Subsurface deltaic sand bodies have produced considerable quantities of hydrocarbon. Recognition of these features and understanding of their geometry and distribution are essential for efficient exploitation. In low-tidal, low-wave-energy deltas that debouch large volumes of sediment, three major types of sand bodies are formed that display reservoir characteristics: crevasse splay or bay fills, distributary mouth bars, and downslope displaced slump deposits. Each of these sand bodies displays characteristic, recognizable vertical sequences and lateral relationships with adjacent deposits. The displaced slump deposits are highly productive in Tertiary sequences. Deltas prograding into regions characterized by high tidal range display three major sand facies: offshore tidal ridges, distributary channel fill, and tidal channel sands. The offshore tidal ridges are exceptionally large, clean sand accumulations and have distinctive isopach characteristics. Channel fill and tidal channels display less lateral continuity but can accumulate to thicknesses on the order of 18-21 m (60-70 feet) and normally display sharp erosional basal contacts. Extreme wave energy along some delta coasts results in the formation of extensive beach-dune complexes that often form laterally continuous blanket sand facies. These sand bodies are normally massive in nature and show little variation in grain size. High quartz content is commonly associated with these deposits. In basins where high tides and high wave energy levels exist, thin (6-9m, 20-30 ft) but laterally persistent tidal flat deposits often form the major sand body type within the delta sequence. Scour and sandy infilling of distributary channels through the tidal flat deposits results in highly complex geometry. In these instances, porosity and permeability relationships often control hydrocarbon accumulation.

Each of the sand bodies will be described in terms of their environmental setting, and processes and descriptions of their internal bedding will be illustrated. Schematic sand body isopachs and log characteristics and variations will be illustrated.