Network modeling and experimental investigation of flow, dissolution, precipitation and fines migration in porous media.

Abstract

This research addresses the problem of permeability reduction (or formation damage), caused by the capture of inert particles and /or the formation and deposition of precipitate within the porous media. A network model is developed to predict the permeability response, effluent concentration histories, and the evolution of the pore structure with time. The heterogeneously complex porous media is represented by a network of interconnected capillary tubes representing the pore throats, and nodes representing the pore chambers. Individual elements, such as particles, are transported through the network using two important concepts: wave front and flow-biased probability. These concepts account for the simultaneous movement of several particles, and the effects of fluid flow on the particle trajectory. Unique features of this model include: monitoring of individual elements traversing through the network, absence of empiricism in predicting the permeability response with time, and versatility in considering both reaction and particle entrapment in porous media. The network model was first used to simulate inert particle capture by straining and direct interception. Three major factors affecting particle deposition, viz. geometric size (particle and pore size distributions), fluid velocity, and deposition morphology were accounted for by the model. Comparison with experimental data of several researchers showed that the model can accurately predict the permeability response and effluent concentration history for the injection of solid particles and emulsion drops. A novel approach using "micro-elements" was introduced to consider reaction within the porous media. The network model was used to simulate equilibrium reactions as well as finite rates of reaction. Model predictions for dissolution in s and stone and limestone were in good agreement with experimental data. The competition between dissolution and precipitation was studied using a ferric chloride/carbonate system. Changes in the pore structure were observed using neutron radiography and Wood's alloy castings. Fluctuations in the pressure drop, predicted by the current model, agreed well with experimental observations. An in-depth underst and ing of the dissolution and precipitation process was obtained by graphing the flow field and the pore evolution predicted by the network model.