Abstract
Alpha field is a sand stone, mixed drive reservoir, located in Cambay Basin of India. The exploitation of the reservoir continued since 1969 resulting in decline in reservoir pressure which in turn made drilling of infill wells, avoiding formation damage difficult. The reservoir was to be put on polymer flooding for which 16 infill wells were to be drilled. A few infill wells drilled in past had shown high formation damage. High mud weight was found to be the root cause. Therefore oil base mud was experimented in one well resulting in no formation damage but at high cost. On economic consideration it was thought to try low gravity water base drilling fluid in one well with a change in the prevailing casing policy. The strategy worked and the well so drilled and completed resulted in no formation damage. The same strategy was followed in remaining infill wells and all of them were successfully drilled. The field trial thus demonstrated how application of low gravity water base drilling fluid with judicious casing policy can control formation damage and may be better alternative to costly non-conventional method like oil base mud.
