Planning, Analysis and Integration of Wireline Formation Testing Mini-DST for Shallow Tight Gas Reservoir in Open Hole Well in Offshore Malaysia: A Case Study

Abstract

Abstract A mini drillstem test (DST) with a Wireline Formation Tester (WFT) tool was performed in a low-perm, unconsolidated gas reservoir in a shallow well in offshore Malaysia to obtain high quality gas samples and to determine main reservoir properties. Single probe WFT attempts were unsuccessful in the offset well because of tightness attributed to high silt content. Consequently, the mini-DST was run in open hole, rather than the normal full-bore DST, which was an option for reservoir characterization. This paper describes a successful reservoir characterization using a mini-DST in an open hole in a shallow low permeability reservoir; it provides background information about the wireline formation tester jobs conducted in an offset well. The paper also addresses the design criteria for performing the mini-DST and delves into the factors that were considered for job planning and proper job performance. The unconsolidated sand posed some challenges, including a significant risk of sand failure during pumpout. Conversely, the low permeability requires more drawdown to flow the tested interval. The paper also includes the steps undertaken to minimize this risk by analyzing real-time data. Despite low permeability, a good radial flow was obtained and used to estimate reservoir properties by creating proper drawdown. The high mobility of the low pressure gas in the reservoir compensated for the reservoir tightness. Although the radius of investigation in a relatively short buildup is not sufficiently high, it can still assist in reservoir characterization for development purposes with the integration of core, petrophysical, and DST data. The paper also demonstrates the contribution of proper job planning and real-time monitoring to overcome operational problems expected while performing mini DSTs in low permeability and unconsolidated reservoirs, and describes methods for addressing those problems.