In recent years, there has been a growing realization that improper treatment of reservoir complexities such as compartmentalization and fluid compositional variation commonly lead to gross inefficiencies in facilities design, production strategies and predicted production; new methods are mandated. (A compartment must be penetrated by a well to drain.) Previous twin working assumptions of homogeneous distributions of hydrocarbons in giant reservoir ‘tanks’ or compartments are now understood to be uncommon; one must prove, not assume the value of the reservoir. It is now understood that reservoir fluids not only exhibit complex distributions, but these distributions are frequently not in equilibrium. Even though the fluids have been in reservoirs for geologic time, there can be active processes involving reservoir fluids such as biodegradation that preclude establishing. In addition, diffusion at the reservoir length scale is slow even on geologic time scales often resulting in preservation of disequilibrium associated with the hydrocarbon charge history. While these complex fluid distributions create difficulties in production, they can be very useful to address reservoir architecture, one of the least understood technical issues in the oil business. Man has been to the moon but not to a subsurface oil reservoir. Sealing barriers that have huge production implications are often not evident in seismic and not even in standard petrophysical logging. Nevertheless, the distributions of reservoir fluids reflect these barriers associated with the hydrocarbon charge. The central questions arise: how can we identify fluid compositional variations in the reservoir and how can we use these measured variations to understand reservoir architecture (all within an acceptable cost structure)?

© 2009 Optical Society of America

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