Quantifying Permeability Changes Due to Gas Hydrate Formation in Undersaturated Oil Sandstone Reservoirs: A Numerical Reservoir Simulation Study

Numerical simulation is used to quantify the resulting permeability effects due to solid phase formation/precipitation during fluid flow in an oil reservoir. The case study consists of a sandstone reservoir saturated with live-oil above the bubble-point pressure that is subject to cold water injection. Due to the relatively low temperature of this over-pressurized shallow reservoir, gas hydrate formation can arise when the reservoir temperature falls below 7 °C, reducing permeability as observed in previous coreflooding tests. Digital representations of the core samples used in the experiments were created with a commercial reservoir simulator to follow the experimental procedures. These include tracing a cooling temperature ramp starting outside of the hydrate stability curve towards inside the hydrate forming region and differential pressure changes due to hydrates plugging the pore space, also implying a permeability alteration. The numerical simulations are compared with the experimental results and explore the hurdles and limitations of modeling this reactive fluid flow with a commercial reservoir simulator on the continuum scale. Reservoir simulation is suitable to model the thermodynamic hydrate formation conditions that result in a realistic spatial hydrate distribution but is not able to capture the microscopic amount of solids precipitation that provide a quantitative analysis of permeability reduction on the centimeter scale. The upscaling of the laboratory coreflooding scale simulations to the field-scale for counter-acting this microscopic behavior resulted in a localized permeability reduction of up to around 40%.