Breaking Down Barriers in Mudstone Investigations: What Oil Shale Can Tell Us about Shale-Hosted Hydrocarbons

Jeremy Boak and J. Frederick Sarg

Production of shale oil and associated gas from oil shale requires artificial heating of immature kerogen, either at the surface or in situ. Development of oil-bearing shale and gas shale depends upon more traditional methods, although applied in more complex ways to oil and gas derived from kerogen that ranges from incipiently mature to overmature. However, the rocks themselves are strikingly similar, even in their compositional and textural diversity. All are very tight, impermeable mudstone (and siltstone), and production of the hydrocarbons, whether natural or synthetic, depends upon fracturing the rock to drain the products. There are, therefore many ways in which understanding of the properties of the broad class of rocks informally called shale can be complementary. The industrial divide between historic shale oil (mined and retorted) and new shale-hosted oil (drilled and produced) should not inhibit mutual understanding. Three major linked areas of investigation are critical to understanding the variations in behaviour of reservoirs in these diverse rocks. 1) Rock Mechanics - properties measured across a range of temperatures and pressures are needed to describe mechanisms of generation, migration and trapping of oil and gas, and to understand the fracturing behaviour of the rock for field development. 2) Chemical Kinetics - understanding generation of hydrocarbons requires experimentation and modeling at temperatures in the range of in situ retorts, so that these experiments are important to understanding both synthetic and natural systems. 3) Petrology and Paragenesis - behavior of shale depends not only on its organic content, but also on its mineralogic composition and the variability of that composition. These properties in turn result from the history of the sedimentary rocks, the depositional environments under which they formed, and the diagenetic alteration that followed their deposition. Using examples from our research on shale/mudstone systems we demonstrate the value of: 1) sedimentologic and petrologic characterization to create an integrated geologic framework. 2) measurement of properties critical to seismic character, rock strength and fracturing behavi. 3) modelling of rock mechanical behaviour under stress Understanding shale systems generically can provide synergistic insights across plays.

AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012