Design and interpretation of transient tests at well's inception
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Copyright 2015, Society of Petroleum Engineers. Operators often avoid conventional drill-stem testing (DST) in offshore environments because it is costly and its value lacks transparency. Short-duration tests may be a promising alternative to conventional DSTs for learning formation conductivity, but they should not be restricted to exploratory wells. Short-duration tests can have a profound impact in any deepwater field-development setting. Stakes are high when unfavorable productivity and injectivity indices may change the well count calculus. Tools such as formation testers provide a credible alternative, but closed-chamber tests (CCT) and/or slug tests are also helpful for situations in which large volumes of formation fluid are sampled. Given that short-duration tests (CCT and slug) can last only a few minutes-particularly in highconductivity reservoirs-we approached the challenge with a two-fold strategy. First, we developed a forward model to design the chamber length to ensure that we collected interpretable test data. Second, we combined the CCT and slug tests so that we could control the total test duration, particularly in high-conductivity reservoirs. The approach presented here allowed individual treatment of slug, CCT, and reverse-slug or injection test for underpressured reservoirs. Overall, the model presents a simple, yet complete approach to design and analysis of these short-term tests.