Achieving accurate, efficient, and cost effective formation evaluations is one of the challenges encountered during the planning stage of a deepwater wellbore. The full laboratory analysis of a quality reservoir fluid sample for development planning and for optimizing hydrocarbon recovery is valuable. Obtaining and analyzing such reservoir fluid(s) can significantly affect the economics of deepwater hydrocarbon targets. Retrieving pressure volume temperature (PVT) fluid sample(s) while avoiding additional rig time and costs would be a significant advantage. Fluid sampling and characterization during the drilling process add value to other logging tool responses and can add confidence to the overall evaluation.
Technology advancements now make it possible to assist in the representation of reservoir fluid(s) when using logging-while-drilling (LWD) tools and associated services. Deploying such a solution on a high-profile project enables safe operations without compromising the advantages provided by proven technologies and execution processes. Similarities to industry-recognized standards and learnings over the last decades of testing and sampling can be implemented to facilitate successful operations. Downhole tool hydraulics efficiency, sampling pad design, flush pump capabilities, and fluid identification measurements are some of the essential features available.
This paper presents a case study of what can be achieved when using LWD technology exclusively to perform testing and sampling during a field test on a deepwater well producer in the Gulf of Mexico. All LWD data acquired and the results obtained are reviewed and described. The evaluation of a laminated sand reservoir was completed using conventional formation evaluation log responses. The high-quality LWD formation pressures determined an accurate oil gradient, which validated offset wireline data. Interpreted mobility information was used as part of the decision making process for the fluid sampling operations, resulting in collecting a total of three PVT and two standard fluid samples at two different depths. The workflow process adopted helped to ensure that the downhole fluid characterization was fully optimized during realtime data monitoring and data analysis, including the pretest parameters, pump-out rates, and fluid contamination estimations.
The paper also discusses sample quality verification from the contamination levels estimated during the pump-out sequence. All of the benefits provided by this new formation evaluation capability are established, including recommendations from lessons learned during the delivery of this step change in deepwater formation fluid evaluation and description.