Complex Volcanic Reservoir Characterization - A Case Study for Southern Songliao Basin, Northeast China

Discovery of a gas accumulation in Lower Cretaceous YingCheng Group volcanic rocks was confirmed by an exploration well in the southern part of Songliao Basin, Northeast China. A workflow and accompanying modified methodologies were applied to compute gas in place (GIP), which innovated from a similar study for the northern part of Songliao Basin. There were 3 volcanic sequences identified in Yincheng formation with 3 major domes on top of the sequences. The lithology was dominated by effusive deposits of rhyolitic composition and interbedded with minor explosive tuffs and tuff breccias. Several vertical and lateral lithology distribution patterns were identified to allow reconstruction of the sequence of volcanic events. Porosity was vesicular, fracture and vuggy along with fracture in lava flows, and micropores, vuggy leached in the pyroclastics and in-situ breccias. Multiple well pressure data analysis indicated that there was an unified pressure system, and that saturations could be obtained from a saturation-height function above free water level and the capillary pressure curves. A reservoir model was built with semi-deterministic simulation and used to calculate reserves in-place.