Depositional Environment and Reservoir Architecture of “JI” Field, Niger Delta

Abstract

This study is a contribution to the understanding of the depositional environment and reservoir architecture of the “JI Field”, Niger Delta Nigeria. The main objective was to integrate sequence stratigraphy and petrophysical evaluation in characterizing the reservoirs encountered in the wells. Well logs from six wells (JI01, JI02, JI03, JI09, JI10 and JI12-ST), biostratigraphic data from two wells (JI01 and JI02) and 3D seismic volume were analyzed to understand the reservoirs correlation pattern with their environment of deposition (EOD), petrophysical properties and fault patterns on the structural map of the field. Result from facies analysis reveals that “JI field” is composed of foreshore sand, upper shoreface sand, lower shoreface sand, tidal channel and channel sands which were deposited in shallow marine setting. Sequence stratigraphic analysis result showed two depositional sequences (SQ1 and SQ2). These depositional sequence are bounded with sequence boundaries (Vail’s law) dated 10.6Ma, 10.36Ma and 7.4Ma.Maximum flooding surfaces (MSF) dated11.6 Ma, 10.4Ma and 7.8Ma were delineated. The delineated system tracts are Lowstand, Highstand and Transgressive Systems Tract with their associated progradation, retrogradation and aggrading stacking patterns. Well correlation showed appreciable net sand reduction along the dip direction. Petrophysical analysisof F-sand reservoir shows an average net to gross thickness of 0.55, average porosity value of 0.29v/v, average permeability value of 2506md and average water saturation of 0.14. This reservoirconsist mainly of tidal channel sand heteroliths belonging to the lowstand system tract. Fault mapping delineate faults composed of major growth faults, listric fault, antithetic and synthetic faults. Structural features such as collapsed crestand of back to back structures constitute the reservoir architecture. Majorfaults trend in NE-SW and dip SE, SW. The structural map shows a two way fault dependent closure for JI field.