Bubblepoint Pressure Mathematical Modelling for Nigeria Crude Oil

Abstract Bubblepoint pressure is a fundamental factor in reservoir management and reservoir engineering calculations. Ideally, the lab measurements of reservoir fluid properties of samples collected from the bottom of the wellbore or from the surface are the primary sources of bubblepoint pressure. Such experimental data are, however, not always available because of one or more of such reasons as samples collected are not reliable or samples have not been taken because of cost saving. In this circumstance the notable among published empirical models are perused and used to predict bubblepoint pressure. These empirical models were developed by fitting equations for a certain range of PVT parameters using large sets of measurements of these parameters. Unfortunately, some of these correlations are incorrect, especially when used to predict bubblepoint pressure of crude from a different region and or different range of crude characteristics. This study examined the available models using classic statistic criteria and developed a new bubblepoint pressure model. I have used more than 2580 unpublished PVT data sets from different locations in Nigeria in developing the model. The model development workflow considered the impact of each independent variable on the bubblepoint pressure, pairwise plots to show evidence of nonlinearity, stepwise regression dimensionality reduction (backward selection method) and variance. Model parameter estimation was based on a search method from the optimization that minimized the norm of residual vector/error. The new model was subjected to standard statistical tests. These tests established logical validity as well as the statistical measures of the suitability of the model. The results of the comparative study between existing correlations and new model show that the new model provides a more remarkable and reliable performance.