报告题目：Hydrothermal dolomite and associated reservoirs in Western Canada Sedimentary Basin: similarity and differences with those from Tarim Basin
报告人：Hairuo Qing 教授
报告人单位：University of Regina Regina SK, Canada
The process of dolomitization and formation of dolomite reservoirs have been a controversial topic for a long time. Since late 80’s, a number of detailed case studies from the Western Canada Sedimentary Basin (WCSB) suggested that hydrothermal fluids played a vital role in formation of massive dolomite and associated reservoirs. In recent years, hydrothermal dolomitization has received so much attention, which has become a new bandwagon that has been applied indiscriminately to some case studies in Tarim Basin in China where the hydrothermal dolomite were, actually, distinctively different from those of WCSB.
The hydrothermal dolomites from the WCSB generally occurred in an open system that delivered Mg as well as heat to the reaction site; whereas most of hydrothermal dolomites in the Tarim Basin occurred in a closed or semi closed system, where Mg is mostly derived via chemical compaction of precursor dolomite. This fundamental difference resulted in a number of unique petrographic and geochemical characteristics of hydrothermal dolomites in two different basins:
(1) he WCSB is characterized by high water/rock ratio of an open system; the Tarim Basin illustrates low water/rock ratio, typically of closed, semi-closed system.
(2) In the WCSB, hydrothermal fluids precipitated large amount of dolomite cement and replaced host precursor limestone; in the Tarim Basin hydrothermal fluids mostly modified earlier dolomites with minor amount dolomite cements.
(3) In the WCSB, the geochemical signatures of hydrothermal dolomite are distinctly different from those of host carbonate rocks; in the Tarim Basin the geochemical signatures of hydrothermal are similar to host carbonate rocks.
(4) In the WCSB, hydrothermal fluids is mostly related to deeply seated fault system and constrained by regional seals; in the Tarim Basin hydrothermal fluids is likely linked to fault systems that were associated with igneous activities.
The fundamental difference of the origin of hydrothermal dolomite from the WCSB and from the Tarim Basin requires a different exploration strategy applied to these two basins. In the WCSB, explorations of hydrothermal dolomite should be focused along regional conduit system along fault and reef chains. In the Tarim Basin, limited amount of hydrothermal dolomite reservoir preferentially occurs along fault systems; and occurrences of hydrocarbon traps require identification of suitable seals for these hydrothermal dolomite reservoirs.