Geomorphology control on the development of reservoir depositional systems, Devonian Donghetang Formation in the Tabei Uplift of the Tarim Basin, China

The Devonian Donghetang Formation is one of the important extensive marine sandstone units for oil/gas exploration on Tabei Uplift of the Tarim Basin, particularly in the Hade and Halahatang oilfields. However, not all of this sandstone is good quality reservoir, and so the sedimentary facies are critical to prediction of reservoir in the area. Based on an analysis of logs, core, outcrop and seismic data, a new hypothesis is proposed for the Donghetang Formation as a 2nd or 3rd order stratigraphic sequence (SQ_Ddh), formed between unconformities Tg22 (top) and Tg3 (bottom), consisting of local transgressive (braided delta deposits) and extensive high-stand (foreshore and shoreface deposits) system tracts. Through networked seismic data, integrated with erosion and decompaction correction, the palaeogeomorphology during development of SQ_Ddh has been reconstructed and several geomorphological units can be distinguished. The sedimentary facies and distribution of SQ_Ddh were related closely to the depositional geomorphology. Between the margin of the northern paleo-uplift zone and the northwestern and northeastern depressions there developed braided deltas during the period of the early TST, and wave-dominated shorelines during the HST period when extensive shorefaces developed across the central low-uplift zone. Beyond the southeastern shoreline, there developed offshore and marine-shelf deposits. The foreshore and delta-front mouth bar sandstones constitute the most favorable reservoir, surrounding the paleo-uplift and the marginal uplift zones.