The Cakerawala, Bulan, Bumi and Suriya gas fields in the MTJDA, northern Malay Basin form a major new development hub for the region, with an estimated total GIIP of 9 Tcf. These large assets are very early in their field life with only 300 Bcf of production from Cakerawala field so far. There has however already been significant (USD 1-2 billion) development investment. There is significant subsurface uncertainty due to geological complexities and a detailed, integrated data gathering and interpretation effort was necessary to better understand the asset. The impact of the study is a deeper understanding of the fields' potential and an insight into how to optimally develop these complex resources. This study covers many aspects of the reservoir characterisation process with examples from the North Malay Basin and has application in other complex fields.
The subsurface geology comprises a thick interval (more than 7,000 ft) of stacked, clastic, fine grained, often clay-rich reservoirs, deposited in an upper delta plain to shallow marine environment. Significant challenges exist in developing these fields due to the large development area, thick zones of interest, large number of reservoirs and challenging depositional setting. There are also petrophysical issues to overcome, including fine scale reservoir heterogeneity, complex mineralogy and the presence of low-resistivity low-contrast (LRLC) pay.
An improved understanding of the factors controlling reservoir quality was achieved by adopting a holistic and multidisciplinary approach. This included the integration of stratigraphic, depositional and lithofacies information along with mineralogical and pore system data.
Key lessons learnt include the importance of acquiring good subsurface rock data and the construction of robust databases. The novel application of Lorenz plots and Winland R35 analysis calibrated to test data provided key rock quality and heterogeneity information for inclusion in geo-engineering models. The definition of LRLC reservoirs proved to be an important milestone which led to the development of a water saturation cut-off for gas-productive reservoirs. These findings are now being incorporated into our forward development strategies in Block A-18 and other assets. Success was achieved on a highly complex problem due to the application of an integrated, multi-disciplinary work flow.