Design aspects of Optimized Zipper Frac

This paper discusses Optimized Zipper Frac (OZF), a fracturing technique developed by the authors for organic shale reservoirs that maximizes near-wellbore complexity and, thus, overall permeability and hydrocarbon recovery. It covers all aspects of OZF design, including the optimum properties and volumes of fluids for ballooning fractures and the optimum stress shadow magnitude to be generated within a given zone before it is fractured. It also presents sensitivity studies into the ballooning of fractures by increasing the volumes or changing the properties of injected fluids. Moreover, it discusses well spacing, perforation clusters, stage spacing, and fracturing schedule. To generate a design methodology for OZF, an advanced commercial reservoir simulator with a hydraulic fracturing module was used to simulate different completion strategies for a variety of organic shale sweet-spots, each of which was described in a data set imported from a different shale play. This simulator was also used to calculate the ballooned fracture dimensions needed to generate the optimum stress shadow for fracturing a given reservoir zone. It is also used to optimize the well spacing, stage spacing, and fracturing schedule. The results affirm the feasibility of OZF. Although a large proportion of the simulated horizontal wells required fluids with higher-than-normal slick-water viscosities or larger-than-normal fluid volumes per frac stage, OZF is more economical than Zipper Frac (ZF) because it does not require that the entire horizontal section be fractured and it allows higher production rates and greater hydrocarbon recovery. Because stress shadows can cause imbalances in the horizontal stress magnitudes when only two wells are simultaneously completed using OZF, this paper advocates completing three wells at a time to avoid asymmetric fracture growth. The results confirm that OZF is a better completion strategy to plan for future re-fracturing than other strategies. A methodology of re-fracturing candidate evaluation is developed and presented.