SEISMIC BASED RESERVOIR CHARACTERISATION OF THE WANDOO OIL FIELD

Abstract

The Wandoo Oil Field of Western Australia's offshore Carnarvon Basin is located in the WA-14-L production licence approximately 70 km northwest of Dampier. Hydrocarbons from the 22 m thick oil column are produced from the informally named Unit A and Unit B of the Vf. australis Sandstone reservoir through 15 extended-reach horizontal wells. Cumulative production from the field is over 30 MMBBL of the estimated 160 MMBBL initial oil- in-place. Production reached a plateau rate of 40,000 BOPD in April 1997 and is now declining in line with the predicted reservoir performance.

A multidisciplinary team was formed to develop a detailed reservoir model using 3D seismic data, a regional 2D seismic database and geological and engineering data from 11 vertical and 19 horizontal wells. The M. australis Sandstone was divided into six depositional units defined by changes in well log character, glauconite content and reservoir quality. These units were subdivided into 27 correlatable flow units and 6 laterally extensive non- reservoir siderite layers.

An estuarine-deltaic depositional system is suggested for the M. australis Sandstone reservoir at Wandoo. The recognition of erosional features at various scales and distinct areas of higher quality reservoir indicate that this system wras subject to frequent changes in relative sea level. The top of the Unit B was identified as the most significant sequence boundary with the overlying Unit A deposited as a transgressive sand of limited distribution.

A 3D geological model honouring the revised interpretation has been constructed and used as input for reservoir simulation resulting in an improved production history match. The concepts developed have been successfully tested by a horizontal multi-lateral production well.