Study on geostress features and influences under multi-seam condition in Laochang Mining Area of East Yunnan

Based on Laochang Mining Area of East Yunnan developed with many seams, the high geostress features would have important influences to the exploration and development of coalbed methane. In order to discover the geostress affected to coalbed methane development, with the analysis on data of hydraulic fracturing well in the mining area, the paper had a discussion on the geostress affected to the reservoir pressure, permeability and over-pressure phenomenon. The study result showed that in Laochang Mining Area, the coal reservoir pressure mostly came from the geostress. The coalbed methane belonged to the pressure dominate stress gas. Meanwhile, the high geostress would have a high contribution to the fluid energy of the seam, would have an important role to keep the pressure status in the deep seam and would also cause big difficulty to the reconstruction of the coal reservoir. The pressure coefficient of each seam and the geostress gradient would have the fluctuation variation on the strata and the partial seam would be overpressure generally. With the min main stress increased, the permeability of the seam would be steadily reduced and the pressure coefficient would be steadily increased. The min main stress gradient of each seam also would have the fluctuation and could show a big difference between the geostress features of each seam. The fluctuation of the stress gradient would have the same to the fluctuation of the pressure coefficient and could approve that he geostress was the one of the main control factors to form the multi layers overlay and independent gas content system.