Conglomerate categories in coarse-grained deltas and their controls on hydrocarbon reservoir distribution: a case study of the Triassic Baikouquan Formation, Mahu Depression, NW China

There is great potential for hydrocarbon exploration in the Triassic Baikouquan Formation, in the Mahu Depression of the Junggar Basin, NW China. Controversy remains around the conglomerate categories in coarse-grained deltas, which has inhibited further exploration in this area. Based on a dataset of cores, test data, well logs and seismic, this study attempts to recognize different genetic types of conglomerates formed within coarse-grained deltas. The Baikouquan Formation conglomerate has been divided into nine facies on the basis of textures, grain size and sedimentary structures. From the associations of these nine facies, three conglomerate categories have been recognized: debris-flow conglomerate (DFC); hyperconcentrated-flow conglomerate (HCFC); and traction-flow conglomerate (TFC). These have diagnostic characteristics that are expressed in core, well logs, seismic character, grain-size distribution curves and maximum particle size/bed thickness analysis (MPS/BTh). A depositional model has been built after analysis of the sediment transport mechanisms to facilitate exploration of the Baikouquan Formation, in the Mahu Depression. The evaluation of reservoir characteristics, physical properties and pore-throat structures of these conglomerate categories has identified the HCFC reservoirs as the primary potential targets for exploration in the study area.