Low-Yield Genesis of Coalbed Methane Stripper Wells in China and Key Technologies for Increasing Gas Production

Abstract

For the problem where numerous coalbed methane (CBM) stripper wells exist in China, this paper analyzes the genesis of the stripper wells from the aspects of geological conditions and development technologies combined with the CBM development of some typical blocks. A series of key secondary stimulation technologies for CBM stripper wells are put forward, including low-damage fracturing fluid for preventing reservoir damages, proppants with multigraded sizes for supporting multilevel fractures, large-scale fracture network stimulation (FNS) for improving reservoir permeability, and coal measure gas development for increasing the exploitable resources within a single well scope, as well as coordinated stimulation of parent–child wells for the overall production improvement of low-yield blocks. Also, it is pointed out that all types of stripper wells could adopt the low-damage fracturing fluid and multigraded proppant and optimize the drainage schedule to inhibit reservoir damage and promote the maintenance of fracture conductivity. For resource-controlled stripper wells, large-scale FNS of coal seams, coal measure gas development, and coordinated stimulation of parent–child wells could be adopted according to the differences in resource abundance and coal seam distribution. For the stripper wells controlled by the coal structure and ground stress, FNS of the surrounding rock could be conducted to construct stable and efficient channels for CBM migration. In addition, by conducting large-scale FNS, the stimulation effect of fracturing-controlled stripper wells improves, while after unblocking and reopening the existing reservoir fractures of the drainage-controlled stripper wells, an optimized drainage schedule could be adopted to prevent reservoir damages and promote the maintenance of fracture conductivity.

Genesis of Low CBM Production in Mid-Deep Reservoirs and Methods to Increase Regional Production: A Case Study in the Zhengzhuang Minefield, Qinshui Basin, China

“…15,16 Low-damage fracturing fluid for preventing reservoir damages, proppants with multigraded sizes for supporting multilevel fractures, and largescale fracture network stimulation for improving reservoir permeability were implemented for increasing gas in low-yield blocks. 17 could achieve a good production-increasing effect in both hard and soft coal seams. 19 Aiming at understanding the causes of low yield in CBM wells, many scholars have studied the CBM storage and productivity factors in the area adjacent to the Zhengzhuang minefield from different aspects.…”

“…Many scholars at home and abroad have analyzed the main factors that affect the production of CBM wells from many aspects, such as geological conditions, − reservoir conditions − and development engineering conditions. − For the CBM low yield caused by serious pollution in the near-well zone, radial hydraulic jet and high-energy electrical pulse-blocking removing technologies were used to increase production. As for the fracture closure and gas production decline caused by improper extraction measures, secondary hydraulic fracturing technology was tried to increase production. , Low-damage fracturing fluid for preventing reservoir damages, proppants with multigraded sizes for supporting multilevel fractures, and large-scale fracture network stimulation for improving reservoir permeability were implemented for increasing gas in low-yield blocks. , Pseudo-reservoir stimulation in horizontal wells could achieve a good production-increasing effect in both hard and soft coal seams …”

“…15 , 16 Low-damage fracturing fluid for preventing reservoir damages, proppants with multigraded sizes for supporting multilevel fractures, and large-scale fracture network stimulation for improving reservoir permeability were implemented for increasing gas in low-yield blocks. 17 , 18 Pseudo-reservoir stimulation in horizontal wells could achieve a good production-increasing effect in both hard and soft coal seams. 19 …”

Characteristics and Geological Impact Factors of Coalbed Methane Production in the Taiyuan Formation of the Gujiao Block

“…There are many factors affecting the productivity of CBM wells, which can be roughly divided into three aspects: geology, engineering, and working system [11]. Geological factors mainly include tectonic form and location, sedimentary environment, groundwater fluid potential, coal seam thickness, buried depth, ground stress, porosity, permeability, and gas content [12][13][14][15][16][17][18][19][20][21][22][23][24]. The Gujiao Block is divided into three working areas.…”