SEQUENCE STRATIGRAPHY OF A FAN-DELTA AND ITS IMPLICATIONS FOR OIL-GAS ACCUMULATION -A CASE OF THE T76 BLOCK ON THE DOWNTHROWN SIDE OF SHENGBEI FAULT IN DONGYING DEPRESSION

Taking the Tuo76 fan-delta of the upper part of the 4^th member of the Shahejie Formation on the downthrown side of the Shengbei fault in the Dongying depression as an example,this paper deals with the characteristics and distribution pattern of parasequnces in a fan-delta depositional system. Based on geological, seismic and well logging data, theTuo76 fan-delta is divided into 4 parasequnces, 18 bed sets and 29 beds. Our data show that the occurrence and boundaries of the parasequences and bed sets change with time. Oil-gas accumulation is related to the distribution of parasequnces and bed sets. The change in porosity and permeability of the reservoir is a function of A/S (Accommodation space/sediment supply) in the parasequence and bed sets consisting of one facies. And reservoir properties and oil-gas saturation show similar pattern of variation.