The effect of heterogeneity on multiple fracture interaction and on the effect of a non-uniform perforation cluster distribution

Multistage hydraulic fracturing is essential for the exploitation of unconventional petroleum resources and to realize new energy sources, such as enhanced geothermal systems (EGS). Multistage fracturing is normally done by increasing the pressure in a well with multiple perforation clusters, with the aim of forcing significant fractures from all perforations. Various methods have been proposed to optimize multistage fracturing treatments, including creating a non-uniform distribution of clusters along the well. Many of these optimization methods have, however, been tested in numerical models assuming homogeneous reservoirs and symmetric growth from the wellbore. An important question is then how heterogeneity affects the multistage fracturing optimization methods. This paper presents a numerical investigation using the modified discrete element method showing how the effect of a non-uniform cluster distribution is affected by the heterogeneity. It is shown that a non-uniform cluster distribution can, in some cases, promote more even contributions from all clusters, but it is sensitive to the reservoir heterogeneity. This indicates that the heterogeneity and fracture complexity have to be accounted for when investigating multistage optimization designs. The focus of this work is the general fracture behaviour during multistage fracturing in heterogeneous rock, aimed at optimizing fracturing designs for EGS and shale gas operations.