A New Method for Reconstructing Hydrocarbon Accumulation History of Deep to Ultra-Deep Carbonate Reservoirs

The fluid inclusion homogenization temperature method is the most widely used approach for reconstructing hydrocarbon accumulation history in deep to ultra-deep carbonate rocks. However, there are three major limitations: (1) The difficulty in restoring the eroded thickness of target strata, leading to uncertainty in the reconstruction of tectonic and burial history. (2) It is common to use the brine inclusion homogenization temperature as a substitute for hydrocarbon inclusion trapping temperature. However, it is often challenging to find coexisting hydrocarbon and brine inclusions within the same host mineral. (3) It is difficult to determine the trapping time based on the trapping temperature. As in multi-cycle superimposed basins, the same trapping temperature may correspond to multiple ages on the tectonic-burial history curve, resulting in non-unique solutions.

The application of laser U-Pb isotopic dating of carbonate minerals and clumped isotope thermometry has addressed these limitations and led to the development of a new method for reconstructing hydrocarbon accumulation history in deep to ultra-deep carbonate reservoirs. (1) Restoration of the eroded thickness of strata is achieved through multi-phase diagenetic mineral age-temperature constraints, effectively resolving the uncertainty in the tectonic-burial history reconstruction. (2) Direct measurement of hydrocarbon inclusion trapping temperature, overcoming the challenge of determining trapping temperature when no coexisting brine inclusions are present in the host mineral. (3) Direct measurement of hydrocarbon inclusion trapping time, addressing the issue of non-uniqueness in accumulation ages for multi-cycle superimposed basins.

This method has been applied to reconstruct the accumulation history of natural gas reservoirs in the Dengying Formation of the Sichuan Basin. It has significantly higher accuracy and success rates compared to the fluid inclusion homogenization temperature method.