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

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.