Formation damage problems in the Brutus A-8 well in the Gulf of Mexico have provided a rich opportunity to study mechanisms of pore plugging. Field data and laboratory experiments have led to the following conclusions.

  • Unexpected reactions can take place between spent organic acids and completion brine, resulting in polymerization and other reactions that can plug formations.

  • These precipitates can be prevented by appropriate acidizing practices, including the use of sufficient (ammonium chloride or other innocuous brine) spacers to maintain separation of the (spent) acid and completion brine and the use of an appropriate post-flush acid to maintain a low pH in the spent acid.

  • If a precipitate does form, it can be cleaned up readily by acid treatment if the acid reaches the occluding precipitate.

  • Organic acids should not be mixed. That is, if completion uses one organic acid, no other organic acids should be used in subsequent stimulation treatments.

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