Characteristics and controlling factors of Cenozoic volcanic reservoirs in Liaohe Basin,NE China

A database involved in the present research includes well-logs and corresponding geological description of 21 boreholes,analytical results of porosity and permeability of 193 rock samples,3D seismic data of the region and structure-lithofacies mapping of Cenozoic volacanic reservoirs in the eastern depression of the Liaohe Basin.Based on these data,11 types of volcanic rocks are recognized,among them trachyte is the best for reservoir development.5 lithofacies and 14 sub-facies are classified,of which the extrusive facies is the most favorable one of effective volcanic reservoirs.5 cycles are identified in the volcanic rock and the reservoir formation mainly are developed in cycle 3,which is in the middle of the volcanic cycles.The reservoir space can be grouped into 2 types,primary and secondary ones,which can be subdivided into 9 sub-types and 14 species.Fractures of tectonic origin are a main controlling factor on the permeability of these reservoirs.In fact,effective reservoirs are an optimized combination of the four factors,i.e.fracture,eruption cycle,lithofacies and lithology.Volcanic reservoirs here concentrate within or around large-scale strike-slip fault zones,especially at a conjunction of main faults and induced faults.Furthermore,faults control spatial distribution of volcanic rocks and development of secondary fractures,while eruption cycles dominate vertical distribution of effective volcanic reservoirs;lithofacies controls reservoir scale and development of primary pores,while lithology determines types of reservoir space and intensity of alteration that results in the secondary porosity.