Filter Cake Breaker Evaluation for Water Injectors: Scale Up From Laboratory to Field Deployment

Abstract

Abstract Water injection wells were planned to provide pressure support to oil producers in two North Sea fields (Field A and Field B). For both fields, water-based drilling fluid was selected to drill the reservoir section. The average permeability of the first field is 1000 mD and the second field is 50-100 mD. A laboratory study was commissioned to evaluate and optimize filter cake breaker systems for use in water injectors to efficiently remove external and internal filter cake in order to attain matrix injection without the need for backflow to clean up the sand face. A time-delayed filter cake breaker system was chosen for evaluation as part of the study. Laboratory-scale formation damage tests indicated significant loss of injectivity, potentially due to deep invasion of xanthan polymers in core plugs along with incomplete dissolution of calcium carbonate from the filter cake. An enzyme package designed to degrade xanthan was included in the revised breaker solution and an improvement in injectivity was recorded. Further adjustments were made to the breaker formulation to optimize performance for density range, corrosion mitigation and dissolution of calcium carbonate, including allowance for the impact of the addition of lubricant to the drilling fluid. Following an extensive and detailed study, a much greater understanding of the design, evaluation and field engineering aspects of chemical breakers has been gained. The recommendations from the study have recently been applied to injection wells on both fields. This paper describes the test procedures adopted for evaluating the various filter cake breaker formulations and the work conducted to develop the systems to be ready for field use. The challenge and consequences around scaling up laboratory results to field conditions is particularly acknowledged. Field results are presented, highlighting both the importance of critical design issues and applied learnings for a successful outcome.