03-Skin Factor and Wellbore Storage

03-Skin Factor and Wellbore Storage - Skin Factor and...

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Skin Factor and Wellbore Storage 3 Upon completion of this section, the student should be able to: 1. List and describe 5 factors that cause skin damage. 2. List and describe 3 factors that cause a geometric skin factor. 3. List and describe 2 ways of stimulating a well. 4. Given formation and fluid properties, be able to calculate skin factor from additional pressure drop due to damage and vice- versa. 5. Calculate the flow efficiency given the skin factor, the wellbore pressure, and the average drainage area pressure. 6. Express skin factor as an apparent wellbore radius and vice- versa, given the actual wellbore radius. 7. Convert skin factor to an equivalent fracture half-length for an infinite-conductivity fracture and vice-versa.
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Skin Factor and Wellbore Storage 4 Mud filtrate invasion reduces effective permeability near wellbore. Mud filtrate may cause formation clays to swell, causing damage.
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Skin Factor and Wellbore Storage 5 • In an oil reservoir, pressure near well may be below bubblepoint, allowing free gas which reduces effective permeability to oil near wellbore. • In a retrograde gas condensate reservoir, pressure near well may be below dewpoint, allowing an immobile condensate ring to build up, which reduces effective permeability to gas near wellbore.
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Skin Factor and Wellbore Storage 6 • Injected water may not be clean - fines may plug formation. • Injected water may not be compatible with formation water - may cause precipitates to form and plug formation. • Injected water may not be compatible with clay minerals in formation; fresh water can destabilize some clays, causing movement of fines and plugging of formation.
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Skin Factor and Wellbore Storage 7 • Consider an undisturbed formation of thickness h and permeability k. • Assume that something (drilling the well, producing fluid from the well, injecting fluid into the well) changes the permeability near the wellbore. One simple model of this effect is to assume that this altered zone has uniform permeability k a and radius r a , and that the rest of the reservoir is undisturbed. • For generality, we allow the permeability in the altered zone to be either smaller or larger than the permeability in the undisturbed formation.
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Skin Factor and Wellbore Storage 9 • We define the skin factor in terms of the additional pressure drop due to damage. • As defined, the skin factor is dimensionless -- it has no units. Nomenclature k = md h = ft q = STB/D B= bbl/STB p s = psi μ = cp
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Skin Factor and Wellbore Storage 10 The skin factor equation may be rearranged to give the additional pressure drop caused by a given skin factor.
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11 The skin factor may be calculated from the properties of the altered zone. If k
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This note was uploaded on 04/05/2011 for the course PETE 689 taught by Professor Staff during the Spring '08 term at Texas A&M.

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03-Skin Factor and Wellbore Storage - Skin Factor and...

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