A novel ECBM extraction technology based on the integration of hydraulic slotting and hydraulic fracturing

Abstract Because most coal mines in China have high gas content with low permeability, it is necessary to increase the efficiency of the CBM extracting technology. Enhanced coalbed methane (ECBM) recovery is a suitable option in this regard. This paper demonstrates a novel ECBM extraction technology, which involves the integration of hydraulic slotting (HS) and hydraulic fracturing (HF). The efficiency of the method is evaluated by field test. The slots produced by the HS method are used to control the extension direction of fracture cracks, and the efficiency of CBM extraction from the single drilling is improved by performing slotting drilling in coordination with fracturing drilling. The numerical software Coupled Analysis of Flow and Solid Mechanics in Rock Failure Process Analysis (RFPA2D-Flow) was used to analyse the direction of the crack propagation in the HF process. The coal-crack-propagation process, hydraulic gradient evolution, acoustic emission phenomena, and the change in the stress of coal body with the propagation of the fracturing crack were studied. The results of the study show that because the water pressure around the fracture bore is affected by the slots created, the hydraulic gradient in the horizontal direction is larger than that in the vertical direction, and the cracks more easily extend along the direction of the larger hydraulic gradient following the initiation of the cracks. After HF, a fully unloading area, a transition pressure-relief area, and the original stress area around the fracturing boreholes are formed. Results of the field test show that once the ECBM extraction is completed, the coal-seam disturbance range of the single drilling increases, and the CBM extraction efficiency is significantly improved. This novel ECBM extraction technology is a very promising method for improving the effect of the CBM extraction in the field.

[1]  Lijun Han,et al.  Application of an Improved Flow-Stress-Damage Model to the Criticality Assessment of Water Inrush in a Mine: a Case Study , 2009 .

[2]  Song Jian-guo,et al.  Study on improving the penetrability of coal seam with the water pressure blasting in the through beds hole , 2004 .

[3]  Experimental and Analytical Study of Hydraulic Fracturing of Cylinder Sample , 2009 .

[4]  C. Tang,et al.  Numerical simulation of progressive rock failure and associated seismicity , 1997 .

[5]  Zhang Hai-bin,et al.  Regional gas control based on drilling-slotting-extracting integration technology , 2011 .

[6]  L. Tham,et al.  Influence of Heterogeneity of Mechanical Properties on Hydraulic Fracturing in Permeable Rocks , 2004 .

[7]  Tingkan Lu,et al.  Improving the gate road development rate and reducing outburst occurrences using the waterjet technique in high gas content outburst-prone soft coal seam , 2011 .

[8]  Wei Wang,et al.  Research on comprehensive CBM extraction technology and its applications in China's coal mines , 2014 .

[9]  Charles Fairhurst,et al.  Initiation and Extension of Hydraulic Fractures in Rocks , 1967 .

[10]  Yingke Liu,et al.  An experimental and numerical investigation on the deformation of overlying coal seams above double-seam extraction for controlling coal mine methane emissions , 2011 .

[11]  I. Song,et al.  Effect of pressurization rate and initial pore pressure on the magnitude of hydrofracturing breakdown pressure in tablerock sandstone , 2001 .

[12]  M. King Hubbert,et al.  Mechanics of Hydraulic Fracturing , 1972 .

[13]  Baohua Guo,et al.  Improvement of methane drainage in high gassy coal seam using waterjet technique , 2009 .

[14]  Jianguo Zhang,et al.  Guiding-controlling technology of coal seam hydraulic fracturing fractures extension , 2012 .

[15]  Bu Wan-kui.  Analysis of Fracture Propagation in Coal Seams During Hydraulic Fracturing , 2008 .

[16]  Shanyong Wang,et al.  A numerical investigation of the hydraulic fracturing behaviour of conglomerate in Glutenite formation , 2013 .

[17]  Thomas Gentzis,et al.  The use of numerical simulation in predicting coalbed methane producibility from the Gates coals, Alberta Inner Foothills, Canada: Comparison with Mannville coal CBM production in the Alberta Syncline , 2008 .

[18]  M. Zoback,et al.  Hydraulic fracturing and wellbore completion of coalbed methane wells in the Powder River Basin, Wyoming: Implications for water and gas production , 2007 .

[19]  Wang Ka,et al.  Change regulation of coal seam permeability around hydraulic flushing borehole , 2013 .

[20]  T. Wong,et al.  Network modeling of the evolution of permeability and dilatancy in compact rock , 1999 .

[21]  Baiquan Lin,et al.  Stress evolution with time and space during mining of a coal seam , 2011 .

[22]  C. A. Tang,et al.  Coupled analysis of flow, stress and damage (FSD) in rock failure , 2002 .

[23]  A. Cheng,et al.  Influence of pressurization rate on the magnitude of the breakdown pressure , 1992 .

[24]  Chun’an Tang,et al.  Micromechanical Model for Simulating the Fracture Process of Rock , 2004 .

[25]  Yang Li,et al.  Simulation of hydraulic fracturing using particle flow method and application in a coal mine , 2014 .

[26]  Andrew P. Bunger,et al.  Initiation and growth of a hydraulic fracture from a circular wellbore , 2011 .

[27]  Jose Adachi,et al.  Computer simulation of hydraulic fractures , 2007 .

[28]  Zhongwei Chen,et al.  Laboratory Study of Gas Permeability and Cleat Compressibility for CBM/ECBM in Chinese Coals , 2012 .

[29]  Ekrem Ozdemir,et al.  Modeling of coal bed methane (CBM) production and CO2 sequestration in coal seams , 2009 .

[30]  Zhai Cheng.  A Numeric Analysis of the Effects Different Factors Have on Slotted Drilling , 2010 .

[31]  Cheng Zhai,et al.  The effect of pulse frequency on the fracture extension during hydraulic fracturing , 2014 .

[32]  Lin-ming Dou,et al.  Directional hydraulic fracturing to control hard-roof rockburst in coal mines , 2012 .

[33]  Baiquan Lin,et al.  Variation of methane adsorption property of coal after the treatment of hydraulic slotting and methane pre-drainage: A case study , 2014 .

[34]  Chunming Shen,et al.  Induced drill-spray during hydraulic slotting of a coal seam and its influence on gas extraction , 2012 .

[35]  C. Özgen Karacan,et al.  Coal mine methane: A review of capture and utilization practices with benefits to mining safety and to greenhouse gas reduction , 2011 .

[36]  Yang Wei,et al.  Permeability-increasing mechanism of network slotting boreholes and application in crossing borehole gas drainage , 2012 .

[37]  M. Biot.  General Theory of Three‐Dimensional Consolidation , 1941 .

[38]  Emmanuel M Detournay,et al.  Toughness-dominated Hydraulic Fracture with Leak-off , 2005 .

[39]  Bingxiang Huang,et al.  Hydraulic fracturing after water pressure control blasting for increased fracturing , 2011 .

[40]  Li Yan-zeng,et al.  Technology and application of directional hydraulic penetration permeability improvement by guided groove , 2012 .

[41]  Md. Mofazzal Hossain,et al.  Numerical simulation of complex fracture growth during tight reservoir stimulation by hydraulic fracturing , 2008 .

[42]  Wancheng Zhu,et al.  The role of pore pressure during hydraulic fracturing and implications for groundwater outbursts in mining and tunnelling , 2011 .

[43]  Yuanping Cheng,et al.  Gas outburst disasters and the mining technology of key protective seam in coal seam group in the Huainan coalfield , 2013, Natural Hazards.