Formation Damage During Drilling and Completion Practices: A Review
Document Type : Original Article
Abstract
Permeability of the reservoir is one of the major characteristics controlling production rate of the wells in which the higher the reservoir permeability, the higher the production rate. Due to some activities such as chemical, mechanical, biological, and thermals the permeability is damaged. The damaged permeability obstacles the natural flow of the well, consequently reducing the production rate. Reduction due to either physical interaction of drilling, completion and stimulation fluids and equipments or changes in reservoir fluid properties is called mechanical formation damage. Fines migration, phase trapping and blocking, external solids entrainment, glazing and mashing, geomechanics and perforation damage are the common mechanical damage mechanisms. The damage induced to the reservoir is called skin, which should be identified using typical well testing methods. Typical methods such as acidizing or hydraulic fracturing should be implemented to restore the original permeability of the reservoir. Gun perforation has been used for more than 40 years for generating a controlled flow channel between oil and gas reservoirs and the bore of an injection or production well. To maximize productivity, perforations must penetrate substantially beyond the zone of drilling damage, and they must be of the highest possible quality but the point is that perforations are never clean and the act of perforating crushes the rock and forces the particles from the hole area into the surrounding formation. Under adverse conditions of too great wellbore pressure and presence of drilling mud or dirty completion fluid, severe additional damage may result.
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