Abstract: After nearly forty years of exploration and production, the Huizhou Depression of the Pearl River Mouth Basin (PRMB) of the South China Sea has entered the stage of duplex exploration.It is urgent to open up new exploration areas. The buried granite hill, which is selected by some scholars as one of the succeeding areas, but questioned by others since no oil reservoir has been encountered so far, is selected in this paper as the research target.In order to open up the new exploration area of igneous reservoirs, therefore, a discovery well was drilled on the structure A of the Huizhou Depression of the PRMB.Specific analysis, such as thin sections and FMI(Formation Micro-Scanner Image)are made for the borehole cores. Three types of fractures are recognized in the reservoir i.e. group fractures, reticulated fractures and isolated fractures, and four segments are divided where fractures are more developed.Secondary dissolution includes those along cracks and dissolution voids. Vertical zonation, which includes the clay zone, fractured zone and bed rock zone, is observed due to differential weathering and leaching. The reservoir space is dominated by associated fractures, which are filled by calcite. RCI (reservoir characterization instrument) and MDT (modular cable reservoir dynamic tester) are adopted to test reservoir conditions, and the conditions for hydrocarbon generation, storage, capping and migration are analyzed individually for evaluation of petroleum geological conditions.