From Regional to the Shotpoint: Chachalaca Discovery, Columbus Basin, Offshore Southeast Trinidad

Natalie Hosein¹, Gene Walton², Ian J. Stewart¹, and Krystel St Clair^1
1 bp, Port of Spain, Trinidad and Tobago
² bp exploration, Sunbury on Thames, United Kingdom

After an intense eighteen month study of the Columbus Basin, the exploration unit of bpTT, resumed operations in an untested region within bpTT's eastern acreage. On 13th December, 2004, the Chachalaca well was drilled as a deviated hole to a total depth of 15633ft below rotary table, at a location about 52 miles east south east off Trinidad's east coast. The well was plugged and abandoned as a Gas Discovery well which resulted in the booking of a total resource of about 2 TCF.

The well was drilled to evaluate the exploration potential of three target reservoirs of Pleistocene age within two depositional sequence sets. These reservoirs were predicted from regional and detailed Gross Depositional Environment (GDE) mapping that identified the areas of the basin with the lowest geological risk.

The reservoirs at Chachalaca are supported by a NE-SW oriented inversion geometry, orthogonal to the NW-SE regional faults, and on trend with another earlier field discovery, Corallita/Lantana. The well successfully tested these reservoirs, which were vertically stacked within five thousand feet, but laterally separated by different fault blocks. The oldest and most significant reservoir lies in the rollover to an early counter-regional fault, and confirmed the depositional model developed in the regional interpretation.

Success was based on regional understanding of the basin, built on detailed work on all aspects of the petroleum system: structural setting, stratigraphy, facies distributions and petroleum migration and timing. Integration has been the backbone of Chachalaca's success. Similar work for future exploration, can provide similar results.