CN109138959B - Supercritical CO2Energy-gathering fracturing method - Google Patents

Abstract

The invention provides supercritical CO₂An energy-gathering fracturing method relates to the field of petroleum and natural gas engineering, and the supercritical CO₂The energy-gathering fracturing method comprises the following steps: step 1, perforating completionPost-treatment of supercritical CO₂Setting the energy-gathering fracturing string into the target interval and supercritical CO₂The energy-gathered fracturing string comprises a plurality of sequentially arranged fracturing sections which are arranged corresponding to the target interval; step 2, injecting CO₂And continuously pressurizing for CO₂After the opening pressure is reached, the corresponding injection through hole, CO, is opened through the fracturing unit of the lowermost fracturing section₂The injection through hole enters a reservoir corresponding to the target layer section and impacts a fracturing reservoir; step 3, continuous CO injection₂Stopping injecting until reaching the designed dosage; step 4, repeating the step 2 and the step 3, and sequentially injecting supercritical CO into the reservoir layer from bottom to top through a plurality of fracturing sections₂. The supercritical CO₂Energy-gathering fracturing method fully combining supercritical CO₂And the characteristic of high-pressure energy accumulation is realized, multiple energy accumulation fracturing of the same interval is realized, and a better yield increase effect is achieved.

Description

Supercritical CO2Energy-gathering fracturing method

Technical Field

The invention relates to the field of petroleum and natural gas engineering, in particular to supercritical CO used in an unconventional oil gas development process₂An energy-gathering fracturing method.

Background

In recent years, with the large-scale development of conventional oil gas, the existing recoverable conventional oil gas resources cannot meet the economic high-speed development requirement of China, and the development of unconventional oil gas resources is gradually promoted. At present, the development of unconventional energy sources such as shale gas, dense gas, coal bed gas and the like generally adopts a conventional hydraulic fracturing method and obtains certain development effect. However, the method has the problems of difficult flowback of the fracturing fluid, large water resource consumption, serious reservoir pollution and the like. Therefore, in recent years, research on novel anhydrous fracturing methods is being carried out, aiming at reducing the amount of water used, avoiding damage to reservoir and natural environment caused by additives in fracturing fluid, and trying to obtain efficient and environment-friendly fracturing development effect.

CO₂Is one of the main components of air, is colorless, tasteless, nontoxic, incombustible and combustion-supporting, has higher density than air at normal temperature and normal pressure, and can be dissolved in water. When the temperature reaches 31.04 ℃ and the pressure reaches 7.38Mpa, CO₂A supercritical state will be reached. Supercritical CO₂Is a special fluid different from gas and liquid, its density is close to liquid, its viscosity is close to gas, its surface tension is close to zero, it is easy to diffuse, and it has strong permeability, and can be fed into any small space whose molecular size is greater than that of said fluid.

Due to supercritical CO₂The unique physical properties of the composite show great advantages when the composite is used for fracturing modification, namely ① CO₂Easy to obtain, non-flammable, non-explosive, easy to control and transport, ② supercritical CO₂Has low viscosity close to gas, low surface tension close to zero, low friction coefficient and easy flowing, ③ supercritical CO₂The fluid can not cause clay expansion in the reservoir, thereby fundamentally avoiding the occurrence of hazards such as water lock effect, rock wettability reversal and the like and effectively protecting the reservoir from being damaged, ④ uses supercritical CO₂⑤ is a clean fracturing fluid with less damage and quick and thorough flowback, and has supercritical CO flow rate and short production period₂The fracturing fluid has strong diffusion capacity and permeability, can easily permeate into pores and microcracks in a reservoir, and is beneficial to generating a large amount of microcrack networks.

Disclosure of Invention

The invention aims to provide supercritical CO₂Energy-gathering fracturing method fully combining supercritical CO₂And the characteristic of high-pressure energy accumulation, multiple energy accumulation fracturing of the same interval is realized, and a better yield increasing effect is achieved compared with the conventional fracturing method.

In order to achieve the above purpose, the present invention provides a supercritical CO₂Method of cumulative fracturing, wherein said supercritical CO₂The energy-gathering fracturing method comprises the following steps:

step 1, after the oil-gas well is perforated and completed, supercritical CO is mixed by an oil pipe₂Setting the energy-gathering fracturing string into a target interval and fixing, wherein the supercritical CO is₂The energy-gathering fracturing string comprises a plurality of fracturing sections which are sequentially arranged from top to bottom, the plurality of fracturing sections are arranged corresponding to the target interval, each fracturing section is internally provided with a fracturing unit, the side wall of each fracturing section is provided with a jet through hole, and the corresponding jet through hole can be opened and closed by the fracturing unit;

step 2, introducing the supercritical CO through the oil pipe₂CO injection into energy-gathering fracturing string₂And continuously pressurizing for CO₂After the opening pressure is reached, the corresponding injection through hole, CO, of the fracturing unit at the lowest part is opened₂Enters the reservoir corresponding to the target layer section through the jet through hole and becomes supercritical CO₂Said supercritical CO₂Impacting and fracturing the reservoir;

step 3, continuously adding supercritical CO₂CO injection into the energy-concentrating fracturing string 100₂Stopping injecting until reaching the designed dosage;

step 4, repeating the step 2 and the step 3, and injecting the supercritical CO into the reservoir layer from bottom to top sequentially through a plurality of injection through holes of the fracturing section₂。

Supercritical CO as described above₂The energy-gathering fracturing method comprises the steps that a fracturing unit comprises a sliding sleeve, a metal ball and a pin, wherein a ball seat correspondingly matched with the metal ball is arranged on the sliding sleeve, the sliding sleeve is sleeved in a fracturing section and correspondingly seals a jet through hole, the sliding sleeve is fixedly connected with the side wall of the fracturing section through the pin, a limiting part is arranged at the bottom end of the fracturing section, the inner diameter of the limiting part is smaller than the inner diameter of the fracturing section to form a limiting step, after the pin is sheared, the sliding sleeve slides down to the limiting step and opens the jet through hole, and the inner diameters of the ball seats of a plurality of sliding sleeves sequentially arranged from top to bottom are sequentially reduced; the step 2 comprises the following steps:

step 21, introducing the supercritical CO₂Throwing the metal ball correspondingly matched with the sliding sleeve at the lowest position into the energy-gathering fracturing string and setting the metal ball on the sliding sleeve at the lowest position;

step 22, feeding the supercritical CO through the oil pipe₂CO injection into energy-gathering fracturing string₂Continuously pressurizing, sliding the set sliding sleeve downwards and opening the corresponding injection through hole when the pin corresponding to the set sliding sleeve is cut off, and CO₂Enters the reservoir corresponding to the target layer section through the jet through hole and becomes supercritical CO₂Said supercritical CO₂Impacting and fracturing the reservoir.

Supercritical CO as described above₂A method of cumulative fracturing, wherein, in said step 2, said supercritical CO is awaited₂CO in cumulative fracturing string₂After the pressure reaches the test pressure value, CO is suspended₂And observing the supercritical CO₂Changing the pressure value in the energy-gathering fracturing string, if the pressure value loss in 5 minutes does not exceed 5 percent, meeting the setting requirement, and continuing to supply the supercritical CO₂Energy-gathering fracturing string CO injection₂。

Supercritical CO as described above₂The energy-gathered fracturing method, wherein the test pressure value is 25 MPa.

Supercritical CO as described above₂Method of cumulative fracturing, wherein said supercritical CO₂The energy-gathered fracturing method further comprises:

step 5, using a sand mixing truck to mix the propping agent and CO₂The mixing forms a mixed fluid and the mixed fluid is pumped into the reservoir to prop a fracture within the reservoir.

Supercritical CO as described above₂Method of cumulative fracturing, wherein said supercritical CO₂The energy-gathered fracturing method further comprises:

and 6, carrying out soaking according to the condition of the producing zone, and carrying out flowback operation after the soaking is finished.

Supercritical CO as described above₂Method of cumulative fracturing, wherein said pinThe shear strength of the nail is 5-8MPa higher than the stratum fracture pressure of the reservoir. Supercritical CO as described above₂A method of cumulative fracturing wherein the height of the sliding sleeve is less than 0.4 meters.

Compared with the prior art, the invention has the following characteristics and advantages:

the supercritical CO provided by the invention₂The energy-gathered fracturing method can realize single-layer multiple synergistic fracturing for the same reservoir stratum, is particularly suitable for the reservoir stratum with difficult expansion of fractures after the initiation of the stratum and difficult formation of effective fracture network, and fully improves the supercritical CO of the reservoir stratum with poor stratum compressibility₂The effect of fracturing.

Drawings

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. In addition, the shapes, the proportional sizes, and the like of the respective members in the drawings are merely schematic for facilitating the understanding of the present invention, and do not specifically limit the shapes, the proportional sizes, and the like of the respective members of the present invention. Those skilled in the art, having the benefit of the teachings of this invention, may choose from the various possible shapes and proportional sizes to implement the invention as a matter of case.

FIG. 1 shows supercritical CO proposed by the present invention₂The structure schematic diagram of the energy-gathering fracturing string;

FIG. 2 is a schematic diagram of the structure of a fracturing unit of the present invention;

FIG. 3 shows supercritical CO proposed by the present invention₂The structure schematic diagram of the energy-gathered fracturing string during the first energy-gathered fracturing;

FIG. 4 shows supercritical CO proposed by the present invention₂The structural schematic diagram of the energy-gathered fracturing string during the second ball shooting;

FIG. 5 shows supercritical CO proposed by the present invention₂And (3) a structural schematic diagram of the fourth energy-gathering fracturing of the energy-gathering fracturing string.

Description of reference numerals:

100. supercritical CO₂Energy-gathered fracturing string; 10. A tubular column body;

11. a fracturing section; 20. A fracturing unit;

21. a sliding sleeve; 211. A ball seat;

22. a metal ball; 23. A pin;

24. a jet through hole; 25. A limiting part;

12. a fracturing section; 13. A fracturing section;

14. a fracturing section; 31. A sliding sleeve;

41. a sliding sleeve; 51. A sliding sleeve;

32. a metal ball; 42. A metal ball;

52. a metal ball.

Detailed Description

The details of the present invention can be more clearly understood in conjunction with the accompanying drawings and the description of the embodiments of the present invention. However, the specific embodiments of the present invention described herein are for the purpose of illustration only and are not to be construed as limiting the invention in any way. Any possible variations based on the present invention may be conceived by the skilled person in the light of the teachings of the present invention, and these should be considered to fall within the scope of the present invention.

Referring to fig. 1 to 5, the present invention provides a supercritical CO₂Energy-gathering fracturing method, the supercritical CO₂The energy-gathering fracturing method comprises the following steps:

step 1, after the oil-gas well is perforated and completed, supercritical CO is mixed by an oil pipe₂Setting the energy-gathering fracturing string 100 into the target interval and fixing, supercritical CO₂The energy-gathering fracturing string comprises a plurality of fracturing sections 11 which are sequentially arranged from top to bottom, the plurality of fracturing sections 11 are arranged corresponding to the target interval, each fracturing section 11 is internally provided with a fracturing unit 20, the side wall of each fracturing section 11 is provided with a jet through hole 24, and the corresponding jet through hole 24 can be opened and closed by the fracturing unit 20;

step 2, converting the supercritical CO into supercritical CO through an oil pipe₂Injecting liquid CO into the energy-gathering fracturing string 100₂And continuously pressurizing for CO₂After reaching the cracking pressure, the corresponding injection through-hole 24, CO, is opened by the lowermost fracturing unit 20₂Through which is passedThe jet through hole 24 enters a reservoir layer corresponding to the target layer section and becomes supercritical CO₂Supercritical CO₂Impacting and fracturing a reservoir;

step 3, continuously returning to supercritical CO₂CO injection into the energy-concentrating fracturing string 100₂Stopping injecting until reaching the designed dosage;

step 4, repeating the step 2 and the step 3, and sequentially injecting supercritical CO into the reservoir layer from bottom to top through the injection through holes 24 of the plurality of fracturing sections 11₂。

As shown in FIGS. 1 and 2, supercritical CO₂ Cumulative fracturing string 100 is including the tubular column body 10 that is the tube-shape, and a plurality of fracturing sections 11 that tubular column body 10 is vertical to be set up and set up including from top to bottom in proper order, and a plurality of fracturing sections 11 all correspond same reservoir stratum, all correspond in every fracturing section 11 and install fracturing unit 20, and seted up on the lateral wall of every fracturing section 11 and jetted through-hole 24, and corresponding jetted through-hole 24 can be opened and closed to fracturing unit 20.

The supercritical CO provided by the invention₂The energy-gathered fracturing method and the tubular column can realize single-layer multiple synergistic fracturing for the same reservoir stratum, are particularly suitable for the reservoir stratum with difficult expansion of fractures after the initiation of the stratum and difficult formation of effective fracture network, and can fully improve the supercritical CO of the reservoir stratum with poor stratum compressibility₂The effect of fracturing.

The supercritical CO provided by the invention₂Energy-gathering fracturing method, high-pressure supercritical CO in energy-gathering fracturing operation₂The instant release is acted on the reservoir, so that more complex fracture networks are formed in the reservoir; high pressure transient fracturing reduces supercritical CO₂The fluid loss and the operation success rate are higher, and the method is also suitable for the fracturing transformation of a reservoir with high permeability and serious leakage; after fracturing is complete, CO₂Easy flowing back and little damage to the reservoir.

Supercritical CO₂Energy-gathering fracturing capable of utilizing supercritical CO₂The special properties, combined with the energy-gathering effect, can produce obvious technical advantages in the fracturing process: (1) supercritical CO₂The permeability is strong, and the micro-crack can enter any micro space with the molecular size larger than the molecular size of the micro-crack, so that the micro-crack is favorably formed; (2) CO2₂After fracturing is finished, flowback is easy, and damage to a reservoir is small; (3) the energy-gathering fracturing mode can impact the reservoir with instantaneous high pressure to form more cracks and crack networks, and the stratum transformation efficiency is higher; (4) the energy-gathering instantaneous fracturing method acts on the time period of reservoir fracture generation, and avoids the phenomenon of supercritical CO₂The high permeability can not establish the result of fracturing caused by high pressure of the reservoir, and is also suitable for fracturing of the reservoir with high permeability and serious leakage; (5) compared with an explosive explosion mode, the energy-gathering fracturing method is stronger in operability, safer and less in damage to a pipe column and tools.

In the present invention, towards supercritical CO₂CO injected into the cumulative fracturing string 100₂Is high pressure liquid CO₂Continuously pumped by a high-pressure pump set on the ground, and the high-pressure liquid CO is₂The specific pressure of (a) is determined based on the downhole pressure, and is typically higher than the formation fracture pressure of the corresponding reservoir. Formation fracture pressure refers to the pressure at which the formation fractures when the formation pressure reaches a certain value in the wellbore, and this pressure is referred to as formation fracture pressure. Before and after drilling, geological parameters are generally tested, such as seismic testing, well logging and other methods, and the formation fracture pressure is obtained through testing in the process.

In the present invention, when high pressure liquid CO is used₂Is heated to high temperature and high pressure by the stratum when continuously descending along the oil pipe₂Specifically, the calculation formula of the formation temperature is as follows: the formation temperature is equal to the surface temperature + (1.5-3) × well depth/100, for example, the bottom temperature of an oil and gas well of about 60 ℃ is about 2000 m, and when the temperature exceeds 31.1 ℃ and the pressure exceeds 7.38MPa, CO is generated₂Is in a supercritical state and thus CO enters the formation₂Is supercritical CO₂The fracturing process is supercritical CO₂And (4) fracturing. The high pressure supercritical CO mentioned above at the moment when the ejection through-hole 24 is opened₂The high-energy shock wave can be generated to the reservoir stratum, and the complex fracture network can be generated. In the above process, although CO is present₂After sudden expansion, the temperature will be due to the Joule Thomson effectReduced, but CO after entering the reservoir₂Can be heated to a supercritical state rapidly and still can generate great impact force on a reservoir.

In an optional example of the present invention, the fracturing unit 20 includes a sliding sleeve 21, a metal ball 22 and a pin 23, the sliding sleeve 21 is provided with a ball seat 211 correspondingly matched with the metal ball 22, a jetting through hole 24 is formed on a side wall of the fracturing section 11, the sliding sleeve 21 is sleeved in the fracturing section 11 and correspondingly closes the jetting through hole 24, the sliding sleeve 21 is fixedly connected with the side wall of the fracturing section 11 through the pin 23, the bottom end of the fracturing section 11 is provided with a limiting portion 25, an inner diameter of the limiting portion 25 is smaller than an inner diameter of the fracturing section 11 to form a limiting step, after the pin 23 is cut, the sliding sleeve 21 slides down to the limiting step and opens the jetting through hole 24, and inner diameters (also inner diameters of the sliding sleeve 21) of the ball seats 211 of the plurality of sliding sleeves 21 sequentially.

Further, step 2 further comprises step 21 and step 22, wherein,

step 21, introducing the supercritical CO₂Putting a metal ball 22 correspondingly matched with the lowest sliding sleeve 21 into the energy-gathering fracturing string 100 and setting the metal ball 22 on the lowest sliding sleeve 21;

step 22, passing the oil pipe to supercritical CO₂CO injection into the energy-concentrating fracturing string 100₂Continuously pressurizing, sliding the set sliding sleeve 21 downwards and opening the corresponding injection through hole 24, CO when the pin 23 corresponding to the set sliding sleeve 21 is cut off₂Enters a reservoir corresponding to the target layer section through the jet through hole 24 and becomes supercritical CO₂The above supercritical CO₂Impacting and fracturing the reservoir.

The supercritical CO provided by the invention₂The energy-gathering fracturing method is characterized in that sliding sleeves 21 with different inner diameters are fixed through pins, metal balls 22 with different diameters are put in before fracturing operation to seat and seal the sliding sleeves 21 with different inner diameters (the inner diameters of the sliding sleeves are gradually increased from bottom to top, and the diameters of the put metal balls are also sequentially increased), multiple times of repeated energy-gathering fracturing operation of the same layer section is realized, the fracturing effect is better, and the yield increasing effect better than that of a conventional fracturing method is achieved.

In the invention, the sliding sleeve 21 has a containing cavity which is through up and down, the ball seat 211 is arranged on the inner wall of the sliding sleeve 21, and after the metal ball 22 is put into the containing cavity, the metal ball is seated on the ball seat 211 to seal the containing cavity of the sliding sleeve 21.

In the present invention, the shear strength of the pin 23 is designed according to the formation fracture pressure; by changing the shear strength of the pins, the supercritical CO can be adjusted₂The pressure in the energy-gathering fracturing string 100 is high, so that the fracturing requirements of different stratums are met, and the practicability of the method is enhanced.

In an alternative example, the cracking pressure is the maximum shear force that the pin 23 can bear (shear strength of the pin), and the maximum shear force that the pin 23 can bear is 5-8MPa higher than the formation fracture pressure of the corresponding reservoir, so as to generate better energy-gathering impact effect.

In an optional example of the present invention, a plurality of injection through holes 24 are formed in a side wall of each fracturing segment 11, and the plurality of injection through holes 24 are uniformly distributed along a circumferential direction of the fracturing segment 11.

In an alternative embodiment of the invention, the height of the sliding sleeve 21 is less than 0.4 m, so as to ensure the whole supercritical CO₂The size of the energy-concentrating fracturing string 100 is not too long, so that supercritical CO is not generated₂And the same layer of fracture (reservoir) can be more easily accessed.

In an alternative example of the invention, the tubular string body 10 includes 4 fracturing stages 11, i.e. supercritical CO₂The energy-gathering fracturing string 100 can perform four times of fracturing on the same reservoir stratum, and generally, the four times of fracturing yield can reach 1.5 to 2 times of the primary fracturing yield.

In an alternative embodiment of the invention, supercritical CO₂The energy-gathered fracturing method further comprises:

step 5, using a sand mixing truck to mix the propping agent with liquid CO₂The mixing forms a mixed fluid and the mixed fluid is pumped into the reservoir to prop the fractures within the reservoir and avoid closing the fractures, thereby completing the energy-gathering fracturing.

In an alternative embodiment of the invention, the proppant comprises 2-5% by mass of the mixed fluid.

In an alternative embodiment of the invention, supercritical CO₂Energy-gathering fracturing squareThe method also comprises the following steps: and 6, carrying out soaking according to the condition of the producing zone, and carrying out flowback operation after the soaking is finished.

In an alternative embodiment of the invention, in step 2, supercritical CO is to be treated₂Liquid CO in the energy-concentrating fracturing string 100₂After the pressure reaches the test pressure value, the liquid CO is suspended₂Injecting and observing supercritical CO₂The pressure value in the energy-gathering fracturing string 100 changes, if the pressure value loss in 5 minutes does not exceed 5 percent, the setting requirement is met, and the supercritical CO can be continuously converted₂Injecting liquid CO into the energy-gathering fracturing string 100₂。

In an alternative example of the invention, the test pressure value is 25 MPa.

Supercritical CO with four fracturing stages₂The energy-gathering fracturing string 100 is taken as an example to explain the supercritical CO proposed by the present invention in detail₂An energy-gathering fracturing method.

As shown in fig. 3, 4 and 5, the supercritical CO₂The energy-gathering fracturing string comprises a fracturing section 11, a fracturing section 12, a fracturing section 13 and a fracturing section 14 which are sequentially arranged from top to bottom, a sliding sleeve 21 is installed in the fracturing section 11, a sliding sleeve 31 is installed in the fracturing section 12, a sliding sleeve 41 is installed in the fracturing section 13, a sliding sleeve 51 is installed in the fracturing section 14, wherein the inner diameter of the sliding sleeve 21 (also the inner diameter of a ball seat 211 of the sliding sleeve 21), the inner diameter of the sliding sleeve 31, the inner diameter of the sliding sleeve 41 and the inner diameter of the sliding sleeve 51 are sequentially increased, correspondingly, the diameter of a metal ball 22, the diameter of the metal ball 32, the diameter of the metal ball 42 and the diameter of the metal ball 52 are sequentially increased.

As shown in FIGS. 3 to 5, the supercritical CO proposed by the present invention₂The specific implementation process of the energy-gathering fracturing method is as follows:

firstly, after cementing and perforating the oil well, connecting supercritical CO by using an oil pipe₂The energy-gathering fracturing string 100 is put into the well and supercritical CO is generated₂The energy-gathering fracturing string 100 enters a target interval (perforation section) at the bottom of the well through a wellhead device and a shaft, and then supercritical CO is introduced into the target interval (perforation section) at the bottom of the well₂The bottom of the energy-gathered fracturing string 100 is hydraulically anchored;

to supercritical CO₂After the energy-gathering fracturing string 100 is put into a target interval and fixed, the energy-gathering fracturing string is put into the sliding sleeve 21The matched metal ball 22, the metal ball 22 seats the sliding sleeve 21, and CO is opened₂High pressure pump, starting to supercritical CO via oil pipe₂Pumping CO into the energy-gathering fracturing string 100₂Stopping pumping when a certain pressure (such as 25Mpa) is reached, and observing supercritical CO₂The pressure value in the energy-gathered fracturing string 100 changes, and the requirement can be met if the pressure loss in the string is not more than 5% within 5 minutes, so that the plugging effect is good (the sealing effect of the whole system is good), and the next operation can be implemented;

opening CO under the condition of good sealing effect of the whole system₂High pressure pump, continuing to supercritical CO₂Pumping CO into the energy-gathering fracturing string 100₂Until the shear strength of the pin 23 is reached, the pin 23 is sheared at the moment, the sliding sleeve 21 and the metal ball 22 slide to the position of the limiting part 25 along the inner wall of the fracturing section 11, the injection through hole 24 is opened, and the high-pressure supercritical CO is obtained₂Entering reservoir in explosive state while continuously injecting CO₂Completing the first energy gathering fracturing until the design requirement is met;

if the first fracturing of the target interval cannot achieve the expected effect, the metal ball 32 is needed to seat the sliding sleeve 31 for second fracturing, the metal ball 42 is used to seat the sliding sleeve 41 for third fracturing, the metal ball 52 is used to seat the sliding sleeve 51 for fourth fracturing, each fracturing process is the same as the first fracturing, the sealing effect must be checked after ball throwing, and the pump is started again for pressurization, so that multiple times of supercritical CO2 energy-gathering fracturing of the same reservoir can be realized;

by using supercritical CO₂Repeatedly accumulating energy, fracturing and fracturing the stratum to form a seam network, and continuing to supercritical CO₂Sand-carrying fluid, displacement fluid and the like are pumped into the energy-gathering fracturing string 100, and the proppant is pumped into the fracture to prevent the fracture from being closed.

And finally, determining the soaking time according to the condition of the producing zone, and finally performing flowback operation to complete the whole fracturing process.

The present invention is not limited to the above embodiments, and in particular, various features described in different embodiments can be arbitrarily combined with each other to form other embodiments, and the features are understood to be applicable to any embodiment except the explicitly opposite descriptions, and are not limited to the described embodiments.

Claims (8)

1. Supercritical CO₂Method of cumulative fracturing, characterized in that said supercritical CO₂The energy-gathering fracturing method comprises the following steps:

step 1, after the oil-gas well is perforated and completed, supercritical CO is mixed by an oil pipe₂Setting the energy-gathering fracturing string into a target interval and fixing, wherein the supercritical CO is₂The energy-gathering fracturing string comprises a plurality of fracturing sections which are sequentially arranged from top to bottom, the plurality of fracturing sections are arranged corresponding to the same target interval, each fracturing section is internally provided with a fracturing unit, the side wall of each fracturing section is provided with a jet through hole, and the corresponding jet through hole can be opened and closed by the fracturing unit;

step 2, introducing the supercritical CO through the oil pipe₂CO injection into energy-gathering fracturing string₂And continuously pressurizing for CO₂After the opening pressure is reached, the corresponding injection through hole, CO, of the fracturing unit at the lowest part is opened₂Enters the reservoir corresponding to the target layer section through the jet through hole and becomes supercritical CO₂Said supercritical CO₂Impacting and fracturing the reservoir;

step 3, continuously adding supercritical CO₂CO injection into energy-gathering fracturing string₂Stopping injecting until reaching the designed dosage;

step 4, repeating the step 2 and the step 3, and injecting the supercritical CO into the reservoir layer from bottom to top sequentially through a plurality of injection through holes of the fracturing section₂。

2. The supercritical CO of claim 1₂The energy-gathering fracturing method is characterized in that the fracturing unit comprises a sliding sleeve, a metal ball and a pin, the sliding sleeve is provided with a ball seat correspondingly matched with the metal ball, and the sliding sleeveThe sliding sleeve is sleeved in the fracturing section and correspondingly seals the injection through hole, the sliding sleeve is fixedly connected with the side wall of the fracturing section through the pin, a limiting part is arranged at the bottom end of the fracturing section, the inner diameter of the limiting part is smaller than that of the fracturing section to form a limiting step, after the pin is sheared, the sliding sleeve slides downwards to the limiting step and opens the injection through hole, and the inner diameters of ball seats of the plurality of sliding sleeves sequentially arranged from top to bottom are sequentially reduced; the step 2 comprises the following steps:

step 21, introducing the supercritical CO₂Throwing the metal ball correspondingly matched with the sliding sleeve at the lowest position into the energy-gathering fracturing string and setting the metal ball on the sliding sleeve at the lowest position;

step 22, feeding the supercritical CO through the oil pipe₂CO injection into energy-gathering fracturing string₂Continuously pressurizing, sliding the set sliding sleeve downwards and opening the corresponding injection through hole when the pin corresponding to the set sliding sleeve is cut off, and CO₂Enters the reservoir corresponding to the target layer section through the jet through hole and becomes supercritical CO₂Said supercritical CO₂Impacting and fracturing the reservoir.

3. The supercritical CO of claim 2₂The energy-gathering fracturing method is characterized in that the shear strength of the pin is 5-8MPa higher than the stratum fracture pressure of the reservoir.

4. The supercritical CO of claim 2₂The energy-gathering fracturing method is characterized in that the height of the sliding sleeve is less than 0.4 m.

5. The supercritical CO of claim 1₂Method for cumulative fracturing, characterized in that in step 2, the supercritical CO is awaited₂CO in cumulative fracturing string₂After the pressure reaches the test pressure value, CO is suspended₂And observing the supercritical CO₂The pressure value in the energy-gathering fracturing string changes, and the setting is required if the pressure value loss in 5 minutes does not exceed 5 percentCalculating, continuing to the supercritical CO₂Energy-gathering fracturing string CO injection₂。

6. The supercritical CO of claim 5₂The energy-gathered fracturing method is characterized in that the test pressure value is 25 MPa.

7. The supercritical CO of claim 1₂Method of cumulative fracturing, characterized in that said supercritical CO₂The energy-gathered fracturing method further comprises:

step 5, using a sand mixing truck to mix the propping agent and CO₂The mixing forms a mixed fluid and the mixed fluid is pumped into the reservoir to prop a fracture within the reservoir.

8. The supercritical CO of claim 1₂Method of cumulative fracturing, characterized in that said supercritical CO₂The energy-gathered fracturing method further comprises:

and 6, carrying out soaking according to the condition of the producing zone, and carrying out flowback operation after the soaking is finished.

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