| Epigenic karstification(EK) and burial dissolution(BD) that are the most important diagenesis in carbonate rocks are similar in undergoing effect of the inner factors such as petrology and composition but great different in effect of the outer controlling factors. EK is predominantly controlled by the development of unconformity and paleostructurses while BD is controlled by the distribution of faults and deep-seated fluids. EK is characteristic of com-plex reservoir network of pores,vugs and fissures with distinguishing vertical zone distribution while BD features in distribution of linear V-shaped caverns and terraces. EK develops some features of typominerals such as calcium crust, paleo-soil, bauxite, rosiness calcite crystals, dissolved pits and ditchs and fallen caverns and karst breccia even as well as lunate, vertical and fibrous infiltration sands or cements; while BD is characteristic of MVT minerals including heteromorphic Fe-dolomite, fluorite, sphalerite and pyrrhotite, as well as collapsed structure, fissured tex- tures and irregular breccia rock bodies. EK develops generally in Ordovician carbonate reservoirs in Tabei region, in- cluding the famous Tahe Oil Field, and BD are common in Ordovician carbonate reservoirs in northwestern Tazhong region where the geological condition of wide-developing EK is absent. |
