Publications

The Sarawak Basin holds about 25% of Malaysias total oil and 51% of its natural gas reserves. Through aggressive exploration and development in blocks SK309 and SK311 since 2001, Murphy Sarawak Oil has successfully discovered significant hydrocarbons. The main reservoirs in this basin are Middle to Early Miocene deltaic sands, ranging in depth from 1000 to 2000 meters.Seismic Amplitude Versus Offset (AVO) analysis has been widely used by the industry as an integral part of seismic interpretation to try to predict hydrocarbon presence. There have been many successes and failures because AVO responses can be caused by many geological factors or processing pitfalls. Having field examples and a sound modelling basis for an area should increase the success rate for fluid prediction. This paper illustrates this point and documents the workflow used.Initially in this Sarawak Basin case study, fluid substitution was performed on nine key wells in order to understand the AVO responses of the major reservoirs. Synthetic seismic gathers were generated at the wells. Where needed, shear wave estimation was carried out for a small number of wells.Using the results to predict hydrocarbon occurrences using real seismic gathers is somewhat challenging, as the gathers may be contaminated by multiples or random noise. Therefore, careful advanced seismic data pre-conditioning was required prior to extracting the amplitude information.Following this study, several wells have been drilled during the 2004 campaign resulting in significant hydrocarbon discoveries. Success in utilizing this method in the Sarawak Basin has become a key factor in lowering the risk of exploration and field development.This paper will document the AVO behaviour of some Sarawak fields: the understanding of which has enabled rapid prospect screening and fluid prediction. It is briefly demonstrated that these examples also serve as a feasibility study for seismic elastic inversion.