| Taking Qianzhong Uplift in Guizhou Province as an example, the characteristics and developmental mechanism of the dolostone reservoir altered by hydrothermal karstification were discussed based on the outcrops survey and experimental analysis.The main lithology of Honghuayuan Formation and Tongzi Formation is dolostone with zebra grain structure, in which some dolomites, calcites and bitumen were filled in dissolution caves or tectonic fractures.The hydrothermal coarse dolomites filled have the features of curved surface and wavy extinction,which also present red cathode luminescence apparently. The δ13CPDB values of the filling dolomites distributed between -2.2‰ and -0.8‰ with an average of -1.47‰; the δ18OPDB values varied from -12.2‰ to -7.6‰ with an average of -9.4‰ , which are more lighter than the matrix dolomites. The filling dolomites have a typical feature of positive Eu anomaly in REE composition with a highest point of 91.9. According to the geological evolution and fluid types, the reservoir development process can be described as follows: In Early Ordovician, there appeared penecontemporaneous dolomitization; from Late Ordovician to Early Silurian, the dolostone reservoir with karst fissure was developed as a result of karstification with the dolostone exposure to surface environment due to the Duyun Movement; in Early Devonian, the dolostones were altered further by tectonic and hydrothermal activities; consequently, the porous dolostone associated with solutional processes became the main reservoir for natural gas. |
