An Experimental Study of Foam Flow in Fractured Systems of Increasing Size
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Although use of foam for gas mobility control is substantially covered in literature, large- scale field implementation is still absent in fractured reservoirs. Current understanding of foam behavior in fractured systems is essentially based on experimental studies, and a recent investigation of foam generation in a rough-walled fractured system by coinjecting surfactant solution and gas showed that foam effectively reduce gas mobility in fractures. Reduced gas mobility favors stabilized gas-oil displacement in heterogeneous reservoirs where high-permeable thief-zones" may result in viscous fingering due to early breakthrough of gas. This experimental thesis investigates foam flow in three different fractured systems, and the overall objective was to evaluate if increased system size (i.e. fracture length) had an impact on foam flow. A total of 13 coinjections with surfactant solution and gas were carried out in fractured systems referred to as System A, B, and C. Systems A and B constitute two fractured marble cores with diameters of two and four inches, respectively, and were successfully drilled, fractured, and reassembled to replicate rough- walled fractures found in reservoirs. During all coinjections, the total volumetric rate was kept constant whereas gas fractional flow (Fg) was varied in pre-defined fractions. Measurements of differential pressure in all three systems indicated elevated flow resistance at "F" _"g" =0.7-0.9, corroborated by observed generation of strong, fine-textured foam at high gas fractional flow. Foam rheology was evaluated using different flow rates in each system, and apparent viscosity of foam was found to decrease at increased flow rates, suggesting a shear-thinning foam behavior. Foam flow did not seem dependent on system size. Coinjections in all three systems obtained the highest flow resistance at high gas fractional flow and pressures gradient curves was highly comparable between the systems. Positron emission tomography (PET) imaging was successfully applied to visualize liquid saturation and distribution during coinjection in System B. PET signals provided access to variation in local surfactant concentrations within the fracture network, and contributed favorable towards understanding observed differences in measured differential pressures. Visual investigation of foam texture during coinjection in System C showed texture changed from uniform, polyhedral bubbles to coarse, dry bubbles at a high gas fractional flow. Findings from this thesis will hopefully contribute to improved understanding of foam behavior in fractured systems.