Isothermal Oil Compressibility Curve Crossing

Abstract Oil compressibility above bubble point pressure is important in reservoir simulation, material balance calculations, design of high-pressure surface-equipment and the interpretation of well test analysis. Accurate calculation of oil compressibility is very important for reservoir evaluation. The oil compressibility above bubble point pressure increases with increasing temperature and decreasing pressure, therefore, curves at the same pressure and different temperatures should not cross each other. The conventional method of obtaining oil compressibility is from individual temperature measurement of pressure-volume data of constant composition expansion test. The oil compressibility determination involves pressure-volume function and its derivative at each temperature. This individual estimation with derivative calculation makes oil compressibility evaluation very sensitive to small derivative change that may lead to an invalid and non physical behavior of curve crossing. This paper presents a special constrained multiple linear regression optimizations that ensures non-crossing of oil compressibility curves above bubble point pressure for multiple temperatures.