Turbidite Slope Channels - Patterns of Reservoir Distribution and Heterogeneity

By

 Mike Mayall¹, Richard Syms², Ed Jones², Jonathan Henton¹

(1) BP, Sunbury, United Kingdom (2) BP, Staines, United Kingdom

 Turbidite slope channels contain potentially complex reservoirs that offer a number of challenges to reservoir development. Although there is a degree of uniqueness to each channel, recognising recurring aspects of channel development, provides a process for systematically evaluating the problems that may need to be resolved during field appraisal and production.

The distribution of the reservoir and the heterogeneity patterns is inevitably a function of three aspects; the facies, multi-phase fill and stacking patterns. The facies is dominated by four components –

-A basal lag which overlies the erosional surface. In most cases this comprises coarse sand and granules but may also be composed of mud-clast conglomerates or ‘by-pass’ shale drapes.

-Slumps and debris flows derived from the walls of the channel or from longer distance transport.

-Stacked high N:G channels dominantly composed of massive sands but also with more interbedded marginal facies.

-Sinuous low N:G channel levees often form the last phase of the channel fill.

This simple pattern is made more complex as the large erosional conduit is re-occupied during several episodes of cutting and filling. This process has at least two important impacts on reservoir volumes and the development of the heterogeneity patterns –

-         Erosion by a later channel may leave the channel axis of previous channels preserved only as erosional remnants

-         One or more of the phases of channel fill may be dominated by muds or debris flows.

Numerous styles of stacking patterns in the large channels can be present and stacking patterns may vary radically over short distances within a field.