Experimental laboratory study of hydraulic fracture interaction with pre-existing fault

Abstract

Hydraulic fracturing remains the primary method of increasing hydrocarbon inflow to a borehole. Despite the many years of experience in using this method and the existence of various hydraulic fracturing simulators, companies often face problems during hydraulic fracturing, which are associated with insufficient elaboration of the physical models used in these simulators. There are a lot of theoretical and experimental studies of the occurrence and propagation of hydraulic fractures. All the models have their limitations, which can be evaluated by conducting experiments on natural or artificial rock samples. An essential aspect of hydraulic fracturing is accounting for the natural fractures of rocks. On the one hand, the natural fractures can increase the hydraulic fracturing efficiency. On the other hand, the interaction of hydraulic fractures with tectonic faults can lead to undesirable consequences in the form of induced earthquakes. We present the results of laboratory experiments on the study of a hydraulic fracture interaction with a preliminary created fracture that simulates a natural fracture. In the experiments, under conditions of triaxial loading, the initiation and growth of a hydraulic fracture in a poroelastic material initially containing a fracture was investigated. A distinctive feature of the experiments is the ability to use an ultrasonic sounding to measure the fracture propagation and opening simultaneously with the fluid pore pressure measurements at the several points of the porous saturated sample. It allows to obtain the pressure distributions at various experiment stages and to establish a relation between the pore pressure distribution and the hydraulic fracture propagation and its interaction with pre-existing fracture. The possibilities of active ultrasonic monitoring have been expanded due to preliminary calibration experiments, which make it possible to measure the fracture opening value by attenuation of ultrasonic pulses. The profile of the existing fracture opening has been restored.The experiments show that the fracture propagation is influenced by the natural fracture. This is caused by the hydraulic fracturing fluid leaks into the natural fracture, so both hydraulic fracture and natural fracture compose united hydraulic system. The results obtained can be used to refine models of secondary fracture network formations during hydraulic fracturing in unconventional fractured reservoirs.