Reservoir fluid PVT is the basis for efficient reservoir development plans, appropriate facilities, and plant design and operation and plays a vital role throughout the production life of the reservoir. Acquisition of representative high quality in- situ reservoir fluid samples is the first step in this process and requires special attention. The challenges of acquiring representative samples depend on a number of factors, including the type of the fluid being sampled, the initial reservoir conditions, and the formation properties. The sampling issues related to various fluids are discussed, such as oils (i.e., heavy, black, volatile) and rich and lean gas condensates. Furthermore, the challenges involved in sampling fluids containing acid gas components and in cases where oil- based mud (OBM) is used during drilling are also outlined. In addition, the challenges of sampling reservoirs that are near- saturated and contain unconsolidated formation are highlighted. Finally, the challenges posed by unconventional plays are also described, such as shale reservoirs that tend to be in transient flow for long periods. The need for a rigorous decontamination technique for OBM contaminated samples is discussed. The following are the key elements for a successful sampling program: 1. A customized pre-job sampling plan 2. Meticulous on-site implementation with proper QA/QC 3. A contingency plan to acquire as best a sample as possible in case of unexpected operational difficulties 4. A rigorous method of decontamination to obtain in-situ composition in case of OBM contamination In this paper, these elements and possible solutions of the formidable sampling challenges are discussed in detail and illustrated with field examples.
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