The Reservoir Geology of Mudrocks

Hall, Craig D.

By definition, commercial mudrock reservoirs are composed predominantly of clay-sized particles, and the majority are also self-sourcing by virtue of their constituent organic matter or kerogen. Reservoir energy and a degree of brittleness are also desirable traits. As with conventional reservoirs, the first order control on the productivity of mudrock reservoirs is the texture and composition, which are determined by source area, climate, and depositional environment. Tectonic setting controls burial history and thus burial diagenesis, which leads to compaction and cementation. However, due to their finer grained textures and more diverse compositions, the pathway to commerciality for mudrock reservoirs is a more complicated one compared to sandstones and carbonates, and the attributes that determine productivity may be different from play to play. The appropriate depositional environment will produce a formation with suitable dimensions and internal stratigraphy that is composed predominantly of clay-sized particles and organic matter, and that will inhibit the destruction of the organic matter by processes operating at or just below the sediment-water interface. Sufficient burial and heating are then required to recrystallize the minerals into brittle cements, and generate hydrocarbons from the organic matter. The net effect of all of these processes is reservoir quality, which can vary from basin to basin, and from formation to formation. Each mudrock reservoir possesses it's own "personality", and recognizing the relative contributions of depositional environment and burial history to the development of the reservoir leads to more accurate risking of new plays.

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