Engineering for Success: Design and Execution of Fluids for Optimum Injectivity - A Case Study

Abstract

Two North Sea water injector wells have achieved high matrix injectivity rates without backflow to clean-up prior to commencing injection. Achieving successful results on direct water injection wells is recognised as a technical challenge, requiring detailed design and validation work around the selection and execution of the drilling and completion fluids. Engineered water-based reservoir drilling fluid and post-drilling chemical "breaker" treatments were utilised for these open hole screen completions. The technology around the use of breaker fluid has evolved in recent years, yet successful application is challenging when two objectives are combined; achieving the required injection rate without clean-up flow prior to injection and keeping the injection pressure below the minimum fracture gradient for uniform matrix injection over the full length of the completed interval. Once suitable fluid formulations have been identified and validated by laboratory testing, detailed engineering procedures are required to ensure that the fluids are maintained within tight design specifications through the execution phase. For example, one critical key to success is ensuring that formation solids and residues incorporated into the drilling fluid are minimised to reduce the risk of plugging the matrix permeability. Once the well is drilled, ensuring that the breaker fluid is placed across the entire zone of interest and the filter cake is removed in a controlled and uniform manner facilitates good injectivity results. This paper describes; the technical challenges presented by this project, the extensive laboratory testing performed as part of front-end engineering and design, an overview of the field execution across the two water injector wells, the results and the lessons learned.