AVO Attributes for Successful Exploration and Field Development: A Case Study from Sarawak Basin, Malaysia

Sigit, Rusdinadar¹, Reza Lasman¹, Norbert Van de Coevering² (1) Murphy Sarawak Oil, Kuala Lumpur, Malaysia (2) CGG, Brentford, United Kingdom

The Sarawak basin holds about 25% of Malaysia’s total oil and 51% of its natural gas reserve. Through aggressive exploration and development in block SK311 since 2001, Murphy Sarawak Oil has successfully discovered many hydrocarbons. The main reservoirs in this basin are Middle to Early Miocene deltaic sands, ranging from 1000 to 2000 meters depth. 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 are many successes and failures: AVO responses can be caused by many geological or pro­cessing pitfalls. Having many field examples from one area would definitely increase the success ratio of fluid prediction. Initially in this block SK311 case study, fluid substitution was done on nine key wells in order to understand the AVO responses of the major reser­voirs: well synthetic gathers were generated. Using the result to predict the hydrocarbon occurrence using real seismic gathers is somewhat challenging, as the gathers may be con­taminated by multiples or random noise. Therefore, careful advanced seismic data pre-con-ditioning 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. The success of utilizing this method in the Sarawak basin has also become key in lowering the risk of exploration and field development. This paper will demonstrate the result of a few AVO field examples for rapid prospect screening and fluid prediction, including its potential failures.