The Geological & Geophysical Evaluation of the S-108 Area
Archie, Curtis1 and Gallari-Raboobar, Nancy
The S-108 area is situated to the north east of the Soldado Main Field, Gulf of Paria, offshore western Trinidad. This well was drilled in 1962 to a depth of 9,622’ and penetrated a normal stratigraphic sequence from the Forest Formation at the surface to the Upper Cretaceous Naparima Hill Formation at total depth.
The Forest Formation outcrops at water bottom in this area, consequently another marker ‘Forest 1’ was chosen to do the initial correlation. Three other markers were subsequently chosen to subdivide the interval into smaller packages. The Forest and Cruse sands have been interpreted as delta deposits that include channel complexes, distributary mouth bars, crevasse splays and interdistributary deposits. These channels generally trend in a South West to North East direction.
The study initially targeted the Forest interval but the Upper Cruse (Cruse 1) sands were later included since amplitude anomalies against faults were observed.
Net Sand and Net Oil Sand Maps were drawn for the individual packages while Structure, RMS Amplitude and Net Hydrocarbon maps for Forest 1 and Cruse 1 were generated. Oil/Water and Gas/Oil contacts were mapped from the wells and RMS amplitudes also showed fit to structure . At the Forest level recoverable reserved are estimated to be 2.6 MMBO and at the Cruse 6.6 MMBO.
S-108 produced 800 barrels of 10.80 API oil from a total of 95’ of NOS from the Forest sands, the well was shut in shortly after due to uneconomic production rates for that time. A new development plan was devised that involved the drilling of 2 high angle wells to increase the amount of reservoir contact and production rates. The first well S-901 was drilled in 2011 to a total depth of 2414’ and encountered well developed sands with 120’ gas, GOC at 1910’, 85’ oil sand and OWC at 2130’ as predicted. While drilling gas breakouts occurred at the seabed around the rig, eventually this was controlled and production casing was run. The second well S-902 was drilled to 1,024’ where 9 5/8" casing was set, drilling was suspended pending a solution to the gas breakouts. The Cruse has not yet been evaluated by drilling, but offset wells in nearby fault blocks have proven productive from similar high amplitudes.
AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013