Characteristics and Applications of Behind-Outcrop Borehole Image Logs of Deepwater Strata

Slatt, Roger¹, Robert J. Davis², Aaron Rothfolk¹ (1) University of Oklahoma, Norman, OK (2) Schlumberger, Oklahoma City, OK

Although cores have been taken from behind outcrops for many years, to our knowledge it was not until 1995 that the first behind-outcrop borehole image log was obtained (from the Mt. Messenger Formation in New Zealand). Since that time, researchers have acquired image logs from behind other outcrops. In this poster, we describe the logs and cores we have accquired from behind the following three turbidite outcrops:

-Two 50-100m research wells into the Miocene Mt. Messenger Formation leveed-channel/sheet sandstone complex;

 -650m research well into the tight-gas Dad Sandstone member of the Cretaceous Lewis Shale leveed-channel/sheet sandstone complex, Wyoming;

 - 77m research well into the Pennsylvanian Jackfork Group channel- and sheet-sandstones, Arkansas.

Wells were logged with either Schlumberger's Platform ExpressTM and FMITM log suites or Baker-Hughes STARTM image log with full log suite. From these three studies, a catalog has been developed of borehole images of deepwater sedimentary structures and stratification sequences which are calibrated to cores and/or outcrops.

The results indicate that good images of a range of sedimentary features can be acquired. Surprisingly, borehole images often highlight subtle sedimentary features not readily observeable in core. In addition, orientations of sedimentary features can be measured from image logs, which is not possible with unoriented cores.

These images have been used to interpret deepwater depositional processes and environments, relative reservoir quality, sediment transport directions, and lateral attributes such as continuity away from a wellbore. In some cases, interpretations based upon borehole image logs have aided in successful drilling of productive wells.