Inner architectural characteristics of wave-dominated shoreface deposits and their geological implications: A case study of Devonian ‘Donghe sandstones’ in Tarim Basin, China

Wave-dominated shoreface sands are important marine clastic reservoirs, the inner spatial superposition of which causes the complex oil-water relationship in this kind of reservoir, restricting further exploitation; they develops widely in Devonian ‘Donghe sandstones’ of the Tarim Basin in China. Controlled by the genetic mode, static drilling and dynamic development data were applied to analyze these sands—focusing on three orders of architectural units namely the composite sand-bodies (5th order), single sand-body (4th order), and internal component units (3rd order). Furthermore, the identification marks and spatial distribution features of inner architectural units were investigated, and the corresponding architectural model established. Based on methods such as model fitting and control, interface identification, and analysis of well data, the single sand-body and its internal component units were identified, and the spatial superposition relationship was analyzed. In retrograding composite sand-bodies, three types of distribution patterns for the single sand-body including thick-layer refill, step migration, and continuous on-lap are present; contrarily, in prograding composite sand-bodies, the superimposed styles of the single sand-body are primarily thick-layer cumulation, step migration, and continuous overlay. The single sand-body is divided into one or more internal component units by the architectural interface of 3rd order, presenting a low-angle landward or seaward migration style. The oil-water distribution in wave-dominated shoreface reservoirs is substantially influenced by sand architecture, and architectural interfaces of different orders separate the sedimentary sand-bodies into relatively independent fluid systems, leading to differences in oil-gas production possibility among the independent layers. The wave-dominated shoreface architectural model can provide reasonable explanations for contentious factors such as the oblique oil-water interface, and production contradictions such as the mismatch between water injection and oil recovery, and resolve disagreements on well-deployment through prediction of the distribution of remaining oil, all of which have great significance for oil and gas exploration and production.