Constant-Pressure Technique for Gas Diffusivity and Solubility Measurements in Heavy Oil and Bitumen

A modified pressure decay method has been designed and tested for more reliable measurements of molecular diffusion coefficients of gases into liquids. Unlike the conventional pressure decay method, the experimental setup has been designed such that the interface pressure and consequently the dissolved gas concentration at the interface are kept constant. This is accomplished by continuously injecting the required amount of gas into the gas cap from a secondary supply cell to maintain the pressure constant at the gas−liquid interface. The pressure decay is measured in the supply cell. The advantage of the new technique is that, assuming the diffusion coefficient to be constant, a simple analysis allows determination of the equilibrium concentration and diffusion coefficient.