Research on efficiency-enhancing development technology of multiple fracturing in low-efficiency CBM wells

After more than six years development and practice in the South Yanchuan coalbed methane field, it has been recognized that lack of fracture-controlled reserves caused by small volume of reservoir reconstruction was one reason for low yield. There is an urgent need to explore efficient development technologies for low-efficiency wells. Theoretical study shows the smaller the horizontal stress difference coefficient (K) is, the easier it is for hydraulic fracturing to form a complex fracture network. The induced stress generated by fracturing can change stress state of reservoir and reduce the K value. Multiple fracturing operations can repeatedly induce the redirection of reservoir principal stress, which helps to form complex fracture network in low permeability coal seams. This paper takes the low-yield wells with short stable yield period and abundant remaining reserves in the field in southeastern margin of Ordos Basin as the research object. The field test of multiple fracturing efficiency enhancement development technology was carried out. It was characterized by increasing displacement by steps, gradually increasing amount of prestage fluid and adding proppant in combination. After the application, the monitored fracture length is more than 3 times that of a single construction, and the fracture morphology changes from a single fracture to a complex fracture network, which effectively expands volume of reservoir reconstruction. The effective support of fracture network was realized by adding sand for times, and the efficient diversion channel was established. After the resumption, the average daily gas-liquid yield was increased by 5 times and 7 times respectively, and the estimated ultimate recovery were increased by about 5 times. The effect of increasing production is remarkable. In the 22 coalbed methane wells that were subsequently popularized and applied, double breakthroughs were achieved in the average daily production and the final cumulative production, which proved that the multiple fracturing and efficiency-enhancing development technology can improve the complexity of the fracture network of deep coal reservoirs and achieve effective support and high efficiency, which is an effective measure for low yield wells with abundant remaining reserves