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Etude stratigraphique, pétrographique et diagénétique des grès d'âge Crétacé-Paléogène de la région ouest du bassin du lac Turkana, Kenya. Conséquences sur leurs caractéristiques réservoir et l'évaluation du potentiel pétrolier du nord-ouest du Kenya.
| Content Provider | Semantic Scholar |
|---|---|
| Author | Thuo, Peter |
| Copyright Year | 2009 |
| Abstract | The northern Turkana region of northwestern Kenya forms the intersection between two important rift systems in Africa, the Cretaceous-Paleogene Central African Rift System (CARS) and the eastern arm of the Paleogene-Present East African Rift System (EARS). The southern Sudanese oil producing basins form part of the Cenomanian-Paleogene rifts and their extension into the Anza rift in northern Kenya makes the area of northern Turkana an important target for oil exploration. Reservoirs are an integral part of a petroleum system, the others being the mature source kitchens, effective migration pathways, competent seals, and trapping mechanisms. Limited past exploration activity in the area leaves the study surface outcrops as the main avenue for understanding the reservoir potential of the fluvial deposits of these rift systems. The outcrops of these potential reservoirs, collectively referred to as “Turkana Grits” in the past are represented, on the western side of Lake Turkana, by the Lapur Sandstone Formation in the north, the Muruanachok Sandstone Formation in the central part of the basin and by the Lariu Sandstones in the south. Equivalent grit outcrops on the eastern side of Lake Turkana are represented by the Mount Porr/Sera Iltomia Sandstone Formation. Radiometric age determination on the basal parts of the Turkana Volcanics have enable the precise dating of the upper parts of the Lapur Sandstone Formation at between 33-37 Ma, while the base of the Formation has been dated as Cenomanian based on the presence of dinosaur bones near the contact with the underlying Precambrian basement. Field observations coupled with subsequent petrographic studies have enable the determination of the diagenetic evolution and the depositional environments for the Lapur Sandstone Formation. The basal and uppermost parts of the formation are interpreted as distal alluvial fan deposits while the middle part is composed of stacked braid channel deposits. The main cement material at the base of the formation is calcite while at the middle of the formation, hematite becomes the dominant cement and at the topmost section, kaolin cement dominates. This distribution of cements is consistent with the palaeoclimatic and palaeogeographic environments that prevailed during the deposition of the formation. During the deposition of the basal parts of the Lapur Sandstone Formation in the Cenomanian, the prevailing climatic conditions were mainly semi arid, which evolved to a predominantly humid conditions during the deposition of the upper part of the formation during Maastrichtian to Eocene/Oligocene. The lack of biostratigraphic data from the LSF however makes it difficult to precisely establish the chronology of the deposition of the formation. The diagenetic evolution of the sandstones has been favourable to the retention of adequate primary intergranular porosity and the creation of secondary intragranular dissolution porosity, mainly through feldspar dissolution and thus preserving the reservoir potential of the Lapur Sandstone Formation. The reservoir characteristics such as the porosity and cementation style of the Lapur Formation are comparable to those of the fluvial sandstone reservoirs of the southern Sudan oil fields and this should positively contribute to the overall petroleum potential of the northern Turkana region. Though the northern Turkana area has remained largely unexplored, it is hoped that the demonstration of the presence of reasonably good reservoir quality sandstones in the Lapur Sandstone Formation which are comparable and possible equivalents of the reservoirs in southern Sudan, will serve to encourage further interest in exploration for oil and gas in the Turkana area. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://tel.archives-ouvertes.fr/tel-00534181/document |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
