| Both water and hydrocarbons are important resources in reservoir exploration. These real reservoirs behave as mixtures or solutions including dissolved gases, and the properties of a solvent can be significantly affected by the type and concentration of gas dissolved in it. A crucial part of any reservoir monitoring research program must experimentally determine the acoustic velocities, compressibilities, and densities of various gas-fluid solutions at varying temperatures, pressures, and concentrations.; A phase-interference method was developed for velocity measurement, where double impulses and double reflectors were combined to fulfill the interference requirements. A robust system and a reliable protocol to measure velocity of gas-fluid solutions were accomplished with high accuracy of 0.05%. Measurement of pure fluids is the first step in obtaining robust and reliable results for unknown gas-fluid solutions. Typical gas solutes, {dollar}rm COsb2, CHsb4, Nsb2{dollar} and NH{dollar}sb3,{dollar} and solvents, water and decane, were selected as the samples for the solution study. We discovered that the two solvents showed reverse trends in velocity when gas was dissolved into them. For gas aqueous solution, the velocity of the solution increases with increasing concentration. Velocity increases up to 50 m/s ({dollar}approx{dollar}3%) and 140 m/s ({dollar}approx{dollar}9%) for CO{dollar}sb2{dollar} aqueous solution and NH{dollar}sb3{dollar} aqueous solution respectively. These results were obtained at room temperature ({dollar}{lcub}approx{rcub}22spcirc{dollar}C) with CO{dollar}sb2{dollar} saturated vapor pressure of 400 psi, and NH3 saturated vapor pressure of 70 psi. Velocity increases only slightly ({dollar}approx{dollar}0.1%) for CH{dollar}sb4{dollar} and N{dollar}sb2{dollar} aqueous solutions. Conversely, for gases dissolved in decane, the velocity of the solution decreases with increasing concentration. Velocity decreases about 100 m/s for CH{dollar}sb4{dollar} ({dollar}approx{dollar}8%), 130 m/s for CO{dollar}sb2{dollar} ({dollar}approx{dollar}10%), and 47 m/s for N{dollar}sb2{dollar} ({dollar}approx{dollar}4%) at saturated vapor pressures of 500 psi, 400 psi, and 600 psi, respectively. Water yielded anomalous properties while decane gave normal results.; A mechanism was proposed based on the interstitial structure of water to interpret the anomalous properties during gas dissolution. Water behaves abnormally because of its hydrogen bonds and special lattice structure, where a vacancy exists in each bonded unit. Free solute molecules can occupy the vacancies in some of the units to strengthen the entire system. |
