CN114352253B - Shale reservoir methane multiple in-situ combustion-explosion fracturing method - Google Patents
Shale reservoir methane multiple in-situ combustion-explosion fracturing method Download PDFInfo
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Abstract
A shale reservoir methane multiple in-situ combustion-explosion fracturing method comprises the steps of putting a gaseous combustion improver into an underground fracturing tool through a continuous oil pipe; increasing the injection pressure to enable the fluke of the hydraulic anchor to extend outwards and to be embedded into the well wall, and enabling the packer to expand and to be seated on the well wall; carrying out electric shock ignition on the methane-gaseous combustion improver mixture in the shaft to ensure that the methane-gaseous combustion improver mixture is subjected to in-situ combustion and explosion in the current fracturing well section; putting the fracturing tool down to the tail end of the fracturing well section again, and performing repeated blasting fracturing; by using supercritical CO 2 Transporting the solid combustion improver particles into the complex fractures formed; forming a complex seam net with larger scale through the multiple in-situ burning and exploding of methane in a shaft and the complex seam; continuously carrying out methane in-situ combustion-explosion fracturing until a highly complex three-dimensional fracture network is formed in the shale reservoir; sequentially completing the fracturing operation of each fracturing well section at different positions of the shaftAnd generating a plurality of groups of complex three-dimensional fracture networks. The method can realize the high-efficiency development of unconventional natural gas such as shale gas.
Description
Technical Field
The invention belongs to the technical field of unconventional oil and gas exploitation and shale gas fracturing yield increase, and particularly relates to a shale reservoir methane multiple in-situ combustion-explosion fracturing method.
Background
At present, unconventional natural gas represented by shale gas becomes an important component of oil and gas supply, and how to realize efficient development of reservoirs of the type becomes a research hotspot in the field of petroleum engineering. But is vulnerable to external invasion fluid due to poor shale gas reservoir quality. For example, in well drilling and completion operations, when water is trapped in internal pores and fractures of the rock, it can lead to an increase in the water saturation of the formation, which in turn can impede the flow of gas; for clay mineral rich formations, the water phase also causes clay minerals to swell and migrate, thereby plugging the gas flow channels. In addition, shale gas development consumes a large amount of water, for example, the water consumption for fracturing a shale gas well is often as high as tens of thousands of parties, and the injected fluid into the formation mostly contains a large amount of chemical components such as bactericides, friction reducers and clay inhibitors, which involves the problems of water resource use and protection. Along with the gradual emphasis on unconventional natural gas resources such as shale gas and the like, new requirements are also put forward on the fracturing technology. In addition to minimizing reservoir damage and environmental pollution, the volume of fracture reconstruction is of greater importance rather than just the length of the fracture. For example, in the case of shale gas, one of the keys to fracturing is how to form highly complex three-dimensional networks of fractures within shale reservoirs. However, in actual operation, the problems of single fracture form, insufficient rock breaking degree of a reservoir and the like frequently exist in shale gas reservoir fracturing, and a series of environmental problems are brought by simply increasing the fracturing scale to improve the fracture complexity. Under the circumstances, the research and development of a novel fracturing process are urgently needed, and the efficient development of unconventional natural gas such as shale gas is realized.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a shale reservoir methane multiple in-situ combustion-explosion fracturing method, which can form a highly complex three-dimensional seam network in a shale reservoir, can effectively enlarge the volume of fracturing modification and can realize the efficient development of unconventional natural gas such as shale gas; meanwhile, the method can greatly reduce the consumption of water resources, help to reduce the damage to the reservoir and also be beneficial to reducing the pollution degree to the environment.
In order to achieve the aim, the invention provides a shale reservoir methane multiple in-situ combustion-explosion fracturing method which comprises a continuous oil pipe, a hydraulic anchor, a packer, a fracturing tool, a ground ignition device and a bridge plug, wherein the continuous oil pipe is connected with the hydraulic anchor; a cable is arranged in the continuous oil pipe, an anchor claw is connected to the hydraulic anchor, and an ignition electrode is arranged in the fracturing tool; the hydraulic anchor, the packer and the fracturing tool are sequentially connected to the tail end of the coiled tubing from front to back; the ground ignition device is arranged on the ground;
the method specifically comprises the following steps;
the method comprises the following steps: the preparation work comprises the following specific steps:
s11: determining a well section needing to be fractured according to the shale reservoir geological parameters and the logging data;
s12: numbering the fracturing well sections in a subsection mode according to the sequence from the bottom to the wellhead, wherein the fracturing well sections at least comprise a first fracturing well section, a second fracturing well section and a third fracturing well section;
s13: conveying a bridge plug into the shaft, and setting the bridge plug at the tail end of the first fracturing well section;
s14: putting the fracturing tool down to the tail end of the first section of the fracturing well section by using a continuous oil pipe, and connecting an ignition electrode with a ground ignition device through a cable;
step two: feeding a gaseous combustion improver;
feeding a gaseous combustion improver into a downhole fracturing tool through a continuous oil pipe, so that the gaseous combustion improver enters a shaft annulus from a nozzle of the fracturing tool and then is mixed with methane to form a methane-gaseous combustion improver mixture; when the gaseous combustion improver is put in, the continuous oil pipe is upwards recovered at a certain speed, so that the fracturing tool is dragged to move towards a wellhead, and the recovery operation of the continuous oil pipe is stopped when the fracturing tool is about to leave the current fracturing well section;
step three: the method comprises the following specific steps of:
s31: after the continuous oil pipe is stopped to be recovered, the injection pressure of the gaseous combustion improver is increased, the anchor flukes of the hydraulic anchors are extended outwards and embedded into the well wall under the action of the fluid pressure, and meanwhile, the packers connected with the fracturing tool are expanded and set on the well wall under the action of the fluid pressure;
s32: carrying out electric shock ignition on the methane-gaseous combustion improver mixture in the shaft through an ignition electrode in the fracturing tool, so that the methane-gaseous combustion improver mixture is subjected to in-situ combustion explosion in the current fracturing well section; the instantaneous high pressure generated by burning and exploding the methane-gaseous combustion improver mixture is utilized to carry out impact fracturing on the stratum around the shaft, and a plurality of radial impact fractures are formed around the shaft;
step four: repeating blasting and fracturing operation on the shaft;
putting the fracturing tool down to the tail end of the current fracturing well section again, then repeating the second step and the third step, performing repeated blasting fracturing on the current fracturing well section, repeatedly impacting the stratum around the shaft by utilizing the high-pressure action of multiple blasting of the methane-gaseous combustion improver mixture, and forming complex cracks around the shaft;
step five: putting a solid combustion improver;
by using supercritical CO 2 Conveying the solid combustion improver particles into the complex cracks formed in the fourth step, and utilizing supercritical CO 2 Adsorption state methane on shale matrix by fluidReplacing the mixture into a free state to form a methane-solid combustion improver particle mixture in the complex crack;
step six: shaft － Performing multiple combustion and explosion fracturing operations on the crack methane;
continuously adding a gaseous combustion improver into the shaft according to the mode in the step two, and performing shaft blasting and fracturing operation according to the mode in the step three; high-temperature high-pressure gas generated by burning and exploding methane-gaseous combustion improver mixture in the shaft is used for detonating the methane-solid combustion improver particle mixture in the complex cracks, in-situ burning and exploding fracturing of methane in the complex cracks is continuously carried out, and the existing complex cracks are promoted to continuously expand and extend to form complex crack nets with larger sizes under the action of multiple in-situ burning and exploding of methane in the shaft and the complex cracks;
step seven: forming a highly complex three-dimensional fracture network in the shale reservoir;
repeating the fifth step and the sixth step, continuously performing methane in-situ combustion-explosion fracturing on the shaft and the stratum around the complex fractures, and promoting the complex fractures to grow until a highly complex three-dimensional fracture network is formed in the shale reservoir stratum;
step eight: completing methane multiple in-situ combustion-explosion fracturing operation of the whole shaft;
and moving the fracturing tool to the next fracturing well section, and repeating the second step to the seventh step until the methane multiple in-situ combustion-explosion fracturing operation of the shale reservoir in all the well sections to be fractured is completed, and generating a plurality of groups of complex three-dimensional fracture networks at different positions of a shaft.
Further, in order to ensure the plugging effect, the pressure bearing capacity of the bridge plug and the packer is not lower than 200 MPa.
Further, in order to make the combustion-supporting effect more ideal, in the second step, the gaseous combustion improver is oxygen.
Preferably, in order to further improve the uniformity of the arrangement of the gaseous combustion improver in the fracturing well section and further increase the mixing degree of the methane and the gaseous combustion improver, in the second step, the recovery speed of the continuous oil pipe is 0.5-1.0 m/s.
Further, in order to ensure that a highly complex fracture network is formed, in the fourth step, the fracturing tool is lowered to the tail end of the current fracturing well section again in a coiled tubing lowering mode, and the second step and the third step are repeated for 3-4 times.
Furthermore, in order to enable the combustion-supporting effect to be better and simultaneously ensure that a solid reactant capable of being filled into the complex crack is formed after combustion and explosion so as to ensure that the crack can not be closed under the action of ground stress after combustion, explosion and fracturing, in the fifth step, the solid combustion-supporting agent particles are potassium permanganate particles.
Furthermore, in order to accurately put the potassium permanganate particles into all the complex cracks, in the fifth step, the potassium permanganate particles and supercritical CO are firstly put into 2 Fully mixing the mixture on the ground to form supercritical CO 2 -potassium permanganate particle mixture, supercritical CO through coiled tubing 2 -the potassium permanganate particulate mixture is conveyed into the complex fracture formed in step four.
Further, in order to increase the supercritical CO 2 And (5) carrying capacity of potassium permanganate particles, wherein in the step five, the volume fraction of the potassium permanganate particles is lower than 15%, and the particle diameter is 0.147-0.210 mm.
Further, in order to reduce the risk of solid particle plugging in the wellbore and fractures, in step five, the supercritical CO 2 The pressure is greater than the fracture propagation pressure of the formation.
Further, in order to ensure that the formed three-dimensional fracture network can have a larger extension range and a higher complexity, in the seventh step, the fifth step and the sixth step are repeated for not less than 3 times.
In the technical scheme, the bridge plug is arranged at the tail end of the first section of fracturing well section in a setting mode, so that the area between the first fracturing well section and the tail end of the shaft can be blocked, and the gaseous combustion improver can be prevented from diffusing to a non-fracturing operation area. When gaseous combustion improver is thrown into a shaft, the fracturing tool is dragged to move upwards, and the gaseous combustion improver can be increased in the process of pressing by the mode of dragging the fracturing tool to throw the gaseous combustion improverThe uniformity of arrangement in the fractured well section can be improved, the mobility of methane and gaseous combustion improver in the shaft can be improved through the movement of the fracturing tool, the contact area of the gaseous combustion improver and the methane in the shaft is increased, the mixing degree of the methane and the gaseous combustion improver can be effectively improved, and simultaneously, the methane-gaseous combustion improver mixture is favorably filled in all positions of the current fractured well section; the fluke of the hydraulic anchor extends outwards and is embedded into the well wall under the action of the pressure of fluid, so that the hydraulic anchor can play a role in fixing a fracturing tool and a continuous oil pipe, and can limit the movement of the fracturing tool in the blasting process, so that impact generated in the blasting process can be intensively applied to the current fracturing well section. Utilize fluidic pressure to make the packer inflation and seat seal on the wall of a well, can make current fracturing well section form sealed space with the bridging plug combined action, like this, not only can make the blasting region inject in current fracturing well section, can also show the effect that improves the impact of current fracturing well section place stratum and send the fracture, can help forming the impact fracture that the extension is wider. The reservoir rock is fractured by instantaneous high-pressure impact generated by burning explosion of a methane-gaseous combustion improver mixture, complex cracks can be formed in a shale reservoir, and meanwhile, the pressure generated by in-situ burning explosion of methane in a shaft and the cracks can reach over 60MPa within tens of milliseconds. By repeatedly carrying out blasting fracturing operation in the current fracturing well section, the extension range and the extension complexity of complex cracks of a shaft can be further increased, the complex cracks formed in the way not only can provide more sufficient blasting space for in-situ blasting of methane in a storage layer, but also can increase the path of expansion of follow-up cracks, and are beneficial to promoting the cracks to expand along more directions, thereby being beneficial to forming a highly complex crack network. Due to supercritical CO 2 Is an inert fluid, contains no water phase, and is in contact with the formationThe fluid is not easy to produce chemical reaction, and supercritical CO is used 2 The solid combustion improver particles are conveyed into the complex cracks as the carrying fluid of the solid combustion improver, so that the solid combustion improver particles can be prevented from being dissolved, and can be isolated from formation fluid, and further the solid combustion improver particles can be isolated and protected, and the solid combustion improver particles can be conveyed into the complex cracks more accurately; when supercritical CO 2 Supercritical CO after the fluid and the solid combustion improver particles carried by the fluid enter the complex cracks 2 The flow rate of (a) will drop rapidly and solid combustion improver particles begin to settle in the cracks; at the same time, due to supercritical CO 2 The composite material has strong diffusion capability and low surface tension, is easy to permeate into shale micropores, can replace adsorbed methane on a shale matrix into a free state, and further can increase the concentration of methane in the cracks, and is favorable for more fully mixing methane and potassium permanganate particles, so that after the solid combustion improver is put in, the uniformity of a methane-solid combustion improver particle mixture formed in the cracks can be better, and the strength and the effect of subsequent blasting can be effectively enhanced. In the process of carrying out multiple combustion-explosion fracturing operation by using methane, the methane-gaseous combustion improver mixture in the shaft and the methane-solid combustion improver particles in the cracks can be comprehensively utilized to carry out in-situ combustion-explosion to generate pressure-induced fracture on the stratum in a mode of arranging different types of combustion improvers in the shaft and the cracks, so that the effective range of conventional combustion-explosion fracturing can be expanded from the periphery of the shaft to the interior of a shale reservoir. Therefore, by implementing the mode of methane multiple in-situ combustion-explosion fracturing in the shaft and the shale reservoir, the in-situ combustion-explosion fracturing effect and range of methane can be exerted to the maximum extent, so that the existing cracks in the shale reservoir can be promoted to expand and extend to form a complex crack network with a larger scale, the volume fracturing of the low-permeability and ultra-low permeability shale reservoir is favorably realized, and the three-dimensional cracks with high flow conductivity are favorably constructed; meanwhile, in the multiple combustion and explosion fracturing process, after methane and solid combustion improver particles in the complex fracture are combusted and exploded, a large amount of solid reactants can be generated, the solid reactants can play a role similar to a propping agent, can be effectively supported and filled in the fractured fracture, and the multiple combustion and explosion fracturing process comprises the steps ofThe opening degree of the crack is increased, and the crack can be effectively prevented from being closed under the action of the ground stress after fracturing is finished. And repeatedly carrying out methane in-situ combustion and explosion fracturing on the shaft and the stratum around the complex fractures, so that the complex fractures can be further promoted to grow, and a highly complex three-dimensional fracture network can be formed in the shale reservoir.
According to the invention, gaseous combustion improver is firstly put into a shaft and mixed with methane in a shale reservoir to form a methane-gaseous combustion improver mixture, then the methane-gaseous combustion improver mixture in the shaft is subjected to in-situ combustion explosion to form an initial crack around the shaft, a methane combustion explosion space in the reservoir is manufactured, solid combustion improver particles are put into the complex crack and mixed with the methane in the shale reservoir to form a methane-solid combustion improver mixture, then the methane-solid combustion improver particle mixture in the crack is detonated through the combustion explosion of the methane-gaseous combustion improver mixture in the shaft, and finally the multiple in-situ combustion explosion fracturing of the methane in the shaft-stratum is realized. The method takes methane in a shale reservoir as fuel, and puts different types of combustion improvers into a shaft and complex cracks on the ground to perform in-situ mixing with the methane in the shale reservoir, so that the traditional combustion-explosion fracturing operation range is expanded from the shaft to the shale reservoir cracks, the combination of methane in-situ combustion-explosion and reservoir modification technology is realized, and meanwhile, the methane in-situ combustion-explosion power can be exerted to the greatest extent, and the fracturing effect on reservoir rocks can be obviously improved.
Drawings
FIG. 1 is a schematic representation of a fracture interval division of the present invention;
FIG. 2 is a schematic diagram of the arrangement of the downhole fracturing tool of the present invention;
FIG. 3 is a schematic illustration of the present invention for delivering a gaseous oxidizer to a wellbore;
FIG. 4 is a schematic illustration of in situ deflagration fracturing of wellbore methane in accordance with the present invention;
FIG. 5 is a schematic illustration of the present invention of the delivery of solid oxidizer particles into a complex fracture;
FIG. 6 is a schematic representation of multiple in situ deflagration fracturing of methane in the wellbore and in the fractures according to the present invention;
FIG. 7 is a schematic diagram of the overall effect of multiple in-situ combustion-explosion fracturing of methane in a shale reservoir according to the invention.
In the figure: 1. shale reservoir stratum, 2 parts of a shaft, 3 parts of a first fracturing well section, 4 parts of a second fracturing well section, 5 parts of a third fracturing well section, 6 parts of a bridge plug, 7 parts of a continuous oil pipe, 8 parts of a fracturing tool, 9 parts of a packer, 10 parts of a hydraulic anchor, 11 parts of oxygen, 12 parts of a methane-oxygen mixture, 13 parts of an anchor claw, 14 parts of a complex fracture, 15 parts of a supercritical CO 2 -potassium permanganate particle mixture, 16, potassium permanganate particles, 17, cubic fracture network.
Detailed Description
The invention will be further explained with reference to the drawings.
As shown in fig. 1 to 7, the invention provides a multiple in-situ methane combustion and explosion fracturing method for a shale reservoir, which comprises a continuous oil pipe 7, a hydraulic anchor 10, a packer 9, a fracturing tool 8, a ground ignition device and a bridge plug 6; a cable is arranged in the continuous oil pipe 7, an anchor claw 13 is connected to the hydraulic anchor 10, and an ignition electrode is arranged in the fracturing tool 8; the hydraulic anchor 10, the packer 9 and the fracturing tool 8 are sequentially connected to the tail end of the continuous oil pipe 7 from front to back; the ground ignition device is arranged on the ground;
the method specifically comprises the following steps;
the method comprises the following steps: the preparation work comprises the following specific steps:
s11: determining a well section needing to be fractured according to the geological parameters and the logging data of the shale reservoir 1;
s12: numbering the fracturing well sections in a subsection mode according to the sequence from the well bottom to the well head, wherein the first fracturing well section 3, the second fracturing well section 4, the third fracturing well section 5 and … … and the nth fracturing well section are sequentially arranged; the fracturing well sections can be arranged continuously or discontinuously, and as a preferable mode, the application is preferably in a discontinuous arrangement mode, namely a certain distance exists between the fracturing well sections, and meanwhile, the number of the fracturing well sections is at least not less than 3, as shown in fig. 1 and 2;
s13: conveying a bridge plug 6 into the shaft 2, and setting the bridge plug 6 at the tail end of the first fracturing well section 3, so as to seal the area between the first fracturing well section 3 and the tail end of the shaft, thereby preventing the combustion improver in the shaft 2 from entering the area; in order to improve the plugging effect, the pressure bearing capacity of the bridge plug 6 is not lower than 200 MPa.
S14: as shown in fig. 2, a fracturing tool 8 is lowered to the tail end of the first fracturing well section 3 by using a coiled tubing 7, and an ignition electrode is connected with a ground ignition device through a cable, so that the ignition electrode can be conveniently started through the ground ignition device;
step two: feeding a gaseous combustion improver;
feeding a gaseous combustion improver to the underground fracturing tool 8 through the continuous oil pipe 7, so that the gaseous combustion improver enters the shaft annulus from a nozzle of the fracturing tool 8 and then is mixed with methane to form a methane-gaseous combustion improver mixture; preferably, in order to make the combustion-supporting effect more desirable, the gaseous combustion improver is oxygen 11, as shown in fig. 3. When the gaseous combustion improver is put in, the coiled tubing 7 is upwards recovered at a certain speed, so that the fracturing tool 8 is dragged to move towards the direction of a wellhead; preferably, in order to further improve the arrangement uniformity of the gaseous combustion improver in the fracturing well section and further increase the mixing degree of the methane and the gaseous combustion improver, the recovery speed of the continuous oil pipe 7 is 0.5-1.0 m/s. When the fracturing tool 8 is about to leave the current fractured interval, the coiled tubing 7 recovery operation is stopped to fill the first fractured interval 3 with a methane-oxygen mixture 12 as shown in figure 2.
Step three: the blasting fracturing operation of the shaft 2 comprises the following specific steps:
s31: after the coiled tubing 7 is stopped to be recovered, the injection pressure of the gaseous combustion improver is increased, as shown in fig. 4, with the increase of the injection pressure of the oxygen 11, the fluke 13 of the hydraulic anchor 10 extends out under the action of the fluid pressure, and then the fluke 13 of the hydraulic anchor 10 can extend out and be embedded into a well wall by utilizing the action of the fluid pressure so as to fix the fracturing tool 8 and the coiled tubing 7 and limit the movement of the fracturing tool 8 in the process of the detonation; simultaneously, the packer 9 connected with the fracturing tool 8 is expanded and set on the well wall by the action of fluid pressure, so that a closed space is formed between the packer 9 and the bridge plug 6; preferably, the pressure bearing capacity of the packer 9 is not less than 200MPa in order to ensure the plugging effect.
Fig. 4 shows a state in which the fluke 13 of the hydraulic anchor 10 is extended outward by the fluid pressure while the injection pressure of the oxygen gas 11 is increased.
S32: the methane-gaseous combustion improver mixture in the shaft 2 is ignited by electric shock through an ignition electrode in the fracturing tool 8, when the gaseous combustion improver is oxygen 11, the object of the electric shock ignition is the methane-oxygen mixture 12, so that the methane-gaseous combustion improver mixture is subjected to in-situ combustion explosion in the current fracturing well section; the method comprises the following steps of performing impact fracturing on a stratum around a shaft by using instantaneous high pressure generated by burning explosion of a methane-gaseous combustion improver mixture, forming impact fractures in a shale reservoir, and simultaneously, in the burning explosion process, overcoming the limitation of ground stress and expanding along different directions of the shaft 2 to form a plurality of radial impact fractures around the shaft 2;
step four: the shaft 2 repeats the blasting and fracturing operation;
lowering the fracturing tool 8 to the tail end of the current fracturing well section again by using a continuous oil pipe 7 lowering mode, and then repeating the second step and the third step to perform repeated explosion fracturing on the current fracturing well section; preferably, in order to ensure that a highly complex fracture network is formed, the second step and the third step are repeated for 3-4 times in the first fracturing well section 3 to repeatedly implement in-situ combustion and explosion of the methane in the shaft, the stratum around the shaft 2 is repeatedly impacted by utilizing the high pressure action of multiple combustion and explosion of the methane-gaseous combustion improver mixture, the extension range and complexity of the fracture around the shaft 2 are further increased, the complex fracture 14 formed as shown in fig. 4 is finally formed around the shaft 2, and a space is provided for subsequent methane combustion and explosion of a reservoir;
step five: adding a solid combustion improver;
by using supercritical CO 2 Conveying the solid combustion improver particles into the complex cracks 14 formed in the fourth step when supercritical CO is adopted 2 After the fluid and the solid combustion improver particles carried by the fluid enter the complex crack 14, supercritical CO is carried out 2 The flow rate of the fuel is rapidly reduced, and the particles of the solid combustion improver are openedBeginning to settle in the cracks; preferably, the supercritical CO is selected to reduce the risk of plugging of solid particles in the wellbore and fractures 2 The pressure is greater than the fracture extension pressure of the formation; as shown in figure 5, the solid combustion improver particles are preferably potassium permanganate particles 16, and the particle diameter of the solid combustion improver particles is 0.147-0.210 mm. Thus, supercritical CO can be utilized 2 The fluid replaces the adsorbed methane on the shale matrix into a free state so as to increase the concentration of methane in the fracture and improve the subsequent blasting strength; after the solid combustion improver particles are put in, a methane-solid combustion improver particle mixture is formed in the crack;
in order to accurately put the potassium permanganate particles into all complex cracks, the potassium permanganate particles 16 and supercritical CO can be firstly put into the process 2 Fully mixing the mixture on the ground to form supercritical CO 2 A mixture of potassium permanganate particles 15, then supercritical CO is fed through the coiled tubing 7 2 The potassium permanganate particle mixture 15 is conveyed into the complex fracture 14 formed in step four. Preferably, in order to improve the conveying effect of the potassium permanganate particles, the supercritical CO is adopted 2 -the volume fraction of potassium permanganate particles 16 in the potassium permanganate particles mixture 15 is lower than 15%;
step six: performing multiple blasting and fracturing operations of shaft-crack methane;
continuously adding a gaseous combustion improver into the shaft 2 according to the mode in the step two, and then performing shaft blasting and fracturing operation according to the mode in the step three; detonating the methane-solid combustion improver particle mixture in the complex fracture 14 by using high-temperature and high-pressure gas generated by the combustion explosion of the methane-gaseous combustion improver mixture in the shaft 2, and continuing to perform in-situ combustion explosion fracturing of the methane in the complex fracture 14; under the multiple in-situ combustion and explosion effects of methane in the shaft 2 and the complex cracks 14, the existing cracks are promoted to continue to expand and extend to form a complex crack network with larger scale; in the process, the opening of the crack is increased by utilizing a solid reactant generated by burning and exploding methane and solid combustion improver particles in the crack so as to prevent the crack from being closed under the action of ground stress; when the solid combustion improver adopts the potassium permanganate particles 16, solid reactants such as potassium manganate and manganese dioxide can be generated after the methane and the potassium permanganate particles 16 in the cracks are exploded, the solid reactants can be filled in the formed cracks to play a role similar to a 'propping agent', and the cracks are prevented from being closed under the action of ground stress after the explosion and fracturing.
Step seven: forming a highly complex three-dimensional fracture network 17 in the shale reservoir 1;
repeating the fifth step and the sixth step, continuously performing different types of methane in-situ explosion fracturing on the stratum around the shaft 2 and the complex fractures 14, and promoting the fractures in the shale reservoir 1 to continuously extend and grow and continuously improve the complexity under the action of shaft-fracture methane multiple in-situ explosion fracturing until a highly complex three-dimensional fracture network 17 is formed in the shale reservoir 1, as shown in fig. 6;
preferably, in order to ensure that the formed three-dimensional fracture network can have a larger extension range and a higher complexity, the number of times of repeating the steps five and six is not less than 3.
Step eight: completing methane multiple in-situ combustion-explosion fracturing operation of the whole shaft 2;
moving the fracturing tool 8 to the next fracturing well section, and repeating the second to seventh steps in the second fracturing well section 4 and the third fracturing well section 5 in sequence until the methane multiple in-situ combustion and explosion fracturing operation of the shale reservoir 1 in all the well sections to be fractured is completed, so that multiple groups of complex three-dimensional fracture networks 17 can be generated at different positions of the shaft 2 and along different positions of the shaft 2, as shown in fig. 7, and the fracturing transformation operation of the whole shale gas well is completed.
According to the shale reservoir methane in-situ blasting process, occurrence characteristics of methane in different spaces are fully considered. After methane is desorbed to a shaft from a shale reservoir, because the shaft has larger space and regular shape, and the fracturing tool can be put down into the shaft through devices such as a coiled tubing and the like, when the combustion improver is put in the shaft, the methane and the combustion improver are fully mixed in the larger space, and the mixing uniformity can be ensured. In order to ensure that the volume fraction of methane in the shaft is within the explosion limit range, factors such as methane density and flow characteristics are comprehensively considered, and the gaseous combustion improver is firstly put into the shaft. If use solid-state combustion improver in the pit shaft, take place harmful phenomena such as solid particle subsides and blocks up easily in the input in-process pit shaft, easily lead to the fracturing tool to be blocked in the pit shaft, like this, not only can't carry out methane normal position burning and exploding fracturing, still can influence the production operation in shale gas well later stage even. If the liquid combustion improver is put in the shaft, the liquid combustion improver can be settled at the lower part of the shaft due to the density difference between the methane and the liquid combustion improver, and the methane can float at the upper part of the shaft, so that the methane and the liquid combustion improver are separated from each other, which is very unfavorable for in-situ combustion and explosion of the methane in the shaft.
For a narrow space in a reservoir fracture (the width of the fracture is less than one centimeter), the flowing state of the fluid in the fracture is mainly laminar flow, and methane is not easily mixed with the gaseous combustion improver. In addition, when the gaseous combustion improver is put into the crack, methane is easily displaced to a shaft by the gaseous combustion improver, so that the volume fraction of the methane in the crack is reduced, and even the combustion and explosion conditions cannot be met. Therefore, in the invention, solid combustion improver particles are selectively put in the cracks, which can effectively reduce the space occupied by the combustion improver in the cracks and increase the volume concentration of methane in the cracks. Moreover, methane can enter gaps among solid combustion improver particles and fully contact with the solid combustion improver, so that the subsequent combustion and explosion effect can be ensured.
Claims (10)
1. A shale reservoir methane multiple in-situ combustion-explosion fracturing method comprises a continuous oil pipe (7), a hydraulic anchor (10), a packer (9), a fracturing tool (8), a ground ignition device and a bridge plug (6); a cable is arranged in the coiled tubing (7), an anchor claw (13) is connected to the hydraulic anchor (10), and an ignition electrode is arranged in the fracturing tool (8); the hydraulic anchor (10), the packer (9) and the fracturing tool (8) are sequentially connected to the tail end of the continuous oil pipe (7) from front to back; the ground ignition device is arranged on the ground;
the method is characterized by comprising the following steps of;
the method comprises the following steps: the preparation work comprises the following specific steps:
s11: determining a well section needing fracturing according to geological parameters and logging data of the shale reservoir (1);
s12: numbering the fracturing well sections in a subsection mode according to the sequence from the bottom to the wellhead, wherein the fracturing well sections at least comprise a first fracturing well section (3), a second fracturing well section (4) and a third fracturing well section (5);
s13: conveying a bridge plug (6) into the well bore (2), and setting the bridge plug (6) at the tail end of the first fracturing well section (3);
s14: a fracturing tool (8) is put down to the tail end of the first section of the fracturing well section (3) by using a continuous oil pipe (7), and an ignition electrode is connected with a ground ignition device through a cable;
step two: feeding a gaseous combustion improver;
gaseous combustion improver is put into the underground fracturing tool (8) through the continuous oil pipe (7), and the gaseous combustion improver enters the annular space of a shaft from a nozzle of the fracturing tool (8) and is mixed with methane to form a methane-gaseous combustion improver mixture; when the gaseous combustion improver is put in, the continuous oil pipe (7) is upwards recovered at a certain speed, so that the fracturing tool (8) is dragged to move towards the wellhead direction, and the recovery operation of the continuous oil pipe (7) is stopped when the fracturing tool (8) is about to leave the current fracturing well section;
step three: the method comprises the following specific steps of:
s31: after the continuous oil pipe (7) is stopped to be recovered, the injection pressure of the gaseous combustion improver is increased, the fluke (13) of the hydraulic anchor (10) is extended outwards and embedded into the well wall under the action of the fluid pressure, and meanwhile, the packer (9) connected with the fracturing tool (8) is expanded and set on the well wall under the action of the fluid pressure;
s32: the methane-gaseous combustion improver mixture in the shaft (2) is ignited by electric shock through an ignition electrode in the fracturing tool (8), so that the methane-gaseous combustion improver mixture is subjected to in-situ combustion and explosion in the current fracturing well section; the instantaneous high pressure generated by burning explosion of the methane-gaseous combustion improver mixture is used for carrying out impact fracturing on the stratum around the shaft, and a plurality of radial impact fractures are formed around the shaft (2);
step four: the shaft (2) repeats the blasting and fracturing operation;
putting the fracturing tool (8) down to the tail end of the current fracturing well section again, then repeating the second step and the third step, performing repeated blasting fracturing on the current fracturing well section, repeatedly impacting the stratum around the shaft (2) by utilizing the high-pressure action of multiple blasting of the methane-gaseous combustion improver mixture, and forming a complex crack (14) around the shaft (2);
step five: putting a solid combustion improver;
by using supercritical CO 2 Conveying the solid combustion improver particles into the complex cracks (14) formed in the step four, and utilizing supercritical CO 2 The fluid displaces the adsorbed methane on the shale matrix to a free state, forming a methane-solid oxidizer particulate mixture within the complex fracture (14);
step six: performing multiple blasting and fracturing operations of shaft-crack methane;
continuously adding a gaseous combustion improver into the shaft (2) according to the mode in the step two, and then performing blasting fracturing operation on the shaft (2) according to the mode in the step three; high-temperature high-pressure gas generated by burning and exploding methane-gaseous combustion improver mixture in the shaft (2) is used for detonating the methane-solid combustion improver particle mixture in the complex crack (14), in-situ burning and exploding fracturing of methane in the complex crack (14) is continuously carried out, and the existing complex crack (14) is promoted to continuously expand and extend to form a complex crack net with larger size through the action of multiple in-situ burning and exploding of methane in the shaft (2) and the complex crack (14);
step seven: forming a highly complex three-dimensional fracture network (17) within the shale reservoir (1);
repeating the fifth step and the sixth step, and continuously carrying out methane in-situ combustion and explosion fracturing on the well bore (2) and the stratum around the complex fractures (14) to promote the complex fractures (14) to grow until highly complex three-dimensional fracture networks (17) are formed in the shale reservoir (1);
step eight: completing methane multiple in-situ combustion-explosion fracturing operation of the whole shaft (2);
and moving the fracturing tool (8) to the next fracturing well section, and repeating the steps from two to seven until the methane multiple in-situ combustion and explosion fracturing operation of the shale reservoir (1) in all the well sections to be fractured is completed, and generating a plurality of groups of complex three-dimensional fracture networks (17) at different positions of the shaft (2).
2. The shale reservoir methane multiple in-situ combustion-explosion fracturing method as claimed in claim 1, wherein the pressure bearing capacity of the bridge plug (6) and the packer (9) is not lower than 200 MPa.
3. The shale reservoir methane multiple in-situ combustion-explosion fracturing method according to claim 1 or 2, characterized in that in the second step, the gaseous combustion improver is oxygen (11).
4. The shale reservoir methane multiple in-situ combustion-explosion fracturing method as claimed in claim 3, wherein in the second step, the recovery speed of the coiled tubing (7) is 0.5-1.0 m/s.
5. The shale reservoir methane multiple in-situ combustion-explosion fracturing method as claimed in claim 4, characterized in that in step four, the fracturing tool (8) is lowered to the end of the current fracturing well section again by means of lowering the coiled tubing (7), and the steps two and three are repeated for 3-4 times.
6. The shale reservoir methane multiple in-situ combustion-explosion fracturing method as claimed in claim 5, wherein in step five, the solid combustion improver particles are potassium permanganate particles (16).
7. The shale reservoir methane multiple in-situ combustion-explosion fracturing method as claimed in claim 6, wherein in step five, potassium permanganate particles (16) and supercritical CO are firstly mixed 2 Fully mixing on the ground to form supercritical CO 2 -potassium permanganate particle mixture (15) and supercritical CO is fed through coiled tubing (7) 2 -feeding the mixture of potassium permanganate particles (15) into the complex fracture (14) formed in step four.
8. The shale reservoir methane multiple in-situ combustion-explosion fracturing method as claimed in claim 7, wherein in step five, the volume fraction of the potassium permanganate particles (16) is lower than 15%, and the particle diameter is 0.147-0.210 mm.
9. The shale reservoir methane multiple in-situ combustion-explosion fracturing method of claim 8, wherein in step five, the supercritical CO 2 The pressure is greater than the fracture propagation pressure of the formation.
10. The shale reservoir methane multiple in-situ combustion-explosion fracturing method of claim 9, wherein in step seven, the times of repeating the steps five and six are not less than 3 times.
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| CN114718539B (en) * | 2022-05-12 | 2024-01-02 | 中国石油大学(华东) | In-situ combustion explosion fracturing method in multi-round methane layer |
| CN114876434B (en) * | 2022-05-30 | 2023-02-03 | 中国矿业大学 | In-situ combustion explosion fracturing method for methane in shale gas reservoir seam |
| CN115234200B (en) * | 2022-08-01 | 2023-05-09 | 中国矿业大学 | Unconventional natural gas reservoir methane in-situ fixed-point blasting fracturing method |
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