L. Rudiger¹, R. Littke¹, P. Gerling², and C. Bonnemann²

¹Institute of Geology and Geochemistry of Petroleum and Coal, RWTH Aachen
²Federal Institute for Geosciences and Natural Resources (BGR), Germany

ABSTRACT: 2D- and 3D-Modelling of Hydrocarbon Generation at the Active Continental Margin off Costa Rica

For the first time a numerical basin modelling study was performed at an active continental margin, the subduction zone off Costa Rica, where the Cocos plate is subducting along the Middle America Trench (MAT) under the Caribbean plate at a current velocity of about 90 mm/a. The study area off Costa Rica was chosen because sediments overlying the Cocos plate contain much organic carbon (up to 2.1% TOC) and because a large number of seismic profiles exist.

Hydrocarbon generation was calculated for different scenarios. These scenarios include changes of subduction velocity, additional heat input by friction and changing of lithologies of the subducted sediments due to subduction erosion. The most significant influence on the amount of generated hydrocarbons within the studied seismic profile is the subduction velocity. Slowing of subduction velocity to one third of the current velocity rises the amount of kerogen which is converted to hydrocarbons in the studied depth interval from about 40% to 70%. The reason for this great difference is the temperature disequilibrium, especially at high subduction velocities. Therefore, zones of petroleum generation are situated at much greater depth than in typical sedimentary basins or at passive margins.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado