Dual-Sensor Technology in Marine Seismic Acquisition Applied to New Play Identification in Central Luconia Province, Offshore Sarawak

Abstract

Central Luconia Province in offshore Sarawak Basin has predominantly in the past been the target of numerous exploration campaigns. Past efforts in this tectono-stratigraphic province focused mainly on Miocene carbonate buildups (Cycle IV & V) ranging from platforms to pinnacles. Discovered fields, the likes of Bijan, Jintan, F12, F6, E8, PC4 and such have proven commercial quantities of hydrocarbons in the carbonates. The pre-carbonate clastic sequences have also been proven prospective but the exploration efforts to date have been impeded to a large extent by seismic imaging issues. PETRONAS has in the past, considered various technological advancements encompassing both acquisition and processing methods thought to be capable of illuminating the pre-carbonate plays. Advance processing techniques helped but the fundamental issues of energy absorption and dispersion rendering ‘wiped-out zone’ and severe seismic attributes attenuation below the carbonate still remain. The idea of dual-sensor (hydrophone and velocity sensors) technology has been discussed as early as 1964 by Schneider and Backus. Yet the issues of resultant noise from the vibration of towed streamer and sensors render the data unusable. Two different approaches were formulated for producing usable dual-sensor data; i.e. simultaneous towing of streamers at different levels and collocation of both sensors in the same streamer. PETRONAS opted to test the latter approach and seek to quantify the improvement in the seismic data image quality. To this end, a marine 2D seismic acquisition initiative utilizing dual-sensor technique was executed in Central Luconia area repeating vintage 1998 2D lines acquired conventionally. The original acquisition specifications were maintained as much as possible and both datasets were processed following similar sequences so that any improvement can be directly attributable to the differences in acquisition technologies. The primary target was imaging the pre-carbonate clastics at 1.5 seconds to 2.5 seconds in two-way time. Indeed, significant improvement of the dataset was observable through out. The amplitude spectrum shows marked differences between the newly acquired dual-sensor and reprocessed vintage 2D datasets. SRME procedure benefited from the wider range of bandwidth accorded by the dual–sensor technique dataset. In the examples, the differences both in the single shot gather and stack section are shown. Accurate Q estimation proves useful in preserving the deeper primary reflections. The dual-sensor dataset gives improved image of deep events as well as the capturing of more usable lower frequency data. Thus, we conclude that the technology is a workable step ahead in imaging pre-carbonate geology in Central Luconia Province.