Effects of Organic and Inorganic Composition and Thermal Maturity on Porosity Development in Woodford and Horn River Shales

Unlike conventional reservoir sandstones and carbonates, shales have extremely low porosity and complex pore structure. To understand the deliverability and storage of shale gas, one needs to know nature and distribution of pores present in shale gas reservoirs and understand the controls on porosity development. Our objective in this research is to document the porosity characteristics of shales and to test the effects of various shale attributes, including total organic carbon, inorganic composition and thermal maturity.

We have examined a series of samples from the Upper Devonian Horn River Shale (Horn River Basin, British Columbia) and Upper Devonian Woodford Shale (Permian Basin), using a combination of imaging, multipoint BET adsorption and desorption experiments and high pressure mercury injection analysis. The Woodford suite includes samples at maturities of 0.65% and 1.2 Ro. Our data pore size distribution shows that the pores in these rocks predominantly nanometer range from less than 2 nm to more than 200 nm. Multipoint BET analysis on the Woodford samples shows that the specific surface area of higher maturity samples is higher than in the lower maturity samples, suggesting that new nanometer-scale pores form as hydrocarbons are generated. In the most thermally mature samples, surface area increases with total organic carbon content. We are working to establish whether porosity is also controlled by rock mineralogy, specifically clay content.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California