Abstract: A method for all-scale pore-throat measurements in tight reservoir cores was established by combining high-pressure mercury injection porosimetry, low-temperature nitrogen adsorption measurements, nuclear magnetic resonance, and centrifugation. On this basis, we compared the characteristics of pore-throat distributions at all scales in tight reservoir cores acquired from Changqing, the periphery of Daqing, and Sichuan. Compared with conventional single-measurement methods for microscopic pore-throat structure, our method for all-scale pore-throat measurements is significantly more accurate in measuring the distribution of micron-, submicron-, and nanometer-grade pore-throats. In very tight cores, our all-scale method measures the distribution of nanometer-grade pore-throats more accurately than high-pressure mercury injection porosimetry measurements. In tight reservoir cores, a lower proportion of fluids is controlled by micron-grade pore-throats, whereas a larger proportion of fluids is controlled by submicronand nanometer-grade pore-throats, as compared to cores with moderate to high levels of permeability. In a comparison between tight sandstone cores and tight limestone cores, the spectral peaks of the latter's pore-throat distribution are biased to the left and exhibit large interpeak spans, thus indicating high levels of heterogeneity. At the same level of permeability, tight cores from Changqing have a larger number of micron-grade pore-throats and a smaller number of nanometer-grade pore-throats, as compared to tight cores from Daqing. It is thus shown that the development efficiency of tight reservoirs in Changqing is likely to be better than that of tight reservoirs in Daqing.

Key words: tight reservoirs, cores, pore-throat measurements, nuclear magnetic resonance, high-pressure mercury injection