Sedimentary features of gentle-slope tide-influenced braided delta: A case study of Carboniferous Kalashayi Formation in Tahe Oilfield

The Carboniferous Kalashayi Formation in Tahe Oilfield is an important area of clastic rock oil and gas exploration. However, its depositional environment and facies types have been controversial, restricting its process in oil and gas exploration. The depositional environment and distribution of sand bodies of the Carboniferous Kalashayi Formation in Tahe Oilfield in this paper are guided by sequence stratigraphy and sedimentology based on well data, logging data, and cores from this formation. The results show that the study area is characterized by both braided river delta and tidal flat sedimentary. And there are 7 types of deposits, such as distributary channel, underwater distributary channel, estuary bar, tidal channel, sand flat, sand and mud mixed flat, and mud flat, that can be identified. In the aspect of plane, the northern part is dominated by braided river delta facies, and the southern part is dominated by tidal deposition. And the central part has a large number of underwater distributary channels transformed by tides. Rivers mainly control the regression period, and the scale of underwater distributary channels is large. The tidal action mainly controls the transgression period, and the scale of the tidal channel is larger. On this basis, the vertical facies sequence and fluvial-tidal sedimentary model of the braided river delta under the gentle slope of the Carboniferous Kalashayi Formation in the Tahe Oilfield are established and can provide a reference for the next step of the exploration in this interval.