The compressibility factor of natural gases is necessary in many petroleum engineering calculations. Some of these calculations are the following: evaluation of a newly discovered formation, pressure drop from flow of gas through a pipe, pressure gradient in gas wells, gas metering, gas compression, and processing. Typically, the gas compressibility factor is measured by laboratory experiments. These experiments are expensive and time-consuming. Occasionally, experimental data became unavailable and the gas compressibility factor is estimated from correlations using gas composition or gas gravity. This paper presents new methods for calculating the gas compressibility factors for gas condensates at any temperature and pressure. The method is based on compositional analysis of 1200 compositions of gas condensates collected worldwide. When the gas composition is known, this study presents a simple mixing rule to calculate the pseudo-critical properties of the gas condensate. The new mixing rule accounts for the presence of the heptane plus fraction and none hydrocarbons. In case the gas composition is unavailable, the study presents a new gas gravity correlation to estimate pseudo-critical properties of the gas condensate. This study also presents an evaluation of eight methods to characterize the plus fraction, three widely used mixing rules, and six methods to calculate the gas compressibility factor. Thus, this study presents an evaluation of one hundred forty-four possible methods of calculating the gas compressibility factor for gas condensates. The accuracy of the new mixing rule and the gas gravity correlation has been compared to other published methods. The comparison indicates that the proposed methods are consistent and provide accurate results.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractCompressibility factor of natural gases is necessary in many petroleum engineering calculations. Some of these calculations are: evaluation of newly discovered formation, pressure drop from flow of gas through pipe, pressure gradient in gas wells, gas metering, gas compression, and processing. Typically, the gas compressibility factor is measured by laboratory experiments. These experiments are expensive and time consuming. Occasionally, experimental data became unavailable and the gas compressibility factor is estimated from correlations using gas composition or gas gravity. This paper presents new methods for calculating the gas compressibility factors for the gas condensates at any temperature and pressure. The method is based on compositional analysis of 1200 compositions of gas condensates collected worldwide. When gas composition is known, this study presents a simple mixing rule to calculate the pseudo-critical properties of the gas condensate. The new mixing rule accounts for the presence of the heptane plus fraction. In case gas composition is unavailable, the study presents new gas gravity correlation to estimate pseudo-critical properties of the gas condensate. The study also presents evaluation of eight methods to characterized the plus fraction, three widely used mixing rules, and six methods to calculate the gas compressibility factor. Thus, this study presents evaluation of one-hundred forty-four possible methods of calculating the gas compressibility factor for gas condensates. Accuracy of the new mixing rule and the gas gravity correlation has been compared to other published methods. The comparison indicates that the proposed methods are consistent and provide accurate results.

Water coning is one of the most serious problems encountered in active bottom-water drive reservoir. It increases the cost of production operations, reduces the efficiency of the depletion mechanism, and decreases the overall oil recovery. Therefore, preventive measures to curtail water coning damaging effects should be well delineated at the early stages of reservoir depletion. Production rate, mobility ratio, well completion design, and reservoir anisotropy are few of the major parameters influencing and promoting water coning. The objective of this paper is to develop a depletion strategy for an active bottom-water drive reservoir that would improve oil recovery, reduce water production due to coning, delay water breakthrough time, and pre-identify wells that are candidates to excessive water production. The proposed depletion strategy does not only take into consideration the reservoir conditions, but also the currently available surface production facilities and future development plan. Analytical methods are first used to obtain preliminary estimates of critical production rate and water breakthrough time, then comprehensive numerical investigation of the relevant parameters affecting water coning behavior is conducted using a single well 3D radial reservoir simulation model.