Deepwater DST Design, Planning and Operations—Offshore Niger Delta Experience

Abstract

Abstract This paper focuses on the complex design, planning and operational aspects for a case study appraisal deepwater well in the Niger Delta, offshore Nigeria. The objectives of the Drill Stem Test (DST) were to plan and execute safe operations, determine well performance and reservoir properties whilst overcoming the challenges of gas hydrate formation and sand production from an unconsolidated formation. Exploration activities are high in the emergent West Africa deep offshore region leading to regular execution of DST’s. However the peculiarities of the locality transform the design, planning and operations involved in execution of such deepwater DST’s into complex challenges. The ability to successfully design, plan and engineer the operations of such tests to obtain relevant results becomes crucial because the accurate determination of well performance and evaluation of reservoir properties of the West African complex faulted reservoirs often prove to be game changers in the development decision making process. The paper begins with a brief discussion of the DST design methodology: simulation of different test scenarios based on prognosed reservoir properties, rate and test sequence definition. The contingent DST design is updated with changes to its data assumptions based on actual well results. Secondly, the planning for the DST project is described including: rig choice, perforation, sand control, downhole completions, tool and equipment choices etc. Furthermore, the operations are described: hydrate inhibition process, equipment layout for DST package, data acquisition and fluid sample acquisition. This paper contributes a demonstration of how in a studied field case, careful design and innovative planning of the operational aspects of a deepwater DST ensured that targets were delivered so that pressure transient analysis yielded crucial information regarding well productivity, reservoir properties and boundaries.