Distal Thin Bedded Pay Analogs in Shelf Edge Delta Deposits of the Columbus Basin, Trinidad and Tobago

Diego I. Sanabria and Rene Winter
BP Trinidad and Tobago LLC, Port of Spain, Trinidad and Tobago

Shelf edge delta deposits of the Paleo Orinoco River constitute the main exploration target in the Columbus Basin of Trinidad and Tobago. The vast majority of the reserves to date are related to massive sandstones in proximal deltaic settings. However, as the basin matures, and in order to maximize the value of the assets, bpTT is becoming increasingly interested in thin bedded pay (TBP).

TBP associated with shelf edge deltas in the basin is found at different levels within progradational successions. Along the proximal reaches of parasequences TBP can be found in tidally influenced distributary channels. In more distal positions, along the lower delta front to prodelta, TBP is primarily related to sediment gravity flows. This study is concerned with outcrop analogs for such distal deposits and their implications for resource estimation and reservoir performance in the subsurface.

Outcrops in southern Trinidad provide a great opportunity to study relatively well exposed occurrences of TBP analogs accumulated in environments of deposition similar to those of nearby production and potential targets in the subsurface. Examination of these outcrops suggests the existence of two contrasting types of distal TBP. The main differences between these two facies associations are related to overall thickness of beds, lateral continuity, and amalgamation ratios which are ultimately controlled by depositional processes. The more laterally continuous facies association is characterized by interbedded sandstones and shales which are primarily tabular as well as heterolithic successions. The discontinuous facies association is dominated by interstratified lenticular sandstones and shales with moderate amalgamation ratios. Sandstones are accumulated in chutes or as lenticular beds with convex upward geometries or flat based with erosional relief along the base.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas