The influence of transport and reaction of wormhole formation in carbonate porous media: A study of alternative stimulation fluids

The transport and reaction of fluids in porous media results in unique pore growth and channel evolution as the media are dissolved. The dissolution phenomenon is complicated by the stochastic nature in which the flow channels develop. This channel evolution is most prevalent during the stimulation of petroleum reservoirs, where the dissolution leads to the formation of highly conductive flow channels, commonly referred to as wormholes. This work focuses on the influence of transport and reaction on wormhole formation with a wide range of fluid systems.; Kinetic studies demonstrate that the mass transport and surface reaction kinetics vary significantly among stimulation fluids such as strong acids, weak acids, and chelating agents. To describe wormhole formation during flow experiments with these fluids, a generalized description of the dissolution phenomenon is developed. The generalized description includes the effects of convection, reactants transport, reversible surface reactions, and products transport. Accounting for these processes reveals a common dependence on the Damkohler number for flow and reaction. The Damkohler number is shown to dictate the type of wormhole structure formed by systems with various degrees of transport and reaction limitations. An optimum Damkohler number for channel formation is observed at approximately 0.29 for all of the fluid systems investigated. To fully describe the dissolution phenomenon, an additional dimensionless kinetic parameter is introduced. An optimum kinetic parameter is observed at a value of about 130. Together, the Damkohler number and the kinetic parameter are shown to completely describe the phenomenon of wormhole formation.; The stochastic nature of the dissolution phenomenon is described using network models. A two-dimensional network model is extended to include the generalized description of the dissolution phenomenon. Simulations are in qualitative agreement with experimental results, but are limited due to the inability of the two-dimensional model to capture the physical characteristics of the natural porous medium. Therefore, a three-dimensional physically representative network model is extended to account for the effects of pore-scale transport and reaction on wormhole formation. The network simulations demonstrate the experimentally observed trends in the permeability response and wormhole structures and substantiate the existence of an optimum Damkohler number.