Michael P. Sullivan¹, Leon Dzou¹, James Lantz², Genaro Montemurro¹, Fernando Alegria³, Oscar Aranibar³, Andrew S. Pepper¹, Nigel Robinson³

(1) BP Upstream Technology Group, Houston, TX
(2) BP, Sunbury-upon-Thames, Middlesex, United Kingdom
(3) Empresa Petrolera Chaco, Santa Cruz, Bolivia

ABSTRACT: Petroleum Systems of the Boomerang Hills Area, Central Bolivia

The Boomerang Hills area represents a spectacular example of a very young petroleum system (reservoirs as young as Upper Oligocene) supplied by very old (Silurian-Lower Devonian) source rocks. We integrated source rock and petroleum geochemistry with 1-D and map and section-based 2-D basin models to understand petroleum expulsion, migration, and trapping patterns.

Traditionally, studies proposed the bulk thickness of organically lean Mid Devonian Los Monos / Limoncito Formations as effective source rocks; however, geochemical analyses of rocks and fluids, together with thermal stress mapping of the kitchens, identify the Silurian Kirusillas and Lower Devonian Boomerang Fms as the two main contributors to the petroleum budget. Only the deepest parts of the basin are mature for oil expulsion from net source intervals in the Mid Devonian upper Limoncito / Los Monos Fm.

Calibrated thermal models illustrate the impact of the multi-phase burial and uplift history of the area. The gas-prone nature of the system overall reflects the depletion of the system's oil potential during Paleozoic foreland basin deposition. Following Mesozoic regional uplift and erosion, re-burial beneath a Neogene-Pleistogene foreland sequence occurred under a heat flow regime lowered by the transient effects of rapid sedimentation. Consequently, the key is to predict the modest amounts of incremental Neogene expulsion.

Petroleum is initially focused by Silurian-Lower Devonian sandstones, either into structural highs, or to its regional subcrop beneath the Mesozoic at the northern basin margin. The Mesozoic-Tertiary structural attitude differs quite markedly from the Paleozic, leading to some unexpected patterns in petroleum distribution.

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