Introduction
Various forms of formation stimulation can be effective in reducing some forms of damage. However, the total effect is a composition of a number factors including:
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Formation damage/ skin
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Completion skin (perforations, gravel pack, liners etc)
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Work by Furui et al [2003] showed that skin due to flow convergence and/or movement through slotted or perforated liners with or without formation damage could be significant
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Partial penetration skin
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In a partial penetrating well, flow restriction can occur due to the restricted perforation region. As streamlines converge to the perforated interval, the reservoir fluid experiences an additional pressure drop. Work by Kamkom [2007] showed that even the effects of undulation in anisotropic reservoirs could have some significant pseudo-skin effects.
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Slanted well skin (or skin due to inclination)
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In this scenario, a well does not penetrate a formation perpendicular to the bedding plane. According to the public literature, when the inclination angle (measured from the vertical) is greater than 10o, the pressure drop due to the loss of productivity can become appreciable.
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Skin due to turbulence
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kin due to turbulence is additional pressure drop caused by high-gas velocity near the wellbore, and only applies to gas wells
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2-Phase Skin
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Apparent skin due to 2-phase flow, often in the context of gas-condensate reservoirs.
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Skin of fracture face
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When a hydraulic fracture is created, the interface between the fracture and the formation may encounter a slight permeability reduction either intentionally (leak-off additives) or unintentionally (e.g., relative permeability effects, non-breaking gel). This is modelled by assuming the presence of a skin on the fracture face as shown below.
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References
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K. Furui, D. Zhu, and A. D. Hill, A Comprehensive Model of Horizontal Well Completion Performance, SPE 84401,SPE Annual Technical Conference and Exhibition held in Denver, Colorado, U.S.A., 5 – 8 October 2003.
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Rungtip Kamkom, Modelling Performance of Horizontal, Undulating, and Horizontal Wells, PhD Thesis. Texas A&M University, 2007.