Impact of Confinement on Hydrocarbon Production from Unconventional Reservoirs Using Thermodynamics

Abstract

Unconventional reservoirs have become the main objective for oil and gas investors since the depletion of conventional reservoirs. This study provides a workflow for obtaining accurate estimates of the production performance for a specific reservoir fluid composition by incorporating capillary pressure and pore-size distribution. It uses a mechanistic model to evaluate the impact on hydrocarbon production, incorporating confinement effects for unconventional reservoirs, such as tight sandstones and shales, which now have a predominant production in the petroleum industry. Variations in fluid thermodynamic properties and fluid-to-rock interactions significantly impact the recovery and performance of unconventional reservoirs. The Peng-Robinson Equation of State coupled with the Young-Laplace equation can provide accurate recovery estimates. Simulations are conducted in bulk thermodynamics and confinement, with the remaining variables constant. The mechanistic model analyzes the impact on depletion variables, such as production modes, pore size distribution, contact angle, and binary interaction coefficients, and also generates uniquely relative permeability curves from capillary pressure curves.

Reservoir simulation for volatile oil in an Eagle Ford formation shows the impact of confinement and relative permeability to obtain consistent cumulative oil and gas productions. Comparing the results with the compositional reservoir simulator under identical conditions shows similar effects where confinement increases oil production and decreases gas production and average pressure in the reservoir.