Quantitative Evaluation of Completion Techniques on Influencing Shale Fracture ‘Complexity’

Abstract

In many of the active shale plays, the extremely low permeability of the shale means simple, bi-planar hydraulic fractures do not provide enough surface area to make an economic well. In these cases, the optimal, economic completion requires stimulation of the natural fracture system -often called increasing the 'complexity' of the stimulation. A number of different multi-well completion techniques have been proposed to enhance shale complexity. The 'simul-frac' technique is where companion wells are stimulated at the same location at the same time, whereas the 'zipper-frac' technique employs companion wells that are stimulated in staggered locations at the same time. The intention with these techniques is to alter either or both the stress field and the pore pressure field to enhance the shearing of natural fractures.In this paper, we present the results of a numerical study to quantitatively evaluate the effectiveness of multi-well completion techniques, particularly the 'modified zipper-frac' technique, to optimize shale completions. The study includes a parametric study of the effects of in-situ stress conditions, natural fracture orientation and fracture friction, and hydraulic fracture layout on changing near and far-field natural fracture shear (complexity). Changes in the stress field, particularly shear stress, are considered the primary means of increasing fracture complexity. The quantitative results of the study provide a means to optimize the application and design of different multi-well completion techniques as a function of the presented parameters. Optimized completion designs mean lower well costs, greater production and, ultimately, improved well economics.

Numerical investigation of fracture spacing and sequencing effects on multiple hydraulic fracture interference and coalescence in brittle and ductile reservoir rocks

“…The intention with these techniques is to alter either or both the stress field and the pore pressure field to enhance the shear failure of weak planes and promote fracture complexity. and C, Modified zipper-frac (Nagel et al, 2013) Traditionally, the hydraulic fracture is believed in a plane perpendicular to the least in-situ principal stress, and multiple fractures are parallel and separated from each other. With the assumptions of bi-wing fracture geometry and rock's tensile failure mechanism, analytical models are developed and widely used for hydraulic fracture design and analysis, such as the KGD model (Khristianovich and Zheltov 1955;Geertsma and De Klerk 1969) and PKN model (Perkins and Kern 1961;Nordgren 1972).…”

Hydraulic stimulation strategies in enhanced geothermal systems (EGS): a review

“…Vermylen and Zoback (2011) investigated the stress shadow effect in multiple lateral wells in Barnett shale, and their results indicated that the zipper fracturing was more effective than the simultaneous fracturing in generating hydraulic fractures with a longer length. Nagel et al (2013) found that by drilling multiple lateral wells and performing hydraulic fracturing in sequence, the reservoir permeability could be significantly enhanced. Izadi et al (2015) modeled the hydraulic fracture propagation and found the largest stimulated volume was achieved by the modified zipper fracturing method compared with simultaneous hydraulic fracturing.…”

Numerical simulation of MZF design with non-planar hydraulic fracturing from multi-lateral horizontal wells

“…However, this study did not consider the non-planar propagation of hydraulic fractures, an important effect when closely spaced fractures are used. By using the discrete element method, Nagel et al (2013) showed that the improvement in well stimulation using the Zipper-Frac and MZF approaches is highly dependent upon the in-situ pore pressure, the natural fracture mechanical properties, and the natural fracture characteristics. Recently, Kumar and Ghassemi (2016) implemented a boundary element model with capabilities to simulate any 70 number of fractures for Sim-HF and Seq-HF scenarios.…”