Analytical criterion predicting the impact of natural fracture strength, height and cemented portion on hydraulic fracture growth

摘要

Natural fractures (NFs) are commonly encountered in unconventional reservoirs, sometimes strongly impacting hydraulic fracture (HF) propagation. The HF-NF interaction has been studied extensively as a 2D problem. However, outcrop and core observations indicate that many NFs are fully or partially cemented. The NF height also is variable relative to the full height of the reservoir layers(s). These features of NFs - including the proportion of the cemented region(s), cementation strength, and NF height - may lead to distinctive interaction behaviors that can only be understood in a 3D setting. This paper presents a new analytical crossing criterion, and its laboratory verification, for predicting the outcome when a HF impinges orthogonally on a NF. Consistent with laboratory results, this criterion captures the dependence of crossing/no crossing behaviors on the proportion of cemented region(s), cementation strength, and the NF height relative to the total reservoir/HF height. Crossing of the NF is shown to be promoted by stronger cementation, larger cemented region, and/or shorter NF height. While these observations are not surprising, quantifying the dependencies using an analytical model that can be deployed within the framework of HF simulators is an unresolved challenge. Here an analytical criterion has been developed based on linear elastic fracture mechanics to quantitatively assess the influence of NF heterogeneity on the HF's crossing/no crossing behaviors. The criterion shows good agreement with hydraulic fracturing experiments. It is therefore shown to be capable of predicting the 3D interaction behaviors of HFs intersecting partially/fully cemented NFs.