MULTIPHASE, MULTICOMPONENT COMPRESSIBILITY IN PETROLEUM RESERVOIR ENGINEERING (COMPRESSIBILITY ISOTHERMAL, WELL TEST, THERMODYNAMICS)

Adiabatic and isothermal compressibility below the bubble point and production compressibility were computed with a thermodynamic model for single and multicomponent systems. The thermodynamic model consists of an energy balance including a rock component, and a mass balance, with appropriate thermodynamic relationships for enthalpy and equilibrium ratios utilizing the virial equation of state. Runs consisted of modeling a flash process, either adiabatically or isothermally and calculating fluid compressibilities below the bubble point for H(,2)O, H(,2)O - CO(,2), nC(,4) - iC(,4) - C(,5) - C(,10), C(,1) - C(,7), and C(,1) - C(,7) - H(,2)O systems. The production compressibility was computed for a gas production, and for production according to relative permeability relationships for a one-component system. Results showed a two-phase compressibility higher than gas compressibility for similar conditions, and a production compressibility that could be larger than either the two-phase compressibility or the gas-phase compressibility, under the same conditions.(,).;The two-phase compressibility results tend to corroborate an observation that a two-phase system has the effective density of the liquid phase, but the compressibility of a gas. Production compressibility is large because of a reduction in the amount of liquid in the system because of the effects of vaporization and production enhanced by the effect of heat available from rock in the system.;Total system compressibility plays an important role in the interpretation of well test analysis, specifically for systems below the bubble point. Accurate information on the total effective fluid compressibility is necessary for the possible isolation of formation compressibility from interference testing in subsiding systems.;Non-condensible gas content of discharged fluid for a steam-dominated geothermal system was studied with the thermodynamic model. An initial increase in the non-condensible gas concentration was observed, followed by a stabilization period and finally a decline in the noncondensible-gas concentration, behavior that resembles actual field results. Study of the behavior of noncondensible gases in produced geothermal fluids is important for planning turbine design.