Mixed sedimentary characteristics and its control action for reservoir in Lower First Member of Shahejie Formation in Lixian Slope

Key words: 
• mixed sediments /
• distribution tule /
• control factors /
• sedimentary model /
• reservoir control effect /
• Lower first member of Shahejie Formation /
• Lixian Slope

Abstract: [Objective]Mixed sediments were widely developed in Lower First Member of Shahejie Formation in Lixian Slope, clarify the mixed sedimentary characteristics and its control on reservoir is of great significance to determines the target area for exploration and development in the next step. [Methods]Based on core, thin section, well logging seismic, as well as laboratory analysis data, the mixed sedimentary types, distribution regularity, control factors, sedimentary model and high-quality reservoir’s formation mechanism in Lower First Member of Shahejie Formation in Lixian Slope were analyzed. [Results]There are two types of mixed sedimentary in the Lower First Member of Shahejie Formation in the study area, mixed sedimentary rock, mixed sedimentary strata, the mixed sedimentary rock can be divided into 6 types in three major categories, mixed sandstones, mixed mudstones and mixed carbonate rocks, the mixed sedimentary strata can be divided into 16 types in four?lithofacies assemblages, terrigenous rock-carbonate rock, terrigenous rock- mixosedimentite, carbonate rock-mixosedimentite, mixosedimentite. The Lower First Member of Shahejie Formation in Lixian Slope have typical mixed features, which can be divided into 8 mixed sedimentary microfacies, including underwater distributary channel, mouth bar sheet underwater diversion bay, mud flat,?sandy beach bar, carbonate beach bar, inner beach and the semi-deep lake mud,?the mixed sediments have the characteristics of rapid phase transformation in the lateral direction, multiple types of rock superimpose frequently in the vertical, the mixed sediments have different distribution characteristics?of different intervals. The mixed sediments were controlled by climatic and water environment, tectonic background and palaeogeomorphology, sediment supply?and lake level changes, two kinds of mixed depositional model are developed,lowstand period and high-stand periods. The mixed sediments plays a significant role in reservoir controlling factors, the sandy beach bar and carbonate beach bar where developed in high-energy facies zone are the favorable mixed sedimentary microfacies, the closed saline water environment is the foundation of reservoir formation, controlled the formation and distribution of high-quality reservoirs, sedimentary cycles controlled the development degree and distribution palace of high-quality reservoirs. [conclusion] the palaeogeomorphology highland in the southwestern are favorable areas for mixed beach bars development and exploration practice.