Font Size: 

The presence of stress and material interfaces in hydrocarbon reservoirs may significantlycomplicate prediction of hydraulic fracture propagation, as the spatial resolution of numericalcodes is usually insufficient to capture the details of the fracture-interface interactionat the early stages of the crossing. Thus, an explicit analytical and experimental investigationof the leading edge of the fracture normally crossing a stress interface (where thestress component normal to the fracture plane is discontinuous) is undertaken under conditionswhen solid toughness, fluid leak-off, and fluid lag are negligible. The analytical planestrain solution corresponds to that of a semi-infinite hydraulic fracture, which propagationvelocity varies with the penetration depth past the interface. When appropriately scaled,the solution depends on a single dimensionless penetration depth parameter or time. Comparisonwith the experimental results for initially penny-shape hydraulic fractures crossinga stress interface in PMMA shows remarkable agreement in a wide range of penetrationvalues.