CHEMOSTRATIGRAPHIC ANALYSIS OF ASN-1 WELL, UGHELLI DEPOBELT, NIGER DELTA

Abstract

Chemostratigraphy is a valuable tool in the correlation of sedimentary successions based on sensitive changes in concentration of key major, minor and trace elements. Fifteen ditch cutting samples collected within the depth range of 5660ft - 8550ft from well ASN-1, Greater Ughelli depobelt, Niger Delta were analysed for their litho logic and elemental concentration with the aim to investigate depositional environment, source area composition, provenance and the weathering index of the samples. The lithologic descriptions were interpreted from gamma ray well logs and petrographically and their elemental values were analysed using AAS Spectrophotometer. The Lithosection indicates shale and sand units’ indexes inferring maturity and area of deposition, the depositional environment is a transitional zone (fluvial deltaic terrain). The weathering indexes CIA, CIW and PIA values ranges from 1.06 to 41.8, on average indicates low to moderate weathering in the source area with weathering of some sand fraction. Various calculated values of the weathering indices: Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA), Chemical Index of Weathering (CIW) and scatter plots of formulated ratios of Al/Na vs chemical index of alteration (CIA) were plotted to determine the weathering indexes. This also inferred their recycling processes are insignificant. The clay content is low and feldspars are averagely high implying immaturity.