FIELD INVESTIGATIONS FOR NORTH WEST SHELF DESIGN CRITERIA

Abstract

Since 1971, when major gas discoveries on the North West Continental Shelf were confirmed, B.O.C. of Australia Limited (BOCAL), as operator for the Northwest Shelf Consortium, has carried out a major programme of environmental data collection. The purpose of the data collection programmes and follow-up studies has been to define engineering design criteria for evaluation of offshore production structures and pipelines.Prior to the commencement of exploration drilling, little was known of the meteorological/oceanographic regimes of this vast offshore area and no published data existed on the sea bed topography or composition. During the past 3½ years a substantial library of environmental information has been assembled using both conventional and the most modern techniques available. Acquisition of field data has been mainly concentrated in the southwestern portion of the Consortium's lease area where the major exploration effort was maintained.During the course of the programme, weather instrumentation on all exploration rigs was upgraded. Wave measurement and current metering programmes were also carried out to ascertain the modes of water movement at various offshore discovery locations. To assess the foundation materials and qualities, test borings were carried out at 6 exploration well sites, including a series of in-situ pile load tests at the North Rankin location. Preliminary surveys over possible offshore pipeline routes were carried out to assess the nature and topography of the sea bed.Information gained from the programme of field-collected data and related environmental studies has enabled BOCAL to proceed confidently with platform design for the production of gas from the North Rankin Field.Work is continuing on the acquisition of further field environmental data in order to improve the understanding of the meteorology and oceanography of the North West Shelf area. This will assist in further evaluation of offshore design criteria for the North West Shelf of Australia.