Reservoirs Characteristics and Formation Mechanism of High Temperature and Overpressure Reservoirs from Miocene in Ying-Qiong Basin

The main exploration strata are gravity flow deposits and high temperature and overpressure reservoirs with silty, fine, medium and coarse sandstone, and with physical characteristics of medium, low and ultra-low permeability, from the Miocene Huangliu-Meishan Formation in the central depression of Ying-Qiong Basin in the northern South China Sea. By studying the characteristics of high temperature and overpressure reservoirs, the formation mechanism of favorable reservoir is determined, which provides geological basis for evaluation of key areas. From Dongfang to Ledong to Ledong-Lingshui Depression, from the slope area of the sag to the center of the sag, the depth is deepened in each diagenesis period because of differences in the geothermal gradient and the formation time and development intensity, of abnormal overpressure, however, the porosity decreases slightly in the longitudinal direction, which is obviously different from the atmospheric reservoir in the slope area. Favorable reservoirs are controlled by the grain size and mudstone matrix of reservoir rock controlled by sedimentary environment, and diagenesis controlled by high temperature, overpressure and thermal fluid.The submarine fan reservoir with overpressure protection is favorable in the center of sag. The medium permeability "sweet spot" reservoir is developed with a large number of secondary pores formed by thermal fluids in the slope.