Comprehensive formation evaluation is performed by integrating logs, cores, well tests, and other geoscience and engineering information. It plays a critical role in resources assessment and is equally important in well-placement development and reservoir surveillance. It is one of the technical focus areas that is fundamental across almost all upstream businesses, from initial exploration through final field abandonment. So how well are we doing in modern formation evaluation?
In resources exploration, we have come a long way from the historical wireline (WL) triple combination of logging of bulk density, neutron porosity, and resistivity for reservoir lithology, porosity, and saturation, respectively. With continuing development in technologies such as acoustic, mud logging, nuclear magnetic resonance, imaging, and formation testing and sampling, we can identify fluid types and contacts; quantify viscosity, free fluid, and mobility; and characterize pore structure and rock mechanical properties. In addition, elemental mineralogy logs have significantly improved multimineral formation evaluation in complex reservoirs, especially unconventional shale formations.
In field development, a paradigm shift has occurred in the last decade in terms of wells drilled (i.e., we are drilling more and more horizontal, multilateral wells for maximum/extreme reservoir contact). Consequently, logging-while-drilling technologies have advanced so much that they can provide almost WL-log quality and capability. To achieve the ultimate goal of maximizing reservoir performance, looking-around and -ahead technologies are also evolving quickly.
In reservoir surveillance, game-changing technologies are emerging that enable us to illuminate the reservoir in four dimensions through measurements across wells, from wellbore to surface, and monitor smart-nanoparticle movement in situ. Development of these reservoir-scale technologies is actually in line with the grand challenges facing the exploration-and-production industry identified by SPE (i.e., developing higher-resolution subsurface imaging and increasing hydrocarbon recovery factor) because they are critical for improvements in identifying bypassed oil and assessing remaining oil.
Core analysis has historically been considered as a reference for log interpretation. Major developments in core analysis in the last decade are digital rock physics and unconventional-resources evaluation. These developments continue to push the envelope of our understanding of rock and of rock/fluid interactions.
In summary, significant progress has been made recently in formation evaluation, and we are in the process of a great journey to help resolve the grand challenges with fit-for-purpose and cost-effective solutions, as demonstrated in the selected papers and recommended additional reading.
Recommended Additional Reading
SPE 170565 Openhole Tractor and High-Tension Conveyance Package Reduce HSE Risk and Save 3 Days of Rig Time for Formation-Fluid Sampling in a Highly Deviated Well, by Michel Akue, Perenco, et al.
SPE 170722 New Method for Determining Mineralogy and Matrix Properties From Elemental Chemistry Measured by Gamma Ray Spectroscopy Logging Tools, by R. Freedman, Schlumberger, et al.
SPE 170730 Characterization of Asphaltene Transport Over Geologic Time Aids in Explaining the Distribution of Heavy Oils and Solid Hydrocarbons in Reservoirs, by Oliver C. Mullins, Schlumberger, et al.
