Stratigraphic Traps as Exploration Targets Examples from Petrotrin’s Soldado Acreage, Gulf Of Paria, Trinidad
Archie, Curtis1 and Gallari-Raboobar, Nancy
To date, most of the exploration and development drilling in Petrotrin’s Soldado fields have targeted accumulations associated with anticlines and fault closures, usually with good success, and after fifty nine years of exploitation all of the easy structural targets have been identified and tested. There is 95% coverage of the acreage by 3D seismic of different vintages, seven producing fields in which around 950 wells have been drilled.
Formations penetrated in the area range from Lower Cruse to the Morne L'Enfer. The Cruse represents a progradational sequence of deep water turbidites to shallow water (delta) sediments. The top of this sequence is marked by an unconformity that is overlain by the Forest Formation, another progradational sequence of prodelta to shallow water delta sediments. The Morne L'Enfer unconformably overlies the Forest. The major structural features within the area are the Erin Syncline which is bounded to the North by the Main Field Anticline and to South by the Southern Anticline.
To replace and grow reserves, a different approach was needed. As part of a re-evaluation of exploration leads in 2002, the 3D seismic was re-interpreted and four major stratigraphic surfaces mapped, the Top Forest Formation, the Top Cruse Formation, the Top Lower Cruse Member and the 10.5 m.a. unconformity. Interval RMS amplitude maps for the Forest interval revealed meanders, channels, point bars never before seen in the area , the unconformity at the base of the Morne L’enfer was also seen in areas to erode deeply into the underlying Forest, truncating the reflectors and associated stratigraphy. This unconformity and its overlying claystone dominated sediments have created a stratigraphic trap on the southern flank of the Erin Syncline. The occurence of a flat spot strongly suggests a fluid contact within the Forest interval.
Traditionally the Lower Cruse interval has been mapped as being dominated by basin floor fans, however a re-examination of the paleobathymetries and log motifs suggest a slope setting. Spectral Decomposition using a frequency of 10 Hz and a time window of 100ms illustrates a channelized system with sand thickness of 513’. A south to north trending progradational feature was mapped, which internally exhibited bidirectional downlap that created potential closures in an up dip direction. This event was also correlated to an oil bearing zone in another exploration well 7,000’ away.
AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013