With technical advances in surface seismic and downhole electrical imaging techniques, it is now possible to not only map the distribution of reservoir sandstones in the subsurface, but to accurately define the orientation of productive fairways, or “sweet-spots”, within the sequence.
Channel sands frequently have favorable reservoir characteristics. Having often been laid down in higher energy settings, they commonly have coarser and better sorted grains, less clay and improved poroperm characteristics. However, they often have limited lateral extent and shoe-string geometries which make them more difficult to predict in the subsurface.
This paper will summarize the results of four case studies and some additional examples of how channel sands, laid down in different depositional settings, have been recognized with borehole imaging. From sedimentary features and palaeocurrent directions within the sands it has been possible to determine their orientation.
Further complexities in reservoir characterization, caused by thin beds or bioturbation; and how these effects can be recognized on the images, and quantified using other electric log data, will be discussed.
A sound understanding of the depositional model and the integration of all the available data (outcrop studies, seismic attributes, cores, logs and downhole imagery) allows channel sands to be identified in a wide range of environments. The ability to orient the channels and so map them in the subsurface provides the basis for reducing risk and optimizing the success ratio of both appraisal and development wells. Because of their potential as stratigraphic traps and production fairways, they offer good prospects for increasing recoverable reserves.
This talk has been presented for the SPWLA as part of their Distinguished Lecturer program.