A DETAILED STUDY OF PALEOGENE FAN DELTA IN BOHAI SEA FOR PREDICTION OF FAVORABLE RESERVOIRS

The study area is located in the overlapping area of the Bozhong sag and Huanghekou sag. The reservoirs of the 3d Member of the Shahejie Formation is a kind of deeply buried and compact fan deltaic sand body distributed in an unclear pattern, by which the development of oil fields is severely restricted. Therefore, to identify the favorable reservoirs and to define the fan delta sand body distribution pattern of the 3rd Member of the Shahejie Formation have become the major concern of the development geologists. The 3rd Member of the Shahejie Formation is the product of the second stage of rifting of the Bohai Bay Basin, and therefore, the study area is a typical fault basin. Sequence stratigraphic study suggests that the 3rd Member was the deposits of transgressive system tract near the basin edge fault. Fan deltas were well developed in the direction towards the lake center. With the rise in lake level, fan deltas retrograded. Taking the retrograded fan-delta outcrops and their characteristics as references to carry out well seismic correlation, using the corresponding relationship between well electrical characteristics and seismic events, conducting seismic time-frequency analysis for division of development stages of fan deltas, and making the statistical distribution of seismic data in valleys, we described the underwater distributary channels of the fan deltas and their trend. Further, according to the relation between sand body thickness and well distance quantitatively to define the position of the pinchout line. Using the above method to describe the distribution of sand bodies and the controlling factors of low permeability reservoir. Upon the basis, prediction of favorable reservoir is carried out as a clue for adjustment of oil production.