Deepwater Reservoir Elements: Mass-transport Complexes and Slides
Slides and mass-transport-related materials constitute large volumes of sediments in deepwater settings. During the past decade, extensive interpretations of 3D seismic data, done by many companies, have indicated that such deposits are quite common along most deepwater margins. In some basins, individual depositional sequences in the upper Pleistocene may consist of more than 50% slides and/or deformed sediments. For example, in deepwater Brunei, such elements comprise 50% of the depositional sequences (McGilvery and Cook, 2003), offshore Nile they average 50% of the depositional sequences and in some areas they constitute as much as 90% of the sequences (Newton et al., 2004), and offshore Trinidad they comprise 50% of the depositional sequences (C. Shipp, personal communication, 2004).
Slides and mass-transport-related sediments are rarely primary reservoirs and are certainly not primary exploration targets in siliciclastic settings. However, we review these deposits here because (1) they constitute important aspects of deepwater sediment fill, (2) they can be important regional seals and, most critically, (3) their distribution in the shallow subsurface is an important factor that should be identified in any assessment of drilling hazards and in geotechnical studies for exploration and development planning.
Specifically, the transportation and deformation of mass-transport complexes and slides causes water expulsion. As a consequence, these features commonly are overcom-pacted in the shallow subsurface, so that drilling through them can decrease drilling rates significantly. With rig costs in deep water averaging $0.25 to $0.4 million/day, shorter drilling times are imperative. The accomplishment of shorter drilling