Gas-Oil Shale, The New Frontier Exploration in Brazil

de Miranda, Frederico S.

Given the three major geologic models of discoveries in Brazil: the Meso-cenozoic turbidites in the 70's and 80's; Aptian and Albian carbonates along the 90's and more recently the "Pre-salt" microbial boom in the late 2000's, the unconventional reservoirs have not been focused by the Brazilian E&P industry so far. Looking trough this perspective it is clear that there is a great business opportunity in Brazil, especially for gas-oil shale. Covering 2.680.000 sq. Km, 31,5% of Brazilian territory, the majority of Paleozoic basins are prolific hydrocarbon producers with well known petroleum systems. Strategically located in the northern-northeastern region, which is currently undergoing a broad and strong economic growth, and in the southeastern region, an area already submitted to scarcity of energy resources, these basins are major targets for the gas-oil shale model.

With a relatively similar geological evolution the Paleozoic Paraná, Solimões, Amazonas and Parnaíba basins (the last in development by OGX and MPX partnership) have thick (up to 660m/2165ft, with 40m/130ft of black shale) Silurian-Devonian shale intervals with a total organic carbon content in the range of 0,1-5% and vitrinite reflectance (Ro) data indicating immature to over mature source rocks, suggesting great potential for gas-oil shale.

Producing since 1937 on conventional reservoirs the aborted mesozoic rift basin of Recôncavo also has its own potential, with thickness up to 1850m/6070ft of lacustrine shales, total organic carbon from 1 to 2% and vitrinite reflectance (Ro) data indicating immature to over mature source rocks that now can be targeted for unconventional reservoirs. In a similar geological context the onshore portion of Potiguar basin holds up to 6500m/21325ft of lacustrine shale with TOC up to 4% and vitrinite reflectance (Ro) from immature to mature.

The polycyclic Proterozoic São Francisco basin has also been focus of exploration due to several gas seeps registered in the 80's that now are being associated with shales and tight sands. Lack of public information doesn't allow further understanding of this play.

It's clear that besides the 226Tcf of technically recoverable shale gas resources estimated from the 2011 EIA report for Brazil the mentioned basins can put oil-gas shale scenario in a whole new perspective. The absence of shale plays regulation in Brazil needs to be overcome in order to unleash the so far unknown potential of these unconventional reservoirs.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013