Application of fluid inclusion analysis for buried dissolution predicting in the Tahe Oilfield of Tarim Basin, NW China

This study was undertaken to establish an evaluation method for buried dissolution of carbonate reservoir in the Tahe (塔河) Oilfield. Because of the difficulty in tracing the dissolution in geologic record, the precipitation is taken as a useful indicator to presume the dissolution reversed. The fluid inclusions data is a useful tool to identify the precipitation. On the basis of the principle that the temperature data of fluid inclusions captured in the calcite fillings of caves and cracks can reflect the fluid activity time, a total of 256 fluid inclusions samples in 12 drills were collected and analyzed to study their forming time in buried environment in the Tahe Oilfield, Tarim Basin, NW China. Results show that the temperature data of fluid inclusions captured by Ordovician cave and crack fillings accumulated in six intervals, which indicated six stages of fluid activity in the area of study. Meanwhile, it is clear that a different number of temperature intervals was captured in different wells, representing a different number of precipitation distributed in space. According to this conclusion, the buried precipitation trend in late Himalayan stage (the sixth stage) was supposed in space and its effectiveness has been approved by the chemical thermodynamics method. This method was also used in all of the other five stages of fluid activity and the comprehensive trend of the buried precipitation in space for Ordovician strata was evaluated. It shows that more temperature intervals were captured in the southwestern region (wells S76, S79, S65 and S75) and the eastern region (well S69) in the area of study, indicating intensive precipitation and weak dissolution in this area. This evaluation method for buried dissolution is a new attempt and may have important implications for further petroleum exploration in the Tarim Basin.