The Role of Neo-Tectonics in Oil Migration, Lake Turkana Region, Kenya

Abstract

ABSTRACT Numerous oil seeps have been documented in the Turkana Basin, western Kenya. However, no commercial oil has been found here to date. Recently discovered substantial oil fields in the nearby Lokichar Basin indicate that oil migration can be complex in these rift basins and may pose an exploration risk. We present a new fault and lineament map of the Turkana-Lokichar Basins, integrated with present-day stress data, oil seeps and known prospects. Digital terrain data, satellite images, geological maps, seep and gravity data were integrated into a GIS-database, to superimpose the data and to test it for spatial correlations. Digital terrain data, satellite images, gravity and structural maps were used to conduct detailed mapping of the fault and lineament network. The seep and prospect maps are based on the integration of different public data sources. Four main fault sets are recognized in the basin (~N-S, W-E, NW-SE and SW-NE). Careful analysis of topographic data along both shores of Lake Turkana reveals numerous fault scarps, indicative of recent tectonic activity (particularly the N-S and NW-SE set). The area is presently under NW-SE oriented extension, implying that most of the rift-parallel N-S faults are under oblique dextral transtension. The majority of the documented oil seeps and slicks are found to be associated with rift-parallel faults but also occasionally with the W-E trending set. Recently published neo-tectonic and isostatic uplift data indicate that the highest level of recent fault activity is presently found close to the rift axis and dominantly on the rift-parallel fault sets. We conclude that ~N-S and W-E oriented faults are the most conductive pathways for hydrocarbons in this region under the present-day stress field (and likely throughout the Mio-Pliocene). We further observe that several prospects of the NW-SE trend have seepages associated with them, which could be indicative of breached traps, especially close to the rift axis where faults are most active. Our assessment should help to better understand migration pathways and exploration risks in the Turkana Basin. We encourage explorers to carefully map fault networks, investigate active fault scarps, age-date them where possible, test them for spatial correlation with oil seeps and evaluate them within the context of the present-day stress field. In consequence these workflows will help mitigate exploration risks in the Turkana-Lokichar Basins and similar tectonic settings.