Re-evaluation of the stratigraphy, structural, and depositional environment of Kolmani field, Gongola sub-basin, northeast Nigeria using outcrop data, ditch cutting data, and well log data for enhanced hydrocarbon exploration

Abstract

The stratigraphy, structural, and depositional environment of the Kolmani field have remained elusive despite ongoing oil and gas exploration in the basin. This study sought to provide a comprehensive re-evaluation of the stratigraphy, structural features, and depositional environment of Kolmani field, Gongola Sub-basin, Northeast Nigeria based on outcrop and ditch cuttings for enhanced hydrocarbon exploration. The outcrop studies revealed a diverse range of clastic and carbonate lithologies, representing various depositional facies. The facies associations of the Bima, Yolde, Pindiga, Gombe, and Kerri-Kerri Formations indicate deposition in environments transitioning from continental to marine settings. These formations predominantly consist of quartz arenites, which, despite their textural immaturity, suggest deposition in stable tectonic settings, such as continental shelves. Five different formations were mapped from the studied outcrops. The Bima Formation is characterized by fining upward facies associated with an erosional base and thin clay that suggests a braided river depositional environment. Overlying the Bima Formation is the Yolde Formation characterized by fining and coarsening upwards lithofacies with shallow marine ichnofacies that indicates estuary to shoreface environments. The Kanawa Member is characterized by interbedded packstone limestone and shale indicating a shallow marine environment with fluctuating depositional conditions. The Sandy Members (Dumbulwa and Deban Fulani Members) show trends of fining and coarsening upward with both wave and tide signatures that suggest a wave-to-tide dominated estuary. The Fika Shale with homogeneous calcareous shale indicates lagoonal or tidal flat conditions. The Gombe Formation shows a dominance of coarsening upward and associated facies association that suggest deposition in deltaic environments. The Kerri-Kerri Formation is characterized by fining upward and the associated facies suggest a braided river. Formation gas was found in the Bima, Yolde, and Gombe formations at depths of 8563 feet (0.35%), 5254 feet (0.31%), and 3306 feet (0.23%), respectively. Across the formations, the sandstones’ porosity and permeability might have been influenced due to the sandstone’s composition, more especially, the feldspars that easily modify porosity during diagenesis stages.