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The heterogeneity of reservoir micro-pores and the multifractal nature of their geometric morphology control the migration of oil and gas in porous media and affect the characteristics of oil and gas accumulation and productivity at the macro-scale. In this paper, based on high-resolution x-ray microscope computer tomography (XCT), combined with fractal and multifractal analysis, the microscopic pore-throat characteristics of 12 igneous rocks cylindrical core igneous rocks in the Huanghua Depression, China, were analyzed. A new DW interpretation chart (D = box-counting dimension; W = width of multifractal spectrum) based on fractal and multifractal analysis is presented to characterize the complexity of pore-throats in igneous rocks and to describe the influence of secondary transformation behavior on pore-throat microstructure. We found that microscopic pore-throat structures of different types of igneous rocks have significantly different fractal and multifractal characteristics. In addition, the complexity of pore-throat microstructure is indicative of the evolution dynamics of reservoir performance. The permeability of igneous rocks with simple microscopic pore-throat structures and strong heterogeneity is more sensitive to changes in porosity, and it is beneficial to the formation of high permeability oil–gas reservoirs. These results show the effect of igneous rock microstructure on macro-reservoirs and will provide a new perspective for the in-depth study of complex igneous oil–gas reservoirs. [ABSTRACT FROM AUTHOR]