Jing'an Area Triassic Sedimentary Facies Study Of The Head Of The Two-reservoir Group

Based on the field profile and outcrop observation of northern Shaanxi area, data of Jin'an area such as drilling cores, tests & analysis, logging and well log was comprehensively used in this paper. With methods and theories of sedimentology, stratigraphy, reservoir sedimentology and petroleum geology, stratum was divided and sublayers were compared, sedimentary system types and characteristics were analyzed; sedimentary facies belt and sand distribution regularity were recovered, reservoir property was studied. On above basis, the hydrocarbon enrichment factors of Chang 2 of Yanchang Formation, Jin'an area were analyzed and the hydrocarbon enrichment regularity was summarized, finally forecasted the favorable target area.By regional correlation marker bed and chronohorizon recognition, "slice method" was used to divide and compare the stratum of Chang 2. The precise and appropriate sublayer division lays good foundation for studying the sedimentary facies and hydrocarbon enrichment regularity of the study area. By field profile and outcrop observation, core description, sedimentary facies of single well analysis and sedimentary profile comparison, the paper believes that the sedimentary facies of Chang 2 is fluvial facies, and from bottom to top, braided channel, meandering stream and anastomosed stream sedimentation were developed. Chang 2 Reservoirs are composed by meandering stream channel sand which is controlled by plain distribution of sedimentary facies, and the channel sand zonal distributes from eastnorth to westsouth. Porosity types of Chang 2 reservoirs are intergranular pore, emposieu and intercrystal pore, pore throat is fina, pore and pore-throat assemblages mainly are mesoporosity and microthroat. In general, the reservoirs belong to the low-medium porosity and low porosity type. Sedimentary environment, compositional and structure of sand and lithogenesis are dominant factors to effect reservoirs property.The plentiful hydrocarbon rock in study area is the material foundation of the lithologic deposit, meanwhile channel sand offers reservoir space for hydrocarbon enrichment. Stability distribution of argillaceous sediment composes favourable district covers. Argillaceous sediment of fluviatile flood-plain and close sand act as updip barrier to make hydrocarbon migrate and enriche along the main channel. Local nosing structure controls hydrocarbon distribution. On the basis of the sand distribution which depends on favourable sedimentary fades, reservoir quality, hydrocarbon enrichment factors and degree of exploration, several favorable areas were forecasted. All of these factors serve as the geological basis for further exploration.