Ten Years of PSC Deepwater Exploration in Nigeria (1993-2003); the Shell Experience

Emmanuel I. Enu
Shell International Exploration and Production, Houston, TX

Deepwater exploration in Nigeria gained momentum in the late 80's to early 90's following the 2D Speculative seismic data acquisition by TGSI-MABON under the guidance of the Department of Petroleum Resources.

Evaluation by prospective deepwater operators stepped up in 1990/91 in preparation for the application for blocks of choice. Deepwater PSC was relatively new at that time, thus, companies decided to spread their risks through farm-in and farm-out as well as cross assignment of working interests with a view to spreading risks.

The geology of the region is now fairly known with turbidite sedimentation as key; the reservoir architecture for the various levels of pay is being deciphered; trap types and charge vary from inboard to outboard areas and a lot of uncertainties still exist.

Exploration period as spelt out in the 1993 PSC document is for a duration often years (1993-2003). Drilling was slow during the first half of the period but picked up towards the later part to enable adequate assessment of the awarded blocks for acreage retention purposes and to help in the decision making for block relinquishment and OML conversion.

Shell initially leveraged on group experience from the Gulf of Mexico turbidite geological model. Also, early regional geology framework efforts of the deepwater region led to a classification of the area into play segments which greatly increased the geological knowledge base. Early 3D acquisition over blocks prior to drilling not only helped to save costs but also allowed a detailed, fine tuned evaluation right from the onset. Hence, Shell was able to record early discoveries such as Bonga-1, followed by the Bonga SW-1 in OPL212 and Ngolo-1, Bolia-1 and Doro-1 in OPL219.