Gas compressibility factor or Z-factor for natural gas system can be determined from Standing-Katz charts using the pseudocritical gas pressure and temperatures. These charts give accurate values for Z-factors. Reservoir simulation softwares need accurate correlations to estimate the values of Z-factor; one of the well-known correlations is Dranchuk and Abou-Kassem (DAK) Correlation. This correlation gives large errors at high gas reservoir pressures, this error could be more than 100%. The error in estimating Z-factor will lead to big error in estimating all the other gas properties such as gas formation volume factor, gas compressibility, and gas in place. In this paper a new accurate Z-factor correlation has been developed using regression for more than 300 data points of measured Z-factor using MATLAB in addition to other data points at low pressure and temperature from Standing-Katz charts and DAK correlation. Old correlations give good estimation of Z-factor at low gas reservoir pressures below 41.37MPa (6000 psia), at high pressures the error started to appear. The developed correlation is a function of pseudoreduced pressure and temperature of the gas which makes it simpler than the existing complicated correlations. The new correlation can be used to deterhiine the gas compressibility factor at any pressure range especially for high pressures the error was less than 3% compared to the measured data. The developed correlation is very simple to be used, it just needs the gas specific gravity that can be used to determine the pseudocritical properties of the gas and at last the Z-factor can be determined. A new formula of reduced gas compressibility was developed based on the developed Z-factor correlation which in turn can be used to determine the gas compressibility. . All degrees in petroleum Engineering. He published more than 30 technical papers and 10 reviewed journal papers. Dr. Mahmoud areas of research are carbonate and sandstone acidizing, formation damage, hydraulic and acid fi'acturing of conventional and unconventional reservoirs, enhanced oil recovery of sandstone and carbonate reservoirs, drilling fluids, advanced well logging, multiphase flow in pipes, filter cake removal and characterization, sequestration and storage of carbon dioxide, and rock petrophysics, Mahmoud holds several patents in the areas of production enhancement and enhanced oil recovery.

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Asphaltene adsorption and deposition onto rock surfaces are predominantly the cause of wettability and permeability alterations which result in well productivity losses. These alterations can be induced by rock−fluid interactions which are affected by well operations such as acidizing, stimulation, gas injections, and so forth. Iron minerals are found abundantly in sandstone reservoir formations and pose a problem by precipitation and adsorption of polar crude components. This is due to rock−fluid interactions, which are dependent on reservoir pH; thus, this research work studied the surface charge development of pyrite, magnetite, and hematite. To ascertain conditions that will result in iron mineral precipitation and adsorption of asphaltene on iron mineral surfaces, zeta potential measurement was carried out. This is to determine the charge and colloidal stability of the iron mineral samples across wide pH values. Experimental results show that the charge development of iron minerals is controlled by mineral dissolution, the formation of complexes, adsorption of ions on the mineral surface, and the collapse of the double layer. The findings provide insights into the implications of iron mineral contacting crude oil in reservoir formations and how they contribute to wettability alterations due to different well operations.

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The reservoir rock is made up of different minerals and its surface chemistry is influenced by the reservoir environment. Well operations implemented during the life of a field induce changes in the reservoir environment (pH) that affect the minerals, resulting in a change of their surface chemistry. These changes result in wettability alterations, which have a significant effect on the overall production. Thus, this research provides insight into the behavior of calcite, feldspar, barite, dolomite, quartz, and sand in varying pH environments to ascertain the effect of pH change on mineral surface charge. This study employed ζ-potential measurements as a measure of the wettability alteration. The findings reveal that these rock minerals have their charge development controlled by mineral dissolution, ionic specie adsorption, and double-layer compression. Furthermore, the rock contacting mineral is critical in the wettability alteration, and an understanding of the effect of well operations on rock surface chemistry is critical.