Gas-Water Distribution and Development Strategy of Xujiahe Tight Sandstone Gas Reservoir in Sichuan Basin, China

Ji, Lidan ¹; Ji, Guang ¹; Jia, Ailin ¹; Zhao, Liang ²; He, Dongbo ¹; Wei, Yunsheng ¹
(1) Research Institute of Petroleum Exploration & Development, Petrochina, Beijing, China. (2) Changqing Oilfield Company, Petrochina, Xi'an, China.

The tight sandstone gas reservoir of Xujiahe formation, Upper Triassic in central Sichuan basin has drawn increasing interest in Chinese unconventional gas research circle. For its low porosity and ultralow permeability, and high original water saturation, the problem of water production and water flooding presents challenges to gas field development. Xujiahe reservoirs in central Sichuan basin are mainly of labyrinth structure, which means the reservoirs are relatively high permeability sand lens, random distributed in the tight sandstone background, which are interconnected or not. Meanwhile, the original water saturation of Xujiahe reservoir is quite high, with the average of 50%. The gas-water distribution rules of Xujiahe reservoir were discussed in this paper: 1, as a whole, the tectonic controls the gas-water distribution; 2, on the local scale, some gas tops, or zones with relatively high gas saturation, exist in the structural high spots within the interconnected reservoirs. It's realized that to optimize perforation programs to avoid shooting the zones of high water saturation, and to moderately enlarge pressure differentials to drain movable water in reservoirs are feasible. On the other hand, spatial drainage gas recovery techniques are utilized to protect gas wells with a certain amount water production from water flooding, which have meet with success in Sichuan basin.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.