CN117803366A - Fracturing method of coalbed methane reservoir and application thereof - Google Patents
Fracturing method of coalbed methane reservoir and application thereof Download PDFInfo
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Abstract
The invention relates to a fracturing method of a coalbed methane reservoir and application thereof, and belongs to the technical field of coalbed methane exploitation. The fracturing method comprises the following steps: sequentially injecting pretreatment liquid, pad fluid, sand-carrying liquid and displacement liquid; the pre-liquid comprises a first combined liquid and a second combined liquid; the first combined liquid comprises a high-viscosity fracturing liquid and a low-viscosity fracturing liquid which are sequentially injected from front to back, wherein the high-viscosity fracturing liquid is used for making main joints, and the low-viscosity fracturing liquid is used for blocking coal rock micro-cracks and cutting lines and expanding a crack network by adding sand in a slug mode; the second combined liquid comprises a high-viscosity fracturing liquid and a medium-viscosity fracturing liquid which are sequentially injected from front to back, wherein the high-viscosity fracturing liquid is used for making long cracks, and the medium-viscosity fracturing liquid is continuously sanded to form net-shaped supporting cracks. The method can fracture to form a main seam and a complex seam network, improves the complexity of the seam, increases the sweep range of the seam and improves the diversion capability of the seam, thereby improving the gas production of the coal seam.
Description
Technical Field
The invention relates to a fracturing method of a coalbed methane reservoir and application thereof, and belongs to the technical field of coalbed methane exploitation.
Background
With the increasing decrease of conventional oil gas resources, coal bed gas is taken as a substitute clean energy source, and is valued by oil gas exploitation enterprises. Coalbed methane has a unique reservoir forming mechanism, coal is coalbed rock generated by plant remains in a specific geological environment, and the coalbed methane is adsorbed in micropores of the coal under the action of pressure. Before decompression and desorption, free gas does not exist in the micropores, and only when the pressure of the coal bed is reduced to a certain degree, natural gas such as methane in the coal rock can be desorbed, and the gas flows through a crack cutting line, enters a coal bed pore network and flows to a shaft through the pore network.
However, sandstone natural gas is greatly different from coalbed methane: the gas storage mode, the fracture structure, the rock physical property, the fracturing construction difficulty, the production curve of gas production, the reserve estimation mode and the like are all quite different, so that the method for developing deep sandstone natural gas is not suitable for coal bed gas exploitation. Therefore, it is important to develop a set of methods for exploiting coal seam gas to improve the production of coal seam gas.
The main mode of the fracturing and yield increasing operation for the coal-bed gas well at present comprises a gel fracturing fluid, a clean fracturing fluid, oil-based fracturing and CO 2 Dry fracturing fluid. The method mainly has the following technical problems in the fracturing operation process of the coal-bed gas well:
in the gel fracturing method, a large amount of gel residues are reserved in a reservoir in the fracturing process, so that the reservoir is seriously polluted; the fracturing is not easy to break after completion of fracturing, blocks a flowback channel of reservoir water, and remarkably reduces the production of a coal-bed gas wellAbility to breathe. The oil-based and clean fracturing fluid method has high construction cost, low safety and difficult control of gel breaking, so that the application degree of the method in fracturing of coal-bed gas wells is low. CO 2 The dry fracturing method has high requirements on equipment and poor sand adding Capability (CO) 2 A large amount of sand cannot be added in the sealing tank, and effective regulation and control on the size and the shape of the crack in the fracturing process cannot be realized.
Disclosure of Invention
The invention aims to provide a fracturing method of a coalbed methane reservoir, which solves the problems that reservoir pollution is serious, safety is low, and the size and the shape of a fracture in the fracturing process cannot be effectively regulated and controlled in the prior art.
The invention also aims to provide an application of the fracturing method of the coal bed gas reservoir in coal bed gas exploitation, so that the gas production capacity of the coal bed gas is improved.
In order to achieve the above object, a first technical solution of the present invention is:
a fracturing method of a coalbed methane reservoir, comprising the steps of: sequentially injecting pretreatment liquid, pad fluid, sand-carrying liquid and displacement liquid; the pre-liquid comprises a first combined liquid and a second combined liquid; the first combined liquid comprises a high-viscosity fracturing liquid and a low-viscosity fracturing liquid which are sequentially injected from front to back, wherein the high-viscosity fracturing liquid is used for making main joints, and the low-viscosity fracturing liquid is used for blocking coal rock micro-cracks and cutting lines and expanding a crack network by adding sand in a slug mode;
the second combined liquid comprises a high-viscosity fracturing liquid and a medium-viscosity fracturing liquid which are sequentially injected from front to back, wherein the high-viscosity fracturing liquid is used for making long cracks, and the medium-viscosity fracturing liquid is continuously sanded to form net-shaped supporting cracks.
The pad fluid forms a main joint and complex joint network by utilizing the process of combining the high-viscosity and low-viscosity fracturing fluid and the high-viscosity and medium-viscosity fracturing fluid, improves the complexity of the joints, increases the sweep range of the joints and improves the diversion capability of the joints, thereby improving the joint control reserve and the gas production of the coal bed. In addition, the fracturing method disclosed by the invention does not cause reservoir pollution and is high in safety.
Wherein, the pretreatment liquid can remove the pollution of the near-wellbore zone and reduce the rupture pressure. The displacement fluid is used for flushing the acid ahead of the well bore into the formation. The sand-carrying fluid is used for forming a main supporting crack of a 'venation' part in the network-shaped crack. The displacing fluid is to displace the fracturing fluid in place and clear the wellbore. Preferably, the displacement fluid is a low viscosity fracturing fluid.
Preferably, the viscosity of the 6 mPa.s.ltoreq.low-viscosity fracturing fluid is < 15mPa.s, the viscosity of the 15 mPa.s.ltoreq.medium-viscosity fracturing fluid is < 25mPa.s, and the viscosity of the 25 mPa.s.ltoreq.high-viscosity fracturing fluid is < 50mPa.s.
In order to better create complex slotted networks, preferably, in the low-viscosity fracturing fluid, the sand-to-liquid ratio of the slug type sand feeding is gradually increased; in the medium viscosity fracturing fluid, the sand-liquid ratio of the continuous sand adding is gradually increased; the highest sand-liquid ratio of the slug type sand adding is not larger than the lowest sand-liquid ratio of the continuous type sand adding.
Preferably, the sand-liquid ratio of the slug type sand adding is 5-11%; the sand-liquid ratio of the continuous sand adding is 13-21%. As the number of slotted nets increases, the amount of sand required to support and plug the slotted nets increases.
Preferably, the mesh number of the proppants used for the slug type sanding and the continuous sanding is 70/140 mesh.
The slug type sand adding device is beneficial to reducing the fluid loss of the fracturing fluid in cracks in order to enable the low-viscosity fracturing fluid to carry the propping agent with small particle size to block micro cracks and cutting lines in coal and rock. In order to enable the medium-viscosity fracturing fluid to carry the small-particle-size propping agent to support cutting lines and micro-cracks in coal and rock, supporting cracks of a 'net' part in the net-shaped cracks are formed, the cracks of the 'net' part can communicate with the cracks of the far end of the coal bed, the influence range of the cracks on the plane of the coal bed is improved, and the gas production is improved.
In order to flush the pad acid completely into the formation, the pad acid preferably also includes a low viscosity fracturing fluid. The low-viscosity fracturing fluid is injected after the pretreatment fluid and before the first combination fluid.
Preferably, the sand-carrying fluid comprises a first sand-carrying fluid and a second sand-carrying fluid which are sequentially injected from front to back, and the particle size of the propping agent in the first sand-carrying fluid is smaller than that of the propping agent in the second sand-carrying fluid. The sand-carrying fluid is firstly added with the sand slugs with medium grain diameter, filled with the slugs, and then added with the sand slugs with large grain diameter, and finally the main support crack of the 'venation' part in the network-shaped crack is formed. A high-permeability artificial main fracture is formed in the coal bed to provide a flow channel for coal bed gas.
Preferably, the number of proppants of the first sand-carrying fluid is 40/70 mesh; the number of propping agents of the second sand-carrying fluid is 30/50 mesh. In order to realize the concepts of effective support and far support, a combination of a propping agent with 40/70 meshes and a propping agent with 30/50 meshes is adopted, a main joint is supported by a propping agent with medium grain diameter, the flow conductivity of cracks with different dimensions is improved, the propping agent with large grain diameter with 30/50 meshes is used for improving the supporting strength of near well zones, simultaneously, the propping agent is prevented from flowing back, the flow conductivity of the joints is enhanced, and the coal dust output is controlled.
In order to better support the cracks, preferably, the sand-liquid ratio of the first sand-carrying fluid is gradually increased, and the sand-liquid ratio is 10-20%; the sand-liquid ratio of the second sand-carrying liquid is gradually increased, and the sand-liquid ratio is 15-30%.
Further preferably, the sand-carrying fluid is a high-viscosity fracturing fluid.
Preferably, the displacement-variable construction is performed in a preposition liquid stage, and the construction displacement is gradually increased; and (5) carrying out constant displacement construction in the sand carrying fluid stage. The greater the displacement, the farther the proppant is transported, while the coal is hydraulically cut, releasing its adsorbed gas. The invention adopts a sleeve injection fracturing mode to improve the construction displacement.
Further preferably, the total displacement of the pre-liquid stage is 250-400 m 3 And/min. The large discharge capacity effectively changes the coal seam stress field, improves pore permeability, and pushes propping agents to the deep part of the reservoir.
Wherein the total displacement of the low-viscosity fracturing fluid is 150-250 m 3 A/min; the total discharge capacity of the medium viscosity fracturing fluid is 70-120 m 3 /min。
Preferably, the total discharge capacity of the sand-carrying fluid is 200-250 m 3 /min。
The second technical scheme of the invention is as follows:
the fracturing method of the coal bed gas reservoir is applied to coal bed gas exploitation.
The fracturing method of the coal bed gas reservoir is used for exploiting the coal bed gas, can effectively desorb the natural gas in the coal bed, and improves the gas production capacity of the coal bed gas.
Preferably, the method comprises the following steps:
(1) Carrying out reservoir evaluation on the coal seam and obtaining evaluation parameters;
(2) Carrying out fracturing reformation on the coal bed methane reservoir according to the analysis result of the step (1);
(3) And after the fracturing operation is finished, mining the coal bed gas according to the production parameters.
Drawings
FIG. 1 is a graph of the Peng Zhen well 8# coal seam core water sensitivity evaluation of the present invention;
FIG. 2 is a graph of the evaluation of alkali sensitivity of the No. 8 coal seam of the Peng Zhen well of the invention;
FIG. 3 is a graph of a well log of the present invention Peng Zhen well Taiyuan;
FIG. 4 is a graph of a Peng Zhen well coal seam fracturing construction of example 1 of the present invention;
FIG. 5 is a graph of a Peng Zhen well coal seam fracturing construction of example 2 of the present invention;
FIG. 6 is a graph showing the variation trend of the seam length under different liquid amounts in experimental example 1 of the present invention;
FIG. 7 shows the variation trend of the flow conductivity of the stratum under different sand amounts in experimental example 1 of the present invention;
FIG. 8 shows the liquid amount of 3500m in experimental example 1 of the invention 3 Sand amount 300m 3 A simulated morphology diagram of the fracturing fracture of the lower target layer;
FIG. 9 shows the liquid amount of 3500m in experimental example 1 of the invention 3 Sand amount 350m 3 A simulated morphology diagram of the fracturing fracture of the lower target layer;
FIG. 10 shows the liquid amount of 3500m in experimental example 1 of the invention 3 Sand amount 400m 3 A simulated morphology diagram of the fracturing fracture of the lower target layer;
FIG. 11 shows a slug type sand feeding (sand feeding amount: 350 m) of experimental example 2 of the present invention 3 ) A fracturing fracture simulation morphological map;
FIG. 12 shows the continuous sand feeding (sand feeding amount: 350 m) of experimental example 2 of the present invention 3 ) A fracturing fracture simulation morphological map;
FIG. 13 is a simulated morphology of a pre-low-mucus (viscosity 6mPa. S) fracture of experimental example 3 of the invention;
FIG. 14 is a schematic representation of a pre-high viscosity (42 mPa.s) fracturing fracture simulated morphology liquid of experimental example 3 of the invention;
FIG. 15 shows the rapid pumping capacity (displacement 6-10-14-16-18-20 m) of experimental example 4 of the present invention 3 /min) a fracture simulated morphology;
FIG. 16 shows the slow pumping capacity (displacement 6-8-10-12-14-16-18-20 m) of experimental example 4 of the present invention 3 And/min) a fracturing fracture simulation morphology map.
Detailed Description
Coalbed methane has a unique reservoir forming mechanism, is adsorbed in micropores of coal under the action of pressure, and is greatly different from deep sandstone natural gas:
(1) The gas storage modes are different. Since conventional sandstone natural gas exists in the rock trap in a macroscopic manner in a free and dissolved state, more than 95% of the molecular state of the gas of the coal bed gas is adsorbed on the surface of the coal bed except in the free and dissolved state, and is adsorbed on the inner surface of micropores under the action of pressure in the form of a monolayer. Before the desorption without depressurization, the micro-pores have almost no free gas, only the gas is adsorbed in the micro-pores, and the coal bed has higher gas storage capacity than sandstone through adsorption. Coal seams have a capacity to store natural gas that is 2-3 times that of sandstone compared to the same volume of sandstone.
(2) The fissure structure is different. Compared with sandstone gas in oil field, the coal bed has the characteristics of cutting and developing cracks, the fracturing fluid pumped on the ground has large fluid loss, propping agent is easy to block by sand, propping agent added into the coal bed is easy to be embedded into the coal bed, so that the crack space formed by the propping agent is reduced, and the yield of the coal bed gas is reduced.
(3) Petrophysical properties are different. The coal seam is rock formed by organic matters such as plants, trees and the like, and the sandstone rock components are mineral matters such as quartz, mica and the like, so that the coal seam is softer than sandstone in texture, propping agents for fracturing and pumping are easy to embed into the coal rock, and gas flow channels formed by the propping agents are reduced and even disappear, so that gas production is influenced. In the process of water drainage and gas production after pressing, coal is loosely cemented, so that some coal dust can be carried to a shaft to block the shaft.
(4) The fracturing construction difficulty is high. Both deep coal bed gas and sandstone reservoirs need to be subjected to fracturing transformation to release gas in the reservoirs. However, compared with deep sandstone layers, the deep coal layer has soft and fragile coal rock texture, easy compression and low Young modulus, and the coal rock texture is soft during fracturing, so that the artificial crack has wide seam width and high construction pressure, more vehicle groups and chemical liquid are required to be additionally prepared, and the construction difficulty is high.
(5) The production curves for gas production are different. The gas production of the coal-bed gas well firstly rises, slowly falls after reaching a peak, and then maintains uniform gas production for a long time. Whereas sandstone natural gas, the natural gas production exhibits a gas production profile with a decreasing trend from peak to depletion.
(6) The reserves are estimated differently. The natural gas reserves of sandstone are estimated using a pore volume method, so that the gas is stored in the rock pore cracks and the natural gas reserves can be measured by the volume of the porosity. The reserves of coalbed methane cannot be calculated using the pore volume method because the coalbed methane content is divided into a desorption gas amount, a loss gas amount, and a residual gas amount. The conventional method is that after a coal block core is lifted to a wellhead, a sealing tank is used for sealing, a desorption instrument is used in a laboratory to measure the change rule of methane in the coal block along with time, and the desorption gas quantity is obtained. And calculating the escape gas quantity according to the exposure time of the coal sample in the process of drilling and sampling, and then crushing the coal blocks in the laboratory to determine the residual gas quantity. And solving the sum of the air suction amount, the residual air amount and the escape air amount to obtain the reserve of the coalbed methane.
(7) The adsorption of coal to methane depends on Van der Waals force, belongs to physical adsorption and is a 100% reversible process. Under certain pressure conditions, adsorbed methane will be separated from the inner surface of the coal into a free phase, which is desorption of the coalbed methane. The production of the coalbed methane goes through 3 stages, which is basically the pressure difference between the matrix in the coalbed rock and the shaft, and the desorption and diffusion of the coalbed methane are controlled.
(8) Unreasonable working regimes affect stable production of coalbed methane. Underground solid particles (propping agent and coal dust) are not carried to the ground after entering the pipe column from the coal bed in the drainage process, but are deposited, accumulated and blocked in the pump cylinder, so that the pump is lost and the underground faults such as pump clamping are caused. Once the problems of pump leakage, coal powder blocking, and the like occur, the production efficiency is reduced, meanwhile, the production of the drainage and production well is restored through pump detection measures, the running cost of the drainage and production well is increased, and irreversible damage to the well is more likely to be caused in the pump detection process.
Because the natural gas exploitation modes of the conventional sandstone and shale are different from the exploitation modes of the coal bed gas, a production method aiming at the characteristics of the coal bed is needed to improve the output degree of the coal bed gas.
Peng Zhen 1 well profile referred to in the following examples: the exploration well is located in a ten-day suitable area, the vitrinite reflectivity of the coal bed is 1.5% -2.0%, the components mainly comprise lean coal and part of anthracite, the structure is mainly a primary+fragmentation structure, and specific parameters are shown in table 1.
Table 1 Peng Zhen well zone coalbed methane well profile parameters
The results of the rock mechanical characteristics test of the Peng Zhen well are shown in table 2. The elastic modulus of the coal seam is 1.32-3.2GPa, the Poisson ratio is 0.232-0.258, the plastic characteristics of low elastic modulus and high Poisson ratio are shown, and short-width seams are easy to form.
Table 2 Peng Zhen well rock mechanical characteristics test results
Peng Zhen 1 well fracturing layer middle reservoir temperature 65.9 ℃. The pressure gradient is 0.67-0.98MPa/100m, and the pressure coefficient is low.
The water sensitivity evaluation results of the Peng Zhen well coal seam are shown in fig. 1. As can be seen from fig. 1, the core water-sensitive damage rate of the coal bed of the Peng Zhen well is 10%, and the core water-sensitive damage rate belongs to weak water-sensitive damage.
The water sensitivity evaluation results of the Peng Zhen well coal seam are shown in fig. 2. As can be seen from fig. 2, the coal seam of the Peng Zhen well has a moderately strong alkali sensitivity, and the liquid anti-swelling performance should be optimized, and the pH value of the fracturing liquid should be controlled within 7.
The oil and gas display table of Peng Zhen well Taiyuan is shown in Table 3.
Table 3 Pengzhen 1 well Taiyuan group oil gas display table
| Well section/m | Thickness/m | Lithology of rock | Total hydrocarbons/% |
| 2196.83-2197.38 | 0.55 | Black coal seam | 0.577↑1.416 |
| 2207.0-2209.0 | 2 | Black coal seam | 0.672↑23.367 |
| 2220.0-2225.0 | 5 | Black coal seam | 1.227↑47.053 |
| 2239.94-2240.4 | 0.46 | Black coal seam | 1.905↑4.762 |
| 2243.24-2243.7 | 0.46 | Black coal seam | 1.905↑3.680 |
| 2245.99-2247.83 | 1.84 | Black coal seam | 1.905↑10.063 |
| 2259.1-2259.66 | 0.56 | Sandstone-containing light gray coal seam | 0.979↑2.128 |
The results of the well log interpretation for the Peng Zhen well Taiyuan group are shown in Table 4 and the well log curves are shown in FIG. 3.
Table 4 Peng Zhen well Taiyuan group logging interpretation result table
The indices referred to in the following examples:
sand to liquid ratio% = sand amount m 3 Liquid purifying amount m 3
Sand concentration kg/m 3 Sand density =sand liquid%sand density (1.45-1.6 kg/m 3 )*10
The materials referred to in the following examples:
the formula of the pre-acid liquor comprises the following steps: 12% hydrochloric acid+3% hydrofluoric acid+2.0% corrosion inhibitor+2% iron ion stabilizer+0.5% cleanup additive;
wherein, hydrochloric acid is a commercial product, and hydrofluoric acid is a commercial product;
the corrosion inhibitor is a commercial product, preferably: acidifying corrosion inhibitor sold by Beijing Baofeng spring Petroleum technologies Co., ltd;
the iron ion stabilizer is commercially available, preferably: iron ion stabilizer sold by Beijing Baofeng spring Petroleum technologies Co., ltd;
the cleanup additive is a commercial product, preferably: an acidulation and drainage aid sold by Beijing Baofeng spring Petroleum technologies Co.
The viscosity of the low-viscosity fracturing fluid is generally more than or equal to 6mPa.s and less than 15mPa.s, and the low-viscosity fracturing fluid consists of the following components in percentage by mass: 0.1 to 0.15 percent of thickening agent, 0.2 to 0.3 percent of clay stabilizer, 0.2 to 0.3 percent of cleanup additive and 0.005 to 0.03 percent of gel breaker; the solvent is water; the relevant properties are shown in Table 7;
the viscosity of the medium viscosity fracturing fluid is generally greater than or equal to 15mPa.s and less than 25mPa.s, and the medium viscosity fracturing fluid consists of the following components in percentage by mass: 0.2 to 0.25 percent of thickening agent, 0.2 to 0.3 percent of clay stabilizer, 0.2 to 0.3 percent of cleanup additive and 0.005 to 0.03 percent of gel breaker; the solvent is water; the relevant properties are shown in Table 6;
the viscosity of the high-viscosity fracturing fluid is generally greater than or equal to 25mPa.s and less than 50mPa.s, and the high-viscosity fracturing fluid consists of the following components in percentage by mass: 0.3 to 0.45 percent of thickening agent, 0.2 to 0.3 percent of clay stabilizer, 0.2 to 0.3 percent of cleanup additive and 0.005 to 0.03 percent of gel breaker; the solvent is water; the relevant properties are shown in Table 5.
Table 5 high viscosity integrated fracturing fluid performance table
Table 6 shows the performance of the fracturing fluid
Table 7 low viscosity integrated fracturing fluid performance table
The preparation method of the low, medium and high viscosity fracturing fluid comprises the following steps: the emulsion is pumped into a stirring cylinder of a pump truck by a pump at a construction site, and is mixed with clear water, a clay stabilizer and a cleanup additive. Compared with the conventional guar gum fracturing fluid, the fracturing fluid system has the advantages that the dissolution speed is high, the viscosity can be changed by the proportion change of the thickening agent, and the pH value is neutral after mixing.
Specifically, the thickening agent is a commercially available product and is polyacrylamide white emulsion. The thickener is preferably: instant emulsion resistance reducing agent sold by Beijing Baofeng spring petroleum technology Co.
The clay stabilizer is a commercial product, preferably: clay stabilizer for fracturing sold by Beijing Baofeng spring Petroleum technologies Co.
The cleanup additive is a commercial product, preferably: an acidulation and drainage aid sold by Beijing Baofeng spring Petroleum technologies Co.
The breaker is ammonium persulfate and is an industrial commercial product.
The technical scheme of the invention is further described below with reference to the specific embodiments.
1. The specific embodiment of the fracturing method of the coalbed methane reservoir is as follows:
example 1
The fracturing method of the coalbed methane reservoir stratum of the embodiment aims at a Taiyuan group perforation interval: 2207.0-2209.0m, the fracturing pumping procedure is shown in table 8 and the construction parameters are shown in fig. 4, and specifically the following steps are adopted:
table 8 Pengzhen 1 well coal seam fracturing pumping procedure
Example 2
The fracturing method of the coalbed methane reservoir layer mainly aims at a Taiyuan group perforation well section: 2220.0-2225.0m, the fracturing pumping procedure of which is shown in Table 9 and the construction parameters of which are shown in FIG. 5.
Table 9 Peng Zhen well coal seam fracturing pump injection procedure
Example 3
The fracturing method of the coalbed methane reservoir layer mainly aims at a Taiyuan group perforation well section: 2259.1-2259.66m, the fracturing pumping procedure of which is shown in Table 10.
Table 10 Peng Zhen well coal seam fracturing pump injection procedure
2. The specific implementation mode of the fracturing method of the coal bed gas reservoir in the coal bed gas exploitation is as follows:
example 4
The specific operation method of the fracturing method of the coal bed gas reservoir in the coal bed gas exploitation of the embodiment comprises the following steps:
(1) Carrying out reservoir evaluation on the coal seam and obtaining evaluation parameters including reservoir sensitivity analysis, rock mechanical properties and logging interpretation results;
the sensitivity analysis results were: the critical mineralization degree of water sensitivity is 4000-5000ppm; acid sensitivity is not caused; the critical pH value of alkali sensitivity is 8.5-10;
the rock mechanical properties are: the Poisson's ratio of the rock is 0.20-0.26, and the rock density is 1.2-1.4 g/cm 3 ；
Logging interpretation results: the stratum resistivity is 800-2000 Ω & m, the porosity is 10-30%, and the acoustic wave time difference is 200-500 μs/m.
(2) And (3) carrying out fracturing reformation on the coalbed methane reservoir according to the analysis result of the step (1), wherein the specific operation adopts the modes of the examples 1-3.
(3) And after the fracturing operation is finished, mining the coal bed gas according to the production parameters.
The specific operation steps of coal bed gas exploitation are as follows:
(1) Lifting the pump and hanging: the pump depth is designed to be increased from 2100m to 1400m, so that a sedimentation space is provided for pulverized coal and fracturing sand, and the influence of blocking a pipe column on liquid outlet is avoided;
(2) Long stroke low stroke frequency: the initial liquid yield is adjusted to about 20 square/day at 30 square/day, and the frequency conversion process is assisted to adjust the frequency of flushing so as to avoid exciting the sand and coal of the stratum;
(3) Adding sand prevention function: the perforated screen pipe and the wire-wound screen pipe are additionally arranged at the inlet of the gas-liquid separator, the length of the wire-wound screen pipe is 20m, the precision is 0.3mm, the number of the perforated screen pipes is 350, and the holes of the perforated screen pipe is 2mm, so that the auxiliary exhaust is carried out;
(4) Real-time downhole pressure monitoring: increasing the liquid level of an electronic pressure gauge, transmitting signals by a steel pipe cable, controlling the initial daily pressure drop to be 0.5-0.6MPa, and providing a basis for determining the coalbed methane discharge and recovery degree when the gas post-daily pressure drop is less than 0.05 MPa;
(5) And (3) optimizing a sleeve deflation system: when the casing is pressurized to 0.5-1MPa, the casing is deflated, the output is gradually amplified by means of control of a nozzle tip and a needle valve, and the bottom hole flow pressure is ensured to slowly drop (less than 0.1 MPa).
3. Experimental example
Experimental example 1 description of simulation procedure of example 1
(1) Liquid injection and sand adding scale optimization
The experimental example is based on geological parameters of Pengzhen 1 well, and the variation trend of the seam length and the seam height under different liquid amounts is simulated by using Frapt fracturing simulation software, and the result is shown in figure 6.
As can be seen from FIG. 6, the liquid volume of the injected liquid is 3500m 3 The length of the seam basically reaches 220m at the longest, the liquid quantity is increased, the change trend of the length of the seam is small, and the liquid quantity refers to the total liquid quantity of pretreatment, front-end fluid, sand-carrying fluid and displacement fluid.
The experimental example is based on geological parameters of Pengzhen 1 well, and also simulates the change trend of the flow conductivity of the stratum under different sand amounts, the result is shown in fig. 7, and the simulation parameter table of the cracks under different sand adding scales is shown in table 11.
As shown in FIG. 7, when the sand amount is 350-400m 3 When the sand flow guiding device is used, the flow guiding capability reaches the optimal flow guiding capability, the sand amount is increased, and the flow guiding capability is basically unchanged.
TABLE 11 fracture simulation parameters table at different sanding scales
The experimental example also simulates the variation trend of cracks under different liquid amounts and different sand amounts, and the results are shown in figures 8-10.
From the simulation results of FIGS. 8-10, the sanding scale was 350m 3 The diversion capacity basically reaches the highest when left and right, and the construction cost is increased when the diversion capacity can not be improved by continuously adding sand. Therefore, the invention adopts the sand adding scale of 350m 3 The sand adding scale is specifically the accumulated total sand amount of the front fluid and the sand carrying fluid.
(2) Pump injection molded optimization
The experimental example simulates the fracturing fracture by changing the sand adding mode, and the results are shown in fig. 11 and 12.
Comparing fig. 11 and 12, it can be seen that the continuous sand feeding crack has a better flow conductivity than the slug type sand feeding. However, in order to improve the construction success rate and manufacture complex seam net, the front-stage slug type sand feeding is performed in the early stage, the coal bed is cut by hydraulic power, the sand is continuously fed in the middle and later stages, the laying concentration of propping agent is improved, and the crack flow guiding is improved.
(3) Viscosity optimization of pad fluid
The experimental example simulates a fracture by changing the viscosity of the pad fluid, and the results are shown in fig. 13 and 14.
Comparing fig. 13 and 14, it can be seen that the seam making of the high-viscosity fracturing fluid in front of the coal seam can effectively increase the length of the seam, while the cutting of the coal seam is developed, so that the low-viscosity fracturing fluid has larger filtration loss and cannot effectively penetrate into the far end of the reservoir. This is in contrast to conventional dense sandstones: the high-viscosity fracture of the compact sandstone fracturing front is larger in fracture height and shorter in fracture length.
(4) Displacement acceleration optimization
The experimental example simulates a fracture by changing the acceleration rate of the displacement, and the results are shown in fig. 15 and 16.
As can be seen from fig. 15 and 16, the quick lift and slow lift displacement have little effect on the fracture height and length. Considering the sufficiency of seam making, the invention selects a quick lift displacement mode.
Experimental example 2 application description
The results of the fracturing method of the present invention and the conventional fracturing gas production method after implementation in Pengzhen 1 well are shown in Table 12.
Table 12 effect of the present invention compared to conventional fracturing gas production methods
As can be seen from Table 12, compared with the conventional fracturing gas production method, the gas production of the fracturing method is greatly improved to 21052m 3 The method comprises the steps of carrying out a first treatment on the surface of the The continuous gas production time is 359 days; the water breakthrough time is 121 days, which is about 2 times of that of KCl solution and guar gum fracturing fluid; after the KCl solution and the guar gum fracturing fluid are fractured, the well bore is easily blocked by stratum coal and propping agents, and the method is not easy to block, so that a good effect is achieved.
Claims (9)
1. A method of fracturing a coalbed methane reservoir, comprising the steps of: sequentially injecting pretreatment liquid, pad fluid, sand-carrying liquid and displacement liquid; the pre-liquid comprises a first combined liquid and a second combined liquid; the first combined liquid comprises a high-viscosity fracturing liquid and a low-viscosity fracturing liquid which are sequentially injected from front to back, wherein the high-viscosity fracturing liquid is used for making main joints, and the low-viscosity fracturing liquid is used for blocking coal rock micro-cracks and cutting lines and expanding a crack network by adding sand in a slug mode;
the second combined liquid comprises a high-viscosity fracturing liquid and a medium-viscosity fracturing liquid which are sequentially injected from front to back, wherein the high-viscosity fracturing liquid is used for making long cracks, and the medium-viscosity fracturing liquid is continuously sanded to form net-shaped supporting cracks.
2. The method of fracturing a coal-bed methane reservoir according to claim 1, wherein in the low-viscosity fracturing fluid, the sand-to-fluid ratio of the slug sand addition is gradually increased; in the medium viscosity fracturing fluid, the sand-liquid ratio of the continuous sand adding is gradually increased; the highest sand-liquid ratio of the slug type sand adding is not larger than the lowest sand-liquid ratio of the continuous type sand adding.
3. A method of fracturing a coal bed gas reservoir according to claim 1 or 2, wherein the slug sand-on-sand ratio is 5-11%; the sand-liquid ratio of the continuous sand adding is 13-21%.
4. A method of fracturing a coal-bed gas reservoir according to claim 1 or claim 2, wherein the proppant used in the slug sanding, the continuous sanding is 70/140 mesh.
5. The method of fracturing a coalbed methane reservoir according to claim 1, wherein the sand-carrying fluid comprises a first sand-carrying fluid and a second sand-carrying fluid which are sequentially injected from front to back, and the particle size of the proppants in the first sand-carrying fluid is smaller than the particle size of the proppants in the second sand-carrying fluid.
6. The method of fracturing a coal-bed methane reservoir of claim 5, wherein the proppant mesh of the first sand-carrying fluid is 40/70 mesh; the number of propping agents of the second sand-carrying fluid is 30/50 mesh.
7. The fracturing method of a coalbed methane reservoir according to claim 5 or 6, characterized in that the sand-to-liquid ratio of the first sand-carrying fluid is gradually increased, and the sand-to-liquid ratio is 10-20%; the sand-liquid ratio of the second sand-carrying liquid is gradually increased, and the sand-liquid ratio is 15-30%.
8. The fracturing method of a coalbed methane reservoir according to claim 1, wherein the displacement is gradually increased by the construction of a pad-in stage variable displacement construction; and (5) carrying out constant displacement construction in the sand carrying fluid stage.
9. Use of a fracturing method of a coal-bed methane reservoir as claimed in any one of claims 1 to 8 in the production of coal-bed methane.
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