Development of New Modified Black Oil Correlations for Malaysian Crudes

Abstract

Abstract In reservoir engineering calculations, reservoir fluid property data are one of the important input data sets. These data can be obtained either by conducting a laboratory study on reservoir fluids or estimated from empirical correlations. Although laboratory results give better accuracy where controlled reservoir conditions can be imposed, the results are heavily dependent on the validity of the reservoir fluid samples, especially when the reservoir has depleted below the bubble point pressure. In situation where the experimental data cannot be obtained or there is a need to cross check the laboratory results, empirically derived PVT correlations can be used to estimate the physical reservoir fluid properties. Since no black oil correlations have been developed for Malaysian crudes and none of the existing correlations give good estimates of fluid property for Malaysian crudes, this paper describes the development of suitable black oil correlations which give results more accurate than any correlations available in the literature. A total of 93 PVT data taken from various Malaysian offshore oil-fields was used in the study. The PVT data consist of oil gravity range from 26.6 "API to 53.2 "API and bubble point pressures of 790 psig to 3851 psig. The crudes are essentially free of hydrogen sulphide with low nitrogen content (maximum of 1.15 per cent). Using both non linear and linear regression analyses, new black oil correlations (of bubble point pressure and bubble point oil formation volume factor) were established for Malaysian crudes. These new correlations were developed based on Standing's existing equations. The most sensitive coefficient in the Standing correlations was determined and expressed as a linear function of other independent variable PVT parameters. The accuracy of the new correlations was determined by conducting statistical and graphical error analysis. The results show that the new correlations give better accuracy in estimating reservoir fluid properties of Malaysian crudes than other known correlations available in the literature. The new correlations give low values of absolute average percent relative error, standard deviation with correlation coefficient values close to an ideal value of 1.0.