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International Journal of Research and Innovation in Applied Science (IJRIAS) | Volume VII, Issue VI, June 2022 | ISSN 2454–6194

Application of Sequence Stratigraphy to Characterization of Thin Reservoirs in “AFUN” Field Deep Offshore Niger Delta

Yemisi. C. Ajisafe1* and Mary T. Olowokere2
1Department of Geology, Ekiti State University, Ado-Ekiti
2Department of Geology, Obafemi Awolowo University, Ile-Ife
Corresponding author*

IJRISS Call for paper

Abstract: The complex facies architecture in turbidite systems has necessitated the use of sequence stratigraphic methods in characterising thin reservoirs of the “AFUN” Field, offshore Niger Delta, Nigeria. 3D post-stack time migrated seismic, biostratigraphic data, core data as well as a suite of composite well log data from six wells drilled within the study area were the dataset used for this study. Sequence stratigraphic analysis of the study area involved the interpretation of biostratigraphic data of AF-SW1 well. Time significant surfaces and their respective ages were identified on this well using the chronostratigraphic correlation of all the well logs across the study area. The stacking trends were used to delineate sequence stratigraphic surfaces and the stacking patterns used to delineate systems tracts, and define stratigraphic sequences. The analysis yielded seven depositional sequences based on dated Sequence Boundaries and Maximum Flooding Surfaces. Six Lowstand Systems Tracts (LST) were delineated and includes the Lowstand Slope Fan (LSF) and Lowstand Prograding Wedge (LPW) varieties. LSF and LPW are predicted to be submarine fan deposits which were vertically smeared by pro-deltaic mud. Seventeen reservoirs exist were identified within the field of study with eleven in the Lowstand System Tracts and six of the reservoirs belonging to the Highstand System Tracts. Most of the reservoirs in “AFUN” Field were deposited during LST while the TST (comprising mainly shales) serve as seals that capped the reservoirs. Reservoir quality of “AFUN” field was interpreted based on depositional features which control reservoir characteristics in different facies of the reservoirs. This study has therefore, revealed that the stratigraphic traps with different reservoir sands can be characterized based on their associated system tracts for field development.

Keywords: sequence stratigraphy, chronostratigraphic correlation, reservoirs, depositional sequences, submarine fan.

I.INTRODUCTION

Data acquired from the deep water systems are usually characterized by extreme complexity and variability due to the inherent heterogeneity of the available data. Hence, the data need to be analysed and interpreted by techniques that will bring out the most geologically reasonable interpretation of the sediments within a time- stratigraphic framework. Therefore, the exploration and exploitation of the deep water reservoirs can be greatly enhanced by applying sequence stratigraphy principles. This technique provides the accurate evaluation of hydrocarbon reservoirs and thus reduction of