HP/HT Gas-Condensate Well Testing for Shell's Onyx SW Prospect

Abstract

This paper covers the HPHT Gas-Condensate Exploration Well, 6406/9–1 on the Onyx SW prospect of the Norway Sea in the late spring of 2005 (Figure 1 and 2). The well test design and execution is presented in the paper, including; up front planning, job design, technology selection and review of the test results vs. the objectives for the well test. The paper also addresses how health, safety and environmental considerations were handled. Traditional well testing methods and equipment have evolved over the years, adapting to changing requirements. This has resulted in requirements for more complex data gathering over a shorter time with much stricter environmental and safety constraints. Coupled with increased needs for more accurate reservoir data for prospect evaluation, this has put a higher emphasis on upfront planning and improved technical performance together with extensive use of advanced fluid data gathering methodologies. This paper demonstrates how the above was addressed for the Onyx SW and how the results compared with the set goals. The application of the latest technologies in Gas-Condensate well testing was used on this job. Experiences from this were later used as the basis for other gas-condensate prospects, including those in the Russian sector of the Barents Sea. This paper focuses in particular on Fluid Sampling, Surface Well Testing and Subsea equipment. As several service companies were involved on this particular job, we have only included some general and limited content for the other services involved. Introduction The Onyx South West exploration well, 6406/9–1, was the second well to be drilled within licence PL 255 (Table 1). The first well 6406/5–1 in the Tott East prospect was drilled in 2002 to intersect sands of the Middle-Lower Jurassic Garn, Ile and Tofte formations2. Well 6406/9–1, Onyx SW, was planned as a vertical exploration well, with a HTHP pressure regime. The HPHT conditions in the well were marginal; however it was designed and executed as if under full HPHT conditions. Maximum anticipated surface pressure, with anticipated reservoir fluids to surface, was deemed to be less than 690 bar. Anticipated bottom hole static temperatures were anticipated in excess of 150°C. This well was drilled using a semi submersible drilling rig. The Geological objectives for the well were to test the Middle and Lower Jurassic; Garn, Ile, Ror/Tofte and Tilje Formations for the presence of Hydrocarbons (see Table 2 for details). The stacked reservoirs were sandstones with intercalated shales belonging to the Fangst and Båt Groups. Separate by shale intervals (Not, Ror) typically formed intra-formational seals. The main objective of the Onyx SW well test was to investigate the stacked formations Ile, Ror/Tofte and Tilje by conducting a multi-zone DST, with each interval being tested separately. Testing of two zones with a third as a contingency was planned to cover the formations of interest. Results from the well logging narrowed this to execution of a two zone DST, from a cost vs. benefit stand point. Key performance indicators One of the most important and basic requirements in the Norwegian and international oil industry is to have control of the activities offshore, to act on issues in a proactive manner, and to capture experience data. For the Onyx SW well the operator used their KPI system to the fullest in close cooperation and supported by the corresponding service company systems. The objectives set for the job were clear and concise;Zero LTI'sZero HPI'sZero Environmental incidents All well test objectives achieved and driven by the operator throughout the planning and execution phases of the job with full support from the service companies.