Estimation of the hydrocarbon loss through major tectonic events in the Tazhong area, Tarim Basin, west China

The Tazhong area, located in the central part of the Tarim Basin, is the major commercial oil and gas province in the Tarim Basin. Hydrocarbons have been discovered in the Ordovician, Silurian and Carboniferous reservoirs. Most of the hydrocarbon reservoirs in the Tazhong area have experienced post-charge and accumulation readjustment or loss associated with multiple post-charge tectonic movements. The relationship between the destroyed hydrocarbon proportion (DHP) caused by tectonic events and tectonic movement intensity (TMI) in 15 well blocks has been established for the entire Tazhong area using TMI analysis. TMI can be quantitatively characterized by the denudation thickness and effective caprock thickness ratio, whereas the DHP can be quantitatively determined by the variations of the palaeo and current oil-water contacts. There appears to be a good relationship between DHP and TMI with a correlation coefficient of 0.9. Most of the original Ordovician hydrocarbon accumulations formed in the late Ordovician had been lost, with an average DHP of up to 70%. The tectonic movement is much weaker in the late Silurian and late Permian period, with the DHPs for the Silurian reservoirs and Carboniferous reservoirs in the eastern Tazhong area averaging 50%. All the DHPs show a gradual increase from west to the east (Figs.17–19). The preservation condition of the reservoirs is generally better in west than in the east.