Mechanically Induced Fracture-Face Skin--Insights From Laboratory Testing and Modeling Approaches
- Andreas Reinicke (GFZ German Research Centre for Geosciences) | Guido Blöcher (GFZ German Research Centre for Geosciences) | Günter Zimmermann (GFZ German Research Centre for Geosciences) | Ernst Huenges (GFZ German Research Centre for Geosciences) | Georg Dresen (GFZ German Research Centre for Geosciences) | Sergei Stanchits (TerraTek) | Björn A. Legarth (Royal Dutch Shell) | Axel Makurat (Royal Dutch Shell)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- October 2012
- Document Type
- Journal Paper
- 26 - 35
- 2012. Society of Petroleum Engineers
- 3 Production and Well Operations, 1.8 Formation Damage, 2.5.2 Fracturing Materials (Fluids, Proppant)
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- 612 since 2007
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In the context of this work, a new formation-damage mechanism is proposed--the mechanically induced fracture-face skin (FFS). This new mechanism results from mechanical interactions between the proppants and the reservoir rock caused by the increasing stress on the rock/proppant system during production. Proppant embedment into the fracture face and proppant crushing lead to fines production and may impair the fracture performance. To achieve sustainable, long-term productivity from a reservoir, it is indispensable to understand the hydraulic and mechanical interactions in rock/proppant systems. In this study, permeability measurements on sandstones with propped fractures under stress using various flow cells were performed, allowing localization and quantification of the mechanical damage at the fracture face. The laboratory experiments identified a permeability reduction at the fracture face of up to 90%. The mechanical damage at the rock/proppant interface began immediately with loading of the rock/proppant system and for fracture-closure stresses less than 35 MPa; the damage was localized at the fracture face. Microstructure analysis identified quartz-grain crushing, fines production, and pore-space blocking at the fracture face, causing the observed mechanically induced FFS. At higher stresses, damage and embedment of the ceramic proppants reduce the fracture permeability further. Numerical modeling of the rock/proppant system identified highly inhomogeneous stress distributions in the granular system of grains and proppants. High tensile-stress concentrations beneath the area of contact between quartz grains and proppants were observed, even at small differential stress applied to the rock/proppant system. These high-stress concentrations were responsible for the early onset of damage at the fracture face. Therefore, even low differential stresses, which are expected under in-situ conditions, may affect the productivity of a hydraulically fractured well.
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