the fluid analysis program are matched to the complexity of the fluid column. This improvement in sampling and testing efficiency enables opera- tors to detect fluid complexity and resolve ques- tions arising from the downhole information. Fluid complexities occur for many reasons.


Kerogen, the major global precursor of petro- leum, consists of selectively preserved, resistant, cellular organic materials (algae, pollen, spores and leaf cuticles) and degraded residues of biological organic matter (amorphous material). The conversion from kerogen and the migration of fluids from source rock to reservoir rock impact fluid properties and composition. In addition, reservoir-scale fluid complexity can be caused by differences in temperature, pressure, gravity, biodegradation, phase transitions and reservoir charging history.


During early deepwater development, much


of the interest in fluid composition measure- ments focused on flow assurance into the well- bore, through pipelines and within production facilities. However, it became evident that even more-significant problems occur in the reservoir. Consequently, the emphasis of fluid analysis has shifted to the reservoir, where knowledge of in situ fluid properties has considerable bearing on well placement, reservoir development, comple- tion strategies and surface-facilities design. Using the downhole laboratory provided by


DFA sensors, reservoir engineers quantify fluid properties with an accuracy that approaches that of surface-laboratory measurements. The advan- tage of DFA is that fluid properties are measured under reservoir conditions. Unlike equivalent


measurements in a surface laboratory, engineers can repeat, validate or use measurements to explain reservoir heterogeneities. A surface labo- ratory can repeat measurements, but only on the same sample. Moreover, DFA employs the same tool, time, temperature, calibration and technical operator—but with different fluids—from one DFA station to the next. DFA measurements can also enable identifica-


tion of reservoir compartmentalization, which is defined as lack of free-fluid flow between different regions of a field over production timescales.3


Flow


units within a reservoir can range from massive to minute, and effective drainage during production requires that the well contact as many compart- ments as is economically feasible. Because com- partments are a major cause of reservoir underperformance, some experts suggest that this


Winter 2009/2010


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