Reservoir Characteristics In Gypsum-salt Strata Of Es4 In Northern Steep Slope Of Dongying Depression

This paper primarily studied the gypsum-salt strata in Northern Steep Slope of Dongying Depression. Combined with results of previous studies, core, logging, seismic, geochemical and other information are used multipurposely, studied the distribution characteristics and mechanism of gypsum-salt rocks, the reservoir micro-properties of gypsum-salt strata, the relationship between reservoir properties and the distributon of gypsum-salt rocks has been summed up.There are three sets of gypsum-salt strata in Northern Steep Slope of Dongying Depression, as the deposition scope and subsidence center of lake varies with time changes, the distribution in vertical and plane of gypsum-salt strata differs, which is controled by palaeotopography, fault, climate cycle and palaeocurrent.This thesis concluded the origin of the gypsum-salt strata with sedimentary structure and geochemistry analysis. The halite of gypsum-salt strata mainly came from deep hot brine, and the gypsum mainy came from the eroding product of terrestrial ancient gypsum layers. When the climate was dry in the early paleogene, the transpiration was strong, the lake water oscillation led to the formation of rhythmic layers with clastic rocks and gypsum-salt rocks. Later, when the climate was a litter humid, the layering effect of salinity in deep water resulted in deposition of gypsum-salt strata.Within gypsum-salt strata of study area, the main types of fan are nearshore subaqueous fan and turbidite fan. The horizontal connectivity of sand bodies underneath gypsum-salt strata are better, longitudinal distribution is discontinuous. Sand-body in gypsum-salt strata are lenticular, thin and small.The characters of diagenesis is particular because of the strong influences of gypsum-salt strata. Some area is less compacted, part of primary pore is reserved, the type, content and degree of carbonate cement are different, acid-base alternating fluid medium controlled by evolution of gypsolith and organic matter promote fledspar and quartz overgrowth. Dissolution is the main reason for the formation of secondary porosity. The diagenetic stage of gypsum-salt strata reservoir is early and interim. The reservoir type has pore, fracture and pore-fracture, include primary pore, secondary emposieu, compressivefracture and diagenetic fracture.Deep reservoirs in the study area developed with overpressure, the major reason of overpressure is as a result of seal and keeping pressure from gypsum-salt strata. Abnormal high pressure is favor to maintain a high porosity and permeability, which improve reservoir property. Different distance from gypsum-salt strata, degree of gypsum-salt strata control on reservoir property vary greatly, the transformation of deep reservoir is selective.