The formation damage that results from the incomplete back-production of viscous, fluid-loss control pills can be minimised if a slow acting internal breaker is employed. In particular, core-flow tests have indicated that combining a succinoglycan-based pill with a hydrochloric acid internal breaker enables a fluid-loss system with sustained control followed by delayed breakback and creates only low levels of impairment. To describe the delayed breaking of the succinoglycan/hydrochloric acid system, a model, based on bond breaking rate, has been used. With this model, it is possible to predict the change of the rheological properties of the polymer as a function of time for various formation temperatures, transition temperatures of the succinoglycan and acid concentrations. Hence, the model can be used to identify optimum formulations of succinoglycan and acid breaker on the basis of field requirements, such as the time interval over which fluid-loss control is needed, the overbalance a pill should be able to withstand and the brine density required.

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