Over the past several years, a combination of data from field and laboratory experiments, published data from commercial treatments, and concurrent analysis and model development activities has led to a better understanding of the processes occurring in coal during stimulation operations. At the same time, better modeling capabilities have been developed. For example, a new hydraulic fracture design model that includes pressure-dependent non-linear leakoff, multiple interacting fractures, and failure in the coal near the fracture plane as a result of changes in effective stress, is being developed and is being used to study fracture propagation in coal. In addition, two- and three-dimensional discrete element and hybrid finite element models that couple the mechanical and multi-phase fluid response of the coal have been applied to analysing problems arising in cavity completion operations.

The paper compares data obtained from field trials in coal seams with model simulations and discusses implications for stimulation design and execution.

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