Study On Reservoir Characteristics And Main Controlling Factors Of Jialassic Da'anzhai Section In Northern

Guided by the theories of sedimentology, reservoir geology, logging geology, seismic stratigraphy and recent progress in domestic and foreign,taking the cores, drilling and logging data as the main study objects, using the method of combination of macro analysis and micro analysis, static data and dynamic data together with the the results of previous studies, the stratum, sedimentary facies, reservoir characteristics and controlling factors of the Lower Jurassic Da’anzhai section have been studied in detail.According to the regional sedimentary characteristics with all kinds of sedimentary facie mark, it can suggest that Da’anzhai section in Northern Chuanzhong mainly develops lacustrine depositional system.Through the study of specific sedimentary feature, Longgang and the surrounding areas can be further divided into shore lake, shallow lake, shallow lake-semi-deep lake and semi-deep lake four sub-phases and a number of micro-phases.The shelly beach in shallow lake is the most favorable micro-phase for reservoir formation and evolution.The deposition of Da’anzhai section is controlled by lake level fluctuation and thick shell limestone is developed at the top of the first sub-menber of Da’anzhai and five shelly beaches are developed in plane.Based on the detailed study of the type and characteristics of sedimentary facies (sub-phases), the distribution of sedimentary facies has been determined through the point-line-surface analysis and comparison. At last, the sedimentary facie model has been established.Through the study of the cores, thin section analysis, SEM data, laboratory test and mercury penetration, the reservoir characteristics of the study area have been systematically studied.The reservoir rock is mainly shell limestone. Da’anzhai unconventional reservoirs is typically dense limestone oil reservoirs with extremely low porosity and permeability characteristics.The main reservoir space are cracks and their associated solution pores or holes.The pore structure has the characteristic of "three particularly high, one special small, one special low". The reservoir is porosity-fracture type. The reservoir formation and evolution is affected by sedimentation, diagenesis and tectonism.Sedimentation is the foundation and it determines the approximate distribution of reservoir and affects the type and intensity of diagenesis.The reservoir is significantly influenced by diagenesis.Compaction and cementation are the main reason for pore disappearing and dissolution is the major constructive role in improving the performance of reservoir porosity and permeability.Crack is the necessary condition for effective reservoir and oil and gas output.Based on the above studies, combining the drilling data and the earthquake prediction results, the article selected the favorable exploration blocks and provided a reference direction for oil and gas exploration.