H.H. Hanafy, SPE, Gulf of Suez Petroleum Company, S.M. Macary, Egyptian Petroleum Research Institute, Y.M. ElNady, SPE, Al Azhar University, A.A. Bayomi, SPE, Al Azhar University, and M.H. El Batanony, Egyptian Petroleum Research Institute Copyright 1997, Society of Petroleum Engineers, Inc.
An accurate description of physical properties for crude oils is necessary for solving many of reservoir engineering and surface production operational problems. Ideally, crude oil properties are determined experimentally in the laboratory on actual fluid samples taken from the field under study. However, in the absence of experimentally measured crude oil properties, especially during the prospecting phase, or when only invalid samples are available, one can resort to empirically derived PVT correlations. During the last five decades, several correlations have been developed to estimate the crude oil properties. However, these correlations may be useful only in regional geological provinces and may not provide satisfactory results when applied to crude oils from other regions. The aim of this work is to derive and test new correlations to predict the fluid properties for Egyptian crudes including bubble point pressure, solution gas-oil-ratio, oil formation volume factor, oil compressibility, oil density, and oil viscosity. These correlations have been developed from the experimental PVT data of 324 fluid samples covering a wide range of crude oils ranging from heavy to volatile oils. The fluid samples have been taken from 176 wells located in 75 fields operated by 16 companies. This data represents 15 productive zones of 123 reservoirs distributed along three different regions of Egypt, including the Gulf of Suez, Western Desert, and Sinai. Sensitivity analysis indicated that the experimentally determined flash liberation gas-oil-ratio, which corresponds to the producing gas-oil-ratio, is the most correlative parameter with the bubble point pressure. Therefore the separator gas-oil ratio was used in this study as the key parameter for predicting the oil properties. The procedure for predicting the fluid properties using the new correlations is simple and straightforward. By starting with the separator gas-oil-ratio then going through good correlations between different pairs of fluid properties, one can obtain a complete set of PVT data for oil properties either at or above or below the bubble point pressure. Finally, this study compares the predicted properties from the new correlations and the commonly used empirical correlations by applying them to the experimental data base available for Egyptian crude oils.
The reservoir fluid data have many applications in different areas of the Exploration and Production process. While reservoir engineers generally have the greatest claim on such data, reservoir fluid analyses are also quite valuable to geologists and production specialists.
The process of collecting fluid samples may be repeated during different phases of a field since discovery till its mature phase.
A geologist may use correlations along with an oil or gas gravity measurement from a near-by well for help in obtaining an estimate of the potential reserves to be found in an exploration prospect.
After the exploration well is drilled and successful, a well test may allow those same correlations to be used with the known gravity, gas-oil ratio, and pressure data from the discovery well. In an ideal situation, a fluid sample may be recovered from the discovery well for analysis.