The geological resource of the Gu Long shale oil is estimated at 15.1 billion tons, making it a recent exploration hotspot in the Daqing Oilfield. Core observation, thin section identification, electron backscatter, secondary imaging and energy spectrum analysis show that a large number of dissolution micropores are developed in the shale oil reservoir. The diameters of the dissolution micropores are mostly between 0.50 micrometers and 500 micrometers with most being 1-2 micrometers, and a few ostracod mold pores can reach 0.5-1.0 mm; they are nearly round, flat round, polygonal, and irregular. The dissolution pores can occur in ostracods, calcite or dolomite, and in clay and feldspar minerals. The dissolution pores and mold pores in ostracods were formed by decarboxylation in the early stage of diagenesis; while most of the dissolution pores in calcite and dolomite are filled,

mostly by organic clay, asphalt and authigenic minerals, and were formed in the later stage of diagenesis. In addition, feldspar minerals are also dissolved to form a large number of dissolution pores. Energy spectrum analysis reveals that the expelled oil or asphalt in the Gu Long shale is enriched in highly volatile and corrosive halogen elements such as F, Br and Cl, indicating that dissolution pores could be a result of the superimposition of magmatic hydrothermal fluids rich in highly volatile and corrosive halogen elements. Most of these dissolution micropores are connected to other fractures, forming a good spatially connected network system and facilitating the development of Gu Long shale oil.