Hydrothermal dissolution of Ordovician carbonates rocks and its dissolution mechanism in Tarim Basin, China

The dissolution of carbonate rocks has a significant control on reservoir quality under deep burial conditions, which has become a focus of studies in recent years. A series of hydrothermal minerals and combinations, such as fluorite, dickite, barite and hydrothermal dolomite, were discovered in the Ordovician strata in some exploration wells in the Tahe area. Moreover, the analysis results of carbon and oxygen isotope, REE, strontium isotope and inclusion homogenization temperature further confirmed that hydrothermal fluids existed in the Ordovician strata of Tahe areas. In this paper, the dissolution mechanism of carbonate rocks under deep burial conditions is discussed. It was considered that the hydrothermal dissolution required three conditions, i.e., the development of fault system, the presence of acidic fluids and a fall in temperature. The major theoretical foundation was the retrograde solubility of carbonate rocks that could be achieved through temperature drop and the upward migration of hydrothermal fluids. The dissolution of carbonate rocks caused by hydrothermal fluids normally occurred in the vicinity of migration pathways (faults or other pathways), which could be identified as good reservoir development zones.