Characteristic of Volcanic Reservoir in Malang Sag in Santanghu Basin

The volcanic reservoir body in Santanghu basin is dominated by neutral-basic volcanic rocks.The main reservoir rocks are composed of vesicular and almond-shaped basalt and andesite in the top of block lava.The key of improvement of such a reservoir quality is the epigenetic reconstruction,mainly including weathering and leaching,dissolution,faulting and micro-fracture,by which form secondary solution pore-vugs and secondary fractures,and become good reservoir body with pore spaces such as solution pore,fissure and structural fracture,constricted fissure,etc.,belonging to porous-fractured reservoir with strong heterogeneity.Controlled by lithology and lithofacies,this reservoir is characterized by short-range vertical migration and accumulation,oil-gas rich belt distribution adjacent to hydrocarbon generation.The top vesicular,almond-belt remained thickness,weathering,leaching and dissolution extent as well as fractural communication are the key factors for its hydrocarbon accumulation.Near the denudation line of Permian and the volcanic erupting and intermittent zone are favorable zones for forming the volcanic reservoir.In the Permian and Carboniferous volcanic reservoirs in Niudong,Mazhong,Tiaozhong and Nanyuan blocks,a hundred million ton-grade potentials for petroleum exploration have been discovered at present.