GEOPHYSICAL OPTIMISATION OF THE MACKEREL FIELD RE-DEVELOPMENT—GIPPSLAND BASIN, AUSTRALIA

Abstract

Mackerel, the third largest oil field in the Gippsland Basin, is a mature field with over 80 per cent of reserves produced from 18 original development wells.

The initial Mackerel development was based on a fairly simplistic reservoir model incorporating the results of the four exploration wells. The net to gross was anticipated at 90 per cent throughout the reservoir and no significant permeability barriers were expected. After 10 years of production a review of field performance indicated the reservoir was not as homogenous as first anticipated.

Redevelopment of the Mackerel Field began in 1990 following the acquisition of the first of two high resolution 3D surveys and culminated in the drilling of 18 additional wells from the Mackerel platform during 1993 and 1994. It was these 3D surveys which changed the entire reservoir model of Mackerel to one of a far more compartmentalised nature.

Seismic attribute analysis, when calibrated to 2D forward modelling was used to predict intra-reservoir seals and the distribution of poorer quality reservoir; both not previously recognised over the field. The truncation points of the intra-reservoir seals against the main field-wide trapping unconformity were accurately mapped using seismic attributes and image enhancement techniques such as ER Mapper. Previously undetectable fault extensions, with throw around 10 m, can act as partial flow barriers and were recognised for the first time via 'sun-angle illumination' of azimuth maps. This allowed optimum well placement and helped explain historical field performance. Horizon slicing techniques and the calibration of volume attributes were used to establish depositional environments and seal capacity of the predicted intra-reservoir seals.

The drilling results have shown that over the production life of the Mackerel Field the reservoir consists of a number of drainage compartments, each separated by seismically resolvable intra-reservoir seals.

The redevelopment of the Mackerel field increased production rate by 18 thousand barrels per day (kBD) in 1993, and proved additional capture reserves of which approximately 40 percent can be directly attributed to the 3D seismic data and the applied interpretation techniques.