DISCUSSION ON REASONABLE DEVELOPMENT WELL PATTERN FOR CARBONIFEROUS GAS RESERVOIRS IN EAST SICHUAN

In Carboniferous gas reservoirs of East Sichuan, the old gas fields, such as Fuchengzhai, Zhangjiachang etc., have good development results. All the production wells have suitable allocation. Balance exploitation is always maintained for the whole gas reservoir. No rapid invasion of edge water happens obviously. The dynamic reserves increase gradually. The stable production period of gas wells is prolonged and the recovery benefit is good. But for new gas fields, such as Yunhezhai, Shuangjiaba etc., it is difficult for the gas wells to control the whole gas reservoir because the sparse well pattern and big well space. The severe pressure drop funnel is formed in 2-5 years after the gas wells are put into production and the ahead water production happens because of the high allocation for each well. Therefore, the reserves of some gas-bearing zones can’t be used because they are watered out or separated by water. The stable production period of gas reservoirs is shortened. It is hard to reach the expected development level. The development benefit becomes poor. With summing up the development experience of more than 20 years for Carboniferous gas reservoirs in East Sichuan and comprehensively comparing the geological mode and well pattern of gas fields and the production process of gas wells, it is found the reasonable density of well pattern is very important for the non-homogenous gas reservoirs with low-medium permeability, and is the key factor to guarantee realization of the development indexes of gas reservoirs in time and improve the ultimate recovery factor and whole development benefit of gas reservoirs. The reasonable density of well pattern should be about 3.0 km2 /well, the reserve controlled by a well should be (0.5-1.0)×109 m3, and the gas recovery rate should be 3.0%-4.0% for the non-homogenous gas reservoirs with low-medium permeability.