Different depositional models of wave-dominated shoreface deposits: An integrated process-oriented analysis (“Donghe sandstones” in Tarim Basin, China)

Wave-dominated shoreface sands are important marine clastic reservoirs. Their depositional characteristics and evolutionary history becomes one of the hot spots for oil and gas exploration and development. Limited by the traditional conception in typical depositional models, the geological contradictions on the late reservoir development of such type become increasingly prominent. The recognition of the different depositional models of wave-dominated shoreface deposits, therefore, becomes an alternative to solve the production problems in the developmental phase. Taking the “Donghe sandstones” of Tarim Basin as an example, the depositional characteristics and facies associations of wave-dominated shoreface deposits in different regions were analyzed on the basis of seismic, core, and logging data. Three types of different depositional models were proposed, namely the wave-dominated shoreface deposits of transgressive type with reworked delta background, wave-dominated shoreface deposits of transgressive–regressive type with shoal background, and wave-dominated shoreface deposits of transgressive type with gentle–slope background. On this basis, the differences of main controlling factors such as source supply and relative sea level change, hydrodynamic conditions, paleogeomorphology, their influences on wave-dominated shoreface deposits, and the evolution and distribution of shoreface sands under unique sedimentary mechanisms were further discussed. Limited by different depositional models, the “Donghe sandstones” showed an overall vertical retrogradational sedimentary sequence, and with similar distribution on the whole, it had distinct features in detail. In Donghe 1 area, it appeared to be with a morphological characteristic of both reworked original delta and latter shoreface deposits; in Hudson area, a sand-bodies superimposition and migration under model framework; and in Tazhong 4 area, a typical distribution of bar and beach sand-bodies. The different depositional models of wave-dominated shoreface deposits expand the explanation on various sub-environments from the point of formation mechanism, and guide the reservoir analysis and further oil and gas exploitation for such reservoirs.