2020, 22(1):129-146.
DOI: 10.7605/gdlxb.2020.01.008
Abstract:
The discovery of a billion-ton conglomerate oil reservoir at central Mahu sag,northwestern margin of Junggar Basin,has driven the research progresses on sedimentary geology and reservoir characterization. This paper reviewed the advances of sedimentology and reservoirs research in the Mahu sag and northwest margin of the Junggar Basin and summarized the following significant advances: (1)new methods in petrological and lithofacies analysis have been proposed for conglomerate reservoirs description; (2)a series of techniques in logging and seismic have been adapted for geophysical reservoir description; (3)obtain new knowledge of the provenance,sedimentary environment,facies and depositional system and models. The retrogradation model of large-scale shallow water fan delta on a gentle slope has been established,which led to the breakthroughs in oil and gas exploration; (4)diagenesis theory guided to find new reservoirs in deeper strata. Depositional system in Mahu sag is consistent since Permian to Neogene. Depositional systems include volcanic and volcano-clastic system,fine-grained and evaporite system,coarse-grained alluvial fan,fan delta,braided river delta and others. Climate variation,structure configuration,and lake level fluctuation controlled the formation and evolution of the depositional system. This research provides strong theoretical support for the discovery of Mahu conglomerate oil field. In turn,oil and gas exploration promotes the continuous development of sedimentology and reservoir research. There are at least three petroleum systems in Mahu sag,which were associated with different depositional systems and reservoirs. However,the studies for different petroleum systems,different kinds of reservoirs,and explorational discoveries are not in the same stage. The authors suggested to pay more attention to the older and deeper strata and to use more new theory and technology in sedimentological and reservoir research of this area. The presented theories and technologies need to be further tested in future exploration activity.
