Seismic Post-Stack Attribute and AVO Seismic-Based Analysis in Delineating New Prospect with Filling-Ratio Approach in Estimating Fluid-Contact for Proposed Well

Abstract Delineating new prospects in a mature field requires a more advanced technique of seismic data interpretation in order to reduce the uncertainty level of success. The most conventional practice was to identify the reservoir using post-stack seismic data. In contrast, pre-stack seismic data are sometimes absent in the analysis due to the lack of data itself or the assumption that post-stack seismic data is deemed to be sufficient. Nowadays, it has been proved that the amplitude characteristics of seismic reflections vary with increasing offset. This finding led to Amplitude Versus Offset (AVO) analysis, which assessed the dependencies of reflectivity with increasing offset. This technique is useful in delineating the Direct Hydrocarbon Indicator or the fluid trend. Fluid-contact values are also essential to determine the vertical boundaries of hydrocarbon-saturated reservoirs. The filling-ratio method can answer the challenge of determining these vertical boundary values in a proposed well, which requires at least one proven and/or producing well to provide a sound basis comparison of fluid contacts from their top structure depth to their deepest fluid contact depth. This filling-ratio approach can then be applied with simple mathematical calculations between the proven and/or producing well and the proposed well in reservoir targets. In this case of work, Cisubuh formation is chosen as the layer of interest. It is known to have a bell-shaped sand reservoir from the log response of a nearby well. Both seismic post-stack and pre-stack are utilized in delineating new prospects in the target layer. The post-stack seismic is analysed to predict the sand distribution, while the pre-stack seismic is analysed to predict the fluid indicator across the area of interest. The delineation prospect from these seismic data sets also shows coherency with the interpreted anticlinal structural trap. Fluid contacts from the proven well, in this case, show convincing test results of hydrocarbon with one other prospected well in the same field that contains such hydrocarbon. The method can be justified with the mentioned proven well test and conservatively bounded the hydrocarbon reserves calculations. Hence, the result of the calculated comparison of fluid-contact depth between the proven well and the proposed wells does not over excessively contain such hydrocarbons.