Abstract

The Ebughu field, located offshore in the eastern Niger Delta, has produced from a thin viscous oil rim at very low rates since 1988. Production has run at 10% of platform potential. Following a change in operatorship, the field was successfully redeveloped during 1999 in less than 10 months. From a standing start, the field was reviewed, new wells were drilled and the platform facilities were filled to capacity. The field is now believed to be ten times larger than originally mapped. Key to this fast tracked success was the adoption of a streamlined redevelopment process.

Key results and conclusions are as follows:

  1. The pooling of knowledge from outside contractors, consultancies and operators, has allowed a small integrated project team to review and redevelop a poorly performing offshore field in 10 months.

  2. Application of 3D seismic and horizontal well technology has transformed the development of a thin viscous oil rim, with both production levels and STOIIP potential being raised ten fold.

  3. Redevelopment of this sparsely explored field was significantly3accelerated through the adoption of an aggressive appraisal-development process. Seven low cost pilot wells were batch drilled up front from two slots and interpreted in real time. This allowed four horizontal development wells to be targeted and drilled in the same drilling program and a successful appraisal well completed for reservoir information.

  4. Effective selection of drilling resources reduced drilling costs substantially and resulted in horizontal wells which were among the fastest, cheapest and longest ever drilled in Nigeria.

  5. The adoption of the "all-in-one" completion concept allowed an 8,200ft well including a 2,100ft horizontal section to be drilled and completed from a new slot in 9.4 days for US$ 2.1million.

Introduction

The Ebughu Field is located in the southern portion of the offshore licence block OPL98 in the eastern edge of the Niger Delta (Fig 1). Addax signed a PSC with NNPC for a 100% interest in the OPL98 licence, which is owned by NAPIMS, in May 1998 and immediately started a review process with the aim of rehabilitating the six mature fields within this licence (Fig 2).

OPL98 lies in a highly prolific region of the Niger Delta with numerous stacked sequences of prograding shallow marine deltaic sands of Mio-Pliocene age (Fig 3). Reservoirs are concentrated in the Biafra Member of the Agbada Formation. A massive submarine channel, the Qua Iboe, cuts and erodes the upper part of the Biafra Member sands. The Qua Iboe Channnel is filled with thick marine shales and forms an effective regional seal (Fig 4). Reservoir quality is generally excellent with porosities in excess of 30% and permeability in the range 1–10Darcy. Sands are generally unconsolidated and sand production is common if no sand exclusion method is applied. The area is gas prone with oil frequently found as a rim underneath a large gas cap. Oil quality is good (20°-40°API) with a strong correlation of PVT properties with depth (Fig 5).

Oil from six offshore fields is exported from OPL98 via a moored FPSO vessel, the Knock Taggart (Fig 2). All the production platforms are in shallow water (30–100ft) and are linked to the FPSO through a pipeline network and manifold platform. Most of the produced water is separated via a single process train on the FPSO. Production from Monipulo's Abana field to the north in OML114 is also exported through the Knock Taggart but is completely processed prior to arrival. A link also exists to Mobil's Ubit field to the West in OML67, via the Akam platform. A number of third party fields and discoveries lie close to licence boundaries raising possibilities of sharing infrastructure and costs.

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