Reservoir characteristics and petrogenesis of volcanic rocks in the Yingcheng Formation of the Shengping gas field,northern Songliao basin
Study of the petrological and physical characteristics, reservoir opening space types and formation and evolution of volcanic rocks in the Cretaceous Yingcheng Formation in the Shengping gas field, Songliao basin, shows that the major volcanic reservoir rocks are lavas, pyroclastic rocks and sedimentary-volcanic rocks, with rhyolite predominating, in addition to small amounts of dacite and andesite. The volcanic gas reservoir spaces are dominated by secondary solution pores (cavities), with subordinate primary pores and fissures. The evolution of the volcanic reservoir rocks involves the early and late phases. The early phase was characterized by volcanic activity, when mainly primary pores including vesicles and pores between volcanic fragments;the late phase included cooling of lavas and epi-petrogenesis of volcanic rocks, which was the main period of formation of volcanic reservoir spaces. The erosion and weathering surfaces as well as faults and fractures in the study area were main conduits for gas migration and also favorable reservoir spaces for gas accumulation.