Shale oil has been found in the argillaceous dolomite reservoir of the Paleogene Xingouzui Formation in the Jianghan Basin. However, the shale oil storage mechanism in these rocks remains unclear, considering that increasing attention has been paid to shales instead of argillaceous dolomites. This article illustrated the microscopic pore structure and distribution of the argillaceous dolomite reservoir, discussed the porosity enhancement potential through dolomite mineral dissolution by organic acids, and indicated the contribution of the dolomite mineral dissolution pores to the porosity. Scanning electronic microscopy images show that the argillaceous dolomite reservoirs mainly contain inorganic pores, including intercrystalline pores, intergranular pores, and dissolution pores. However, organic pores are observed to be sporadically distributed. Nano computed tomography data show that the pores of argillaceous dolomite vary in morphology and size and are unevenly spatially distributed. There are some isolated pores and unevenly distributed throats, among which larger throats are located in areas with well-developed pores. The pores of the shale reservoirs are mainly related to the dolomite mineral rather than other minerals. With increase in the dolomite mineral content, porosity and pore connectivity are improved, indicating that a high dolomite mineral content has greatly promoted both the porosity and permeability of the argillaceous dolomite reservoir in the study area. The organic acid experiment confirmed this conclusion that the porosity enhancement potential by dissolution reactions is notable when the dolomite mineral content in the samples is over 16%. The porosity enhancement through dolomite mineral dissolution ranges from 0.48 to 4.85%, with an average of 2.34%. Thus, dissolution pores are considered to be a significant reservoir space for shale oil storage in the argillaceous dolomite reservoir in the Paleogene Xingouzui Formation from the Jianghan Basin.