Influencing factors on gas production effect of acid fractured CBM Wells in deep coal seam of Daning-Jixian Block

The No.8 deep coal seam in Daning-Jixian Block is large, thick, widely distributed, and rich in coalbed methane(CBM) resources. After volume acid fracturing, a breakthrough has been achieved in the producing test. However, the productivity of the testing wells varies greatly, and the major controlling factors of productivity are not clear, severely restricting the CBM development. In this paper, the testing wells in the No.8 coal seam with a buried depth of more than 2 000 m of the Upper Carboniferous Benxi Formation in Daning-Jixian Block were taken as the research object, and 28 typical evaluation indicators were selected from geological conditions, acid fracturing construction and drainage technology. The grey correlation method was applied to analyze the production sensitivity of CBM wells after acid fracturing, and corresponding technical measures were presented. The results show that factors of acid fracturing construction have a greater impact on productivity than geological factors and drainage factors. Sand volume, acid dosage, water production index before CBM breakthrough, mud content and array induction resistivity(M2RX) are the main controlling factors of productivity. The M2RX and mud content can be used as important indicators to screen out favorable areas. Low density and small particle size proppants are proposed to increase the migration distance of proppants and the propped fracture length. Gas production rate is controlled below 200 m³/d to ensure the smooth and continuous production of deep CBM. This research could provide reference for the selection of favorable areas, optimization of construction parameters and adjustment of drainage and production systems.