Structural Development and Petroleum System of the Sandino Fore-Arc Basin, Central America

Imke Struss¹, Bernhard Cramer², Manuel Duarte³, and Jutta Winsemann^1
1 Universität Hannover, Hannover, Germany
² Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany
³ Dirección de Desarollo Petrolero, Managua, Nicaragua

The Sandino fore-arc Basin belongs to the Central American arc-trench system and developed since Late Cretaceous times. The basin is filled with up to 10.000 m thick Cretaceous to Pleistocene marine and continental deposits. 4 wells have been drilled in the offshore section of the Sandino Basin in which oil and gas shows were encountered. From onshore Nicaragua an oil seep is documented. Reflexion seismic data and well-log information were combined with results from extensive outcrop logging to reconstruct the structural and sedimentological evolution of the basin. In addition, type and maturity of kerogen in well-cuttings and in rocks from onshore outcrops as well as the geochemistry of seeping oil were investigated to characterise the petroleum system. For simulating the thermal history of the Sandino Basin and the petroleum generation from different source rocks 1D/2D petroleum systems analyses were conducted. As results we conclude that rocks of the Eocene Brito and Oligocene Masachapa formations act as effective source rocks when reaching sufficient burial depth. As another possible source rock Upper Cretaceous organic rich shales of the Loma Chumico formation are documented from the southern part of the Sandino Basin and the adjacent Tempisque Basin. Petroleum generation from Tertiary source rocks started in Middle Miocene times and still continues. In contrast, generation from the Upper Cretaceous already ceased during the Upper Miocene. Favourable conditions for hydrocarbon traps are expected at the outer structural high and anticlines of the Sandino Basin.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005