Foam displacement in fractures [electronic resource] : experimentation and modeling
Keywords: Energy Resources Engineering.

Foam flooding has been implemented in oil field applications, ranging from enhanced oil recovery (EOR) and oil well stimulation to workover and remedial well operations. In the EOR applications, foam has proven to be a promising tool for gas mobility control in gas injection processes. Increased oil recovery is mainly due to the reduction of channeling, gravity override, and viscous fingering. The mechanisms of foam flow resistance, generation, and coalescence are similar among fractured and unfractured media but the macroscopic expression of non-linear foam physics is different. Unlike foam bubble shape in porous media that is governed by pore configurations, the shape of bubbles in fractures is deformed freely according to interfacial tension and gas compressibility. The possibility of continuously varying gas-liquid curvature and the relationship of curvature to foam apparent viscosity results in different pressure drop behavior in fractures as gas flow rate and foam quality are varied. The use of the foam population-balance approach is extended to include the description of foam transport in fractures. We study numerically and experimentally foam flow resistance as a function of gas and liquid velocities and the degree of fracture heterogeneity. The full physics foam model is modified by incorporating the relationship of gas-liquid curvature change with foam flow conditions in the simulations. The foam flow resistance parameter is then calculated locally. The simulated fracture models include 1- and 2-dimensional heterogeneous and a radial homogeneous models. Model predictions compare favorably to experimental literature data. Investigation of the flow resistance of pre-generated foam flow was performed via coreflood experiments. Foam characteristics and flow resistance were studied using a visualization cell and a differential pressure transducer at different flow conditions. The use of an X-ray computed tomography (CT) scanner made it possible to investigate core characterization and in-situ liquid saturation within the core. The experimental results show the dependency of foam bubble characteristics on foam flow resistance. The foam injection demonstrates a mobility reduction factor of 4 to 6 when compared with the gas injection. Foam has an ability to divert injected fluids from fractures into the matrix. This ability, however, is affected by the contrast between fracture and matrix permeabilities. The population balance method of foam in fractures that incorporates the relationship of bubble configuration and foam resistance was verified and a good agreement was found between experimental results and model predictions. A fracture network model that consists of multiple fractures with various transmissibilities was used to study the ability of foam to increase sweep efficiency and redistribute injected fluids in the fracture network. Foam dynamics were investigated visually through a transparent plastic sheet on top of the model while differential pressures were measured using a differential pressure transducer. The experiment confirms that foam texture and bubble configuration play an important role in defining foam flow characteristics in fractures. Foam also demonstrates the ability to direct injected fluids from the higher permeability fractures to the lower permeability zone. Again, the population balance method of foam in fractures was verified and the model accurately reproduced experimental results.