During 2001 an intensive geophysical, geological and reservoir engineering, analysis was carried out on Nexen's 100% WI Buffalo Project located in the Bonaparte Basin. The work resulted in the successful drilling of two infill wells, during March / June 2002. The value, reserves and economic life of the Buffalo Project has been extended by 2 years with additional recovery of approximately 8 MMbbl.

This paper will review the original geologic / geophysical model and the non-unique nature of the Reservoir Engineering history match. The pre-stack depth migration [PSDM] work and results will then be described in detail, along with an explanation of the revised geologic model for Buffalo and how it changed our concept of the upside in the field. The reservoir simulation, decision tree, production forecasts and reserve summary will then be described.

The PSDM work indicated that the field is a tilted fault block, analogous to other fields in the Bonaparte Basin, instead of a rollover anticline. In the rollover anticline model, both original producers, Buffalo 3 and Buffalo 5, were located along the central crest of the anticline. The new tilted fault block model indicated both a "Northern Attic" and a "Western Attic". The infill drilling program was designed to drain the yet unswept attic oil at Buffalo.

Since Buffalo has a very strong water drive, typical reservoir simulation would not "see" the presence of the attics in the field, and the simulation results are not unique. Nexen had developed a comprehensive decision matrix, which reduced risk and created maximum flexibility. The Buffalo 7 well was critical to proving the new geologic model of the field. The well was drilled and completed in March-April 2002 and was followed Buffalo 8, Completed as Buffalo 9, in May-June 2002.

Nexen used a multi disciplinary team to review Buffalo, which has resulted in a successful project. Nexen has applied its expertise gained in Western Canada, the Gulf of Mexico and Yemen to its operations in Australia.

The successful redevelopment of Buffalo has increased reserves, extended productive life and increased the value of Buffalo to Nexen. The work has enhanced the companie's reputation in Australia as an operator with experience in both exploration and exploitation.

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