NEW TECHNOLOGY—A MAJOR IMPACT ON A PRODUCING FIELD: NORTH RANKIN GAS FIELD, NORTH WEST SHELF, AUSTRALIA

Abstract

New technology, especially the significant advances in 3D seismic interpretation techniques and drilling technology, has had a major impact on the development planning for the North Rankin Field.

Significant advances have been made through the application of: horizon attribute processing, seismic amplitude analysis and long-reach drilling technology.

Horizon attribute processing, including image processing techniques, has led to a better understanding of the structurally complex region on the northern flank of the field. These studies, coupled with new geological concepts related to opposing fault regimes, have concluded that good reservoir communication should exist across a fault zone previously thought to subdivide the field into compartments. The drilling of expensive, long-reach wells into the northern sector has thus been deferred, and may never be required, because of the newly developed structural model.

Seismic amplitude analysis, coupled with geological modelling, upgraded the North Rankin West area and culminated in the recent significant appraisal/development well NRA22. This well was drilled from the North Rankin 'A' (NRA) platform to a target outside the main North Rankin Field in the adjacent Searipple Graben. NRA22 encountered well developed gas-bearing sands of Bathonian age which flowed at high rates (140 MMSCFGD).

The application of long-reach drilling technology within Woodside has also had significant impact on development planning. The original development plan for North Rankin included a second platform in the northeast of the field. Better than expected production performance from NRA, related to across-fault reservoir communication, removed the necessity for a second platform. Large gas reserves in the Lower Jurassic 'NC' unit in the northeast have, however, required dedicated wells to improve ultimate recovery from this unit. The drilling of long-reach wells (at record drift) into the NC unit has provided better access to these reserves.

Although North Rankin has been producing for over seven years with a total of 23 development wells drilled, understanding of the geological structure is still being improved by using new technology and ideas.