Cleat Compressibility

Introduction

Cleat or void volume compressibility of a coal, analogous to pore volume compressibility of conventional
reservoirs, is a measure of coal fracture volume loss due to applied loads. In coals, this rock property certainly depends on coal age, rank, purity, and other coal properties.

This property, also termed formation compressibility, primarily affects reservoir behaviour in undersaturated coals above desorption pressure.

As a coal seam depletes, decreases in reservoir pressure are matched by increases in rock stresses to support the lithostatic load. Voids in the coal, comprised of both coal cleats and pores of various sizes, deform over the course of depletion in response to these stress changes. Coal cleat compressibility, like pore volume compressibility of conventional reservoir rocks, is expressed mathematically as:

See Also:

CSG Cleat Compressibility Examples

References:

• John Seidle, Fundamentals of Coalbed Methane: Reservoir Engineering, 2011, PennWell Corporation.