In the past decade the industry has embraced unconventional resources; namely, shale oil and shale gas. After the initial drill-to-hold stage, multiwell pad drilling and stimulations are employed to exploit the acreage. Zipper fracturing is a technique that reduces the standby time (up to 50% reduction, when combined with the plug-and-perf isolation method). Because of this operational efficiency improvement, zipper fracturing has become one of the most common fracturing practices for unconventional reservoir stimulation. It has also been purported to increase production, which several authors have previously reported. There are also other studies showing no benefit of zipper fracturing on production performance.

In this paper we have used a complex fracture network model, which we refer to as the Unconventional Fracture Model (UFM), to study zipper fracturing. The model simulates complex (branched) fracture propagation, associated stress shadows, fluid flow, and proppant transportation in the complex fracture network. The model solves the fully coupled problem of fluid flow in the fracture network and elastic deformation of the fracture. A key difference between UFM and the conventional planar fracture model is being able to simulate the interaction of hydraulic fractures with preexisting natural fractures (also referred as planes of weakness). The UFM simulates interwell and interstage stress shadows and honors both sequential fracturing and zipper fracturing scenarios' geomechanical interaction.

In this paper, we present the results of a zipper and sequential fracturing study that includes the completion design optimization and the associated production performance in the Eagle Ford Shale. The study provides a workflow to optimize the completion and stimulation designs in pad development and to improve rate of return. The quantitative results show that zipper fracturing may not deliver a production benefit when compared with sequential fracturing and is a function of well spacing and perforation cluster spacing in a given area.

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