Evaluating the Benefits of Zipper Fracs in Unconventional Reservoirs

Abstract

In cemented and cased wells, perforation cluster spacing is optimized based on the type of reservoir fluid, permeability, fracture conductivity, proppant distribution, and associated stresses to place multiple fractures along horizontal wellbores. Specifically, in very low-permeability reservoirs, the requirement for smaller perforation or fracture spacing might not be possible because of the geomechanical interference between fractures. In this case, the commonly used zipper-frac technique can provide a means to create fractures in projects with closer spacing.The benefits of zipper fracs can be maximized by generating proper fracture geometry and properly staggering the perforation/fracture system. This paper reviews and discusses numerical reservoir-modeling results of zipper fracturing that demonstrate the individual or combined effects of the perforation/fracture staggering, comparing these to the fracture length, fracture overlap, fracture conductivity, and/or proppant distribution effects of a conventional completion that does not use the staggered zipper-frac approach. The simulation results are assessed over a wide range of unconventional reservoir permeabilities for both gas and light oil. IntroductionExploitation strategies in unconventional reservoirs that produce wells at commercial rates and maximize the reservoir fluids' recovery factor (RF) are required in nanodarcy (nd) permeability reservoirs. To align with these strategies, operators have implemented various drilling strategies, horizontal well placement, fluid-type testing, single well or well group completions/stimulations (e.g., the zipper-frac methodology), and others. As documented by Rafiee et al. (2012), Warpinski et al. (2009), and Water et al. (2009), zipper-frac methodology has the potential to increase a stimulated fracture area and induce more fracture complexity in unconventional reservoirs.Once the drilling, mechanical completion, and lateral well spacing have been optimized, completion efficiency must be addressed. For the cases of unoptimized fracture spacing, industry-reported completion efficiencies within the range of 30 to 75% resulted in lower well productivity and lower RF.Where multiple wells are drilled or completed from the same pad by staggering the induced fractures or zipper fracturing, lower completion efficiency is still an issue, which affects the productivity and RF, particularly when the staggered, induced fracture spacing had not been properly optimized. For staggered, overlapping fractures, Sahai et al. (2013) reports that, because of the stimulated reservoir volume's (SRV's) competency, a maximum of 50% overlapping can help ensure a positive net-present value (NPV). For staggered and overlapping fractures, another issue to consider is well interference, as reported by Mayerhofer et al. (2005).In this paper, various parameters, including reservoir properties, such as fracture conductivity, fluid composition, optimized staggered fracture spacing, completion efficiencies, and overlapping fracture lengths, are co...

Thermal cooling to improve hydraulic fracturing efficiency and hydrocarbon production in shales

“…Ways of improving hydraulic fracturing efficiency and hydrocarbon recovery are continuously being explored, however, from straightforward manipulation of hydraulic pressure and injection flow rate, changing well and frac spacings, increasing proppant loading, etc., to more elaborate techniques that for instance aim to favorably manipulate in-situ stress contrasts, (Patel et al, 2016;Sierra et al, 2014;Settari and Warren, 1994;Chen et al, 1995;Wojnarowski and Rewis, 2005;Dunn-Norman et al, 2009). In this paper, it is shown that hydraulic fracturing can be enhanced by cooling down the wellbore and the fracture surfaces, i.e.…”

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Research on the Interaction Mechanism of Multi-Fracture Propagation in Hydraulic Fracturing

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