Source rock potential of two Loperot shales of Lodwar South sub-basin, Tertiary Rift Valley, Kenya

摘要

Lodwar South sub-basin is within the Kenyan component of the Tertiary Rift Valley. It is west of Lake Turkana. The Tertiary Rift set in with Oligocene-Early Miocene volcanism apparently contemporaneous with the Tertiary rifting associated with the older Cretaceous to Tertiary Anza Basin that also straddles the Lodwar South sub-basin. The Tertiary Rift appears to have developed in three main phases; Oligocene to Early Miocene, Middle Miocene N-S trend and Late Miocene to Pliocene NNE-SSW and N-W trends. The Lodwar South sub-basin is an Oligocene-Early Miocene phase. The Lodwar south sub-basin has two Loperot shales source rock units. One is a barely mature shale while the other is highly mature. The barely mature Loperot Shale exhibits a thickness of 52m, has excellent source richness and excellent source potential and comprises a Type I oil prone kerogen deposited in a lacustrine environment. The highly mature Loperot Shale has a thickness of 165m has good source richness and fair source potential. Its kerogen type is indeterminate. Oil encountered in Loperot # 1 well drilled in this Lodwar south sub-basin has a gravity of 16°API, is a paraffinic oil of low maturity and is lacustrine in origin. The oil correlates well with the barely mature shale. The correlation of the oil and the shale is based on composition, waxiness, biodegradation, maturity and environment of deposition, GC and GCMS clues. The barely mature Loperot Shale wireline log character shows it to have Gamma Ray (GR) log (GAPI) values ranging from 60 to 90 with a sampled average of 52 of these values giving an average value of 75. Total Organic Carbon (TOC) values for this Loperot Shale range from 4.4 to 17.5% with average of 9.57%.