Sedimentary model from delta front to deep water area and its significance: a case study of the first sand group of Member 2 of Sangonghe Formation in the Well Pen-1 West sag, Junggar Basin

To make clear the sedimentary characteristics, sedimentary models, lithologic traps, and exploration fields of lithologic reservoirs from delta front to deep water area of the first sand group of Member 2 of Sangonghe Formation in the Well Pen-1 West sag of Junggar Basin, the palaeogeomorphology was reconstructed by stratum thickness method; the sedimentary microfacies, reservoir properties and hydrocarbon-bearing properties were analyzed according to core observations, heavy mineral analyses, reservoir characterizations and drilling data. The research proposes that the sand bodies of sandy debris flow developed in the deep water area are favorable for lithologic traps. The study area has been divided into three zones by two-stage circular slope breaks, i.e., the inner front delta, the outer front delta and the deep water zone. The underwater distributary channel microfacies of the inner front delta has high reservoir quality and good oil-bearing properties; the channel terminal deposits and sheet sand microfacies of the outer front delta are dominated by tight reservoirs, showing poor oil-bearing properties; in terms of the reservoir quality and oil-bearing properties of the sand bodies of sandy debris flow, the deep water zone is similar with the inner front delta, presenting good top and bottom conditions; further, shielded by tight reservoirs of the outer front delta in the lateral direction, it is conducive to the formation of lithologic traps, and thus is the most favorable oil and gas exploration area in the next step. © 2019, Editorial Office of ACTA PETROLEI SINICA. All right reserved.