Geosciences and Geophysics

Biography

Biography: Prince Suka Momta

Abstract

Depositional and structural elements confer significant impact on hydrocarbon flow behaviour. These geologic elements were evaluated to understand possible causes of rapid production decline. The oilfield where this study is carried out is located within the shallow offshore area of the Niger Delta, Nigeria. The field experiences high decline in oil rate and sharp increase in water-cut two years after commencement of production. This research provides a predictive insight into coning behaviour and also serves as a blueprint for post-breakthrough performance analysis. Key objectives considered include: To identify subsurface structure capable of hydrocarbon entrapment; determine depositional characteristics of facies/depositional environment of key reservoirs; and to determine possible causes of rapid production decline in the field. The methods adopted include; well log correlation and sequence stratigraphic technique to establish the continuity of key horizons; electrofacies/seismic characterization of the gross depositional setting of key reservoirs and 3D seismic volume attribute analysis for stratigraphic and structural characterization. The 3D seismic volume attribute procedure for generating attributes follows a defined Petrel workflow that uses established algorithms to output anticipated results. The results showed that eight continuous sand horizons occurred within six depositional sequences of 7000 ft thick paralic Agbada Formation. A depth structure map generated over the N5.2 sand revealed a structural saddle; an elongate four-way dip closure with two structural culminations. Further analysis using 3D seismic attributes on time slice 0 to 4000 milliseconds showed four facies distribution patterns. They include: Dispersed facies; linear/parallel facies; isolated pattern, and meandering configuration. Depositional attributes inferred include: Beach-barrier-shoreface deposits; deep sea channel, chaotic turbidite sands, and stratigraphic pinchouts. Areas with high seismic root-mean-square amplitude represent sand-prone facies; low amplitude areas may be interpreted as pelagic or hemipelagic sedimentation, or water-bearing facies. The N5.2 producing sand has excellent reservoir quality and natural fractures. Inappropriate choke management, water injection, excellent reservoir quality and vertical fractures are factors that aggravated significant fluid flow and early water breakthrough, resulting in rapid production decline. The 3D seismic horizon slices is suitable for amplitude display, gross rock bodies identification, selection of possible drilling locations and for strati-structural modeling.