FormationFormation DamageDamage What is formation damage ? •Impairment of the reservoir permeability by any process / system, resulting in decreased production / injection of the well is termed as formation damage. –Fast production / injection decline of affected well –Reduced near well bore permeability Damage characterization •To characterize formation damage & its identification we should know: –Type of damage –Location of damage –Extent of damage –Its effect on well productivity / injectivity Damage quantification •Skin value is used to quantify formation damage •Then what is skin S= (k/ks-1) ln rs/rw Objective of removal of damage • Enhance hydrocarbon Bypassing damaged zone production • Increase recoverable reserves Prefrac: Radial flow pattern • Develop uneconomical/ Post frac : Area greatly increased marginal reserves 6 Introduction Wellbore Area Linear Flow Pay Zone damage Area How Stimulation Improves Productivity • Stimulate to increase the production rate – Treated length effectively increases r'w – Can connect to existing fracs – But can also connect to water/gas zones • Stim. past damage to restore production – Treated length just longer than damaged length • Increase Pwf for a given production rate – Enables flow to pipeline pression Importance of Permeability Figure -1 - Approximate Fracture Half-length Desired for Different Perms. Elkins, .: ‘Western Tight Sands Major Research Requirements’, Proceedings First International Gas Research Conference, Chicago, 1980 Note: This chart is be illustrative only It may contain assumptions that prevent applications to other wells Fracture Half-Length (100 ft) In-situ Gas Perm (md) Formation Damage mechanism •Natural damage –Due to the production of reservoir fluid •Induced damages –Due to external operations on the well
