Characteristics of Pore-throat structure and Mass Transport in Ultra-low Permeability Reservoir

Low permeability reservoir is one of the most important petroleum reserve types in China. Therefore, some basic scientific problems about low permeability reservoir such as pore-throat size distribution, principle of porous flow should be deeply studied. Pore-throat size distribution, based on 69 cores from Changqing and Daqing oilfield of China, has been measured by comprehensive using Constant-Rate Mercury Injection and Nuclear Magnetic Resonance. It has been found that the Nano-pore-throat takes more than 60 percent of the total pore-throat of the low permeability reservoir and it is the key factor affecting the flow capacity when the permeability is less than 0.5x10(-3)mu m(2). The nano-pore-throat takes less than 40 percent of the total pore-throat and micron-pore-throat takes more than 45 percent when the permeability is larger than 5x10(-3)mu m(2). And Micron-pore-throat is the key factor affecting the flow capacity of low permeability reservoir. But when the reservoir permeability is between 0.5x10(-3)mu m(2) and 5x10(-3)mu m(2), its flow capacity is determined by the sub-micron-pore-throat and the amount of micron-pore-throat. Additionally, the key forces in micro-, sub-micro- and nanoscale pore-throat has been got by analyzing. The electrokinetic coupling matrix of mass transport has been gotten by analyzing the characteristics of the mass transport in small tube at different Debye ratio and pore-throat size distribution of ultra-low permeability.