Many important oil-and-gas reservoirs occur in clastics of the Early to Middle Jurassic Cuyo Group along the crest of the Huincul Arch. The initial discovery of oil in the Neuquen Basin was made by YPF in 1918 at Campamento Uno field within an octagonal-shaped lease block designated Octogono Fiscal. Campamento Uno field produces from shoreline sandstones of the Lajas Formation with minor production from basal sandstones of the overlying Challaco Formation. Oil was subsequently discovered in the western part of the Octogono at Campamento Dos field in numerous, lenticular, fluvial sandstones of the Challaco. In recent years, considerable amounts of flee gas have been found in Challaco sandstones in the northern part of the Octogono.

A stratigraphic model was developed to explain the origin, distribution and dimensions of Challaco reservoir sandstones in and adjacent to a pilot water-flood project in Campamento Dos field. Challaco sandstones are interpreted to have been deposited in coarse-grained, high-sinuosity fluvial systems. The rate of creation of accommodation space was relatively high compared to the sediment supply, resulting in frequent avulsion of the fluvial systems and a moderate “net-to-gross” ratio of reservoir to non-reservoir lithologies. Individual point bar deposits, averaging about 0.25 km² in area and about 10 m in thickness, were mapped along the trends of numerous fluvial systems. The sandstone bodies are probably not in communication one with another. A few of the sandstones represent mature meanderbelts with coalesced point bars. We believe the fluvial model developed for the Octogono is broadly applicable to Challaco reservoirs elsewhere on the Huincul Arch.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah