Mini-DST to Characterize Formation Deliverability and Heterogeneity in Thin Hydrocarbon Reservoir Sequences

Abstract

A robust workflow is established to identify low-resistivity pay in thinly laminated sands with silty and/or shaly layers. The workflow integrates data from gas-while-drilling, conventional logging and nuclear magnetic resonance (NMR) logging for picking intervals for further examination using a wireline formation tester (WFT). A mini-DST is performed by means of a WFT equipped with either a single probe or a dual packer to determine the fluid type and productivity of each individual level. Two field examples are presented to compare well performance predicted by the micro-scale mini-DSTs with macro-scale production tests. In both cases, the traditional DST is eliminated from the drilling/completion program. The final verification consists of comparing individual level contributions derived from the mini-DSTs with production logs. In the first case, mini-DSTs are able to provide the fluid type and individual level transmissibility (kh/μ) for 8 out of 13 distinct levels. A cost-effective approach of running mini-DSTs by means of a WFT equipped with a single probe is demonstrated to investigate multiple levels in the thin hydrocarbon reservoir sequence. Guidelines are provided when a WFT with a dual packer is deployed to perform a mini-DST in the laminated formation. In the second case, the same workflow was applied to derive the fluid type and transmissibility for two wells consisting of more than 30 distinct levels in the same field. After integrating mini-DST results from the two wells located 750 m apart, a framework is constructed to establish both vertical and lateral heterogeneities of thinly laminated reservoirs. The integration helps visualize a multiple-layered reservoir. Our examples confirm mini-DSTs effectively define individual layer producibilities in multiple-layered reservoirs. The benefits are illustrated through case histories that demonstrate our ability to manage expectations of well performance in thin hydrocarbon reservoir sequences.