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.