(309d) High Accuracy Density Measurements at Pressures up to 200 Mpa for Light Synthetic Natural Gas-like Mixtures

Accurate knowledge of the PVT behavior of gases is necessary for the production, transmission, custody transfer and utilization of natural gas. Collecting highly accurate natural gas density data at very high pressures is a challenge. Yet, to be able to simulate reservoir conditions, high-pressure density measurements are necessary. Density plays a key role in determining the economic value of natural gas for custody transfer, and it is important to have data covering the broad range of pipeline conditions. It is also essential to have such data to validate or develop equations of state (EOS) that can calculate phase equilibrium properties and provide accurate density predictions. For pipeline conditions, accurate cricondentherm and cricondenbar values are necessary to avoid two-phase flow (liquid + gas) in compressors. We have a state-of-the-art magnetic suspension densitometer (MSD) for density measurements in our laboratory. The MSD can measure isothermal densities up to 200 MPa from 100 to 500 K. Temperature stability in the apparatus is ±5 mK and pressures have an uncertainty of ±0.002%. The MSD can provide densities accurate to ±0.06%. For this work, we have measurements up to 200 MPa at temperatures between 200K and 450K. The mixtures used are two lean synthetic natural gas like mixtures having components C1 to C5 as well as nitrogen and carbon dioxide. Both the mixtures have ~90 mol% methane but different C5 compositions.