Papers by Author: P.U. Ohirhian

Abstract: New equations for calculating the Gas Deviation Factor (z) and the Compressibility of Nigerian Natural Gas have been developed. The equation for the Gas Deviation Factor was developed from a plot of the logarithm of the ratio of Pressure to Temperature versus the logarithm of the ratio of the Pressure to the Gas Deviation Factor.. The plot gave a linear relationship that gave the Gas Deviation Factor equation. A differentiation of the Gas Deviation Factor equation produced the new equation for calculating the Gas Compressibility. Values from the new equation for calculating the Gas Deviation Factor were compared with experimental Pressure, Volume, Temperature (PVT) measurements and the following statistical measurements of accuracy were obtained: Average percent error of 3.050, average absolute percent error of 3.649 and standard deviation of 3.910. Over 75% data tested showed error less than 5 %. A big advantage of the new equations is that they are simple and do not require pseudo critical pressure and pseudo critical temperature needed to obtain z from the current popular equations of state used in the Oil Industry. The data used to develop the model in this work came from Gas associated with produced oil in the Niger Delta. API gravity of the oil, ranged from 17.4 to 44. Pressure ranged from 15 psia to 4015 psia and Temperature ranged between 127 and 205 degree Fahrenheit. This range of data covers at least, ninety five percent of data used in the upstream sector of the Nigeria Oil and Gas Industry.

Abstract: A new equation for the viscosity of Natural Gas under Reservoir conditions has been developed. The equation was obtained by the analysis of experimental Pressure, Volume and Temperature (PVT) Data of Gas associated with Nigerian Crude Oil. The PVT Data were those of renowned companies that operate in Nigeria. The pressure ranged from 144 psia to 4100 psia, and a temperature variation between 130oF and 220oF. Comparison of the equation formulated in this work with experimental PVT viscosity gave an average absolute error of 1.55%, a maximum absolute error of 4.878% and a standard deviation of 1.29. A comparison of viscosity obtained from the charts of Carr et al and the equation of Lee et al with Nigerian PVT Viscosity showed that the new equation gave more accurate result. Since some Correlations perform better when applied to data from which they were derived, a further comparison test was performed. In this test, the new equation was used to solve two problems for which solutions by the method of Carr et al were available. The first problem from the Handbook of Natural Gas Engineering by Katz et al gave a viscosity of 1.158cp while the new equation gave 1.157cp. The second problem from Ikoku’s book (Natural Gas Production Engineering) gave a viscosity of 1.178cp and the new equation also gave 1.178cp. This closeness of the viscosity of the new equation to the values from the Carr et al method proved the applicability of the new equation to any type of Natural Gas.