UNDERSTANDING HYDRAULIC FRACTURE PROPAGATION: MAPPING THE SOURCE MECHANISMS AND SPECTRAL CHARACTERISTICS OF MICROSEISMIC EVENTS DURING FRACTURE GROWTH

Hydraulic fracturing is increasingly important as unconventional hydrocarbon resources are needed to meet the demand of the world’s energy. Although there has been research on fracture mechanics and hydraulic fracturing techniques, the mechanisms by which the fracture propagates is seen as purely tensile in some case and in others a combination of shear and tensile mechanisms. Laboratory experiments, with a correct scaling to mimic field conditions, enable the growth and propagation of fractures to be extensively analyzed using microseismic data without the noise of the field. Two experiments are conducted using Polymethyl methacrylate (PMMA) blocks; one with a pre-existing crack (acting as “fault”) and the other without this feature. Microseismic data is collected during each experiment from 24 sensors, 8 groups of 3, in a Galperin arrangement, on the blocks. Pressure data is also collected to observe the pressure changes throughout fracture propagation.

If hydraulic fractures can be said to be similar to magmatic fractures, as both are fluid-driven cracks, then the spectral characteristics of the microseismic events taking place during fracturing will show elements of both tension and shearing related to the opening and closing of fractures, fracture propagation and interaction with pre-existing cracks. The overall objective is to combine techniques of full moment tensor inversion and spectral analysis for the events in the data, to compare their characteristics to those in nature, to create a catalog for the expected types of microseismic events taking place during each stage of fracturing and to map these events.