Forming Conditions, Types and Characteristics of Lithological Reservoirs in Melut Basin: Implications for Hydrocarbon Exploration in Mature Rift Basins of Africa

Abstract

African rift basins develop rich hydrocarbon resources, and after decades of exploration, the mature basins are facing challenges of discovering new plays and new prospects. Against this background, the latest research and exploration progress on lithological reservoirs in Melut Basin will be presented, which will give an implication for African mature basins. Melut Basin is located in central Africa with an area of 33,000 km2, and most structural prospects have been drilled over the past years, so it is particularly urgent to carry out lithological reservoir exploration for new discoveries. With the wire-logging, mud-logging and coring data from near 200 wells and 4,000 km2 3D data, the source rock evaluation, sedimentary facies and fault feature were researched, which indicated that Melut Basin has the lithological oil reservoir forming conditions. The research guided the exploration deployment and breakthrough of lithological oil reservoirs, and three types of lithological reservoirs were discovered: beach-bar reservoir, fan delta reservoir and structural-lithological reservoir. The first two types of lithological reservoirs developed in Galhak Formation of Cretaceous with good oil source condition as in-source lithological reservoirs, and the structural-lithological reservoirs developed in the upper member of Yabus Formation of Paleogene as the above-source lithological reservoirs. Due to the deeper burial depth, the reservoir quality is the main risk for in-source lithological traps, so the prediction and evaluation of reservoir determines the success rate. In contrast, the above-source lithological traps usually have better reservoir quality with shallow burial depth, and the oil source is the main risk due to being far away from Cretaceous oil kitchen, so it is very important to study vertical migration pathway and hydrocarbon charging. The practices showed that the exploration deployment of above-source lithological trap should be conducted in mature areas with deep understandings on hydrocarbon accumulation rules, and the structural-lithological traps controlled by oil-source faults are more favorable than sandstone lens traps. The researches and discoveries in Melut Basin indicated that the lithological oil reservoir exploration may promote step-out exploration and upgrade reserves of highly-explored area. So, it is a good attempt to carry out lithological reservoir research and exploration for new discoveries in other African mature rift basins.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018