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. However, in the absence of experimentally measured crude oil properties, one can resort to empirical PVT correlations. The purpose of this paper is to evaluate most of the empirically derived PVT correlations found in the literature during the last five decades by applying them to the Egyptian Crude Oils. The PVT measurements of 324 fluid samples covering a wide range of crude oils ranging from heavy to volatile oils have been used in this study. These samples were collected from 75 fields distributed along three different regions of Egypt including, the Gulf of Suez, Western Desert, and Sinai. In order to have a fair evaluation of the different correlations, special care was given to the limitations of data and nature of parameters used to derive these correlations. The results of this study were also compared with the results of similar studies performed on Egyptian oils as well as crude oils from other regions worldwide. Because the total separator gas-oil ratio is the key parameter to estimate the reservoir oil properties from most of the popular empirical correlations, this paper presents a new approach to correct the primary stage separator gas-oil ratio to estimate the total gas-oil ratio using the data base available for Egyptian oils. This paper concludes that due to regional ranges in crude oil compositions, a universal correlation that can be applied to different types of crude oils would be difficult to obtain. Therefore, correlations for a local region, where crude oil properties are expected to be uniform, would be a necessary alternative.
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.
One can resort to empirical PVT correlations to estimate the reservoir fluid data in the following cases:
inability to obtain a representative sample,
sample volume is insufficient to obtain a complete analysis,
collected sample is nonrepresentative,
quality check lab analysis,
lab analyses are in error,
estimating the potential reserves to be found in an exploration prospects,
evaluating the original oil in place and reserve for a newly discovered area before obtaining the laboratory analysis to justify a primary development plan.
This study evaluates the accuracy of the empirically derived PVT correlations relative to the experimental PVT for 324 Egyptian oil samples taken from 123 reservoirs in 75 fields. Table 1 presents the PVT data range for the available samples. The tested Correlations are used to estimate the bubblepoint pressure, oil formation volume factor, isothermal oil compressibility, oil density, and oil viscosity. Before measuring the accuracy of different correlations, it should be pointed out that the effective use of the correlations lies in an understanding of their development and knowledge of their limitations.
Correlations Development and limitations Sutton and Farshad presented a detailed review about the development and limitations of the most widely used correlations. P. 733