WELL-SITE DIAGNOSIS OF THE STRATIGRAPHIC TOP OF AGBADA FORMATION FROM INTEGRATED PHYSICAL AND SEDIMENTOLOGICAL DATA: NW NIGER DELTA

Abstract

Accurate lithostratigraphic correlation is the key to the successful performance of a well-site geologist’s functions. The recognition of the stratigraphic top of the Agbada Formation is a pre-requisite for effective lithostratigraphic correlation in the NW Niger Delta. It is the Agbada Formation that contains the drilling objective sands in this portion of the Niger Delta. The lithostratigraphic interval is determined by diagnosing sedimentary environments, using integrated physical and sedimentological data. The physical data are formation natural radioactivity (expressed as gamma ray values), spontaneous potential and resistivity and penetration rate measurements. The key sedimentological data is the presence of glauconite. The stratigraphic top of the Agbada Formation is fixed at the base of the fluvial continental lithofacies. This is automatically the top of the shallowest marine facies. This approach is easier than using marine fauna method to define the top of the shallowest marine shales. Integrated physical and sedimentological data gives a more credible result because the top of the Agbada Formation is not a sharp boundary. Real time accurate correlation is facilitated if MWD [measurement while drilling] or LWD [logging while drilling] resistivity and gamma ray data are available.