Impact of compositional gradient on gas–oil contact determination in nano-confined shale gas-condensate reservoirs

Nano-confinement effects significantly alter fluid properties and influence gas–oil contact (GOC) prediction and multi-phase flow behavior in shale reservoirs. This study, for the first time, integrates nano-confinement effects into a compositional gradient model to determine the GOC. Results show that incorporating critical property shifts of fluid components in nanopores increases the GOC depth. The nano-confinement effect partially offsets compositional gradient changes caused by gravitational differentiation. Production above the GOC leads to a sharp decline in oil production and an increase in gas output due to gravitational differentiation. Conversely, production below the GOC enhances oil recovery while reducing gas production. The nano-confinement effect moderates the rate of compositional gradient variations, thereby mitigating these shifts. Additionally, it elevates the produced gas–oil ratio by reducing the dew point pressure, prolonging single-phase gas production. Validation using a real reservoir model confirms that accounting for both nano-confinement and compositional gradients improves predictive accuracy.