Shale fracture surface area measured by tracking exchangeable cations

Hydrocarbon production from oil shale and shale gas is increasingly important for securing the energy supply to society. Such shale reservoirs, however, typically have low permeability, and hydraulic fracturing is required to facilitate economic production. Hydraulic fracturing significantly increases fracture-matrix contact areas (through activating pre-existing fractures as well as creating an artificial fracture network), which is of key importance for efficient production. In this context it is vital to estimate this contact area and associated fracture network structures. Conventional techniques, i.e. micro-seismic mapping and pressure transient analysis, however, only deliver limited information. We thus propose here a new experimental technique, which can measure fracture-matrix contact areas; and the accuracy of contact area measurements can be considerably improved. The proposed technique is based on cation exchange processes and chemical tracer measurements. We verified this technique experimentally with laboratory measurements and demonstrated that fracture-matrix areas can be measured with good precision. It is furthermore possible to gather information about the fracture network structure by conducting transient measurements. We conclude that the proposed technique is feasible, and can be combined with conventional techniques to significantly improve measurement accuracy.