A Cost Effective and User Friendly Approach to Design Wireline Formation Tests

Abstract

Problem statement: Wireline formation testing (also named Mini-DSTs) are gaining more and more popularity as a possible alternative to conventional well testing especially where there are major environmental and economical constraints. The increased offshore exploration activity, which often implies highly risky and huge operational costs, makes the conventional well testing less attractive in favor of other technologies that can provide some of the key dynamic information about the well-reservoir system through relatively quick and less expensive operations. The design phase is recognized to be one of the most critical aspects in order to guarantee an acceptable value of information in exploration scenarios where very limited data is available. The success of any mini-DST operation can be significantly compromised if two major issues are not addressed in the design phase: possibility to clearly identify the radial flow behavior and avoidance of noise in the pressure response due to the gauge resolution. Approach: The study consisted in the development of a new tool for mini-DST design to easily identify whether this technology can be successfully applied. The tool comprises dimensionless and dimensional charts, which are of general validity because they can be applied to any lithological environment and for any type of hydrocarbon. Results: Field applications proved the reliability of the charts: First of all the test durations were optimized to collect interpretable bottomhole pressures and to obtain valid reservoir characterizations. Besides, a cost saving effectiveness was achieved avoiding the acquisition of useless extra-data affected by noise due to gauge resolution. Conclusion/Recommendations: The use of the charts is strongly suggested at the early stage of decision making for new exploration/appraisal operations; they are a user-friendly tool for assessing the feasibility of a mini-DST test. Additionally, the charts are more versatile with respect to available commercial software in managing uncertainties of the major input parameters.