A Successful Water Shut Off Treatment in Gas Well of Bassein Field by Polymeric Gel System

Abstract

Abstract Worldwide excessive water production in gas reservoirs has always been regarded as one of the most formidable problems, which hampers the productivity of the well to any extent and in the extreme cases may lead to ceasure of the well due to water loading although the reservoir contains sufficient amount of recoverable reserves. The source of water production can be a channel behind casing due to poor cementation, casing leaks, coning, encroachment, water breakthrough and flow through natural and induced fractures. In the process of shutting off /mitigation of unwanted water production, the identification of source of water inflow in the well is the most important step for choosing a correct technique. However, the problem becomes even more complex if multiple mechanisms of water invasion are simultaneously active in the well. There are various mechanical and chemical techniques to deal with excessive water production. The mechanical means provide a seal in the near-wellbore openings. However, most of the time, it is desirable to achieve matrix or small fissure penetration of the sealing material. Among the chemical methods, polymer gels are considered as one of the most commonly applied technique on account of relatively low cost, ease of pumping and ability to penetrate deeper into the reservoir. Bassein is a major gas field in the western offshore basin of India and is producing gas since 1988. The entire structure of the field is a gas cap gas reservoir, which is underlain by very thin oil column and large aquifer and producing gas under partial aquifer drive. The field recovery has crossed 60% of GIIP and presently most of the wells of BC and BE platforms are either producing large amount of water or have ceased to flow due to water loading leading to huge loss of well productivity and making them suitable candidates for water-shut-off treatments. The well BC-2, which was/ had ceased to flow due to water loading, but could not be brought back on production even after mechanical water shut off method was chosen as a pilot well for treatment with deep penetrating high temperature resistant gel system. After gel treatment, the well was put on sustained production along with reduction in water production by 90%. This paper discusses the laboratory studies for polymeric gel optimization, methodology of job design with operation sequence and results obtained from the field.