Subsurface Mapping of the Early Miocene Retrench Sandstones Along the La Fortune Anticline, Oropouche Oilfield, Southern Basin, Trinidad, W.I.

Abstract

Abstract

The Early Miocene Retrench sandstone are found encased within the heavily folded deepwater Golconda Marls of the Cipero Formation within the Southern Basin of Trinidad. These sandstones serve as the primary reservoir for the onshore Oropouche oilfield along the west south westerly plunging, south easterly verging detached La Fortune Anticline. During the Early-Middle Miocene, the apparent eastward migration of the leading edge of the Caribbean Plate resulted in an oblique collision with the attenuated northern margin of South America Continental Crust, generating foredeep settings in the Southern Basin of Trinidad, into which the Retrench turbidites were deposited in tectonically related pulses within synclinal lows. Continued transpression into the Pleistocene resulted in the sands being incorporated within the Present Day heavily imbricated and tear fault dissected La Fortune Anticline.

From 1955 to 2015 a total of one hundred and fifteen wells have drilled and tested the prolific Retrench sandstones along the La Fortune Anticline, yet very little scientific evaluation of these reservoirs have been undertaken. In May 2015, the current operator, API Petroleum, embarked on a three well drilling campaign, including development and semi-appraisal wells. Realizing the increase in step-out well challenges, a first-of-its-kind integrated subsurface mapping of the Retrench reservoirs was undertaken to better understand the properties of the reservoirs and to de-risk future drilling. The subsurface evaluation workflow integrated petrophysical correlation of vintage electric logs, operations and drilling data, as well as paleontological reports. Interpretation along semi-regional 2D and 3D seismic datasets allowed for the generation of structure, net sand and net oil sand maps. Rock cuttings from the recent drilling campaign were used to generate thin sections to evaluate the texture, mineralogy and depositional environment of the primary reservoir. Detailed biostratigraphic analysis of the rock cuttings were undertaken to relate the benthic to planktonic foraminiferal ratio in an attempt to assess the water depth of the depositional environment.

Finally, structural restorations along seismic cross sections were undertaken to simulate the evolving bathymetry of the Early Miocene foredeep for the Retrench reservoirs, aiding in the prediction of the turbidite fairway and de-risking future drilling prospects within the Oropouche oilfield, La Fortune Anticline.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016