Hydraulic Fracture Growth Through Frictional Interfaces in Adelaide Black Granite: Phase I Experiments

[摘要] Hydraulic fracturing is a vital technology used to increase the permeability of petroleum and geothermal reservoirs to fluid flow. Unconventional gas and geothermal reservoirs, which comprise an important part of the Australian and Worldwide emerging energy portfolio, are typically naturally fractured and therefore the little-understood problem of hydraulic fracture growth through naturally fractured rocks is an important area of research. In order to better understand this issue, ten experiments have been completed in which hydraulic fractures have beencreated in Adelaide Black Granite specimens such that they impinge orthogonally on a frictional interface. Depending on the conditions of each experiment the fractures either cross or are blunted at the interface. The experiments are designed in light of scaling principles in order that the relative importance of different physical processes can be understood, particularly when comparing these small scale laboratory experiments with large scale field treatments. Ultrasound monitoring, which was developed in conjunction with these experiments, was successful provided that the transducers were close enough to the fracture plane. In one example, non-symmetric fracture growth about the injection point was determined based on ultrasound data and corroborated with observations. The crossing behaviour observed in all ten experiments, combined with past experiments, contributes to an emerging picture of hydraulic fracture growth through an orthogonal natural fracture that is not dependent on the friction coefficient of the interface. This result challenges the current modelling paradigm in which the details of the interface plasticity are considered to be vital for understanding whether and how a hydraulic fracture will cross a natural fracture. If additional experiments in other rock types also give indication that the friction coefficient of the interface is not a parameter governing the crossing behaviour, then a new paradigm ought to be proposed in which interface plasticity plays a reduced role.

[发布日期] 2010-09-24 [发布机构] CSIRO

[学科分类] 地球科学(综合)