RIASSUNTO
Abstract
The Agbara field is operated by Agip Energy and Natural Resources (AENR) under a service contract with the Nigerian National Petroleum Corporation (NNPC). The field lies approximately 30-40 Km from the coast in the Niger Delta offshore in water depth ranging between 55-70 m. It is located in the offshore depo-belt of the Niger delta basin where thick pliocene-clastic sequences of Agbada formation have been deposited in a deltaic-fluvio-marine to inner shelf environment.
Agbara field has been on production since June 1989 and its block, OPL 472, was converted into the Oil Mining Lease 116 (OML116) on September 1999. As at December 2009, the cumulative production is approaching 100 MMBBL with an average production of about 10,000 BOPD. With over twenty years of production, the Agbara case history presented in this paper constitutes a unique example of rejuvenation of a mature oil field. This paper will provide a description of single well optimization process that led to sensible production gain in a short time frame with about 40% increase in net oil production over a six months period
as well as exploration and reservoir engineering practices that provided the basis for further exploration and development opportunities in the field. An extensive review of the field and reservoir description will be provided along with the development history. This paper, the first case history of Agbara focuses on both the well engineering and the reservoir engineering aspects. Suggested or implemented workflows and technology ranging from well and reservoir characterization, candidate selection, classical water shut off, stimulation to innovative new technology such as the use of Ejector (ENI R&D) and relative permeability modifiers are described. An overview of the future potentiality of such mature field is also described.
Introduction
Agbara field is located about 40 km from the shore at a water depth of 65m within the OML116 block which is a contractual area operated by Agip Energy and Natural Resources (Nig) Limited under a service contract agreement with NNPC (Figure 1 - OM116 location map).
Agbara field is located in the offshore depositional belt of the Niger Delta basin within the OML 116 where thick Pliocene Clastic sequences of Agbada formation have been deposited in a deltaic -fluvio-marine to the inner shelf environment. The Agbara field area is characterized by a complex fault pattern and the structure is controlled by a shale diapir induced counter regional fault, which lies south of the Agbara field and has an East-West trend. It is a typical rollover structure with a dip / fault closure trapping mechanism. All reservoirs encountered so far in this field are trapped by this closure. The other fault is a North South trending fault, which separates the Agbara field from the adjacent minor-fields Bala & Eweri (Figure 2 - Depth Structure Map - U Reservoir).