Study on Physical Simulation Experimental Technology of Ultra-low Permeability Large-scale Outcrop Model

Abstract Ultra-low permeability reserves have accounted for a very large proportion of China's proven reserves and undeveloped reserves at present, so it is very urgent to deeply study the seepage flow law of ultra-low permeability reservoirs. This paper proposed a rock screening criterion for large outcrop models. Meanwhile, encapsulation and saturation methods, pressure and flow field test methods for large outcrop models were developed according to the reservoir characteristics and fluid seepage flow characteristics of ultra-low permeability oilfields in each oil region. Based on those new experimental technologies, the 2D nonlinear seepage flow law of ultra-low permeability reservoirs has been studied with the large outcrop models. Experimental results indicate during the fluid seepage flow in a large outcrop model, there is a non-flow area, a nonlinear seepage flow area, and a quasi-linear seepage flow area on plane; in addition, the variation law of pressure gradient field and flow with different displacing pore volumes has been analyzed, thereby laying a substantial foundation for establishing the evaluation methodology for the effective driving pressure system of ultra-low permeability reservoirs. Introduction Ultra-low permeability reserves have accounted for a very large proportion of China's proven reserves and undeveloped reserves and developed ultra-low permeability oilfields have become more and more in recent decades[1]. Therefore, it is very urgent to deeply study the seepage flow law of fluids in ultra-low permeability porous media for providing guidance to reasonable development of ultra-low permeability oilfields. At present, all analyses and theoretical studies of the seepage flow law of ultra-low permeability reservoirs are based on one-dimensional physical simulation experiments and microtubule flow experiments[2,3,4] instead of fluid seepage flow experiments on ultra-low permeability plate models, so the corresponding research findings can neither be applied in real ultra-low permeability reservoirs to a relatively large extent nor indicate the nonlinear plane seepage flow law of ultra-low permeability reservoirs. Experimental studies of domestic and foreign large plate models[5,6,7] focus on EOR, the models are basically sand-packed models, and there are rare large outcrop models used to study the seepage flow law of ultra-low permeability reservoirs. Therefore, this paper has analyzed and studied large outcrop models in terms of rock screening, model making, physical simulation experiment unit, pressure and flow field test methods, fluid seepage flow law in large outcrop models, etc. so as to form a physical simulation experiment technology of ultra-low permeability large outcrop models and lay a substantial foundation for establishing the evaluation methodology for the effective driving pressure system of ultra-low permeability reservoirs.