Experimental Study on the Fracture Propagation in Tight Sandstones During Hydraulic Fracturing

Abstract

AbstractHydraulic fracturing is an efficient method in tight reservoirs for enhanced oil recovery. However, as for tight reservoirs, fracture propagation in tight reservoirs is quite complex during hydraulic fracturing. In this work, we experimentally investigate the fracture propagation in a tight sandstone core sample. Acoustic monitoring technique is applied to detect the sound events occurring in the core sample, which is consequently used to analyze fracture propagation. Meanwhile, wellhead pressure is also used to infer the occurrence or propagation of fractures in the core sample. At the initial stage of hydraulic fracturing, fractures are scarcely formed; the sound events are mainly resulted from the expansion or closure of the natural fractures or fluid flow in the core matrix. In the second fracturing stage where displacement is increased to a high level, the system pressure is almost constant throughout this fracturing stage. At this stage, there is no obvious fracture propagation in the tight sandstone core, while the injected fracturing fluids mainly filters into the core matrix. Fractures are mainly formed at the third fracturing stage, at which the wellhead pressure fluctuates obviously. By cutting the fractured core sample into several pieces, we observe that the fracture propagation is highly influenced by the core beddings and the distributions of the natural fractures. In the second hydraulic fracturing, sound events are mainly caused by the connection between natural fractures, and less fracture is formed in this fracturing process. This study is expected to provide basic experimental data in explaining the mechanisms of fracture propagation during hydraulic fracturing in tight sandstone reservoirs. KeywordsFracture propagationHydraulic fracturingAcoustic monitoring techniqueTight sandstoneWellhead pressure