CN112145144B - Based on multistage liquid CO2Phase-change composite fracturing transformation system and method - Google Patents
Based on multistage liquid CO2Phase-change composite fracturing transformation system and method Download PDFInfo
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- E—FIXED CONSTRUCTIONS
- 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
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
- E21B43/267—Methods for stimulating production by forming crevices or fractures reinforcing fractures by propping
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- E—FIXED CONSTRUCTIONS
- 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
- E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
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Abstract
The invention relates to a multi-stage liquid CO-based gas turbine2Phase-change composite fracturing modification system and method, and composite fracturing modification systemA combined fracturing modification system comprising liquid CO2The system comprises an injection unit, a conventional fracturing fluid injection unit, an underground blasting fracturing unit and a ground control unit; the liquid CO2The injection unit and the conventional fracturing fluid injection unit are connected with the underground blasting fracturing unit through a fracturing string; the ground control unit is connected with the underground blasting fracturing unit through a cable; and provides a method for compound fracturing reformation according to the compound fracturing reformation system. The composite fracturing modification system provided by the invention passes through multi-stage CO2The phase change and one-trip pipe column realize CO2Prepositive energization and full utilization of CO2The safety of phase change blasting effectively reduces the fracture pressure of low-permeability or deep compact oil and gas reservoir rock; the driving pressure of underground crude oil can be increased by 2-5 MPa, the flowback rate of fracturing fluid can reach more than 80% after 4h of fracturing, and the effective period of fracturing can be prolonged by 6-18 months.
Description
Technical Field
The invention belongs to the technical field of petroleum engineering, and particularly relates to a multi-stage liquid CO-based fuel tank2A phase change composite fracturing modification system and method.
Background
Fracturing is a key technology for yield increase modification of oil fields, and for low-permeability or deep compact oil and gas reservoirs with abnormally high fracture pressure and serious blockage, the conventional fracturing modification method is difficult to crack rocks. Every year, construction failure of partial reservoirs due to abnormal difficult pressing exists, and a large amount of manpower and financial resources are wasted. There is therefore a need to provide effective technical support for abnormally high burst pressures and plugging of severely hypotonic or tight hydrocarbon reservoirs.
In recent years, liquid CO2Dry fracturing has been widely focused and studied domestically due to its low damage and easy flowback, but with pure liquid CO2Low viscosity, serious fluid loss, poor sand-carrying capacity and difficult crack formationThe effective support of (2). Liquid CO is currently proposed2The method combining pre-energization and hydraulic fracturing not only makes up for liquid CO2The defects of dry fracturing also overcome the problems of low flowback rate, long flowback time, difficult formation energy supplement and the like of the fracturing fluid of the traditional hydraulic fracturing. However, liquid CO2The preposed energy increasing and hydraulic fracturing transformation method is used for solving the problem that the fracturing construction is hindered due to the fact that reservoir rock is still difficult to crack under the conditions of conventional fracturing equipment for low-permeability or deep compact oil and gas reservoirs with abnormally high fracture pressure and serious blockage.
Therefore, in order to reduce the fracture pressure of reservoir rock and eliminate the influence of the plug on the fracture pressure, acid fracturing or acid pretreatment technology and composite fracturing technology (such as CO) are generally adopted at present2Blasting-hydraulic fracturing reconstruction yield increasing method and explosive blasting-liquid CO2Fracturing method), etc. The acid fracturing or acid pretreatment technology can change the micro-pore structure of the reservoir, change the mechanical parameters of the rock and increase the permeability of the reservoir, thereby achieving the purpose of reducing the fracture pressure. However, when a stratum seriously blocked by mud is faced, on one hand, acid liquor is difficult to percolate, and the dissolution speed of a blockage is low; on the other hand, the acid liquor component is not properly selected, so that secondary damage to a reservoir is easily caused, and particularly, the formed acid sludge is difficult to flow back. In recent years, liquid CO2The phase change blasting technology overcomes the defects of large destruction degree, high danger coefficient and the like in the traditional explosive blasting, and in addition, CO2The gas can also create an inert gas-like environment, has the characteristics of explosion suppression and combustion suppression, and has good effects in engineering practices of improving the air permeability of a coal seam, improving the gas drainage efficiency, controlling the top and bottom plates of a roadway, clearing and blocking a coal bunker and the like.
The carbon dioxide blasting-hydraulic fracturing reformation and yield increasing method for the oil-gas well, disclosed by Chinese patent document CN110541696A, comprises a prefabrication blasting scheme, prefabrication of blasting and fracturing equipment, blasting operation and hydraulic pressure and result monitoring. But for hypotonic or deep tight hydrocarbon reservoirs with abnormally high burst pressures and severe plugging, this single stage CO2The blasting technology is limited by the volume of a liquid storage container, so that on one hand, the blasting energy is obviously insufficient, and on the other hand, the blasting technology is not limitedCan form pulse shock waves, is difficult to form a plurality of radial cracks to reduce the cracking pressure of rocks, influences the transformation efficiency and effect of hydraulic fracturing, and simultaneously has single-stage liquid CO2The energy in the blasting technology is released at one time, and the size of the released energy is difficult to control in engineering; and the patent does not mention the concrete implementation measures of hydraulic fracturing, and the practical construction of the oil field is difficult to be guided.
Chinese patent document CN105221129A discloses a hydraulic bursting crack-initiating-CO2The permeability increasing method for the reservoir stratum with the proppant fracturing comprises the steps of charging, water injection and hole sealing, hydraulic blasting and supercritical or liquid CO2A fracturing step; wherein, before the charging step, the method further comprises drilling and cementing so as to form a drilling well by utilizing the production casing; if necessary, at least one layer of technical casing is arranged between the surface casing and the production casing; before the fracturing step, a sand mixing pump is used for mixing the ceramic proppant with supercritical or liquid CO2Fully mixing the components according to a set proportion, and adding necessary additives to form a spare fracturing fluid; in the fracturing step, the method also comprises the step of adopting a microseism monitor to carry out real-time monitoring on the extension of the crack so as to accurately monitor the influence range of the crack. However, the method has the advantages of complex construction, high explosive blasting risk, short loading time and easy influence on well cementation quality; and single liquid CO2The fracturing is difficult to carry sand, the fracture is difficult to effectively support, the fracturing transformation effect is seriously influenced, and in addition, the water-based fracturing fluid is difficult to drain back in the conventional hydraulic fracturing process, so that the reservoir is easily damaged.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a multi-stage liquid CO-based liquid CO2The composite fracturing transformation system and method of phase change fully utilize liquid CO2The safety of phase change blasting realizes that the blasting energy is released step by step, effectively reduces the rock rupture pressure, and simultaneously realizes CO through one flow2The method has the advantages of high efficiency, environmental protection and little damage to the reservoir.
The main technical scheme of the invention is as follows:
based on multistage liquid CO2A phase change composite fracturing modification system comprising a fluidState CO2The system comprises an injection unit, a conventional fracturing fluid injection unit, an underground blasting fracturing unit and a ground control unit; the liquid CO2The injection unit and the conventional fracturing fluid injection unit are connected with the underground blasting fracturing unit through a fracturing string; the ground control unit is connected with the underground blasting fracturing unit through a cable;
the liquid CO2The injection unit comprises liquid CO2Storage tank, liquid CO2The device comprises a supercharging device, a gas-liquid separation device and a high-pressure pumping device; the liquid CO2Storage tank, liquid CO2The pressurizing equipment, the gas-liquid separation equipment and the high-pressure pumping equipment are sequentially connected through a pipeline, and the high-pressure pumping equipment is connected to the liquid CO2Storage tank and liquid CO2A closed loop is formed on a pipeline between the supercharging devices;
the conventional fracturing fluid injection unit comprises a water-based fracturing fluid storage tank, a proppant storage tank, a sand mixing device and conventional pumping equipment, wherein the conventional fracturing fluid injection unit is used for injecting liquid CO2A storage tank; the water-based fracturing fluid storage tank, the proppant storage tank, the sand mixing equipment and the conventional pumping equipment are filled with liquid CO2The storage tanks are connected in sequence through pipelines;
the underground blasting fracturing unit comprises a wellhead device, and a sleeve is arranged below the wellhead device; the sleeve is internally provided with a fracturing string, a packer and multi-stage liquid CO2A phase change blasting device; the bottom end of the fracturing string and multi-stage liquid CO2The phase change blasting device is connected through screw threads, and the packer is positioned on the casing and the multi-stage liquid CO2A shaft closed space is formed between the phase-change blasting devices;
the multi-stage liquid CO2The phase change blasting device comprises a shell, wherein 2-4 liquid CO are arranged in the shell2A phase change generating device; the liquid CO2The phase change device comprises an inflation plug, an air release hole is formed above the inflation plug, a straight notch matched with an inflation nozzle is formed below the inflation plug, a one-way valve is arranged at the center hole of the inflation plug, a heating pipe is connected to the tail end of the inflation plug, the inflation plug is in clearance fit with a high-pressure generating device, the lower end of the high-pressure generating device is in clearance fit with the deflation plug, and the center of the deflation plug is in clearance fit with the center of the high-pressure generating deviceThe hole is provided with a shear slice.
According to the invention, the shell is preferably of a tubular structure, the outer diameter of the shell is 60-80 mm, and the inner diameter of the shell and the liquid CO are preferably equal to each other2The phase change generating device is in clearance fit; the open end of the shell is provided with a wiring hole and is connected to each stage of liquid CO2A phase change generating device front end; the open end surface of the housing is threaded and can be connected to a fracturing string.
Preferably, the wiring holes are round holes, and the number of the wiring holes is 2; the number of the air release holes is 8-16, the air release holes are uniformly distributed on the central axis of the shell and are perpendicular to the central axis. The diameter of the air vent is 8-10 mm.
Preferably, according to the invention, the liquid CO2The phase change generating device is a cylinder, and the length of the tube is 400-1000 mm.
According to the invention, the heating pipe is preferably in a semi-straight groove type cylinder shape, the heating wire is arranged in the heating pipe, the heating wire is fixedly arranged in the middle of the heating pipe, the heating pipe is isolated by insulating materials and is not in contact with the outer wall, and the heating pipe can be heated to 100-150 ℃ within 1-2 min after being powered on.
According to the invention, the opening pressure of the front end of the one-way valve is preferably 5-10 MPa.
According to the invention, the fracture pressure of the shear slice is preferably 90-100 MPa.
Using the above-mentioned multi-stage liquid CO-based2The method for performing composite fracturing reconstruction by using the phase-change composite fracturing reconstruction system comprises the following steps:
step 1, analyzing the abnormal high pressure or serious blockage position of a stratum according to an oil-gas reservoir and logging data, determining a well section of a target stratum, and designing corresponding construction parameters according to the abnormal pressure or the blockage degree;
step 3, igniting the liquid CO step by step at intervals of 5-15 s in an electric heating mode through a ground control unit2A phase change blasting device;
step 5, after pre-energizing is finished, starting a conventional fracturing fluid injection unit, injecting the water-based fracturing fluid into the shaft, and mixing the proppant and the water-based fracturing fluid through sand mulling equipment in the pumping process until the whole fracturing operation is finished;
Preferably, according to the invention, in step 2, the liquid CO is2The pretreatment of the phase change generating device comprises the following specific processes: liquid CO to each stage2CO is filled in the phase change generating device2Gas, then liquid CO2The phase change generating device is assembled into multi-stage liquid CO2Phase change blasting device.
Preferably, in step 3, the interval time is 8-10 s.
Preferably, in step 5, the amount of the water-based fracturing fluid is greater than or equal to 65% of the total amount of the proppant and the water-based fracturing fluid.
Has the advantages that:
1. compared with the acid fracturing or acidification pretreatment technology, the composite fracturing modification system provided by the invention has the advantages that when a stratum with serious blockage is encountered, multi-stage CO is generated2High-pressure gas released by phase change can penetrate through a pollution area near a well zone to communicate with natural cracks of a stratum, so that the flow conductivity of an oil layer is improved; and CO2The pressure wave formed in explosion reflects the vibration and scouring action of pressure pulse on stratum caused by superposition, and can break the binding force between blocking particles and reservoir stratum to produce loosening action and remove mechanical impuritiesAnd (4) blockage.
2. The composite fracturing modification system provided by the invention passes through multi-stage CO2Phase change realizes CO2Prepositive energization and full utilization of CO2The safety of phase change blasting effectively reduces the fracture pressure of low-permeability or deep compact oil and gas reservoir rock; the driving pressure of the underground crude oil can be increased by 2-5 MPa, the flowback rate of the fracturing fluid can reach more than 80% after fracturing for 4 hours, the fracturing effective period can be prolonged by 6-18 months, the formation energy is effectively increased, the driving pressure of the underground crude oil flowing is enhanced, the flowback time of the fracturing fluid is shortened, and the fracturing modification effective period is prolonged.
3. The invention provides multi-stage CO in a composite fracturing modification system2The phase change blasting device makes up the traditional single-stage CO reduction in the process of pressure burst of a low-permeability or deep compact oil and gas reservoir2The problem of insufficient blasting energy. Multistage CO2The phase-change blasting device forms a large amount of initial cracks under the combined action of stress waves and high-energy gas in the first phase-change process, and after the phase-change blasting for the second time and the third time, a large amount of high-energy gas is wedged into the initial cracks formed by the first impact, and the microcracks begin to expand to a certain extent, so that the subsequent liquid CO is favorably used2And the implementation of hydraulic fracturing. And, multi-stage CO2The phase change blasting device can realize the gradual release of blasting energy by means of a delay switch, achieves the effect similar to pulse pump injection, and is more favorable for rock cracking and expansion.
4. The invention provides multi-stage CO in a composite fracturing modification system2The phase change blasting device can be in CO2After the phase change fracturing is finished, a tool is not needed to be pulled down, and the pre-energization and hydraulic fracturing construction is directly carried out by adopting a one-time pipe column and a flow, so that the operation is simple, and the waste of time and manpower is reduced; simultaneously makes up for the conventional liquid CO2The viscosity of the fracturing fluid is low, the sand carrying capacity is poor, the water-based fracturing fluid is difficult to flow back and the like. At the same time, a large amount of CO enters the reservoir2The additive is mixed with crude oil, so that the flow of the crude oil in a reservoir stratum is facilitated; can efficiently replace methane and CO2The adsorption capacity of the shale layer is far greater than that of methane, so that the methane can be effectively replaced, and the yield is improved; and the resulting slightly acidic environment maySo as to inhibit the clay mineral from swelling and reduce the water sensitivity and water lock effect.
Drawings
FIG. 1 is a multi-stage liquid CO-based process2And (3) an overall schematic diagram of the phase-change composite fracturing modification system.
FIG. 2 is a multi-stage liquid CO2The structure schematic diagram of the phase change blasting device.
FIG. 3 is a single stage liquid CO2The structure of the phase change generating device is schematically shown.
FIG. 4 is a multi-stage liquid CO2The phase change blasting device is a schematic perspective view.
In the figure: 1-liquid CO2Storage tank, 2-liquid CO2The method comprises the following steps of pressurizing equipment, 3-gas-liquid separation equipment, 4-high-pressure pumping equipment, 5-water-based fracturing fluid storage tank, 6-proppant storage tank, 7-sand mixing equipment, 8-conventional pumping equipment, 9-ground control equipment, 10-wellhead device, 11-casing pipe, 12-cable, 13-fracturing string, 14-packer and 15-multistage liquid CO2Phase change blasting device, 16-shell, 17-primary liquid CO2Phase change generating device, 18-two-stage liquid CO2Phase change generating device, 19-three stage liquid CO2The method comprises the following steps of a phase change generating device, 20-wiring holes, 21-air release holes, 22-inflation plugs, 23-one-way valves, 24-heating pipes, 25-high pressure generating devices, 26-shear pieces and 27-deflation plugs.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.
Example 1
As shown in FIGS. 1-4, a multi-stage liquid CO-based fuel cell2A phase change composite fracturing modification system comprising liquid CO2The system comprises an injection unit, a conventional fracturing fluid injection unit, an underground blasting fracturing unit and a ground control unit; the liquid stateCO2The injection unit and the conventional fracturing fluid injection unit are connected with the underground blasting fracturing unit through a fracturing string 13; the ground control unit comprises ground control equipment 9, and the ground control equipment 9 is connected with the underground blasting fracturing unit through a cable 28;
the liquid CO2The injection unit comprises liquid CO2Storage tank 1, liquid CO2The device comprises a supercharging device 2, a gas-liquid separation device 3 and a high-pressure pumping device 4; the liquid CO2Storage tank 1, liquid CO2 The supercharging equipment 2, the gas-liquid separation equipment 3 and the high-pressure pumping equipment 4 are sequentially connected through pipelines, and the high-pressure pumping equipment 4 is connected to the liquid CO2Storage tank 1, liquid CO2A closed loop is formed on a pipeline between the supercharging devices 2;
the conventional fracturing fluid injection unit comprises a water-based fracturing fluid storage tank 5, a proppant storage tank 6, a sand mixing device 7 and liquid CO of a conventional pumping device2 A storage tank 8; the water-based fracturing fluid storage tank 5, the proppant storage tank 6, the sand mixing equipment 7 and the conventional pumping equipment are filled with liquid CO2The storage tanks 8 are connected in sequence through pipelines;
the underground blasting fracturing unit comprises a wellhead device 10, and a casing 11 is arranged below the wellhead device 10; a fracturing string 13, a packer 14 and multi-stage liquid CO are arranged in the casing 112A phase change blasting device 15; the bottom end of the fracturing string 13 and multi-stage liquid CO2The phase change blasting device 15 is connected through threads; the packer 14 is positioned in the casing 11 and the multi-stage liquid CO2A shaft closed space is formed between the phase change blasting devices 15;
the multi-stage liquid CO2The phase change blasting device 15 comprises a shell 16, and three liquid CO are arranged in the shell 162Phase change devices, respectively, of primary liquid CO2 Phase change device 17, two-stage liquid CO2 Phase change device 18 and three-stage liquid CO2 Phase change device 19, three liquid CO2The phase change devices are connected in sequence;
the liquid CO2The phase change device comprises an inflation plug 22, a straight notch matched with the inflation nozzle is arranged on the inflation plug 22, and a central hole of the inflation plug 22 is provided with aThe tail end of a check valve 23 and an inflation plug 22 is connected with a heating pipe 24, the inflation plug 22 is in clearance fit with a high-pressure generating device 25, the lower end of the high-pressure generating device 25 is in clearance fit with a abandoning plug 27, and a shearing sheet 26 is arranged at the central hole of a deflation plug.
The shell 16 is of a tubular structure, the outer diameter of the shell is 80mm, and the inner diameter of the shell and liquid CO are2The phase change generating device is in clearance fit; a wiring aperture 20 is provided at the open end of the housing 16 and is connected to each stage of liquid CO2The front end of the phase change generating device is provided with threads at the opening end of the shell and can be connected to a fracturing string 13, and the tail end of the shell 16 is provided with an air vent 21. The wiring holes 20 are round holes, and the number of the wiring holes is 2; the number of the air release holes 21 is 10, and the air release holes are uniformly distributed on the central axis of the shell 16 and are vertical to the central axis. The diameter of the air vent is 8 mm.
The primary liquid CO2The phase change generating device 17 is a cylinder, and the length of the tube is 800 mm; the secondary liquid CO2The phase change generating device 18 is a cylinder, and the length of the tube is 600 mm; the three-stage liquid CO2The phase change generating device 19 is a cylinder, and the length of the tube is 400 mm.
The heating pipe 24 is in a semi-straight groove type cylinder shape, an electric heating wire is arranged in the pipe, the electric heating wire is fixedly arranged in the middle of the pipe and is not in contact with the outer wall, an insulating material is arranged between the electric heating wire and the outer wall, and the heating pipe can be heated to 100-150 ℃ within 1-2 min after being powered on.
The opening pressure of the front end of the one-way valve is 5 MPa; the fracture pressure of the shear slice is 90 MPa.
Example 2
Multistage liquid CO-based, as described in example 12The phase-change composite fracturing modification system is characterized in that the multistage liquid CO is adopted24 liquid CO are arranged in the phase change blasting device 152Phase change generating device. The liquid CO2The tube lengths of the phase change generating devices are 800mm, 600mm, 400mm and 400mm respectively.
Example 3
Multistage liquid CO-based, as described in example 12The phase-change composite fracturing modification system is characterized in that the multistage liquid CO is adopted2The phase change blasting device 15 is internally provided with2 liquid CO are arranged2Phase change blasting device. The liquid CO2The tube length of the phase change blasting device is 800mm and 600mm respectively.
Example 4
Multistage liquid CO-based, as described in example 12The phase-change composite fracturing modification system is characterized in that the primary liquid CO2The phase change generating device 17 is a cylinder, and the length of the pipe is 1000 mm; the secondary liquid CO2The phase change generating device 18 is a cylinder, and the length of the tube is 800 mm; the three-stage liquid CO2The phase change generating device 19 is a cylinder, and the length of the tube is 600 mm.
Example 5
Based on multistage liquid CO provided by embodiment 12The method for performing composite fracturing reconstruction by using the phase-change composite fracturing reconstruction system comprises the following steps:
step 1, analyzing the abnormal high pressure or serious blockage position of a stratum according to an oil-gas reservoir and logging data, determining a well section of a target stratum, designing corresponding construction parameters according to abnormal pressure or blockage degree, taking a certain well as an example, the burial depth is 2408.7m, the reservoir fracture pressure is 78.2MPa, the bottom hole pressure is 26.7MPa, setting the number of stages of a multi-stage two-oxidation phase-change blasting device to be 2, and setting the number of stages of a first-stage liquid CO device to be 22The length of the phase change generating device is 1000mm, and the second stage of liquid CO2The length of the phase change generating device is 800mm, and liquid CO is filled in the first stage2The amount was 0.62g/cm3The peak pressure reached by the first stage is 123.5MPa, and the liquid CO is filled in the second stage2The amount was 0.55g/cm3The peak pressure achieved by the second stage is 80.3 MP.
step 3, igniting the liquid CO step by step at intervals of 5s in an electric heating mode through a ground control unit2A phase change blasting device;
step 5, after pre-energizing is finished, starting a conventional fracturing fluid injection unit, injecting the water-based fracturing fluid into the shaft according to the condition that the using amount of the water-based fracturing fluid is 50% of the total amount of the proppant and the water-based fracturing fluid, and mixing the proppant and the water-based fracturing fluid through sand mixing equipment in the pumping process until the whole fracturing operation is finished;
After the composite fracturing transformation of the embodiment, the near-wellbore zone formation pressure reaches 29.7MPa, the fracturing fluid flowback rate reaches 82% after 4h of fracturing, and the effective fracturing period is prolonged by 12 months.
Example 6
The method of composite fracture reformation as in example 5, except that in step 3, the liquid CO is ignited in stages2The interval time of the phase change blasting device is 10 s.
In the composite fracturing reconstruction of the embodiment, the near-wellbore zone formation pressure reaches 30.1MPa, the fracturing fluid flowback rate reaches 88% after 4h of fracturing, and the effective fracturing period is prolonged by 18 months.
Example 7
Based on multistage liquid CO provided by embodiment 12The method for performing composite fracturing reconstruction by using the phase-change composite fracturing reconstruction system comprises the following steps:
step 1, analyzing the abnormal high pressure or serious blockage position of the stratum according to the oil and gas reservoir and logging data, determining the well section of the target stratum, designing corresponding construction parameters according to the abnormal pressure or blockage degree, taking a certain well as an example, burying depth3070.6m, the reservoir fracture pressure is 85.5MPa, the formation pressure is 32.1MPa, the number of stages of the multistage oxidation phase-change blasting device is 4, the first stage liquid CO2The length of the phase change generating device is 1000mm, and the second stage of liquid CO2The length of the phase change generating device is 800mm, and the third stage of liquid CO2The length of the phase change generating device is 600mm, and the fourth stage of liquid CO2The length of the phase change generating device is 400mm, and liquid CO is filled in the first stage2The amount was 0.82g/cm3The peak pressure reached by the first stage is 231.4MPa, and the liquid CO is filled in the second stage2The amount was 0.62g/cm3The peak pressure reached by the second stage is 123.5MPa, and the liquid CO is filled in the third stage2The amount was 0.52g/cm3The peak pressure reached in the third stage is 68.3MPa, and the liquid CO is filled in the fourth stage2The amount was 0.44g/cm3The peak pressure reached at the fourth stage was 33.4 MPa.
step 3, igniting the liquid CO step by step at intervals of 5s in an electric heating mode through a ground control unit2A phase change blasting device;
step 5, after pre-energizing is finished, starting a conventional fracturing fluid injection unit, injecting the water-based fracturing fluid into the shaft according to the condition that the using amount of the water-based fracturing fluid is 50% of the total amount of the proppant and the water-based fracturing fluid, and mixing the proppant and the water-based fracturing fluid through sand mixing equipment in the pumping process until the whole fracturing operation is finished;
In the composite fracturing reformation of the embodiment, the near-wellbore zone formation pressure reaches 36.6MPa, the fracturing fluid flowback rate reaches 92% after 4h of fracturing, and the effective fracturing period is prolonged by 18 months.
Claims (10)
1. Based on multistage liquid CO2A phase change composite fracturing modification system comprising liquid CO2The system comprises an injection unit, a conventional fracturing fluid injection unit, an underground blasting fracturing unit and a ground control unit; the liquid CO2The injection unit and the conventional fracturing fluid injection unit are connected with the underground blasting fracturing unit through a filling pipeline; the ground control unit is connected with the underground blasting fracturing unit through a cable;
the liquid CO2The injection unit comprises liquid CO2Storage tank, liquid CO2The device comprises a supercharging device, a gas-liquid separation device and a high-pressure pumping device; the liquid CO2Storage tank, liquid CO2The pressurizing equipment, the gas-liquid separation equipment and the high-pressure pumping equipment are sequentially connected through a pipeline, and the high-pressure pumping equipment is connected to the liquid CO2Storage tank and liquid CO2A closed loop is formed on a pipeline between the supercharging devices;
the conventional fracturing fluid injection unit comprises a water-based fracturing fluid storage tank, a proppant storage tank, a sand mixing device and conventional pumping equipment, wherein the conventional fracturing fluid injection unit is used for injecting liquid CO2A storage tank; the water-based fracturing fluid storage tank, the proppant storage tank, the sand mixing equipment and the conventional pumping equipment are filled with liquid CO2The storage tanks are connected in sequence through pipelines;
the underground blasting fracturing unit comprises a wellhead device, and a sleeve is arranged below the wellhead device; the sleeve is internally provided with a fracturing string, a packer and multi-stage liquid CO2A phase change blasting device; the bottom end of the fracturing string and multi-stage liquid CO2The phase change blasting device is connected through threads; the packer is arranged in the sleevePipe and multi-stage liquid CO2A shaft closed space is formed between the phase-change blasting devices;
the multi-stage liquid CO2The phase change blasting device comprises a shell, wherein 2-4 liquid CO are arranged in the shell2A phase change generating device; the liquid CO2The phase change device comprises an inflation plug, an air release hole is formed above the inflation plug, a straight notch matched with an inflation nozzle is formed below the inflation plug, a one-way valve is arranged at the center hole of the inflation plug, a heating pipe is connected to the tail end of the inflation plug, the inflation plug is in clearance fit with a high-pressure generating device, the lower end of the high-pressure generating device is in clearance fit with the deflation plug, and a shear slice is arranged at the center hole of the deflation plug.
2. The composite fracture reformation system of claim 1, wherein the casing is of a tubular structure, has an outer diameter of 60-80 mm and an inner diameter of liquid CO2The phase change generating device is in clearance fit; the open end of the shell is provided with a wiring hole and is connected to each stage of liquid CO2A phase change generating device front end; the open end surface of the housing is threaded and can be connected to a fracturing string.
3. The composite fracture modification system of claim 2, wherein the wiring holes are round holes, and the number of the wiring holes is 2; the number of the air release holes is 8-16, the air release holes are uniformly distributed on the central axis of the shell and are perpendicular to the central axis, and the diameter of each air release hole is 8-10 mm.
4. The composite fracture reformation system of claim 1, wherein the liquid CO2The phase change generating device is a cylinder, and the length of the tube is 400-1000 mm.
5. The composite fracturing modification system of claim 2, wherein the heating pipe is a semi-straight groove type cylinder, an electric heating wire is arranged in the heating pipe, the electric heating wire is fixedly arranged in the middle of the heating pipe, is isolated by an insulating material and is not in contact with the outer wall, and the heating pipe can be heated to 100-150 ℃ within 1-2 min after being powered on.
6. The composite fracturing modification system of claim 2, wherein the opening pressure of the front end of the one-way valve is 5-10 MPa, and the fracture pressure of the shear slice is 90-100 MPa.
7. The method of performing composite fracture reformation according to the composite fracture reformation system of any one of claims 1 to 6, characterized by comprising the steps of:
step 1, analyzing the abnormal high pressure or serious blockage position of a stratum according to an oil-gas reservoir and logging data, determining a well section of a target stratum, and designing corresponding construction parameters according to the abnormal pressure or the blockage degree;
step 2, arranging well sites, connecting ground equipment and carrying out liquid CO treatment2Preprocessing by a phase change generating device;
step 3, igniting the liquid CO step by step at intervals of 5-15 s in an electric heating mode through a ground control unit2A phase change blasting device;
step 4, opening the ground liquid CO2The injection unit is used for establishing the basic pressure in the pipeline when the pressure value reaches 1.2-1.6 MPa, and the pressurization process is finished; by liquid CO in a storage tank2Reducing the temperature of the equipment and the pipeline to be below 20 ℃, and finishing the circulating precooling process; liquid CO is mixed according to the design amount2Pumping into wellbore, and introducing liquid CO2Flow through multistage liquid CO2The air-release plug and the blast hole of the phase-change fracturing device enter the stratum to realize CO2Pre-energizing;
step 5, after pre-energizing is finished, starting a conventional fracturing fluid injection unit, injecting the water-based fracturing fluid into the shaft, and mixing the proppant and the water-based fracturing fluid through sand mulling equipment in the pumping process until the whole fracturing operation is finished;
step 6, after the pump injection construction is finished, after the water-based fracturing fluid is broken, opening the well and returning the fracturing fluid, controlling the return discharge volume according to the pressure condition, and CO is generated when the fluid is discharged from the well mouth2When the material is returned out, the returning discharge is stopped.
8. The composite fracture of claim 7The transformation method is characterized in that in the step 2, the liquid CO is2The pretreatment of the phase change generating device comprises the following specific processes: liquid CO to each stage2CO is filled in the phase change generating device2Gas, then liquid CO2The phase change generating device is assembled into multi-stage liquid CO2Phase change blasting device.
9. The method for composite fracture reformation according to claim 7, characterized in that in the step 3, the interval time is 8-10 s.
10. The method of composite fracture reformation according to claim 7, characterized in that in step 5, the amount of the water-based fracturing fluid is 65% or more of the total amount of the proppant and the water-based fracturing fluid.
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