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Devonian Fracture Reservoir Play Classification After Ultra-Deep Exploration in the Southern Subandean Belt of Bolivia

LACR Andes Basins Research Symposium 2020
AAPG Distinguished Lecture

Authors: Tomas Zapata (presenter), Sergio Sarmiento, Melanie Louterbach, Daniel Peña, Judith Vila, Massimo Bonora, Victor Hugo Goitia, Camilo Restrepo, Repsol

Borehole information captured during drilling and testing operations of the Boyuy X2 well allowed building a comprehensive catalogue of geological and geomechanical conditions of this part of the SubAndean Belt. At depths of 7500 m the state of stress is strike-slip (as SHmax is horizontal), and the maximum horizontal effective stress ratio (ESR SHmax) is around 1.2. Thus, the vertical principal stress (σ2) magnitude is close to SHmax. This study proposes a classification on of the gas accumulations of the Devonian Huamampampa Fm based on the changes on regional geomechanical settings, reservoir fracture geometry and seal hydrodynamics that occur at different depths as it follows: A) Shallow Accumulations (1800 m or shallower): normal stress field, breached seal, only lithological seal capacity left, mostly liquid hydrocarbon accumulations. Normal hydrostatic regime. B) Intermediate Accumulations (2000 – 4500 m): Normal to strike-slip stress field, hydrodynamic seal, enhanced fracture connectivity, regional aquifer. C) Deep Accumulations (4000 – 6200 m): Strike-slip stress field, ESR Shmax > 1.5, fracture connectivity variable, hydrodynamic seal, fault compartment and hydraulically independent tectonic blocks.D) Ultradeep Accumulations (>6500): Strike-slip stress field, ESR Shmax <1.5, low fracture connectivity, hydrodynamic seal, fault compartment and hydraulically independent tectonic blocks. Example: Boyuy X2 discovery.Regionally, an ultra-deep commercial potential accumulation for the Huamampa Fm. reservoir is hard to visualize, since most of the current identified deep structures are deeper than 6500 m. Such potential accumulations may not be able to deliver commercial flow rates since the actual stress field would not support open fractures in any orientation.


Tomas Zapata, Repsol

Tomas earned a geology degree from the University of Buenos Aires; Argentina; a PhD from Cornell University, Ithaca New York; and was part of the Director Development Program (PDD) at the IAE School of Business, Universidad Austral, Argentina.

With 25 years of experience in the industry, he currently is Director of Exploration Americas Assets for Repsol USA Corp. at The Woodlands, USA, where he is responsible for the whole Exploration Business Activities (Planning, access, execution, abandonment) of Repsol in the Americas Region (Bolivia, Peru, Colombia, Guyana, Brazil, Mexico, US. GOM, Alaska). He has previously held positions at YPF S.A., Argentina, and at University of Buenos Aires as Associate Professor of Petroleum Geology).

Tomas is a member of AAPG and AGGEP (Spain).

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