Application of deterministic fault-seal analysis for fault-bounding trap: a case study in Than Nong 1B prospect, Block 05-1(a), Nam Con Son basin, offshore Vietnam

Fault-seal analysis has long been applied for predicting potential hydrocarbon column for mitigating risk in exploration and appraisals. Than Nong 1B structure in Block 05-1(a), located nearby Dai Hung field, is a fault-bounding structure; thus, the fault seal capacity plays a major role in trapping hydrocarbon. In this study, the H50 reservoir is taken as an example of how fault-bounded prospects are evaluated in Block 05-1(a). For the case of Than Nong 1B, to meaningfully determine the potential of the structure, the fault geometric analysis is conducted to fully understand the 3D geometry of the structure. Moreover, vertical displacement of the faults is inspected to ensure the quality of input data and to understand how faults and horizons affect each other. After structural description conducted, the study applies all common methods of fault-seal analysis from the 1980s to the newest workflow published in 2016, such as 3D sand-shale juxtaposition analysis, SGR analysis, height-column-prediction algorithms by Yielding et al. (2010). The results of these methods are then combined by using Trap analysis workflow, proposed by Peter Bretan in 2017, to determine a unique location of fault leak point defining the trappable hydrocarbon column of the structure. The results suggest that the faults in Than Nong 1B prospect are able to hold a maximum column of 183 m hydrocarbon in H50 reservoir, significantly higher than the column of 125 m hydrocarbon defined by Fault-leak point. Furthermore, this study also proves that the Trap analysis is an effective method for evaluating structures with high level of fault linkage.