During completion and workover operations high rate fluid loss is encountered in many wells due to the presence of highly permeable and naturally fractured, depleted formations. Several methods to obtain temporary plugging have been studied to select the most versatile technique for different field conditions. In addition to the laboratory results, field trials have been performed for detailed and comparative evaluation of loss control compositions. These compositions included polymers and sized calcium carbonate systems, polymers and sized micronized (fibrous) cellulose combinations, polymers and sized salt systems (medium and high temperature formulations), crosslinked polymer gel plugs, and delayed swelling, stabilized (extended life) polymer systems. The role of fluid chemistry in prevention of formation damage, extension of gelation temperature, and temperature stability was also investigated. The temperature and differential pressure of the formations (sandstone limestone, conglomerate, metamorfite, etc) varied between 60-170 °C, and 1-15 MPa respectively. Fluid compositions without imposing severe permeability damage were selected, which can be broken down chemically. Case studies of field operations performed in Hungary are also presented.

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