Sedimentation and depositional environments of the Barremian-Cenomanian Debre Libanose Sandstone, Blue Nile (Abay) Basin, Ethiopia

Abstract

Exploration of oil and gas deposits in the Blue Nile Basin targeted the Debre Libanose Sandstone as a reservoir objective. The unit was deposited in broad alluvial plains, and shows some elements of the Platte type braided river sedimentation in the lower and middle succession. The braided river sedimentation is dominated by single storey and multistorey amalgamated sandstone bodies, and is characterized by high- and low-flow regime sedimentation. The upper part of the unit is characterized by well-developed cyclicity, fining-upward trend, lateral accretion surfaces, flood-plain sediments, point bar deposits, and calcrete are consistent with of meandering river sedimentation. The siltstones, mudstones, and shales were developed from suspension-dominated waning flood water. The presence of black mudstones and black shales in the uppermost part of the unit possibly indicate lacustrine environments. The unit has a complex diagenetic history and is cemented dominantly by silica, calcite, kaolinite, and hematite. The maximum porosity and permeability reaches up to 22.2% and 809 mD, respectively. The fine- to medium-grained sandstones are potential oil and gas reservoirs. The low-permeability siltstones and mudstones are possible gas reservoirs.