OBEN GAS DEVELOPMENT PROJECT

Chapter One Introduction, Administrative & Legal Framework
1.1 INTRODUCTION
CHAPTER ONE
The Oben Field is situated in OML 4 ca. 60 km North East (NE) of Warri (Figure 1.1, Appendix I). A
major structural building growth fault separates the field into two blocks. To the south, the downthrown
block is a simple elongated rollover structure trending in the East West (EW) direction parallel to the
major growth fault while the upthrown block is a footwall closure dipping toward the north.
The field was discovered in 1972 on two-dimensional (2D) seismic dataset and came on stream in 1974
with oil production peaking at 40 Mbopd in 1985. A total of 32 wells drilled in the Oben Field
encountered hydrocarbons. Well 33 was drilled off structure. In the shallower reservoirs (C, D and E
sands) the hydrocarbons are located in the downthrown block while in the deeper reservoirs (F, G and
H) sands; the hydrocarbons are mainly in the upthrown block.
Shell International Exploration and Production (SIEP) carried out a detailed Field Review in 1982, which
formed the basis for a limited Field Development Plan of 1990. This led to the drilling of Oben-29 to
Oben-32 in 1990 and 1991. Oben Field supplies non-associated gas through drainage points in 3
Oben Wells (Oben-26, -27, -28) to NGC via ELPS. The existing flow station and gas plant has
throughput capacities of 60 Mb/d and 90 MMscf/d respectively. The 1990-limited FDP suggested that
the reservoir and fluid characteristics (strong aquifer, light crude and high GOR) make the use of gaslift
unattractive due to low commercial value.
A 3D seismic data (290 sq. km of 3000% multiplicity) was acquired over the Oben Field in Q3 1998 and
processed in Q4 1999. This 1998 seismic data formed the basis for the Integrated Petroleum
Engineering Studies (IPES) carried out in 2002. A total of seven key horizons namely C8, D2, E1, E3,
F7, G2 and H1 (Figures 2.1 and 2.2) were correlated over the entire field. Interpretation was done in the
Charisma workstation. The interpretation of the 3D seismic data led to a better understanding of the
structural configuration of the Oben Field with resultant revisions in the volumes booked in the ARPR
1/1/2004. There are significant changes in the structural pattern in the footwall closure against the major
boundary fault compared to the previous 2D maps. The seismic interpretation and mapping of the year
2002 were extended to cover the NAG reservoirs, however, no detailed study in terms of 3D static and
dynamic reservoir modeling and integrated study were carried out for any of the NAG reservoirs.
Due to the increasing Western Domestic Gas demands from both existing and new customers in the
network and the demand occasioned by the West Africa Gas Pipeline (WAGP), an Oben Field NAG
reservoirs study team was set up in 2003 to carry out a detailed study of the NAG reservoirs.
Eight (8) major gas reservoirs (D2000M, D6500M, E6000M, E7000M, E8000M, F7000M, G1000M and
D5000M--selected on the basis of FGIIP and depth), constituting about 60% of the field GUR, were
modeled using SPIDER and MoReS.
These models were considered sufficient by the team since they captured the subsurface uncertainties
in the reservoirs and hence have been used for this study.
Compared to 1/1/2005 ARPR there was a 1.2 % and 17 % reduction in Exp FGIIP and UR
1-1