells 5 a-5 b), and a fluid outlet 10 of the second-stage ejector 9b is aligned with inlets of the fracturing well group (radial horizontal wells 6 a-6 b). The second stage injector 9b used has an ignition electrode 11 built in and the coiled tubing 7 has a cable 12 built in. The front end of the cable 12 is connected with an ignition electrode 11 in the fracturing tool and a switchable sliding sleeve 13 on the ejectors 9 a-9 b (figures 4 and 5), and the tail end of the cable is connected with an ignition device 14 on the ground and a switchable sliding sleeve controller 15. As shown in fig. 4, before the fracturing operation is performed, the sliding sleeves 13 of the injectors 9a to 9b are all in a closed state, and fluid cannot enter the well bore 1 from the fluid outlets 10 on the injectors.
In addition to the surface ignition 14 and the switchable sleeve controller 15, the surface equipment also contains a fluid injection system and coiled tubing equipment. The fluid injection system comprises an air cylinder group 16, CO2Cylinder group 17, gas booster 18, air compressor 19 and heater 20, air cylinder group 16 and CO2The outlets of the cylinder groups 17 are respectively connected with the inlets of the gas superchargers 18, the outlet of the air compressor 19 is connected with the other inlet of the gas superchargers 18, the outlet of the gas superchargers 18 is connected with the inlet of the heater 20, and the outlet of the heater 20 is connected with the injection end of the coiled tubing 7. The coiled tubing equipment comprises a coiled tubing operation vehicle 21, a coiled tubing roller 22 and a coiled tubing injection head 23 besides the coiled tubing 7, wherein the coiled tubing roller 22 is arranged on a frame of the coiled tubing operation vehicle 21, one end of the coiled tubing 7 is wound on the coiled tubing roller 22, the other end of the coiled tubing 7 is connected with the fracturing tool, and the coiled tubing injection head 23 is arranged on the coiled tubing 7 exposed out of a wellhead device.
4) Supercritical CO2And (5) performing displacement operation. The surface switchable sleeve control 15 is activated to move the sleeve 13 in the first stage injector 9a downwardly to open the sleeve 13 (fig. 5) and the fracturing tool internal volume is now in communication with the main wellbore 1 through the fluid outlet 10 in the fracturing tool. Turning on the CO as shown in FIG. 62Cylinder set 17 valve for CO2The fluid 24 enters the gas booster 18 through a ground pipeline, and the gas booster 18 drives the air compressor 19 to supply CO into the gas booster 182The fluid 24 is pressurized above the critical pressure (7.38MPa) and then heated above the critical temperature (31.1 ℃) by the heater 20. At this time, the fluid injected through the coiled tubing 7 is supercritical CO2A fluid 25. Supercritical CO2After entering the well bottom, the fluid 25 flows out from a fluid outlet 10 on a fracturing tool body 9a, and under the sealing action of a first-stage packer 8a and a second-stage packer 8b, a closed space is formed between the packers and radial horizontal wells 5 a-5 b of an injection well group, and supercritical CO2The fluid 25 will seep into the surrounding reservoir of the radial horizontal wells 5 a-5 b of the injection well group. Due to supercritical CO2The adsorption strength with shale is far greater than that with methane, so the supercritical CO2The methane adsorbed on the shale can be replaced when flowing in the reservoir and replaced into a free state. With supercritical CO2And continuously injecting the fluid 25, gradually displacing the free methane gas in the reservoir to the periphery of the fractured well group, and further flowing into the radial horizontal wells 6 a-6 b of the fractured well group from the reservoir to form the free methane 26. In supercritical CO2Under the continuous displacement action of the fluid 25, supercritical CO is formed between the injection well group (radial horizontal wells 5 a-5 b) and the fracturing well group (radial horizontal wells 6 a-6 b)2 Displacement zone 27, supercritical CO2A methane mixing zone 28 and a methane accumulation zone 29. The methane accumulation zone 29 will cause the methane concentration around the radial horizontal wells 6 a-6 b to increase and significant amounts of methane 26 will enter the wellbore. In supercritical CO2Supercritical CO during the displacement2The injection pressure of fluid 25 is slightly above the formation pressure of the reservoir and below the reservoir fracture or fracture propagation pressure.
5) And pumping air into the fracturing well group. By controlling the ground switchable sliding sleeve controller 15 to move the sliding sleeve 13 in the first-stage injector 9a upwards so as to close the sliding sleeve according to the state shown in fig. 4, and controlling the sliding sleeve 13 in the second-stage injector 9b to move downwards so as to open the sliding sleeve according to the manner shown in fig. 5, the fluid in the coiled tubing 7 can enter the radial horizontal wells 6 a-6 b through the fluid outlet 10 on the second-stage injector 9 b. As shown in fig. 7, the valve of the air tank set 16 is opened, and the air 30 flowing out of the air tank set 16 is pressurized by the gas booster 18 to form high-pressure air 31 in the manner of step 4). When the high pressure air 31 is pumped in, the heater 20 is in a closed state, i.e., the air injected into the bottom of the well is not heated. After entering the bottom of the well, the high pressure air 31 enters the fracturing well group (radial horizontal wells 6 a-6 b) of the interval through the fluid outlet 10 on the second stage injector 9b and mixes with the methane 26 in the well bore to form a methane-air mixed fluid.
6) And (5) methane blasting and fracturing operation. As shown in fig. 8, the ground ignition device 14 is activated to ignite and explode the methane-air mixture fluid in the radial horizontal wells 6a to 6b with the electric spark discharged from the ignition electrode 11 in the second stage injector 9 b. Impact waves generated by methane instantaneous blasting and high-temperature and high-pressure gas impact reservoir rocks, and complex cracks 32 are formed around the radial horizontal wells 6 a-6 b, so that methane blasting fracturing in the shale reservoir is realized. Because the methane explosion action time is short, the pressure rise speed in the radial horizontal well is high, the complex fracture 32 generated by methane explosion fracturing not only contains conventional tension fracture, but also is damaged along with the shearing of reservoir rock, and causes complex mechanical behaviors such as slippage, dislocation and the like of the fracture surface. Because the dislocation and the slippage of the rocks on the two sides of the shear fracture in the reservoir are unrecoverable, the self-supporting capacity of the fracture is greatly enhanced, the fracture closure after the fracturing can be effectively prevented, and the fracturing effect of the reservoir is improved.
7) As shown in fig. 9, the fracturing tool in the main shaft 1 is lifted to the second fracturing operation interval 3 by recovering the coiled tubing 7, and the arrangement scheme of the fracturing tool is the same as that of the step 3): the first-stage packer 8a of the fracturing tool is positioned below an injection well group (radial horizontal wells 5 c-5 d) of the interval, the second-stage packer 8b is positioned between the injection well group (radial horizontal wells 5 c-5 d) and a fracturing well group (radial horizontal wells 6 c-6 d), the third-stage packer 8c is positioned above the fracturing well group (radial horizontal wells 6 c-6 d), and the fluid outlets 10 of the first-stage ejector 9a and the second-stage ejector 9b are respectively aligned with the inlets of the injection well group and the fracturing well group of the interval. The switchable sliding sleeve 13 in the two-stage injector is in a closed state.
8) Repeating the steps 4) to 6), and continuing to perform supercritical CO2Displacing and methane burning explosion fracturing operation, supercritical CO in the second fracturing operation layer section 32The displacement and methane detonation fracturing effects are shown in fig. 10 and 11.
9) And as shown in fig. 12, repeating the steps 7) to 8) until the methane explosion fracturing of the shale reservoir of the whole main shaft 1 is completed.
The shale reservoir methane explosion fracturing method provided by the invention firstly utilizes the radial horizontal well technology to provide larger explosion space and farther explosion position for shale reservoir methane, expands the operation mode that fuel or explosive can only be exploded in a main shaft in the conventional explosion fracturing into deep explosion of the reservoir, and forms complex artificial cracks in the reservoir, thereby effectively solving the limitation of insufficient crack expansion range in the explosion fracturing. In addition, the instantaneous impact effect generated by methane explosion can overcome the limit of ground stress on the crack expansion direction, and the crack expansion and extension along a single direction can be avoided, so that a complex crack net can be formed in a reservoir. Because the methane explosion action time is short, the pressure boosting speed in the radial horizontal well is high, cracks generated by methane explosion fracturing not only contain conventional tension fracture, but also are sheared and damaged along with reservoir rock, and complex mechanical behaviors such as slippage, dislocation and the like of crack surfaces are caused. Because the dislocation and the slippage of the rocks on the two sides of the shear fracture in the reservoir are unrecoverable, the self-supporting capacity of the fracture is greatly enhanced, the fracture closure after the fracturing can be effectively prevented, and the fracturing effect of the reservoir is improved.
Claims (4)
1. A shale reservoir multi-level radial horizontal well methane combustion and explosion fracturing method is characterized by comprising the following steps:
1) determining a fracturing layer section: according to the logging data of the shale gas main shaft and the geological characteristics of a drilled reservoir, dividing the shale reservoir into a plurality of fracturing operation intervals, wherein each interval is used as an independent working process;
2) sidetrack drilling of a radial horizontal well by using a coiled tubing: the method comprises the following steps of drilling a plurality of radial horizontal wells perpendicular to a main shaft on the inner side of a fracturing operation interval of a shale gas reservoir by adopting a coiled tubing sidetracking method, wherein the radial horizontal wells in each fracturing operation interval are arranged in an upper layer and a lower layer, the radial horizontal wells in the same fracturing operation interval are collectively called a construction well group, the radial horizontal well group on the lower layer is called an injection well group, and the radial horizontal well group on the upper layer is called a fracturing well group;
3) arranging downhole tools and surface equipment: after all the construction well groups are drilled, putting down a fracturing tool to the bottom of the well through the continuous oil pipe, and installing and connecting ground equipment; the fracturing tool comprises a first-stage ejector, a second-stage ejector, a first-stage packer, a second-stage packer and a third-stage packer, wherein the first-stage packer, the first-stage ejector, the second-stage packer, the second-stage ejector and the third-stage packer are sequentially connected, the first-stage ejector and the second-stage ejector are respectively provided with a switchable sliding sleeve for opening and closing a fluid outlet on the ejector, and an ignition electrode is further arranged in the second-stage ejector; the ground equipment comprises a fluid injection system, coiled tubing equipment, a ground ignition device and a switchable sliding sleeve controller, wherein a cable is arranged in the coiled tubing, the front end of the cable is respectively connected with an ignition electrode and a starting device of the switchable sliding sleeve, and the tail end of the cable is respectively connected with the ground ignition device and the switchable sliding sleeve controller;
in the initial stage, the fracturing tool is firstly put down to the lowest fracturing operation interval, and the specific arrangement scheme of the fracturing tool is as follows: the first-stage packer is positioned below an injection well group of the fracturing operation interval, the second-stage packer is positioned between the injection well group and a fracturing well group, the third-stage packer is positioned above the fracturing well group, and fluid outlets of the first-stage ejector and the second-stage ejector are respectively positioned at the same depth as inlets of the injection well group and the fracturing well group; before fracturing operation, the switchable sliding sleeves in the ejector are all in a closed state, and the internal space of the fracturing tool is not communicated with the shaft at the moment;
4) supercritical CO2And (3) displacement operation: opening the switchable sliding sleeve in the first-stage ejector, and injecting supercritical CO into the injection well group through the ground fluid injection system through the coiled tubing2Fluid, supercritical CO2After entering the bottom of the well, the fluid flows into an injection well group of the fracturing operation interval from a fluid outlet on a first-stage ejector, a closed space is formed between the packer and a radial horizontal well hole of the injection well group under the sealing action of a first packer and a second packer, and supercritical CO is generated under the action of fluid pressure2Will permeatePenetrating to a reservoir layer around a radial horizontal well of the injection well group; supercritical CO2Can displace methane adsorbed on shale during flowing in a reservoir and displace the methane into a free state along with supercritical CO2Continuously injecting, wherein free methane gas in the reservoir is gradually displaced to the periphery of the fracturing well group above the fracturing layer section, and further flows into the fracturing well group from the reservoir; in supercritical CO2Under the displacement action of the fracturing well group, a large amount of methane gas flows into the radial horizontal well bores of the fracturing well group, and a methane accumulation zone is formed in a reservoir stratum around the radial horizontal well bores of the fracturing well group, so that the methane concentration of the reservoir stratum around the radial horizontal well of the fracturing well group is increased;
5) pumping air into the fracturing well group: closing the switchable sliding sleeve in the first-stage ejector, then opening the switchable sliding sleeve in the second-stage ejector, injecting air into the radial horizontal well holes of the fracturing well group through the ground fluid injection system through the continuous oil pipe, and mixing the air injected into the fracturing well group with methane existing in the radial horizontal well holes to form a methane-air mixed fluid;
6) methane combustion and explosion fracturing operation: starting a ground ignition device, igniting the methane-air mixed fluid in the radial horizontal well bore of the fracturing well group by using electric sparks released by an ignition electrode in the second-stage ejector, so that the methane-air mixed fluid is combusted and exploded, and impacting reservoir rock by using instant shock waves generated by methane combustion and explosion and high-temperature and high-pressure gas to form complex artificial cracks around the radial horizontal well bore, thereby realizing methane combustion and explosion fracturing of the shale reservoir;
7) lifting the fracturing tool: lifting the fracturing tool in the main shaft to the next fracturing operation interval in a continuous oil pipe recovery mode, wherein the arrangement scheme of the fracturing tool is the same as that in the step 3);
8) repeating the steps 4) to 7), and continuing to perform supercritical CO2And (4) performing displacement and methane combustion and explosion fracturing operation until the methane combustion and explosion fracturing of the shale reservoir of the whole main shaft is completed.
2. The shale reservoir multi-level radial horizontal well methane combustion and explosion fracturing method according to claim 1, wherein in the step 2), the number and the orientation of radial horizontal wells in each layer in each fracturing operation interval are the same.
3. The shale reservoir multi-level radial horizontal well methane combustion and explosion fracturing method according to claim 1, wherein in the step 4), supercritical CO is adopted2Is higher than the formation pressure of the reservoir and lower than the reservoir fracture pressure or fracture extension pressure.
4. The shale reservoir multi-level radial horizontal well methane combustion and explosion fracturing method as claimed in claim 1, wherein in the step 3), the fluid injection system comprises an air bottle group and CO2Bottle group, air compressor, gas booster and heater, air bottle group and CO2The gas outlet of the bottle group is respectively connected with the inlet of the gas booster, the outlet of the air compressor is connected with the other inlet of the gas booster, the outlet of the gas booster is connected with the inlet of the heater, and the outlet of the heater is connected with the injection end of the continuous oil pipe.
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