Development of a New Reservoir Drilling Fluid to Achieve Matrix Injection

Abstract

Injector wells comprise a small portion of the wells drilled globally; however, they pose unique drilling fluid challenges. Required for pressure support and production maximization, these wells can be costly if the desired level of injectivity cannot be achieved without first flowing them back. Traditional drill-in fluids (DIFs) contain starch and xanthan, the latter is known to impair injectivity due to its poor acid solubility. This paper describes the development of an aqueous reservoir drilling fluid targeted for injector wells. A brine-based reservoir drilling fluid was designed and developed utilizing a novel dual-functional xanthan-free additive to provide the necessary rheological and fluid loss properties without impairing injectivity. A thorough qualification was undertaken to evaluate fluid performance under a variety of conditions. Properties investigated included rheology, static-age stability, fluid loss, lubricant compatibility, and contamination susceptibility. A delayed-action filter cake breaker fluid was also designed and tested for suitability with the new reservoir drilling fluid. Return injectivity measurements were performed on both aloxite discs and core plugs to simulate the ability to achieve matrix injection without flowback. The novel additive provided excellent rheology, suspension, fluid loss control in the reservoir drilling fluid tested in the laboratory. Return injectivity testing demonstrated that the new DIF significantly outperformed existing fluids that contain xanthan or diutan without adjusting the delayed-action breaker formulation. The rheological performance of the new fluid was found to be stable and can be adjusted either though the novel additive concentration itself or through particle size optimization. Evaluation of the spent filter cake breaker effluent demonstrated that the novel additive was fully degraded, as compared to the traditional DIF in which an iodine test indicated the presence of whole starch persisting after several days contact with low-pH breaker. Existing DIF solutions function adequately for oil and gas producing wells given the low lift-off pressure resulting in minimal impairment to productivity. When considering injection wells, superior performance was achieved using this newly developed DIF which provides the potential to reduce well construction costs by eliminating the requirement to flow reservoir fluids back to a production facility before injecting.