In-situ fluid phase variation along the thermal maturation gradient in shale petroleum system and its impact on well production performance

In-situ fluid phase behavior is important in determining hydrocarbon contents and the multiphase flow through shale reservoirs. The gas-to-oil ratio (GOR) has been recognized as the critical indicators of fluid types. However, little is known about the impact of fluid phase variation across the thermal maturity on shale oil/gas production (e.g., estimated ultimate recovery, EUR). According to the specific gravity ratio of oil/gas, the producing GOR was converted and normalized into a mass fraction of gas in total hydrocarbons (MGOR) to compare North American shale oil/gas plays with Chinese shale oil and hybrid gas-condensate plays. A correlation between MGOR, the fluid phases and production data was established to identify five phase stages of flow. MGOR varies systematically with the different production zones, which shows promise in rapidly indicating the well production performance and high-production stages of shale oil/gas plays. The hybrid shale gas-condensate index, Tmax, total gas contents were integrated to present the fluid types and maturity of shale gas-condensates, which indicates fluid phase and production variation across thermal evolution. The results offer a unique perspective on the shale oil reservoir producibility based on the impact of GOR on fluid phases and EUR from the global dominant oil/gas plays.