Analysis On The Difference And Main Controlling Factors Of Gas-water Productivity Of CBM Straight Wells In Zhengzhuang South Qinshui Basin

During the production process of CBM wells, the productivity is not the same, because there are differences at the reservoir, geology, topography and other conditions among different CBM wells. In the paper, based on the reservoir geological characteristics and drainage data of CBM straight wells and engineering factors in Zhengzhuang Block, Southern Qinshui Basin, and based on the analysis of the reservoir and geological characteristics of the No.3 coal seam in the study area, the distribution and variationcharacteristics of gas-water productivity of CBM wells are discussed in the study area. Combined with characteristics of gas-water productivity of CBM wells, the influences of geological and engineering factors on gas-water productivity of CBM wells were analyzed further, screening of main controlling factors of CBM wells productivity.The study area is divided into Zheng 1, Zheng 2, Zheng 3 well block; and the type of gas producing are classified into four types: high production well, middle production well, low production well and water production well; the water production is divided into: 0~2m3/d, 2~5m3/d, 5~10m3/d, 10~15m3/d, 15~20m3/d, 20m3/d six grades, according to the distribution and gas production characteristics of CBM vertical wells in the study area,Analysis found that the average daily gas production of CBM wells is between 100~3325m3/d in the study area, the average is about604.6m3/d, the productivity of CBM wells is relatively low. High-productivity wells are mainly distributed in the axis of the fold or the wide and gentle slope zone, and no high-productivity wells appear near the fault. The average daily water production of CBM wells is between 0.15~32.2m3/d, the average is about4.4m3/d, high-productivity of CBM wellsare mainly concentrated in the south Zheng 1 well block that the area is low-lying, CBM wells that near the fault part water production is also higher.The coal reservoir parameters, construction conditions, hydrological conditions and engineering factors and the average daily gas production capacity and water production were analyzed in the study area. Coal reservoir buried depth, thickness, gas content, permeability, structural conditions, hydrological conditions and drainage system and other factors have a greater impact on gas production, but the coal reservoir pressure and the fracturing parameter influence to the CBM well gas production is small. The water production of CBM straight well is mainly influenced by the groundwater condition, reservoir permeability, structure condition and drainage system. Based on grey correlation degree method, the main control factors of gas and water productivity of coalbed methane wells in the study area were evaluated. It is concluded that the gas production is mainly controlled by the depth and permeability of the coal reservoir in the study area; the water is mainly controlled by the head height and permeability.