Multiple Fracture Growth in Modified Zipper Fracturing

Operational parameters, such as multiple-cluster and well spacing, flow rates, and injection time, play a vital role in the deviation and growth of multiple-cluster hydraulic fractures during the implementation of modified zipper fracturing technology. Fundamental analysis of the dynamic zipper fracture growth because of changing flow rates, well spacing, and injection time does not appear to have been studied in the literature, although it is of critical importance for fracturing optimization. In this study, a fully coupled two-dimensional (2D) extended finite-element method (XFEM)-cohesive zone model (CZM) in combination with a phantom-node method (CPNM) was used in ABAQUS to investigate the initiation and propagation of multiple hydraulic fractures with 10 injection clusters that are distributed in two horizontal boreholes. This study aims to assist fracturing design to achieve minimal deviation in multiple fracture propagation and create deeper and much wider fractures between two horizontal boreholes of a modified zipper fracture (MZF) completion pattern. The growth of a hydraulic fracture in an XFEM region were verified by Khristianovic-Geertsma-de Klerk (KGD) zero toughness solution and good agreement with a negligible error of <2.5% was obtained. A series of simulation scenarios was carried out with various flow rates and three well spacings of 40, 60, and 80 m, over a long injection period to identify the optimum injection time in which a fracture grows straight with minimal deviation. The results show that to create smooth and deeper multiple hydraulic fractures in zipper fracturing, an increase in the flow rate is preferred, but the duration of the injection period should be optimized. The results of this study could be used to better address operational difficulties, such as multiple-fracture crossing and closure that is associated with unfavorable injection times, well spacing, and flow rates in MZF operations.