Abstract

The acquisition of seismic data over the areas of rugged karst topography in Papua New Guinea (“PNG”), which successfully images the clastic reservoir at the target depth, has the potential to significantly reduce structural risk and improve exploration success. Innovative project management can obtain good quality seismic data at a cost significantly lower than previous surveys, and also achieve world-class safety performance.

In 1997/98, five separate surveys were acquired by Santos Asia Pacific Pty Ltd (“Santos”), as operator, on behalf of the PPL 106, PPL 155, PPL 189, PPL 158 and PPL 191 Joint Ventures (the “Seismic Programme”) over a variety of karst terrains within the foldbelt and foreland areas of PNG that were previously considered unsuitable for seismic acquisition. The conventional modus operandi of seismic surveys was replaced by in-house management of the project, rental of recording equipment, and hiring of key consultants and field contractors.

Financial risk was significantly reduced by turnkey contracts and reducing the levels of equipment and professional field personnel. A strong emphasis was placed on health, safety and environment (“HS&E”) and the implementation of a safety training observation programme which resulted in zero lost time incidents over the 635,952 man-hours accumulated. Landowner relations were a crucial concern and were undertaken by Santos community affairs officers before, during and after each survey.

All medical supplies, office communications and HS&E equipment necessary for the efficient management of field operations were purchased. A 760 channel seismic recording system was leased by Santos, with recording personnel provided by a Brisbane-based contractor.

Field operations differed from conventional methods. Shot and geophone holes were drilled to depths of 15 m and 5 m respectively, with both 12 kg dynamite charges and single downhole geophones being cemented in-hole to improve seismic coupling. Shot-holes for PPL 191

were drilled to 10 m depths with 10 kg charges. Geophones along the entire line were live, allowing the recording of long offsets and a maximum fold of approximately 300.

Data quality on field records is fair to poor due to the presence of unattenuated noise, however the high fold stacked sections clearly images the structures at the target depth. The probability of delineating structural closure improved considerably from 20% before seismic to approximately 80% after seismic. The risk reduction in structural uncertainty provided by good quality seismic data is a breakthrough in technology for the Papuan Foldbelt play.