Cenozoic Source Rocks of the Southwestern Nicaraguan Rise, Caribbean Sea: Distribution, Burial History, and Maturation

Carvajal Arenas, Luis Carlos¹; Mann, Paul; Bissada, K. K. (Adry); and Saunders, Mike
¹[email protected]

Understanding the burial and thermal maturation histories of the main source rocks in the Southwestern Nicaraguan rise (SWNR) is critical for defining and characterizing the petroleum systems in this frontier region characterized by localized, fault-bounded depocenters. This study utilized data from five exploratory wells with TOC%, four ODP-DSDP wells, more than 5500 Km of 2D seismic, and surficial - bottom hole heat flow measurements. Exploration wells have previously documented oil and gas shows in the stratigraphic interval from Lower-Middle Eocene through Miocene in SWNR. Lower-Middle Eocene source rocks encountered in these wells correlate with the Yellow Limestone and Chapelton Formations of Jamaica; Jamaican samples show Total Organic Matter (TOC %) of 15.32%; with an average of 3.83%. Miocene source rocks present in Perlas-3 well (Nicaragua) share same age range and similar TOC% as Monterey interval in California (maximum 6.23%, average 2.76%) indicating the possibility of the same Monterey paleoceanographic event affecting large areas of the Caribbean Sea. The purpose of this work is to establish the lateral continuity of the Eocene-Miocene source rocks into the SWNR, to define zones that have reached the oil window, and to examine potential migration pathways.

Source rocks found in the SWNR corresponds to 1) Lower Eocene, dark greenish-gray , calcareous clay with total thickness of 56 m; 2) Middle Eocene calcareous limestone-claystone with thickness average of 132.3 m; 3) Middle Miocene greenish-gray, foram-rich chalk with 139 m of total thickness.

In order to determine the Source Potential Index (SPI) (Tissot et al., 1980), adjacent wells were used to extrapolate known TOC % values across the 225,000 km² study area. TOC% values range from 2.76 to 3.83%, and heat flow values vary between 2.5°C to 3.5°C per 100m.

Considering all the limitations present in SWNR, we conclude that i) an expulsion of 10.5 MMBO of oil per km², ii) main depocenters were recognized ranging between 3 to 8 km depth; in which, according to subsidence plots, source rocks reached the oil window between the intervals 3 to 3.5 km, and iii) the migration is most likely vertical than laterally drained due to the high angle faulting (polygonal faults) present between the Eocene-Miocene intervals; iv) therefore, we consider that the main possibility to find hydrocarbon accumulations is close to the depocenters of the source rocks. Possible reservoirs and seals are illustrated.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013