Abstract Geochemical data from drill cuttings of a 3,392 m deep well drilled on the shores of Lake Albert-Uganda, East Africa were used to investigate a longterm paleoenvironmental history of the Lake Albert rift basin-Uganda. The Ngassa-2 well was drilled through loose and coarse-grained sands in the upper section, massive mudstone deposits interbedded with siltstones in the middle sedimentary section, and a thin conglomerate at the base. Statistical treatment of data by using Principal Component Analysis shows that Fe, Ti and Rb (silicate mineral elements) account for much of the variability in the data, with about 40% of the total variance compared to 20% for total organic carbon (TOC) and Si (organic and quartz). Results from XRF data and TOC are indicative of warm and wet conditions around the late Miocene, later developing into cooler and dryer climatic conditions around the late Pliocene. Anoxic lacustrine conditions in the early Pliocene are documented by a dramatic rise in TOC and coinciding trends with iron for the depth interval 3,000–3,250 m. Lithological observations, seismic data attributes, and down-hole gamma ray logs provide evidence of a basin that transitioned from fluvial to mixed fluvial-lacustrine and subsequently dominantly lacustrine environment before shifting back to fluvial and shallow lacustrine system in the late Pleistocene and Holocene.

Abstract Modern lake basins set within active continental rifts provide useful analogs for exploration efforts in ancient extensional basins that are known to be rich in hydrocarbons. Lake Albert is one of the Great Lakes of Africa and is located at the northern end of the western branch of the East African rift system. This large, but comparatively shallow, eutrophic, and probably geologically ephemeral lake basin serves as an end-member example of the modern tropical lake systems that occupy this extensional province. Seismic reflection and gravity data sets indicate that the basin contains a maximum of 5 km (3.1 mi) of synrift, dominantly lacustrine sedimentary fill, in two subbasins separated by a midbasin high. In contrast to other large rift basins in the western branch of the rift valley, the Lake Albert Rift is not a highly asymmetrical half-graben basin, but instead has subsided nearly symmetrically and continuously in the late Cenozoic along two extensive boundary fault systems on either side of the basin. Seismic sequences from across the basin were correlated to borehole stratigraphy from a deep well drilled on the Ugandan margin. These observations suggest that the basin has experienced a long-term change from a continuously open lacustrine, possibly deep lake system in the Miocene or early Pliocene, to an alternating shallow lacustrine and fluvial system in the mid and late Pleistocene. This history of basin evolution has led to the development of a rich hydrocarbon system.

Abstract Beach Energy has been the sole interest holder and operator of the 7,200 km 2 Lake Tanganyika South block since 2010. The block is located within the western arm of the East African Rift System. The prospectivity of the lake sequence was enhanced by large oil discoveries in the similar geological environment of Lake Albert in Uganda and in the eastern part of the rift in Kenya. The lack of wells drilled in the lake to date make predicting sedimentary sections difficult. In 2010 Beach Energy commissioned CGG to fly a FALCON Airborne Gravity Gradiometer (AGG) and a high-resolution airborne magnetic (HRAM) survey over the Lake Tanganyika South block in order to map the basin structural framework and the depth to magnetic basement. The FALCON AGG survey facilitated the imaging of the architecture of the rift zone and the interpreted sediment thickness provided an indication of prospective petroleum target areas. This information was used to plan a subsequent 2D marine seismic survey, which was shot in 2012. The preliminary results from the 2D marine seismic survey has confirmed a rifting structure similar to that encountered further north at Lake Albert in Uganda. A number of targets over tilted fault blocks, low-side rollovers and mounded features, have been identified for follow-up from the seismic sections. Natural oil seeps evident on the surface of Lake Tanganyika, which have been sampled and analyzed by Beach Energy, also indicate that a working petroleum system is present in the sedimentary section of the rift beneath the lake.