Solution-gas Drive In Heavy Oil Reservoirs

Experimental study and new three-dimensional kinetic modeling of foamy solution-gas drive processes

Foamy solution-gas drive processes in heavy oil reservoirs are very complex. The influence of some microscopic factors on this process is not fully understood due to limitations of traditional depletion tests. This study aims to investigate foamy solution-gas drive by experiments and simulations. First, the effects of the pressure depletion rate on critical gas saturation and foamy solution-gas drive processes were investigated by laboratory experiments. Second, a new three-dimensional foamy oil model that captures many important characteristics of foamy solution-gas drive, such as non-equilibrium behavior, gas evolution kinetics, and the effect of viscous forces on gas mobility, was developed. Last, the effects of some important parameters on foamy solution-gas drive were systematically investigated,and a model application was conducted in a typical foamy oil reservoir. The results indicate that the new model is capble of simulating many of the unusual behaviors observed in foamy solution-gas drive on a laboratory and field scales. High oil recoveries were obtained with a high oil viscosity, high depletion rate, long sandpack, and low solution gas-oil ratio. Foamy solution-gas drive processes are sensitive to the depletion rate, length, and critical gas saturation. The oil viscosity, solution GOR and diffusion coefficient are not sensitive factors.

A new mathematical model and experimental validation on foamy-oil flow in developing heavy oil reservoirs

To model foamy-oil flow in the development of heavy oil reservoirs, three depletion experiments were conducted with foamy oil treated as a pseudo-single-phase flow. In this pseudo single phase, dispersed bubbles are viewed as a part of the oil, and the redefined effective permeability varies with the changes of pressure depletion rate, oil viscosity, and gas saturation. A mathematical expression for the effective permeability was developed based on experiments, where the viscosity of foamy oil is assumed to be approximately equal to the saturated oil under equivalent conditions. The compressibility coefficient of foamy oil is treated as a volume-weighted compressibility coefficient of that of oil and gas phases. A new mathematical model for foamy-oil flow was proposed with consideration of foamy-oil supersaturation. To validate the mathematical model, the oil recovery and the production gas-oil ratio (GOR) calculated by the new model, conventional black oil model, supersaturation model and pseudo-bubble-point (PBP) model were all compared with those of the experimental data. The new model provided a substantially improved fit to the experimental data compared with the rest three models, which verifies the suitability of the mathematical model presented for simulating foamy-oil flow in the development of heavy oil reservoirs.

Growing bubbles in a slightly supersaturated liquid solution

We have designed and constructed an experimental system to study gas bubble growth in slightly supersaturated liquids. This is achieved by working with carbon dioxide dissolved in water, pressurized at a maximum of 1 MPa and applying a small pressure drop from saturation conditions. Bubbles grow from hydrophobic cavities etched on silicon wafers, which allows us to control their number and position. Hence, the experiment can be used to investigate the interaction among bubbles growing in close proximity when the main mass transfer mechanism is diffusion and there is a limited availability of the dissolved species.