Abstract

Pematang Bow Field is located near the southeastern termination of a strike-slip fault system in central Sumatra. Structurally, the field is a northwest-plunging anticline, bounded on the southeast by a normal fault system. This anticline is masked on seismic data by a complex velocity gradient, and early attempts to seismically map Pematang Bow met with limited success, resulting in several dry holes. A 4.3 kilometer by 3.6 kilometer 3-D seismic survey was shot, processed, and interpreted from August, 1988 to August, 1989, and a two-layer model (each layer with its own velocity gradient) was used to convert from time to depth. The cost of the 3-D survey was comparable to the cost of a single dry hole in Pematang Bow. The low cost resulted from four factors: careful planning and surveying, a sparsely populated location (which allowed surveying to be done months in advance of shothole drilling), the hiring of extra drilling crews, and a shooting technique which allows the recording instruments to operate almost continuously. As a result of the survey, significant updip reserves were revealed, and several potential dry hole locations were avoided. The conclusion drawn is that at Pematang Bow Field, 3-D seismic was a very effective reservoir management tool.