The Zaoyuan Oil Field, Dagang, Tianjin:Crack-type volcanic reservoirs and their controlling factors

The complexity and heterogeneity of crack-type volcanic reservoirs are considered to be key factors controlling the exploitation of the ZaoyuanOil Field in Dagang, Tianjin. The data on boreholes, thin sections, CT scanning electron photomicrographs, mercury-injection method, well logs and production regimes show that the Zaoyuan volcanic rocks are assigned to basalts, which may be subdivided into vesicular basalt, dense basalt, volcanic breccias and tuff. The lithofacies may be subdivided into two subfacies including the flood and explosion subfacies, and four microfacies including the vesicular basalt, dense basalt, volcanic breccia and tuff microfacies. The reservoir spaces include three types and twelve subtypes, which may be grouped into five reservoir-permeability associations represented by the reservoir-permeability models for the crack-porosity type and composite macropore-macrocrack and micropore-microcrack type.The assessment and classification are further made on the validity of the matrix and crackson the basisof lithology, crack and pore space development, physical property and reserves.The main controlling factors for the cruck-type volcanic reservoirs include tectonism and lithofacies.