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Abstract The removal and discharge of coal powders from coalbed methane wellbore is the key to maintaining continuous production. For this reason, based on the submerged jet theory, the force and migration starting conditions of coal powder particles deposited at the bottom of the coalbed methane well are analyzed by analyzing the cohesiveness of coal powders, and a model for the starting and migration of coal powders at the bottom of the well under submerged jet conditions is established; Considering the adhesion between coal dust, the adhesion coefficient is used to characterize the adhesion between particles, a mechanical model of coal dust particles deposited at the bottom of the well is established, and the corresponding calculation formula for the outlet flow rate of the coal dust cleaning nozzle is derived. The fluid mechanics parameters of the bottom of the well coal dust cleaning under different conditions are obtained, and the numerical simulation method is used to simulate the whole process of jet flushing of the bottom of the well coal dust deposited, and the effect of the bottom of the well jet flushing of coal dust deposits is analyzed, providing a theoretical basis for the bottom of the well coal dust flushing process.

Hydraulic fracturing is a widely used technique for increasing the permeability of coal seams. Its impact on the production capacity of coalbed methane(CBM) wells is significant. This paper makes detailed observations on the exposed coal seams and fracture distribution of 5 CBM wells in Tunlan block of Xishan coalfield, and studies the distribution characteristics of coal structure, microfractures, quartz sand and coal fine by using stereoscopic microscope, scanning electron microscope, and micro CT. The fracturing effect and influencing factors of CBM wells are analysed by combining regional geostress and hydraulic fracturing construction parameters. The research results indicate that the macroscopic fractures morphology produced by hydraulic fracturing are complex and diverse, including horizontal, vertical, X and T-shaped fractures. The degree of coal body fragmentation increases with distance from the CBM well. The coal body closer to the CBM well is mainly composed of fragmented and granular coal, while the coal body further away is mainly composed of undeformed coal with primary fractures. The quartz sands are mainly deposited in horizontal fractures, with only a small amount in T-shaped fractures. Quartz sand rubs, collides, and embeds strongly with the coal fracture surface. The fracturing fluid is then superimposed to fracture the coal body, resulting in a large amount of coal fines. This causes the coal fines to wrap around the quartz sand and block the fractures. The coal fines within the macroscopic fracture are primarily a result of the fracturing of the coal body, the flushing of the coal body by fracturing fluid, and the friction between the quartz sand and the fracture surface during hydraulic fracturing. Coal fine generation in micro-fractures during coal body fracturing. Coal fines and quartz sand accumulate in the fractures, creating enormous resistance to the carrying fluid and preventing the quartz sand from migrating to the far end of the CBM well. The magnitude and direction of the geostress, as well as the strength of the coal seam roof and floor, are important factors that influence the opening and direction of the hydraulic fracturing fractures. The low viscosity of the carrying fluid cannot suspend quartz sand, and the accumulation of quartz sand and coal fine can block the fractures, easy to cause quartz sand and coal fine to aggregate and block fractures.

The removal and discharge of coal powders from coalbed methane wellbore is the key to maintaining continuous production. For this reason, based on the submerged jet theory, the force and migration starting conditions of coal powder particles deposited at the bottom of the coalbed methane well are analyzed by analyzing the cohesiveness of coal powders, and a model for the starting and migration of coal powders at the bottom of the well under submerged jet conditions is established; Considering the adhesion between coal dust, the adhesion coefficient is used to characterize the adhesion between particles, a mechanical model of coal dust particles deposited at the bottom of the well is established, and the corresponding calculation formula for the outlet flow rate of the coal dust cleaning nozzle is derived. The fluid mechanics parameters of the bottom of the well coal dust cleaning under different conditions are obtained, and the numerical simulation method is used to simulate the whole process of jet flushing of the bottom of the well coal dust deposited, and the effect of the bottom of the well jet flushing of coal dust deposits is analyzed, providing a theoretical basis for the bottom of the well coal dust flushing process. [ABSTRACT FROM AUTHOR]

In order to solve the problem of perforation and screen tube blocking and fixed valve leakage caused by the adhesion of coalbed gas well pulverized coal in the perforation, screen tube, pipe wall, pump barrel and pump valve. Based on the theory of static adhesion, a startup model of variable passage dynamic adhesion of pulverized coal was established, and the dynamic adhesion mechanism of pulverized coal on the pipe wall of coalbed gas well was analyzed. Through the combination of theoretical modeling and indoor experiment, the influence of well fluid temperature, pulverized coal mass concentration, pulverized coal particle size, well fluid velocity, etc. on the dynamic adhesion law of pulverized coal pipe wall was comprehensively considered. Based on the control variable method, the experiments of various factors affecting the dynamic adhesion of pulverized coal pipe wall are carried out. The dynamic adhesion characteristics of pulverized coal on the tube wall under different well fluid temperature, well fluid velocity, pulverized coal mass concentration and pulverized coal particle size were obtained, and the dynamic adhesion rules of pulverized coal on the tube wall under different conditions were given. The results show that the pulverized coal adhesion rate increases with the increase of pulverized coal particle size, pulverized coal concentration and well fluid temperature, and decreases with the increase of well fluid flow rate. It is concluded that the adhesion characteristics of pipe wall pulverized coal provide theoretical basis for the design of coalbed gas well pipe wall pulverized coal flushing process, and have important significance to ensure the continuous and stable production of coalbed gas well. [ABSTRACT FROM AUTHOR]

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In Guizhou Province, there are many coal-bearing structural units, many layers of coal, thin thickness, and most of them are low permeability reservoirs, so it is advisable to adopt the process of “staged fracturing and combined layer drainage and production” to develop coalbed methane. Taking Banguan syncline coalbed methane well as an example, this study analyzed the fracturing effect of two vertical Wells on the basis of the scale of fracturing reconstruction, and then studied the influence of fracturing reconstruction effect on the gas and water production of coalbed methane Wells, and finally summarized the reasonable threshold of efficient fracturing construction parameters of Banguan syncline coalbed methane Wells. The results show that hydraulic fracturing is an effective way to increase permeability of low permeability reservoir, and the permeability increase multiple is closely related to the scale of fracturing reconstruction. The differences of sand addition, liquid addition and single-hole displacement per meter of coal seam between the two Wells of Banguan syncline lead to the permeability ratio of 55∶1 after fracturing reconstruction, and the permeability difference after reconstruction is large. Increasing the liquid addition, sand addition and single hole displacement per meter of coal seam is beneficial to improving the transformation effect of coal seam and gas production. It is recommended that the liquid addition per meter of coal seam should not be less than 400 m3, the sand addition per meter of coal seam should not be less than 20 m3, the fracturing construction displacement should not be less than 8 m3/min, and the single hole displacement should be controlled above 0.2 m3/min. According to the permeability of the coal seam after fracturing and reconstruction, it can be appropriate to quickly discharge and depressurize the coalbed methane Wells with good reconstruction effect. Otherwise, the intensity of discharge and production should be controlled to reduce the sensitivity damage of the reservoir caused by fast discharge and depressurization. The research results can provide technical reference for the permeability and energy improvement of low permeability coal seam in this block.

The Shouyang Block was selected as the research subject. Comprehensive analysis was conducted using coalbed methane (CBM) well production data, geochemical test data on water produced from the coalbed methane well, and fundamental geological information. The findings reveal the water dynamics in the Shouyang Block are characterized by weak groundwater runoff or retention in most areas. The groundwater head height exhibits a gradual decrease from the north to south, which is closely associated with the monoclinic structure of the Shouyang Block. Overall, water production is relatively high. As the average water production increases, the average gas production gradually decreases. A concentration of high water production wells is observed in the northern part of the Shouyang Block, which gradually increases towards the southeast direction. A comprehensive analysis was conducted on the factors influencing water production, including total water content of coal seams, coal seam porosity, groundwater stability index, groundwater sealing coefficient, D value of the fracture fractal dimension, fault fractal dimension, and sand–mud ratio. The correlation degree was calculated and ranked in order of magnitude through grey correlation analysis. The order of factors that influence water production, from strongest to weakest, is as follows: sand–mud ratio > porosity > fractal dimension of fault > fracture fractal dimension D value > groundwater sealing coefficient > groundwater stability index > total water content of coal seams. The dissolution amounts of carbonate and sulfate are both small, and the water source may mainly come from the sandstone aquifer. Attention should be paid to the distribution and lithological combination of sandstone aquifers in coal-bearing strata in the future exploration and development process of the Shouyang Block. This will help to avoid the potential influence of fault structures and enable the identification of favorable areas for low water and high gas production. [ABSTRACT FROM AUTHOR]

Coalbed methane well sand (pulverized coal) problem restricts the production life of coalbed methane well, resulting in high maintenance costs, reduce productivity, and because of the large contact area between thin interbed coal seam and surrounding rock, the problem of sand production (pulverized coal) is prominent. In the Surat Basin of Australia, the coal seam cementation is loose and the coal/mud/sandstone interlayer is complex. In the statistical wells, 100% of the production wells have different degrees of sand production problems, and 33.5% of which have serious sand production, frequent workover operations, and high production costs. Based on the systematic analysis of the reservoir characteristics, sand production characteristics and production rules in Surat Basin, the comprehensive sand discharge prevention technology of “expansion packer + blind tube” and “screw pump + slurry rotor + automatic shunt valve + drilling through casing shoes” is adopted according to the research on the particle settlement law, combined with the prediction of sand production level and the optimization of sand control technology. The problem of sand production in coal measure strata in Surat Basin has been solved in stages. The field application results show that the average continuous production time of a single well increases from 275 days to nearly 400 days, and the workover frequency is reduced by nearly 50%.

A large amount of pulverized coal is easy to be produced in the process of hydraulic fracturing of coalbed methane reservoir. The accumulation and settlement of pulverized coal will cause serious blockage to the fractures formed by fracturing, and reduce the permeability and conductivity of fractures and affect the effect of fracturing stimulation of coalbed methane wells. Therefore, a new type of coal powder dispersant MFFS-2 was developed through a large number of laboratory experiments and combined with the reservoir characteristics of the target CBM block, and its comprehensive performance was evaluated. The experimental results show that when the mass concentration of MFFS-2 reaches 0.3%, the surface tension of water solution can be reduced to less than 25 mN/m, and the contact angle of coal surface can be reduced from 115.3° to less than 60° with good surface activity and wettability; when the suspension of coal powder is standing for 10 hours, the suspension rate of coal powder can reach more than 30% with the addition of 0.3% MFFS-2. When 0.3% MFFS-2 solution is used to displace for 2 hours, the yield of pulverized coal can reach more than 60%, which indicates that MFFS-2 has good suspension dispersion and carrying effect on pulverized coal; in addition, the damage rate of MFFS-2 to the matrix permeability of block coal core in the target area is less than 10%, and the damage degree of fracturing fluid system to the permeability of coal core is reduced after adding MFFS-2 into the active hydraulic fracturing fluid. The field fracturing operation results of coalbed methane well show that the fracturing operation of S-1 well is smooth after adding new coal powder dispersant MFFS-2, a large amount of coal powder is carried out in the backflow fluid, and the gas production is high, which achieves the expected fracturing effect. Moreover, the construction effect of the new active hydraulic fracturing fluid in the same block is significantly better than that of the conventional active hydraulic fracturing fluid.

The viscous resistance caused by the relative motion of plunger and pump barrel is an important factor in the dynamic analysis of the drainage and production mechanism during coalbed methane exploitation. Existing studies mostly focus on deep well (1000–3000 m) large-displacement pump (usually 80–300 m3/d), and the interstitial medium is mainly crude oil. Regression fitting is mainly carried out based on empirical formula or experimental simulation method, without considering the characteristics of shallower coalbed gas well (400–800 m) small-displacement pump (<10 m3/d). The variation of the clearance between plunger and barrel and the variation of viscous resistance between plunger and barrel are not revealed. Based on the Navier-Stokes equation and Newton's internal friction law, a mathematical model of the annular viscous resistance between the plunger and the pump barrel is established, and an analytical method is used to describe the influence of stroke times, annular clearance, and differential pressure between the upper and lower plungers on the viscous resistance. The results show that the plunger stroke is directly proportional to the variation range of viscous resistance, and low stroke is beneficial to reduce the viscous resistance. The effect of differential pressure between upper and lower plunger of rod pump on viscous resistance of small displacement coalbed gas well is significantly greater than that of plunger running speed. The annular clearance is directly proportional to the differential pressure between the upper and lower parts of the plunger, the inertia force of the plunger, and the shear force of the moving fluid. The annular viscous resistance model between plunger and pump barrel is helpful to improve the calculation accuracy of suspending point load of coalbed gas well pumping unit, analyze the working condition of coalbed gas drainage gas production process, and provide basis for the optimization design of coalbed gas well rod pump clearance. [ABSTRACT FROM AUTHOR]

The scientific understanding of the fluid flow and mass transfer mechanism in pores and fractures of coal seam are the fundamental strategy to achieve the efficient production of coalbed methane (CBM). During CBM development, the occurrence, migration, and production characteristics of coalbed water not only determine the drainage and depressurization effect of CBM well, but also significantly affect the desorption, migration, and production process of CH4, which is crucial to the efficient drainage and production control of CBM well. Taking the Fanzhuang block in the southern Qinshui Basin as an example, based on the occurrence form, production process, and flow form of coalbed water, the research on the mechanism of phase change and mass transfer process of coalbed water has been carried out. The threshold pore diameter of phase change and the mass transfer process of coalbed water in anthracite reservoir under the engineering background have been quantified, and its engineering implications for CBM production have been discussed. The results show that the occurrence state of coalbed water can be changed dynamically, and the fluid pressure difference is the main mechanism of its dynamic change. In the single-phase flow stage of water, the migration of movable water is mainly affected by the surface tension. Under the engineering background, the migration and production of movable water in pores and fractures with macropore (pore diameter > 50 nm) is the precondition of the overall release of coal seam pressure, and lays the foundation for a high and stable production of CBM well. In the gas-water two-phase flow stage, the transformation of bound water (capillary water) to movable water is greatly affected by the wettability of coal, and the interface property and interaction between gas and water. The pressure condition requirements of the transformation of bound water (capillary water) to movable water increase due to the capillary effect. In the bubbly flow and plug flow stage, CH4 desorption promotes the transformation of bound water (capillary water) to movable water in some pores and fractures with mesopore (2−50 nm) scale, which determines the overall release of coal seam pressure. This also indicates that after the CBM well has casing pressure, the overall release of the coal seam pressure is the result of the joint action of the gas and water, and the slow transition from the water production stage to the depressurization and gas production stage is necessary for the high production of the CBM well. The continuous casing pressure holding may lead to early formation of slug flow in pores and fractures with mesopore scale, which is not conducive to the high and stable production of CBM well. Moreover, with the decrease of coal seam pressure, the liquid water in pores and fractures with the equivalent pore size > 40 nm can be vaporized and separated to the gaseous free water, which forms competitive adsorption/desorption with the adsorbed CH4. However the water in pores and fractures with the equivalent pore size < 40 nm is preserve with liquid or transported by wetting migration, and has little influence on the transformation of bound water (capillary water) to movable water in the gas-water two-phase flow stage.

The Shouyang Block was selected as the research subject. Comprehensive analysis was conducted using coalbed methane (CBM) well production data, geochemical test data on water produced from the coalbed methane well, and fundamental geological information. The findings reveal the water dynamics in the Shouyang Block are characterized by weak groundwater runoff or retention in most areas. The groundwater head height exhibits a gradual decrease from the north to south, which is closely associated with the monoclinic structure of the Shouyang Block. Overall, water production is relatively high. As the average water production increases, the average gas production gradually decreases. A concentration of high water production wells is observed in the northern part of the Shouyang Block, which gradually increases towards the southeast direction. A comprehensive analysis was conducted on the factors influencing water production, including total water content of coal seams, coal seam porosity, groundwater stability index, groundwater sealing coefficient, D value of the fracture fractal dimension, fault fractal dimension, and sand–mud ratio. The correlation degree was calculated and ranked in order of magnitude through grey correlation analysis. The order of factors that influence water production, from strongest to weakest, is as follows: sand–mud ratio > porosity > fractal dimension of fault > fracture fractal dimension D value > groundwater sealing coefficient > groundwater stability index > total water content of coal seams. The dissolution amounts of carbonate and sulfate are both small, and the water source may mainly come from the sandstone aquifer. Attention should be paid to the distribution and lithological combination of sandstone aquifers in coal-bearing strata in the future exploration and development process of the Shouyang Block. This will help to avoid the potential influence of fault structures and enable the identification of favorable areas for low water and high gas production.

Accurate classification of drainage and extraction reservoir types of coalbed methane wells can lay a foundation for the study of pressure propagation in drainage process. Taking 3# coal seam of Changcun Mine Field as the research object, the main parameters affecting the conductivity of coal reservoir and the recharge capacity of surrounding rock in the process of drainage and extraction are analyzed and selected. The method of obtaining these parameters is proposed, and the critical value is determined. The study area is divided into four types of drainage reservoirs. The water production and gas production of CBM wells in the field verify the reliability of the theory. The significance of classification of drainage and extraction reservoir types was discussed. The results show that the study area can be divided into high-conductivity weak supply reservoir, high-conductivity strong supply reservoir, low-conductivity weak supply reservoir and low-conductivity strong supply reservoir. Among them, the high conductivity and weak recharge reservoir is most conducive to reduce coal reservoir pressure, showing the characteristics of small water production and short casing pressure time. The low conductivity and strong recharge reservoir shows the characteristics of large water production and long casing pressure time.

Coalbed methane (CBM) development in coal mining area has good safety, economic and energy benefits, but methane emission is common in surface well sites. In view of this, taking the CBM wells in Qinshui County of Shanxi Province as an example, the methane emission location and emission volume of CBM wells are obtained, and the prediction model of methane emission volume is established through field investigation and multiple regression analysis. The results show that 81% of CBM wells have methane emission. Wellhead and drainage outlet are the two main positions of methane emission. The proportion of wells with emission volume between 0-10 m3/d is 59%. On the whole, the emission accounts for 1.53% of the gas well production. There is almost no methane emission in the single liquid phase flow stage. The methane emission in the gas-liquid two-phase flow stage is positively correlated with the bottom hole flow pressure, times of stroke and gas production, and negatively correlated with the pump embedment and water production. The bottom hole flow pressure and the pump embedment have the greatest impact on the methane emission. In the single-phase gas flow stage, methane emission is positively correlated with gas production and casing pressure, and negatively correlated with stroke frequency and water production.

CBM (CBM) development in coal mining area has good safety, economic and energy benefits, but methane emission is common in surface well sites. In view of this, taking the CBM wells in Qinshui County of Shanxi Province as an example, the methane emission location and emission volume of CBM wells are obtained, and the prediction model of methane emission volume is established through field investigation and multiple regression analysis. The results show that 81% of CBM wells have methane emission. Wellhead and drainage outlet are the two main positions of methane emission. The proportion of wells with emission volume between 0 and 10 m3/d is 59%. On the whole, the emission accounts for 1.53% of the gas well production. There is almost no methane emission in the single liquid phase flow stage. The methane emission in the gas-liquid two-phase flow stage is positively correlated with the bottom hole flow pressure, times of stroke and gas production, and negatively correlated with the pump embedment and water production. The bottom hole flow pressure and the pump embedment have the greatest impact on the methane emission. In the single-phase gas flow stage, methane emission is positively correlated with gas production and casing pressure, and negatively correlated with stroke frequency and water production.

Aiming at the high gas content at the wellhead and drainage outlet of coalbed methane well site, which affects the normal safety production and is a serious waste of resources. The shortages of the existing wellhead sealing device and water pipeline gas separation device are analyzed, the gas collection technology for the coalbed methane well site is proposed. The self-adjusting deflected wellhead sealing device and the water pipeline gas separation and collection device are introduced, and the process flow of gas separation and collection in gas- containing water pipeline of coalbed methane well is designed. The simulation test shows that the simulation test shows that the technology can separate and pressurize the gas in the gas-liquid mixture up to 0.2 MPa, which verifies the feasibility of this technology.

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Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to solve problems of existing pressure and temperature data collecting modes of coalbed methane well such as information island caused by manual collection, inability to collect data consecutively, water leakage of pressure sensor and temperature sensor and so on, a pressure and temperature monitoring system of coalbed methane well was proposed. System structure was given as well as compositions of hardware and software. Design scheme of a new type of sensor was focused on, which adopted MEMS technology, vacuum encapsulation and resistive load modulation mode to send collected data. Testing and trail running results show that the system has better reliability, real-time performance and operability, which can reduce field personnel and accidents effectively.

Based on the theory and technology of combined stimulation, this paper, the second of a two-part series, presents an application of the combined stimulation technology to a low-deliverability CBM well in the Sunan Syncline, Anhui Province, China. During the stimulation, a low-damage fracturing fluid was adopted. Based on the laboratory test results, the property of the low-damage fracturing fluid is analyzed. Additionally, the stimulation effect is evaluated according to the calculation of the reservoir permeability and the drainage conditions. Results show that the low-damage fracturing fluid has good compatibility with the reservoirs, and can effectively prevent the reservoir to be damaged by water sensitivity, water blocking effect and flow rate sensitivity, and decrease the migration resistance of fracturing fluid in both tubing and reservoir fractures. The calculated reservoir permeability during the stimulation indicates good fracturing results for different kinds of reservoirs. The reservoir permeability at the early drainage stage after the combined stimulation is 3.4 times of the reservoir permeability after the first stimulation of this well. After conducted the combined stimulation, the daily gas production of the well has excessed 1000 m 3 /d since 21st December 2017 which indicates a successful application of this technology. [ABSTRACT FROM AUTHOR]

Copyright of Oil Drilling & Production Technology / Shiyou Zuancai Gongyi is the property of Shiyou Zuancai Gongyi Bianjibu and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Supercritical CO 2 fracturing can form a more complex fracture network in rocks than hydraulic fracturing and avoid aqueous phase trapping damage in reservoirs. Thus, it is a promising alternative to hydraulic fracturing for enhancing the production of low-permeability hydrocarbon reservoirs. In this study, a new numerical model for predicting the wellbore temperature and pressure during supercritical CO 2 fracturing was established based on thermodynamics, heat transfer, fluid mechanics, and a numerical solution method. In the new model, the physical properties of CO 2 are calculated with the Span–Wagner and Vesovic models, and the heat generated by fluid friction losses is absorbed by the tubing and CO 2 according to the contact coefficient. The model was used to examine the influences of the injection rate and temperature on the wellbore pressure and temperature. The results indicated that both the heat transfer and pressure in the wellbore are transient processes in the initial stage of injection; as the injection time increases, the heat transfer and pressure in the wellbore can be considered steady processes. The CO 2 temperature in the wellbore is considerably affected by both the injection temperature and rate, whereas the wellbore pressure is greatly affected by the injection rate but weakly affected by the injection temperature. The CO 2 pressure in the wellbore decreases rapidly as the well depth increases because of high fluid frictional resistance, so a drag reducer suitable for liquid CO 2 needs to be developed. [ABSTRACT FROM AUTHOR]

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Copyright of Oil Drilling & Production Technology / Shiyou Zuancai Gongyi is the property of Shiyou Zuancai Gongyi Bianjibu and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Coal rock is a type of fractured rock masses in which lots of cleats, fractures and weak planes develop, and these structures make the coal rock mechanics properties largely different from those of conventional sandstone rock. Previously established calculation models for the fracture initiation pressure of fracturing of conventional reservoirs cause large deviations when used to calculate the fracture initiation pressure of coalbed methane fracturing. In order to accurately calculate the fracture initiation pressure of coalbed methane fracturing, a new calculation model needs to be established while taking coal rock mechanical properties into consideration. In this paper, first, we carry out the macroscopic measurements and scanning electron microscopy (SEM) observation experiments on coal rock samples to describe the cleats distribution characteristics of coal rock samples. Second, we have carried out tests on rock mechanical parameters of different coring directions to obtain the anisotropy of coal rock mechanical parameters. Third, a calculating model has been established to determine the elastic modulus and Poisson’s ratio of coal rock based on the equivalent continuum mechanical methods, and then the model gets validated using the results of mechanical parameters tests. Finally, we have established the calculation models for borehole wall stress and fracture initiation pressure of hydraulic fracturing, which is based on the calculation model for equivalent coal rock mechanical parameters, to analyze the influence of mechanics properties of coal cleats on initiation pressure. The research result provides a new kind of research idea and approach for the calculation of fracture initiation pressure of coal hydraulic fracturing. [ABSTRACT FROM AUTHOR]

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Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Oil Drilling & Production Technology / Shiyou Zuancai Gongyi is the property of Shiyou Zuancai Gongyi Bianjibu and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

According to complicated dynamic influence factors of coalbed methane well production in Liulin Block, rational production increasing measures and other problems were hard to be set up. The drainage and extraction dynamic law of over 50 wells within the block was analyzed and the influence factors of the output performances in different type wells were discussed. The results showed that the wells within the block were medium and low production wells mainly, the gas production at the initial period was high and the gas production was seriously reduced at the late period. Related to the vertical well and cluster well, gas production of the horizontal well would be stable and high. The seam thickness and hydrological condition were the main geological parameters affected to the production capacity of seams in Shanxi Formation and Taiyuan Formation individually. The further analysis combined with the engineering factors showed that the coal reservoir within the block was high in sensitivity and the fracture scale and reservoir damage were the main causes to cause the low production of the vertical well within the block. Meanwhile, the relevant index of the production increased parameters was provided: Sand added quantity would be over 35 m and the construction fluid quantity would be over 400 m³. A drop speed of the liquid level controlled would be 2 ~ 10 m/d and a casing pressure after the gas production was 0. 1 ~0. 3 MPa. The number of the well to be closed should be reduced and the time to stop the drainage and extraction should be less than 20 days. [ABSTRACT FROM AUTHOR]

In order to get the reservoir parameters, an injection and pressure drop method was applied to the comparison tests and analysis on the coal reservoir parameters under the open hole, casing, perforation in casing, different stage after the fracturing and other different well completion type. The results showed that under the stable condition of the well hole, an open hole type well test method should be applied. Under a quite poor stability condition of the well hole, an inner casing test would be applied and the injection and pressure drop test would be conducted after the perforation in casing. The open hole type well test results could more accurately reflect the coal reservoir features and the fracturing test results could directly guide the initial drainage and extraction work of the coalbed methane well. After the perforation in the casing, due the tests influenced by the well cementation, perforation and other procedure, the test results would not be accurate to the test results of the open well and fracturing well. The well test in casing should expand the test time, injection pressure and other controlled factors in order to have more reliable test results. [ABSTRACT FROM AUTHOR]

The migration law in the cracks of variable density proppant particles had been researched, for effective support fracture length of CBM hydraulic fracturing was too short and seam sanding concentration distributed uneven. The mutual influence of the fracture proppant particles was considered using Pseudo Fluid model, and the corresponding calculation software was written with the Visual Studio 2012 design platform, then the accuracy of the calculations was checked through comparison with the value of field monitoring software. The effective law to seam sanding concentration and effective support slot length of the fracturing fluid viscosity, wall cracks, displacement and proppant density parameters were discussed, and the broken rate of the ultra-low density proppant was analyzed at different confining pressure and temperature conditions. The results show that broken rate of a nut shell proppant is less than 2% in the condition of confining pressure 69 MPa and the ambient temperature 90°C,which meet the site requirements; With the increase of fracturing fluid viscosity, the construction displacement and fracture bracing length, the seam sanding is more uniform; with the proppant particle diameter increases, the crack support length decreases; compared to single ceramic sand, using variable-density proppant makes effective support half-slot length increasing 19.5 m, and the sanding effect is more uniform. [ABSTRACT FROM AUTHOR]

In order to improve the production capacity of a coalbed methane well, the paper analyzed the coalbed methane drainage mechanism and gas drainage stage. From a geological structure, roof and floor lithology, fracturing liquid, well net layout and other aspects, the paper discussed the main factors affected to the coalbed methane drainage in Tunliu Minefield. The study held that the fold would highly be affected to the drainage effect of the coalbed methane well and the breaking of the roof and floor would be certainty affected to the coalbed methane drainage. The fracturing technology was applied to the intensified reconstruction of the coal reservoir, the assistant drainage effect of the activated water + nitrogen gas fracturing liquid system was better than the activated water fracturing and the assistance drainage effect of the clean fracturing liquid was the worst. The coal reservoir features of the study zone determined that the coalbed methane well within Tunliu Minefield would be hard to have a high production, but could have a long production time. The study held that the well net of the coalbed methane wells in the study zone could be small well net structure with an inter-row distance of 200 mx250 m and the layout of well position should be parallel to the extension direction (northeast direction) of the main fracture. [ABSTRACT FROM AUTHOR]

In order to determine the reasonable structure and working parameters of coal particles cleanout jet device in coalbed methane wells, and realize the optimization design and efficient operation of coal particles cleanout jet system, theory analysis on the working principle of coal particles cleanout and motion process of coal particle was done. The bottom hole coal particles cleanout jet flow field can be divided into six areas; free jeting area, jet impinging area, radial flowing area, reflux area, vortex area and negative pressure suction area, which resulted in the spiral uprising motion state of coal particle. Coal particles cleanout experiments were designed by uniform design method, regression equation was found by quadratic polynomial stepwise regression method, the intercoupling influence relation of nozzle structure parameters, jet parameters and coal particle characters to impinging depth was revealed. The results show that the arrangement of these parameters is jet distance, nozzle diameter, nozzle flow rate, and coal particle diameter according to their effects on impinging depth. The influence of nozzle flow rate, nozzle diameter and jet distance on impinging depth was obtained in detail by further single factor experiment, and got the conclusion that on the condition that impinging depth reached 500 mm without moving the tubes, the nozzle flow rate can't be lower than 15 m³/h, and the jet distance should be less than 100 mm. [ABSTRACT FROM AUTHOR]

In order to realize the harmless treatment and reuse of coalbed methane produced water in Qinshui basin, according to the characteristics of the coalbed methane produced water in Qinshui basin, the produced water was treated by coagulation-Fenton oxidation method. Firstly coagulant was added into produced water, then Fenton reagent was added into the produced water after coagulation treatment. The results showed that the removal rate of suspended matter was about 100%, the removal rate of COD was 97. 29% and the removal rate of chroma was 98.89%, the produced water treated by coagulation-Fenton oxidation method reached the primary standard of GB 18918-2002 Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant. The damage degree of reservoir caused by Qinshui river water and the treated produced water was evaluated by formation sensitivity flowing experiments. The results showed that the damage degree of reservoir caused by Qinshui river water was 52.87%, but the damage degree of reservoir caused by the treated produced water was only 4.86%, the treated produced water as drilling fluid had excellent ability of reservoir protection. [ABSTRACT FROM AUTHOR]

During the process of drainage to coalbed methane ( CBM) well, the change of conductivity of hydraulic fractures directly affects the extending range of pressure drop funnel,which can further influence the gas production level. The change regular pattern of fractures conductivity in coal reservoir during the process of drainage was simulated physically in the laboratory by means of the FCES-100 fracture long-term flow conductometer, and by using coal samples made by No. 3 coal of Sihe Mine in Jincheng Anthracite Mining Group and Lanzhou sand as the proppant. According to the analysis of the experiment, the conductivity of hydraulic fractures has a fairly strong stress sensitivity during the process of drainage, which controls the reservoir pressure dropping slowly and ensures that before the pressure drop funnel is fully extended,the stress sensitivity does less damage to the conductivity. Increasing sand ratio is considered to decrease the effect of proppant embedment and selecting higher-strength proppant aims to overcome the damage of its break in deep well. Instability and intermittent drainage is another important reason for the rapid decreasing of fracture conductivity, and only by adhering to draining continuously, slowly and stably can the damage of stress sensitivity and drainage velocity sensitivity be avoided and ensure coalbed methane wells development with good results achieved. [ABSTRACT FROM AUTHOR]

Based on the moving off conditions of pulverized coal and the suspended migration conditions coal particles, a porosity and permeability model regarding pulverized coal fall off, migration and blockage was developed in this study,which was used to study the influence of porosity and permeability from the discharge amount of pulverized coal. According to the model,and the theory of pulverized coal proper discharge,the pulverized coal proper discharge model and the critical fluid speed coal model were established. Once the fall off of coal powder is discharged, and the seepage channel is dredged, subsequently, the permeability and gas production are increased. The results show that the porosity and permeability of coal seam are improved by peeling of pulverized coal, and are reduced by the sedimentary and jam of peeled pulverized coal; if the fall off coal powder is not removed, the porosity and permeability of coal seam will not change. If the fall off coal powder moves near wellbore and no reduction, the coal seam porosity and permeability will unchange, however, the porosity and permeability away from wellbore will increase, and the porosity and permeability near wellbore will decrease. Because of the permeability reduction, the overall gas production is affected. The permeability increase follows a quadratic relationship with the amount of pulverized coal discharge. When the support particle size is 20/40 in the stimulation of coalbed methane well,the largest discharge coal particle size is 0. 16 mm. When liquid output volume is 13. 53 m³/d, it is good for discharging the pulverized coal with a size smaller than 0. 1 mm,which improves the permeability of coal seam,and increases the coalbed methane gas production. [ABSTRACT FROM AUTHOR]

Abstract: Production characteristics of coalbed methane wells in Fanzhuang and Hancheng mining areas, which are typical high and mid rank coal fields, are analyzed, compared, and summarized. And the effects of perforating thickness, number of perforated layers, unloading technology and stimulation treatment on gas production are analyzed. Coalbed methane wells in Fanzhuang and Hancheng mining areas are divided into four categories: high gas-production wells, middle gas-production wells, low gas-production wells and little gas-production wells. High gas-production wells have gas production of more than 3 000 m3/d, long stable production period, slow and smooth declining rate, high peak production and short unloading period. Middle gas-production wells have gas production between 1 000 m3/d and 3 000 m3/d, shorter stable production period, longer unloading period and quick declining rate at the early stage. Low gas-production wells have gas production of less than 1 000 m3/d, short stable production period, high water output, long unloading period and discontinuous production. Little gas-production wells have large water output, slow reducing rate of liquid level and a low or zero surface casing pressure. Based on the production characteristics, three types of production modes of coalbed methane wells are summed up. In view of specific examples, it is discussed quantitatively and qualitatively how different factors affect the gas production of coalbed methane wells. It turns out that, generally, the perforating thickness of coalbed methane wells should be larger than 5 m and the layers of perforation should not exceed 3 layers. A proper unloading system is needed to maintain stable and persistent high gas production, and secondary stimulation treatments can bring about significant production increase. [Copyright &y& Elsevier]

Abstract: To reduce the current high completion cost for steel slotted screen pipes in coalbed methane wells and to develop low-intensity non-metal completion pipes to perform low-cost completion, this paper adopts electric survey to measure the collapsing strength and bending strength of J55 steel screen pipe and PVC non-metal screen pipe, and makes a comparative analysis of the effect of slot width and slot density on the strength of both kinds of screen pipes. The research results indicate that: the collapse of steel screen pipes mainly results from stiffness reduction or radial unstableness, showing the whole pipe deformation or the slot becoming wide or narrow at the internal or external wall along the short axis, accompanied with the tearing at the slot end-point; while the PVC screen damage mainly results from the material itself. For both steel and PVC screen pipes, the pipe''s collapsing/bending strength declines with increase of the slot width and density, but the PVC screen pipes do not show such an obvious trend, making it possible to apply wider and denser slots on PVC pipes to increase the passing area. [Copyright &y& Elsevier]

Focused on the characteristic of coal seam in southern Qinshui Basin and analysis on the process and difference of production from one group well, the conclusions are shown that: in different group single-well, the gas production has a large change, production effect has obvious difference, water production capacity is also difference; in the process of CBM production, in order to avoid sand is brought out and compression-sensitivity, the production intensity and institutional adjustment are not be too large and frequent. Using different working system in different stages of CBM production, in the early stage is mainly drainage, the core of working system is controlled by the fluid level; in the medium-late stage is mainly gas production, the core of working system is controlled by the casing pressure (bottom hole flowing pressure). In the process of CBM production, on the premise of keeping a certain back pressure and ensuring coal seam security, as possible as decreases casing pressure to product in order to decrease the average pressure of coal seam, enlarge the range of CBM adsorption and get high gas production. [ABSTRACT FROM AUTHOR]