Hydraulic fracturing technology for deep coalbed methane horizontal wells:A case study in North Changzhi area of Qinshui Basin

Reservoir reconstruction is an important means to improve the productivity of coalbed methane (CBM) wells with low permeability.Although China is rich in deep coalbed methane resources,it is faced with the difficulty of poor geological adaptability of reservoir reconstruction technology under different geological conditions of CBM reservoir due to low permeability.Taking the northern area of Changzhi in Qinshui Basin as an example,this paper introduces the geological situation and development mode of the study area,and analyzes four kinds of deep CBM well hydraulic fracturing technology and application effect.The result shows that the main approaches of large-scale development of deep CBM resources are characterized by horizontal wells and inter-well interference after fracturing.The casing fracturing technology can achieve large-scale fracturing,but it is easy to cause reservoir pollution and poor adjustability.The coiled tubing fracturing technology has high degree of automation and operation efficiency,which is the mainstream fracturing technology at present,but the cost and supporting facilities are high.The conventional tubing fracturing technology can realize the integration of perforation,fracturing and packer operation,and the jet effect is highly directional,but it cannot operate under pressure,which is easy to cause pressure excitation and “opening the back and plugging the front”.Therefore,the authors have independently developed a new fracturing technology of conventional tubing with pressure.The technology is based on conventional tubing fracturing.The pressure stabilizing devices are installed in the wellhead and downhole tubing to control the pressure state inside and outside the tubing during the fracturing process.With the wire rope fishing device,the lifting and lowering procedure is optimized,so as to realize the pressure drag fracturing operation.The fracturing operation curve of this technology is mainly of stable pressure type,which can form a continuous and straight fracture channel,and reduce reservoir damage.Micro-seismic monitoring shows that the two wings of the fracture are 70 m,and the daily gas production of the test well is more than 4 000 m3.At the same time,the operation cost is saved and the fracturing efficiency is improved.