LEGENDRE: MATURATION OF A MARGINAL OFFSHORE OIL DISCOVERY TO DEVELOPMENT PROJECT

Abstract

Commercialisation of the Legendre hydrocarbon resources represents the culmination of over 30 years of exploration and appraisal and more recent development planning, following the discovery by the first well to be flow-tested on the North West Shelf, Legendre–1, in 1968. By application of 3D seismic, reservoir modelling and simulation techniques, horizontal drilling and innovative development options, the WA-l-P Joint Venture is confident of achieving an economic return on a relatively small resource base.

The two separate accumulations, Legendre North and Legendre South, are together expected to contain some 14 million m3 (90 MMSTB) of oil-in-place. The oil column in the northern accumulation is 45 m at its maximum, whilst a 20 m column is present in the southern accumulation. Reservoir quality is generally very good with mostly massive sandstones with little or no internal stratification. The reservoir contains a light oil and aquifer support is expected from communication with the underlying Angel Formation sandstones.

The subsurface development plan has been designed to optimise the recovery of the oil in place in the two accumulations. Production wells with horizontal sections of 750 m will be used to minimise drawdown and ensure good sweep. Production is expected at a plateau rate of 4,800 to 6,400 m3/d (30−40,000 BOPD). Produced gas will be disposed of by means of a re-injection well downdip of the producers.