Hydrocarbon exploration in the Berkine Basin, Grand Erg Oriental, Algeria

Hydrocarbon exploration during the 1990s in the Berkine Basin of eastern Algeria resulted in discovery of more than two billion barrels (bbl) of recoverable oil. Although exploration focused on Triassic quartz sandstones, flow rates of more than 5000 bbl condensate per day CBCPD) and 50 million cubic feet of gas per day (MMCFGD) have been recorded from Lower Devonian through Carboniferous reservoirs. Uppermost Devonian and Carboniferous hydrocarbon-charged reservoirs first were discovered in the basin during the early 1990s phase of exploration. Understanding the evolution of Anadarko's exploration model is instructive in defining remaining hydrocarbon potential of the Berkine Basin. The exploration model evolved from a single Silurian hydrocarbon source filling a single primary Lower Devonian reservoir to a dual Lower Silurian and Upper Devonian hydrocarbon source with a complex maturation and trap-filling history of multiple reservoirs. Migration-path modeling shifted the primary area of exploration focus from western updip margins, where successively older Paleozoic strata are truncated by the Hercynian unconformity, to a more downdip position relative to the present day structural axis. This shift takes advantage of a more complete Paleozoic section and use of regional fault systems as sites of vertical migration and entrapment. Employment of geophysical data as the primary tool for definition of prospects evolved from reprocessing of existing 2-D seismic data to acquisition of new 120-fold and 240-fold 2-D seismic grids. Three-D seismic surveying is now employed as the primary tool for field development. Existence of high-quality source rocks and reservoirs, a Liassic evaporite "superseal," favorable tectonic history with respect to hydrocarbon generation and expulsion, and high-quality hydrocarbon migration carrier beds lead us to conclude that the primary exploration risk for additional reserves involves seismic imaging of reservoirs and traps. Comparison of generated hydrocarbons to discovered volumes of hydrocarbons suggests that the Berkine Basin is immature with respect to hydrocarbon exploration, and significant undiscovered fields are feasible. Subcrop traps in Paleozoic reservoirs below the Hercynian unconformity should exist. Lochkovian, Strunian, Visean, and Carnian siliciclastic reservoirs will continue to be important exploration reservoir objectives.