CN113622891B - Dredging type fracturing method of high-rank coal reservoir - Google Patents

Abstract

The disclosure provides a dredging fracturing method for high-rank coal reservoirs, including: determining the depth range of primary coal in the high-rank coal reservoirs according to well logging data; Perforating in the central region of the depth range where the primary coal of the coal reservoir is located, forming multiple holes in the inner wall of the wellbore; injecting the first fracturing fluid through the multiple holes to form the first fractures in the primary coal of the high-rank coal reservoir; The second fracturing fluid is injected through multiple holes to form a second fracture in the primary coal of the high-rank coal reservoir, the first fracture communicates with the second fracture, and the second fracturing fluid is the first fracturing fluid and fracture proppant The mixed fluid; inject displacement fluid from the wellbore, and replace the first fracturing fluid and the second fracturing fluid in the primary coal of the high-rank coal reservoir; stop injecting fluid into the wellbore, and flow back directly without stuffing the well. The disclosure can carry out fracturing transformation on primary coal in high-rank coal reservoirs, and improve the gas production of gas wells.

Description

Dredging fracturing method for high-rank coal reservoirs

technical field

The disclosure relates to the technical field of coalbed gas exploitation, in particular to a dredging fracturing method for high-rank coal reservoirs.

Background technique

Hydraulic fracturing technology is an important means to stimulate high-rank coal reservoirs. Hydraulic fracturing utilizes the performance of fracturing fluid to transmit pressure, and pumps the fracturing fluid into the well based on the surface high-pressure pump group. When the bottom hole pressure is greater than the ground stress near the well wall and the tensile strength of the reservoir rock, the formation will crack and produce fractures. Then pump the sand-carrying fluid containing sand proppant to fill the fractures and extend the fractures, forming sand-filled fractures with high conductivity at the bottom of the well, increasing the permeability and achieving the purpose of increasing production.

Due to the influence of stress during the formation of high-rank coal reservoirs, different degrees of fragmentation will occur, and different types of coal structures will develop and form in the reservoirs. The coal body structure of high-rank coal reservoirs includes primary coal and structural coal. Among them, primary coal is hard coal with high strength, while tectonic coal has poor cementation, low strength and is easily broken.

During hydraulic fracturing, the fracturing fluid first breaks through the structural coal with weak strength, forming a vadose zone with high conductivity at the position of the structural coal. Moreover, the pressure in the wellbore cannot reach the fracture pressure strength of the original coal, so the original coal cannot achieve reservoir reconstruction. Due to the low gas content of structural coal, the gas production of gas wells after hydraulic fracturing is also small.

Contents of the invention

The embodiments of the present disclosure provide a dredging fracturing method for high-rank coal reservoirs, which can perform fracturing reconstruction on primary coal in high-rank coal reservoirs, and increase the gas production of gas wells. Described technical scheme is as follows:

An embodiment of the present disclosure provides a dredging-type fracturing method for a high-rank coal reservoir. The dredging-type fracturing method includes: determining the primary coal in the high-rank coal reservoir according to logging data. The depth range in the wellbore is perforated in the middle region corresponding to the depth range of the primary coal of the high-rank coal reservoir, and a plurality of holes are formed on the inner wall of the wellbore; the first fracturing fluid is injected through the plurality of holes, A first fracture is formed in the primary coal of the high-rank coal reservoir; a second fracturing fluid is injected through the plurality of holes to form a second fracture in the primary coal of the high-rank coal reservoir, and the first fracture is formed in the primary coal of the high-rank coal reservoir. A fracture communicates with the second fracture, and the second fracturing fluid is a mixture of the first fracturing fluid and fracture proppant; a displacement fluid is injected from the wellbore, and the first fracturing fluid and the The second fracturing fluid is replaced in the primary coal of the high-rank coal reservoir; the fluid injection into the wellbore is stopped, and the well is not blocked and flowed back directly.

In an implementation manner of an embodiment of the present disclosure, the determining the depth range of the primary coal in the high-rank coal reservoir according to the logging data includes: obtaining the high-rank coal reservoir The well logging data in different areas in the above-mentioned well logging data include: resistivity of high-rank coal reservoirs, acoustic time difference of high-rank coal reservoirs, natural gamma ray values of high-rank coal reservoirs and high-rank coal reservoirs at least one of the density logging of layers; and determining the depth range of primary coal in the high-rank coal reservoir according to the logging data.

In another implementation manner of the embodiment of the present disclosure, the determining the depth range of the primary coal in the high-rank coal reservoir according to the logging data includes: if the logging data satisfies the first determination relationship area, then determine the depth range of all areas satisfying the first determination relationship in the high-rank coal reservoir as the depth range of primary coal in the high-rank coal reservoir, and the first determination relationship Including at least one of the following: the resistivity is greater than 3000Ω·m, the acoustic transit time is between 370μs/m and 410μs/m, the natural gamma value is between 30API and 80API, and the density logging is between 1.3g/m Between cm ³ and 1.6g/cm ³ .

In another implementation manner of the embodiment of the present disclosure, the perforating in the middle region of the depth range corresponding to the primary coal of the high-rank coal reservoir in the wellbore includes: the high-rank coal reservoir in the wellbore Concentrated perforation is carried out in the central area of the depth range of the primary coal in the seam, the perforation density is 10 holes/m to 20 holes/m, the perforation depth is 2.5 meters to 3.0 meters, and the perforation direction is perpendicular to the minimum principal stress direction of the coal seam .

In another implementation manner of the embodiment of the present disclosure, the second fracturing fluid is injected through the plurality of holes, and before the second fractures are formed in the raw coal of the high-rank coal reservoir, the dredging The fracturing method further includes: injecting a third fracturing fluid from the plurality of holes, so that the fracture proppant in the third fracturing fluid supports the first fracture, and the third fracturing fluid is the first fracturing fluid. A mixture of fracturing fluid and fracture proppant, the fracture proppant content of the third fracturing fluid is lower than the fracture proppant content of the second fracturing fluid; the injection through the plurality of holes The second fracturing fluid is used to form a second fracture in the primary coal of the high-rank coal reservoir, comprising: injecting the second fracturing fluid from the plurality of holes, making the second fracturing fluid in the The primary coal of the high-rank coal reservoir forms the second fracture and makes the fracture proppant in the second fracturing fluid support the second fracture.

In another implementation manner of the embodiments of the present disclosure, the injecting the second fracturing fluid from the plurality of holes includes: gradually increasing the injection speed of the second fracturing fluid and the first The second fracturing fluid is injected into the first fracture from the plurality of holes according to the mass percentage of the fracture proppant in the second fracturing fluid.

In another implementation manner of the embodiments of the present disclosure, the injection rate of the second fracturing fluid and the mass percentage of fracture proppant in the second fracturing fluid are gradually increased, Injecting the second fracturing fluid into the first fracture from the plurality of holes includes: sequentially and continuously injecting the second fracturing fluid into the first fracture according to a first speed, a second speed and a third speed. Fracture fluid, the first velocity is less than the second velocity, the second velocity is less than the third velocity, when the second fracturing fluid is injected according to the first velocity, the second fracturing fluid The mass percentage of the fracture proppant is the first content, and when the second fracturing fluid is injected according to the second speed, the mass percentage of the fracture proppant of the second fracturing fluid is the second content , when injecting the second fracturing fluid at the third speed, the mass percentage of the fracture proppant in the second fracturing fluid is a third content, and the first content is less than the second content, The second content is less than the third content.

In another implementation manner of the embodiment of the present disclosure, the three fracturing fluids include: potassium chloride, clay stabilizer, the fracture proppant and water, and the mass percentage of the potassium chloride is 1.0% to 2.0% %, the mass percentage of the clay stabilizer is 0.2% to 0.5%, the mass percentage of the fracture proppant is 6.0% to 8.0%, and the balance is water; the second fracturing fluid includes: potassium chloride, Clay stabilizer, the fracture proppant and water, the mass percent of the potassium chloride is 1.0% to 2.0%, the mass percent of the clay stabilizer is 0.2% to 0.5%, the mass percent of the fracture proppant It is 12% to 20%, and the balance is water.

In another implementation manner of the embodiment of the present disclosure, the fracture proppant is a sand proppant, and the sand proppant of the second fracturing fluid includes three propping sands with different particle sizes, wherein the particle size The mass percentage of the smallest support sand is 16.7%, the mass percentage of the support sand with the largest particle size is 33.3%, and the mass percentage of the support sand with the particle size between the support sand with the smallest particle size and the support sand with the largest particle size is 50.0% %, the particle size of the sand proppant of the third fracturing fluid is the particle size of the sand proppant of the second fracturing fluid between the support sand with the smallest particle size and the support sand with the largest particle size Support sand.

In another implementation manner of the embodiments of the present disclosure, the first fracturing fluid includes: potassium chloride, a clay stabilizer and water, the mass percentage of the potassium chloride is 1.0% to 2.0%, and the clay The mass percentage of the stabilizer is 0.2% to 0.5%, and the balance is water.

In another implementation manner of the embodiment of the present disclosure, the dredging fracturing method further includes: measuring the wellhead pressure, and determining the flowback parameter according to the wellhead pressure; the determining the flowback parameter according to the wellhead pressure includes: If the wellhead pressure is greater than 20Mpa, use a nozzle with a diameter of 6mm for flowback; if the wellhead pressure is 10Mpa to 20MPa, use a nozzle with a diameter of 10mm for flowback; if the wellhead pressure is 5Mpa to 10MPa, Use a nozzle with a diameter of 12mm for flowback; if the wellhead pressure is less than 5MPa, use a nozzle with a diameter of 14mm for flowback.

The beneficial effects brought by the technical solutions provided by the embodiments of the present disclosure at least include:

The dredging fracturing method for high-rank coal reservoirs in the embodiment of the present disclosure first identifies the coal body structure development characteristics of high-rank coal reservoirs based on well logging data, locks the development intervals of primary coal in high-rank coal reservoirs, and determines Find out the position of the primary coal in the high-rank coal reservoir; then, perforate in the middle area of the depth range corresponding to the primary coal of the high-rank coal reservoir in the wellbore, and form multiple holes on the inner wall of the wellbore. After the holes are formed in the wellbore, the first fracturing fluid is injected into the high-rank coal reservoir from multiple holes to form the first fracture at the primary coal in the high-rank coal reservoir, so as to initially reduce the seepage resistance of the reservoir and realize Increase production. At the same time, the second fracturing fluid is injected into the first fracture from a plurality of holes to further expand the direction and depth of the first fracture in the reservoir, so that the first fracture in the reservoir can be formed deeper in the reservoir. Second fractures, thus forming long fractures in high-rank coal reservoirs. And support the long fractures with the help of fracture proppant in the second fracturing fluid. Under the action of the second fracturing fluid, the main fractures in the reservoir extend multiple sub-fractures along different lateral directions of the main fractures to form a network fracture system, which improves the fracture-making effect and reduces the seepage resistance of the reservoir. Then, a displacement fluid is injected from the wellbore to replace the first fracturing fluid and the second fracturing fluid in the raw coal of the high-rank coal reservoir to ensure that both the first fracturing fluid and the second fracturing fluid can fully support the first fracturing fluid. The first crack and the second crack make the network crack system more stable. Finally, after the displacement fluid is pumped, the non-stuffy well is used for direct flowback, which can quickly reduce the reservoir pressure to the original formation pressure, reduce the degree of fracturing fluid fluid loss and pollution of the reservoir, and guide high-pressure liquid and coal powder Rapid drainage keeps the fractures clean, and more effectively alleviates the rise of reservoir pressure and the expansion of fracturing fluid erosion to the surrounding area.

In the embodiments of the present disclosure, the depth range of the primary coal in the high-rank coal reservoir is determined through the logging data, and then perforation is performed at the depth corresponding to the primary coal in the wellbore, thereby avoiding the fracturing of the related technology. The liquid is easy to form a vadose zone with high conductivity at the structural coal position. Realizing the transformation of primary coal in high-rank coal reservoirs can increase the gas production of gas wells; at the same time, by injecting the first fracturing fluid and the second fracturing fluid respectively to form a network fracture system, the fracture-making effect is improved and production increase is realized.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings that need to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present disclosure. For those skilled in the art, other drawings can also be obtained based on these drawings without creative effort.

Fig. 1 is a flow chart of a dredging fracturing method for a high-rank coal reservoir provided by an embodiment of the present disclosure;

Fig. 2 is a flow chart of another high-rank coal reservoir dredging fracturing method provided by an embodiment of the present disclosure.

Detailed ways

In order to make the purpose, technical solution and advantages of the present disclosure clearer, the implementation manners of the present disclosure will be further described in detail below in conjunction with the accompanying drawings.

Fig. 1 is a flowchart of a dredging fracturing method for a high-rank coal reservoir provided by an embodiment of the present disclosure. As shown in Figure 1, the fracturing method includes:

S101: Determine the depth range of primary coal in the high-rank coal reservoir according to the logging data.

S102: Perforating in the central area of the wellbore corresponding to the depth range of the primary coal of the high-rank coal reservoir, forming a plurality of holes on the inner wall of the wellbore.

S103: Injecting the first fracturing fluid through multiple holes to form first fractures in the primary coal of the high-rank coal reservoir.

S104: Injecting the second fracturing fluid through multiple holes to form second fractures in the primary coal of the high-rank coal reservoir.

Wherein, the first fracture communicates with the second fracture, and the second fracturing fluid is a mixture of the first fracturing fluid and fracture proppant.

S105: Injecting a displacement fluid from the wellbore, displacing the first fracturing fluid and the second fracturing fluid in the primary coal of the high-rank coal reservoir.

S106: Stop injecting liquid into the wellbore, and flow back directly without stuffing the well.

The dredging fracturing method of the high-rank coal reservoir in the embodiment of the present disclosure first determines the depth position of the primary coal in the high-rank coal reservoir according to the logging data, that is, the fracturing method is based on the logging data Identify the coal body structure development characteristics of high-rank coal reservoirs, lock the development intervals of primary coal in high-rank coal reservoirs, and determine the position of primary coal in high-rank coal reservoirs; then, corresponding high-rank coal in the wellbore Perforation in the central area of the depth range where the primary coal of the coal reservoir is located forms multiple holes in the inner wall of the wellbore, that is, dense holes are formed. Since the boundary area of the depth range where the primary coal is located is mostly structural coal with weak strength, if the perforation position completely corresponds to the position of the entire primary coal, the fracturing fluid will enter into the structural coal and form a high conductivity hole at the structural coal position. The seepage zone is not conducive to the hydraulic fracturing of primary coal. Therefore, in the embodiment of the present disclosure, the central region where the primary coal of the high-rank coal reservoir is located is selected for perforation, which can effectively avoid the hydraulic fracturing process. The liquid enters the structural coal to ensure the effect of reservoir stimulation. After dense holes are formed in the wellbore, the first fracturing fluid is injected into the high-rank coal reservoir from multiple holes. When the first fracturing fluid suppresses the pressure at the bottom of the well, the pressure is greater than that of the high-rank coal reservoir where the multiple holes are located. When the strength of the primary coal is moderate, the primary coal in the high-rank coal reservoir will generate cracks (that is, the first crack), and the first crack formed at the primary coal in the high-rank coal reservoir will initially reduce the seepage resistance of the reservoir , increasing the penetration rate and increasing production. At the same time, the second fracturing fluid is injected into the first fracture from multiple holes, and the direction and depth of the first fracture in the reservoir are further expanded by using the second fracturing fluid, so that on the basis of the first fracture in the reservoir, The second fracture is formed deeper in the formation, and the second fracture is connected with the first fracture, thereby forming a long fracture in the high-rank coal reservoir. Under the action of the second fracturing fluid, the fractures in the reservoir can continue to extend into the reservoir, and on the basis of the first fracture and the second fracture as the main fracture, along different sides of the main fracture Multiple sub-fractures are extended in the direction to form multiple branched fractures, that is, the main fractures and sub-fractures intersect each other to form a network fracture system, which improves the fracture-making effect and makes the formation of primary coal in high-rank coal reservoirs The network fracture system can further reduce the seepage resistance of the reservoir to increase the permeability and increase production. Then, a displacement fluid is injected from the wellbore to replace the first fracturing fluid and the second fracturing fluid in the raw coal of the high-rank coal reservoir to ensure that both the first fracturing fluid and the second fracturing fluid can fully support the first fracturing fluid. The first fracture and the second fracture make the network fracture system formed at the primary coal in the high-rank coal reservoir more stable and reliable. Finally, in the embodiment of the present disclosure, after the displacement fluid is pumped, the non-congestive well is used to directly flow back, which can quickly reduce the reservoir pressure to the original formation pressure, reduce the degree of fracturing fluid filtration and pollution of the reservoir, and guide The high-pressure liquid and coal powder are quickly discharged to keep the fractures clean, and more effectively alleviate the rise of reservoir pressure and the expansion of fracturing fluid erosion to the surrounding area. Therefore, compared with the construction technology in the related art of hydraulic fracturing and flowback after a bored well, the dredging fracturing method provided by the embodiment of the present disclosure can control the rise of reservoir pressure, reduce fracturing fluid loss and pollute the reservoir It can effectively increase the production of coalbed methane reservoirs. In the embodiment of the present disclosure, when performing fracturing, the depth position of the primary coal in the high-rank coal reservoir is determined through the logging data, and then perforation is performed at the depth corresponding to the primary coal in the wellbore, thereby avoiding the related technical problems. During fracturing, because the fracturing fluid is easy to break through the structural coal with weak strength first, and forms a high-conductivity vadose zone at the position of the structural coal, so as to realize the transformation of the primary coal in the high-rank coal reservoir. Coal has high gas content, so it can increase the gas production of gas wells; at the same time, by injecting the first fracturing fluid and the second fracturing fluid respectively, a network fracture system with the first and second fractures as the main fractures is formed, which improves the fracture creation rate. The effect is to reduce the seepage resistance in the area where the primary coal is located in the high-rank coal reservoir, so as to increase the permeability and increase production.

Fig. 2 is a flow chart of another high-rank coal reservoir dredging fracturing method provided by an embodiment of the present disclosure. As shown in Figure 2, the fracturing method includes:

S201: Determine the depth range of primary coal in the high-rank coal reservoir according to the logging data.

Among them, the well logging data can be measured by the production capacity test before the use of the gas well, and the production capacity test can measure various data. Identify and determine the distribution position of the coal body structure in the reservoir.

Because the coal body structure of high-rank coal reservoirs includes primary coal and structural coal, structural coal includes crushed coal, crushed coal and mylonitic coal. Moreover, different types of coal structures have different response relationships with the four logging data, so high-rank coal can be identified based on the combination of resistivity, acoustic time difference, natural gamma ray and density logging. The coal body structure of the reservoir.

The logging data used in S201 to identify and determine the distribution position of the coal body structure in the high-rank coal reservoir may include: the resistivity of the high-rank coal reservoir, the acoustic time difference of the high-rank coal reservoir, the At least one of natural gamma ray values and density logging of high-rank coal reservoirs.

The coal body structure of the high-rank coal reservoir in the embodiment of the present disclosure can be determined according to the following data table:

When determining the position of the primary coal in the high-rank coal reservoir based on the logging data, first obtain the logging data of different areas in the high-rank coal reservoir, and determine the high-rank coal reservoir according to the logging data Depth location of native coal in the layer. Combined with the above table, if there are areas satisfying the first determination relationship in the high-rank coal reservoir, the depth range of all areas satisfying the first determination relationship in the high-rank coal reservoir is determined as the primary Coal depth position. Wherein, the first determination relationship may include at least one of the following: the resistivity is greater than 3000Ω·m, the acoustic time difference is between 370μs/m and 410μs/m, the natural gamma value is between 30API and 80API, and the density logging is between 1.3g /cm3 to 1.6g/cm3. If there is an area satisfying the second determination relationship in the high-rank coal reservoir, the depth range of all areas satisfying the second determination relationship in the high-rank coal reservoir is determined as the depth of the fragmented coal in the high-rank coal reservoir Location. Among them, the second determined relationship includes: the resistivity is between 1000Ω·m and 3000Ω·m, the acoustic time difference is greater than 380μs/m, the natural gamma value is less than 60API, and the density logging is between 1.2g/cm ³ and 1.35g/cm ³ between. If there is an area satisfying the third determination relationship in the high-rank coal reservoir, the depth range of all areas satisfying the third determination relationship in the high-rank coal reservoir is determined as the crushed coal or minced coal in the high-rank coal reservoir. The depth position of the ribbed coal. Among them, the third determination relationship includes: the resistivity is greater than 1000Ω·m, the acoustic time difference is greater than 410μs/m, the natural gamma value is less than 60API, and the density log is between 1.1g/ ^cm3 and 1.25g/ ^cm3 .

S202: Perforating in the central area of the wellbore corresponding to the depth range of the primary coal of the high-rank coal reservoir, forming a plurality of holes on the inner wall of the wellbore.

S202 may include: performing concentrated perforation at the location of primary coal in the high-rank coal reservoir in the wellbore. Among them, the perforation density is 16 holes/m, and the perforation depth is 2.5 meters to 3.0 meters. The purpose of concentrated perforation is to make the pressure of hydraulic fracturing more concentrated during the fracturing process, so as to facilitate the creation of long fractures. In the embodiment of the present disclosure, the perforation direction may be chosen to be perpendicular to the minimum principal stress direction of the coal seam. The purpose of setting the perforation direction to be the direction of the minimum principal stress of the vertical coal seam is to make the resistance relatively small in the process of fracturing fracture propagation, so as to achieve the purpose of creating long fractures.

S203: Injecting the first fracturing fluid into the high-rank coal reservoir through multiple holes to form first fractures in the primary coal of the high-rank coal reservoir.

S203 may include: pumping the first fracturing fluid into the area where the primary coal is located in the high-rank coal reservoir through a plurality of holes. The first fracturing fluid can be a pre-fluid, and the fracturing operation is started on the coal seam where the perforation has been completed. The pressure of the first fracturing fluid at the bottom of the well is greater than the strength of the primary coal in the high-rank coal reservoir at the position of multiple holes. When , the first fracturing fluid produces the first fracture in the primary coal area in the high-rank coal reservoir. Wherein, the first fracturing fluid is an active water fracturing fluid, which may include potassium chloride, clay stabilizer and water, the mass percentage of potassium chloride is 1.0% to 2.0%, and the mass percentage of clay stabilizer is 0.2% to 0.5% %, the balance is water. The active water fracturing fluid with the above composition is not only low in cost, but also can effectively solve the swelling problem of coal rock and clastic rock clay, and further reduce the damage to the reservoir during the fracturing process. Wherein, the clay stabilizer may be various clay stabilizers such as 2-ethyltrimethylammonium chloride, quaternary ammonium clay stabilizer, etc., which are not limited in the embodiments of the present disclosure.

In S203, the pumping rate of the first fracturing fluid may be 4.0m ³ /min to 5.0m ³ /min, and the pumping volume may be 70m ³ to 100m ³ . Exemplarily, the pumping rate of the first fracturing fluid may be 4.0m ³ /min to 4.5m ³ /min, and the pumping volume may be 90m ³ . The pumping speed and pumping volume of this first fracturing fluid can controllably create fractures at the position of the original coal in the high-rank coal reservoir, and can further expand into other positions in the high-rank coal reservoir, such as structural Coal position and weak surface combined with other rock types.

S204: injecting a third fracturing fluid into the first fracture through a plurality of holes, so that the fracture proppant in the third fracturing fluid supports the first fracture.

Wherein, the third fracturing fluid is a mixed fluid of the first fracturing fluid and fracture proppant, and the fracture proppant content of the third fracturing fluid is lower than that of the second fracturing fluid. Exemplarily, the third fracturing fluid may include: potassium chloride, clay stabilizer, fracture proppant and water. The mass percentage of potassium chloride is 1.0% to 2.0%, the mass percentage of clay stabilizer is 0.2% to 0.5%, the mass percentage of fracture proppant is 6.0% to 8.0%, and the balance is water.

The pumping rate of the third fracturing fluid in S204 is 2.5m ³ /min to 4.5m ³ /min, the pumping volume can be 150m ³ to 200m ³ , and the amount of fracture proppant can be 5m ³ to 15m ³ . Exemplarily, the pumping rate of the third fracturing fluid can be 3.0m ³ /min to 4.0m ³ /min, the pumping volume is 180m ³ , and the fracture proppant consumption can be 10m ³ . The pumping speed and pumping volume of the third fracturing fluid can further expand the direction and depth of the first fracture in the coal seam, making it penetrate into the coal seam, which is beneficial to the formation of long fractures in the coal seam. Wherein, the fracture proppant can be a sand proppant, and the sand proppant in the third fracturing fluid can be selected from natural quartz sand with a particle size of 20-40 mesh. In this way, the natural quartz sand in the third fracturing fluid is used to fill and support the first fracture, making the first fracture more stable and reliable.

S205: Inject the second fracturing fluid into the first fracture through a plurality of holes, so that the second fracturing fluid forms a second fracture in the raw coal of the high-rank coal reservoir and supports the fracture proppant in the second fracturing fluid Two cracks.

Wherein, the second fracturing fluid may include: potassium chloride, clay stabilizer, fracture proppant and water. The mass percentage of potassium chloride is 1.0% to 2.0%, the mass percentage of clay stabilizer is 0.2% to 0.5%, the mass percentage of sand proppant is 12% to 20%, and the balance is water. That is, in the embodiment of the present disclosure, both the third fracturing fluid and the second fracturing fluid include fracture proppant, and the content of the fracture proppant in the third fracturing fluid is lower than that of the fracture proppant in the second fracturing fluid. content.

In S205, the pumping volume of the second fracturing fluid may be 200m ³ to 250m ³ . For example, the pumping volume of the second fracturing fluid may be 220m ³ . The second fracturing fluid based on the pumping volume can not only support fracturing and fracture creation, but also ensure that the formed fractures are filled with fracture proppant, which effectively improves the fracture creation effect.

In S205, by continuing to pump the second fracturing fluid into the reservoir through multiple holes, a second fracture connected to the first fracture is formed in the primary layer of the high-rank coal reservoir, so that the fracture can continue to flow toward the high-rank coal The interior of the reservoir is extended, and multiple branched fractures filled with fracture proppant are formed in the high-rank coal reservoir. The branched fractures refer to the first fracture and the second fracture as the main fractures, and multiple sub-fractures extending along different directions. The effect is to reduce the seepage resistance in the area where the primary coal is located in the high-rank coal reservoir, so as to increase the permeability and increase production.

Optionally, the fracture proppant in the second fracturing fluid may be a sand-type proppant, and the sand-type proppant in the second fracturing fluid may include: three kinds of propping sands with different particle sizes, among which the smallest particle size is The mass percentage of the support sand is 16.7%, the mass percentage of the support sand with the largest particle size is 33.3%, and the mass percentage of the support sand with the particle size between the support sand with the smallest particle size and the support sand with the largest particle size is 50.0%. Exemplarily, the sand proppant in the second fracturing fluid may be composed of sand proppants with multiple particle sizes, and the sand proppant combination with multiple particle sizes includes natural quartz sand with coarse, medium and fine particle sizes. That is to say, the multi-size sand proppant combination includes the support sand with the smallest particle size, the support sand whose particle size is between the support sand with the smallest particle size and the support sand with the largest particle size, and the support sand with the largest particle size. And according to the mass percentage, the support sand with the smallest particle size, the support sand with the particle size between the support sand with the smallest particle size and the support sand with the largest particle size, and the support sand with the largest particle size are 16.7%: 50.0%: 33.3%. Among them, the particle size of the support sand with the smallest particle size is 12 mesh to 20 mesh, the particle size of the support sand between the support sand with the smallest particle size and the support sand with the largest particle size is 20 mesh to 40 mesh, and the particle size of the support sand with the largest particle size is 20 mesh to 40 mesh. The particle size of the support sand is 40 mesh to 70 mesh. And the amount of sand proppant in the second fracturing fluid can be 25m ³ to 35m ³ .

The supporting sand in the above-mentioned implementations can be natural quartz sand, so that the second fracture and multiple branched fractures are filled and supported by the natural quartz sand in the second fracturing fluid, so that the second fracture and the formed network fractures The system is more stable and reliable. In the embodiment of the present disclosure, the second fracturing fluid combined with sand proppant with multiple particle sizes is used to carry out the hydraulic fracturing reconstruction process, so that the sand proppant can be filled into multiple fractures formed in the high-rank coal reservoir , so as to form a long-distance extended network fracture system in the high-rank coal reservoir to effectively support the fractures at all levels and keep the fracturing fractures open.

In S205, injecting the second fracturing fluid through the plurality of holes may include: sequentially injecting the second fracturing fluid into the first fracture according to the first speed, the second speed and the third speed, the first speed being lower than the second speed, The second speed is lower than the third speed, when the second fracturing fluid is injected according to the first speed, the mass percentage of sand proppant in the second fracturing fluid is the first content, and the second fracturing fluid is injected according to the second speed When , the mass percentage of the sand proppant in the second fracturing fluid is the second content, and when the second fracturing fluid is injected according to the third speed, the mass percentage of the sand proppant in the second fracturing fluid is For the third content, the first content is less than the second content, and the second content is less than the third content. Exemplarily, the first speed is 3.0m ³ /min to 4.5m ³ /min, the second speed is 5.0m ³ /min to 6.5m ³ /min, and the third speed is 7.0m ³ /min to 8.5m ^{3 /} min min, and the first content is 12% to 14%, the second content is 15% to 17%, and the third content is 18% to 20%. In the embodiment of the present disclosure, the second fracturing fluid is pumped by using the variable speed method of gradually increasing the pumping speed. The pumping process is as follows: the pumping speed of the second fracturing fluid is controlled from 3.0m ³ /min to 4.5m ³ /min , 5.0m ³ /min to 6.5m ³ /min, ^{7.0m 3} /min to 8.5m ³ /min, and the pumping speed is 4.0m 3 /min, 5.5m ³ /min, ^{7.5m 3} /min. Correspondingly, the mass percentage of the sand proppant in the second fracturing fluid is controlled to be 12% to 14%, 15% to 17%, 18% to 20%, for example, the mass of the sand proppant in the second fracturing fluid Percentages can be 13%, 16%, 18%. In the embodiment of the present disclosure, the second fracturing fluid is pumped by stepwise increasing the pumping speed to ensure the extension distance of the main fracture, and the pumping speed of the sand-carrying fluid and the content of sand proppant are gradually increased to further expand the main fracture The extension range of nearby branch fractures increases the range of fracturing reconstruction and forms a long-distance support fracture network in the coal seam.

S206: Injecting a displacement fluid from the wellbore, displacing the first fracturing fluid and the second fracturing fluid in the primary coal of the high-rank coal reservoir.

In S206, the displacement liquid may include potassium chloride, clay stabilizer and water, the mass percentage of potassium chloride is 1.0% to 2.0%, the mass percentage of clay stabilizer is 0.2% to 0.5%, and the balance is water. The third fracturing fluid and the second fracturing fluid remaining in the wellbore can be displaced into the high-rank coal reservoir by the displacement fluid.

S207: Stop injecting liquid into the wellbore, and flow back directly without stuffing the well.

During flowback in S207, the wellhead pressure can be measured, and flowback parameters can be determined according to the wellhead pressure. In order to complete the flowback in the embodiment of the present disclosure, the flowback process can be installed in the following manner: if the wellhead pressure is greater than 20Mpa, use a nozzle with a diameter of 6mm for flowback; if the wellhead pressure is 10Mpa to 20MPa, use a nozzle with a diameter of 10mm nozzle for flowback; if the wellhead pressure is 5Mpa to 10MPa, use a 12mm diameter nozzle for flowback; if the wellhead pressure is less than 5MPa, use a 14mm nozzle for flowback. The embodiment of the present disclosure adopts the non-stuck well after fracturing, fast flowback, so that the formation pressure can quickly drop to the original formation pressure, reduce the degree of fracturing fluid filtration and pollution of the reservoir, guide the high-pressure liquid and coal powder to be discharged quickly, and maintain The fractures are clean, which more effectively alleviates the rise of formation pressure and the expansion of fracturing fluid erosion to the surrounding area.

Taking the high-rank coal reservoir in the Zhengzhuang block in the Qinnan area of Shanxi as an example, the depth of the high-rank coal reservoir ranges from 703.65 meters to 709.65 meters, and the thickness is 6 meters. The roof and floor of the high-rank coal reservoir It is mudstone and sandy mudstone, and the middle part of the high-rank coal reservoir is primary coal, accompanied by fragmented coal and a small amount of crushed coal on both sides.

Firstly, the coal structure identification model was established by using the response characteristics between well logging data and different types of coal structures, and the primary coal distribution of the high-rank coal reservoir was determined to be distributed in the depth range of 704.85 meters to 708.35 meters according to the well logging data , with a thickness of 3.50 meters, the top of the high-rank coal reservoir is mostly cracked coal, and the bottom is cracked coal and a small amount of broken coal. Then, perforating is carried out in the central area of the wellbore corresponding to the depth range of the primary coal of the high-rank coal reservoir, and a plurality of perforations are formed on the inner wall of the wellbore. And the control perforation density is 16 holes/m, the perforation thickness is 3 meters, the perforation depth is 705.0 meters to 708.0 meters (that is, the middle area of the depth range), and the number of perforations is 48. Next, pump the first fracturing fluid. The first fracturing fluid includes 1.0% KCl by mass, 0.2% clay stabilizer, and the balance is water. The pumping speed of the first fracturing fluid is controlled to be 4.5 m ³ /min, pump 90m ³ of the first fracturing fluid into the high-rank coal reservoir through multiple holes for fracturing construction, and form the first fracture in the high-rank coal reservoir. Then, the third fracturing fluid is pumped, and the third fracturing fluid includes 1.0% KCl, 0.2% clay stabilizer, 8.0% natural quartz sand, and water as the balance. Control the pumping speed of the third fracturing fluid to 3.5m ³ /min, and pump 180m ³ of the third fracturing fluid into the first fracture. The sand proppant in the third fracturing fluid is Lanzhou quartz sand with a particle size of 20 mesh to 40 mesh, and the dosage is 10m ³ , so that it enters the first fracture and supports the fracture. Then, the second fracturing fluid is pumped, and the second fracturing fluid includes 1.0% KCl, 0.2% clay stabilizer, and sand proppant combination in the second fracturing fluid, and the sand proppant combination includes the mass percent 13%, 16%, and 18% natural quartz sand, the sand proppant combination includes coarse sand with a particle size of 15 mesh, medium sand with 30 mesh and fine sand with 60 mesh, and the amount of sand proppant combination is 30m ³ . When pumping, control the pumping speed of the second fracturing fluid to 4.0m ³ /min, ^{5.5m 3} /min, and 7.5m ³ /min in turn, and accordingly, control the quality of the sand proppant in the second fracturing fluid The percentages are 13%, 16%, and 18% in turn, and the amount of the second fracturing fluid pumped is 220m ³ . Then, the third fracturing fluid and the second fracturing fluid remaining in the wellbore are displaced into the high-rank coal reservoir by using a displacement fluid with a mass percentage of 1.0% KCl, 0.2% clay stabilizer, and water as the balance. The pump is stopped, the well is not stuffy, the flowback parameters are reasonably controlled by pressure measurement, the flowback is rapid, and the rise of reservoir pressure and reservoir pollution are controlled. Through the above fracturing method, the single well gas production of coalbed methane reaches 1800m ³ to 3200m ³ , and the average daily gas production of single well is 2100m ³ . The cumulative gas production is 1.56 million m ³ , and the stable production period is 11-23 months. The dredging fracturing technology has effectively increased the single well production and improved the overall development effect of the block.

The above are only optional embodiments of the present disclosure, and are not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included in the protection scope of the present disclosure Inside.

Claims (8)

1. a dredging formula fracturing method of high-rank coal reservoir, it is characterized in that, described dredging formula fracturing method comprises: Determining the depth range of primary coal in the high-rank coal reservoir according to the logging data; perforating in the central area of the wellbore corresponding to the depth range of the primary coal of the high-rank coal reservoir, and forming a plurality of holes in the inner wall of the wellbore; injecting a first fracturing fluid through the plurality of holes to form a first fracture in the raw coal of the high-rank coal reservoir; Inject a third fracturing fluid from the plurality of holes, so that the fracture proppant in the third fracturing fluid supports the first fracture, the third fracturing fluid is the first fracturing fluid and the fracture A mixed fluid of proppant, the fracture proppant content of the third fracturing fluid is lower than the fracture proppant content of the second fracturing fluid; According to the first speed, the second speed and the third speed, the second fracturing fluid is sequentially and continuously injected into the first fracture from the plurality of holes, so that the second fracturing fluid is The primary coal of the reservoir forms a second fracture and supports the fracture proppant in the second fracturing fluid, the first fracture communicates with the second fracture, and the second fracturing fluid is a mixture of the first fracturing fluid and fracture proppant, the first velocity is less than the second velocity, and the second velocity is less than the third velocity, When injecting the second fracturing fluid according to the first speed, the mass percentage of the fracture proppant in the second fracturing fluid is the first content, and injecting the second fracturing fluid according to the second speed When injecting the second fracturing fluid, the mass percentage of the fracture proppant of the second fracturing fluid is the second content, and when the second fracturing fluid is injected at the third speed, the fracture propping agent of the second fracturing fluid The mass percentage of the agent is the third content, the first content is less than the second content, and the second content is less than the third content; Injecting a displacement fluid from the wellbore, displacing the first fracturing fluid and the second fracturing fluid in the raw coal of the high-rank coal reservoir; Stop injecting fluid into the wellbore, and flow back directly without stuffing the well. 2. the dredging type fracturing method of high-rank coal reservoir according to claim 1, is characterized in that, described according to logging data to determine the primary coal in the high-rank coal reservoir in the described high-rank coal reservoir Depth range, including: Obtain the logging data of different areas in the high-rank coal reservoir, the logging data includes: the resistivity of the high-rank coal reservoir, the acoustic time difference of the high-rank coal reservoir, the natural at least one of gamma and density logging of high-rank coal reservoirs; Determining the depth range of primary coal in the high-rank coal reservoir according to the logging data. 3. the dredging type fracturing method of high-rank coal reservoir according to claim 2, is characterized in that, described according to described logging data, determines the depth range of the primary coal in described high-rank coal reservoir, comprises : If the logging data satisfies the area of the first determination relationship, then determine the depth range of all the areas satisfying the first determination relationship in the high-rank coal reservoir as the original high-rank coal reservoir coal depth range, The first determination relationship includes at least one of the following: the resistivity is greater than 3000Ω·m, the acoustic time difference is between 370μs/m and 410μs/m, the natural gamma value is between 30API and 80API, the density The logs lie between 1.3g/ ^cm3 and 1.6g/ ^cm3 . 4. The dredging-type fracturing method of the high-rank coal reservoir according to claim 1, characterized in that, the perforation in the central region corresponding to the depth range of the primary coal of the high-rank coal reservoir in the wellbore, include: Concentrated perforation is carried out in the central area of the depth range of the primary coal of the high-rank coal reservoir in the wellbore, the perforation density is 10 holes/m to 20 holes/m, and the perforation depth is 2.5 meters to 3.0 meters. The hole direction is perpendicular to the minimum principal stress direction of the coal seam. 5. The dredging fracturing method for high-rank coal reservoirs according to claim 1, wherein the third fracturing fluid comprises: potassium chloride, a clay stabilizer, the fracture proppant and water, The mass percentage of the potassium chloride is 1.0% to 2.0%, the mass percentage of the clay stabilizer is 0.2% to 0.5%, the mass percentage of the fracture proppant is 6.0% to 8.0%, and the balance is water; The second fracturing fluid includes: potassium chloride, clay stabilizer, the fracture proppant and water, the mass percentage of the potassium chloride is 1.0% to 2.0%, and the mass percentage of the clay stabilizer is 0.2% % to 0.5%, the mass percentage of the fracture proppant is 12% to 20%, and the balance is water. 6. The dredging fracturing method for high-rank coal reservoirs according to claim 1, wherein the fracture proppant is a sand proppant, and the sand proppant of the second fracturing fluid includes granular Three types of support sand with different diameters, among which, the mass percentage of the support sand with the smallest particle size is 16.7%, and the mass percentage of the support sand with the largest particle size is 33.3%. The mass percentage of the support sand between the support sand is 50.0%, The particle size of the sand-type proppant of the third fracturing fluid is that of the support sand whose particle size is between the support sand with the smallest particle size and the support sand with the largest particle size in the sand-type proppant of the second fracturing fluid . 7. The dredging type fracturing method for high-rank coal reservoirs according to any one of claims 1 to 6, wherein the first fracturing fluid comprises: potassium chloride, clay stabilizer and water, the The mass percentage of the potassium chloride is 1.0% to 2.0%, the mass percentage of the clay stabilizer is 0.2% to 0.5%, and the balance is water. 8. The dredging-type fracturing method of the high-rank coal reservoir according to any one of claims 1 to 6, characterized in that, the dredging-type fracturing method further comprises: Measuring the wellhead pressure, and determining flowback parameters according to the wellhead pressure; The determining flowback parameters according to the wellhead pressure includes: If the wellhead pressure is greater than 20Mpa, use a nozzle with a diameter of 6mm for flowback; If the wellhead pressure is 10Mpa to 20MPa, use a nozzle with a diameter of 10mm for flowback; If the wellhead pressure is 5Mpa to 10MPa, use a nozzle with a diameter of 12mm for flowback; If the wellhead pressure is less than 5MPa, use a 14mm nozzle for flowback.

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