Identification of favorable underwater reservoirs in a conglomerate fan delta

Abstract

Conglomerates are the main components of fan delta-front and usually the important reservoirs in an oilfield, but the cyclicities of the conglomerate deposition readily lead to stratigraphic multiplicities. Therefore, the accurate prediction of the distribution patterns and scales of the conglomerate fan delta has great significances for the oil and gas exploration and production. The conglomerate fan delta of the Triassic Baikouquan Formation (TBF) in the west slope of the Mahu Sag, Junggar Basin is a research hotspot because billions of petroleum resources have been discovered in this Formation. However, the stratigraphic correlation of the conglomerate of the TBF is still unclear for the particularly heterogeneous of the conglomerate strata, which caused the paleogeomorphology and favorable underwater reservoirs of the TBF are yet to be determined. In this study, the integrated methods of seismic interpretation, well logging, well curves and heavy minerals are applied to study the paleocurrent directions, ancient trench distribution and shoreline positions of the lake. The results show: (1) There are two ancient trenches developed in the west slope of the Mahu Sag. (2) The shoreline positions are generally distributed along the shape of ancient trenches. And (3) the favorable underwater reservoirs in a conglomerate fan delta are distributed in the front of the shoreline as a progradation deposits of the fan delta. The lake level elevation and paleotopography jointly controlled the lithology and reservoir physical properties, and the underwater facies belt in the ancient trench are the favorable exploration zones.