Impact of Dynamic Changes in Natural Fracture Fluid Pressure on the Propagation and Geometry of Hydraulic Fracture Networks

Summary In past studies, pressure changes in natural fractures that are filled with fluids have been ignored when studying the interaction of hydraulic fractures with natural fractures, leading to limitations in fracture design and production optimization. To overcome these limitations, changes in natural fracture fluid pressure are fully accounted for in an integrated fracturing-production model to assess their effect on fracture growth in naturally fractured formations and subsequent production from the complex fracture network. An efficient approach that uses the Skempton’s coefficient is adopted to estimate the variation of fluid pressure in natural fractures induced by variations in stresses. The importance of capturing changes in natural fracture fluid pressure is first demonstrated, followed by an extension of the model to investigate the effect of in-situ stress contrast and fracturing sequence on the geometry of hydraulic fractures. The results show that (1) variations of natural fracture fluid pressure significantly impact the interaction between hydraulic and natural fractures, changing the geometry of the created fracture network and the subsequent production rate; (2) a larger stress contrast (the anisotropy between maximum and minimum horizontal stress) tends to reactivate far-field natural fractures that are optimally oriented and critically stressed, increasing the complexity of the fracture network that includes backbone and isolated fractures but leading to a shorter backbone fracture and a lower production rate; and (3) staggered zipper fracturing, strategically sequencing the fracturing process, is expected to generate better fracture patterns and improve well performance.