Microseismic Monitoring Of Hydraulic Fracturation Using Surface Recording Network: A Vaca Muerta Fm Case Study, Neuquén, Argentina

Marc Grausem
Head of Geophysics, Total Austral

Monitoring the geometry and the behavior of hydraulic fractures in the Vaca Muerta oil & gas shale in Argentina is an important aspect for future development plans. The hydrocarbon production is presently in its very early stages and very few vertical wells are available to be used as close-by monitoring wells (<500m distance) for microseismic. For that reason it has been decided, in Total Austral to evaluate passive seismic recording of microseismicity related to the fracturation treatments in the Vaca Muerta by using a surface seismic network.

During 2008-2009, learning has been acquired by monitoring several fracturation jobs in the Mulichinco tight sands (~1600 m deep) in the Neuquén basin using surface seismic recording network compared to recording systems in the wells. The detected events of a former Mulichinco treatment were transposed at 2800 m depth (~Vaca Muerta) in order to simulate the energy of the induced fractures recorded at the surface, to design the surface seismic network geometry to be used and to estimate the amount of traces necessary to sample the first arrival signal.

During April 2012 we recorded, with a surface network of 2500 traces, the microseismicity response from several stages of fracturation in the Vaca Muerta performed in a vertical well.

Recording microseismicity with a surface network gave us the ability to analyze the focal mechanism of the microseismic events which were detected and re-located in space. The results of 2 stages are presented as well as an interpretation of the focal mechanisms and the alignment of the events compared to the knowledge of the local tectonic context and the fault trends in the basin. This interpretation allowed us to distinguish between newly tensile opened fractures directly related to the frac treatment and the re-activation of a pre-existing fault/fracture system.

An evaluation of the uncertainties in positioning of the events is also presented as well as a comparison with the image logs and the fracture analysis from the well data.

AAPG Search and Discovery Article #90165©AAPG 2012 GEOSCIENCE TECHNOLOGY WORKSHOP, 2-4 December 2012, Buenos Aires, Argentina