Abstract
Delineation of bitumen saturated zones in Agbabu, southwestern Nigeria was carried out using an integrated geophysical methods involving the groundmagnetic and electrical resistivity methods. A total of four magnetic traverses were established in the East-west direction, each covering a total length of 130m. The groundmagnetic results revealed geologic structures favourable to accumulation of bitumen and its occurrence at near-surface. It was also revealed that the bituminous zone trend in the East- West direction of the study area. Two techniques was adopted under electrical resistivity method, the horizontal electrica profiling (HEP) and the vertical electrical sounding (VES). The HEP was used to measure the subsurface electrical variations and lateral extent of bitumen over the study area. Four traverses were established in the North-South direction for HEP and were used to generate electrical profiling curves, which showed low resistivity signatures over the study area. The low resistivity signatures were attributed to the intrusion of saline water to the bituminous zones. Two vertical electrical soundings (VES) were carried out, VES1 and VES2 which were carried out on traverse 1 and traverse 3 had five and six geologic layers respectively. The bitumen saturated zones were found to be within layers three and four and underlained by saline water. The average depth to the bitumen saturated zones was found to be between 3.1m and 23.3m downwards. The near-surface occurrence of natural bitumen and the intrusion of saline water might hinder the feasibility of pure and quality water from the shallow hand-dug wells within the study area.
Highlights
Bitumen is described as a viscous liquid, or a solid, consisting essentially of hydrocarbons and their derivatives, which is soluble in trichloroethylene and is substantially nonvolatile and softens gradually when heated
Since the purpose of using magnetic method for this research work is to look for areas of abnormally low magnetic responses or signatures and suspect the area as bituminous zone, so from findings so far, presence of bitumen even at shallow depth is suspected
The method revealed some geologic features such as fractures, contacts and others that could be described as weak zones within the study area which has probably assisted the migration of the bitumen to the near-surface by serving as pathway
Summary
Bitumen is described as a viscous liquid, or a solid, consisting essentially of hydrocarbons and their derivatives, which is soluble in trichloroethylene and is substantially nonvolatile and softens gradually when heated. It is black or brown in colour and possesses waterproofing and adhesive properties. Bitumen is referred to as heavy oil and it constitutes an important energy resource. It is highly viscous oil with API < 20°C and it is regarded as the biogenic product of crude oil found in the sedimentary environment [2]
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