A strict geological definition of shale is any “laminated, indurated (consolidated) rock with > 67% clay-sized materials” (Jackson, 1997). Approximately 50% of all sedimentary rocks are classified as shale. Shales are often deposited in low-energy depositional environments where the fine-grained clay particles fall out of suspension.
Reference: Jackson, J.A. (1997). Glossary of Geology, 4th Ed. American Geological Institute
What is Organic Shale?
When organic matter is present in high concentration, in rocks such as shale they can sometimes form a hydrocarbon source rock, from which most oil and gas contained in conventional reservoirs originated. A fine-grained, organic-rich, sedimentary rock characterized by thin layers of clay or mud, organic shale has wide variations in geology, geochemistry, geomechanics and production mechanisms. These variations occur from one resource play to the next, sometimes even within the same organic shale. No two organic shales are alike as each offers its own set of unique technical challenges and learning curves.
Producing gas from shales leaves little margin for error
Organic shale is unique in that it often contains both free and adsorbed gas. Generally, very little adsorbed gas is initially commercially produced. Free gas is the major contributor to production. Initially, organic shales have high production rates, quick decline curves, and then long-term steady production. And because shale has extremely low matrix permeability, the major challenge is obtaining economically viable gas or oil production.
For shale gas and oil plays, obtaining commercial production rates requires organic-rich shales to be hydraulically fractured, to create a reservoir volume that maximizes contact and connectivity into the shale's natural fracture systems, matrix porosity, and free porosity within the kerogen to allow access to the gas. The rewards, however, can be significant. Shale plays tend to be large in scale and offer long-lived production with attractive finding costs.
Understanding the challenges of shale gas and oil production
With first-hand experience in almost every shale gas and oil play in the world, Halliburton knows the challenges these differences create. To answer these challenges, we have proven solutions through every phase of shale gas and shale oil development.