The success in matrix acidizing carbonate-formations depends entirely on the ability to create long wormholes that bypass the damaged near-wellbore region. Recently, much work has been performed to understand the wormhole propagation. This has led to various criteria and models to optimize matrix-acid treatment design for volumes, fluids, and flow rates. In many publications, the existence of an optimum flow rate for wormhole propagation has been described and efforts have been made to design treatments around these criteria.
This paper will discuss several of the criteria and models that can be used to determine the optimum flow rate in both radial and linear flow and will introduce a new and simple criterion for both radial and linear flow that is based on diffusivity, reactivity, porosity, and surface area. Most of the criteria have been developed based on laboratory results or simulations in controlled and idealized environments.
Under field conditions, many additional factors must be considered. Because of certain parameters such as significant heterogeneities in the formation, uncertainties in formation data, uncertainties in fluid placement, and operational constraints, the environment is neither controlled nor ideal. This paper will discuss the impact of these field conditions on the criteria and models to determine the optimum injection rate and verify their validity under field conditions. Examples and a case history are included to emphasize the need for consideration of these parameters. In addition, constraints are given to the validity of the criteria for the optimum flow rate under field conditions. This paper will further discuss the best practices and recommendations for cases where these constraints cannot be easily met or in cases where the data is uncertain.