Development and investigation of integrated reservoir-wellbore flow model

Abstract

The understanding of fluid flow from a reservoir to a wellbore is one of the major concerns in the oil and gas, as well as the coal seam drainage industry. Being able to reliably predict fluid flow behaviour, pressure drop and fluid production along the horizontal wellbore is crucial to enhancing its performance and reducing potential risks to the safety of underground coal mining operations. Much research to date focuses on developing wellbore flow models with defined wall inflow/outflow, while other research looks at developing reservoir simulators with specific boundary conditions at wellbore locations. Many petroleum engineering processes however, require a coupled modelling of reservoir and wellbore flow with fewer simplifying assumptions at the interface of these two domains. The integrated flow of fluids through reservoir and wellbore requires further study to examine the influence of reservoir flow on wellbore flow and vice versa.In this study, a three-dimensional model for the simulation of integrated reservoir-wellbore flow was developed to examine the effect of the different wellbore geometries, completions, and orientations on; flow characteristics, wall friction factor, the overall pressure drop and wellbore productivity index. Computational Fluid Dynamics (CFD) simulations were carried out using a finite volume based software, ANSYS FLUENT, using a high performance computing cluster. The developed model can be used for different reservoir and wellbore conditions including mining and petroleum engineering applications.In the first stage of the study, the effects of the wellbore diameter and length on flow field behaviour and pressure drop was examined within a large-scale model of coal seam drainage. It was seen that increasing the wellbore diameter leads to a decrease in pressure through the coal seam, and a higher productivity index of the wellbore. The wellbore length variation did not influence the pressure distribution remarkably, however it did enhance the productivity index due to a larger wellbore flow rate. The CFD model developed provides a robust tool for examining high gradient flow conditions near wellbores and the effect of different wellbore completions.Secondly, for a perforated pipe, the effect of perforation parameters including density, diameter and phasing angle on wall frictional losses and overall pressure drop was investigated. The wall friction factor, shear stress and pressure drop all increase with a higher number of perforations along the wellbore. The variation in perforation diameter was found to influence flow resistance to some extent, while the perforation phasing angle did not influence frictional losses.Finally, using the integrated model developed, the production performance of horizontal wellbores was compared with that of vertical wellbores, to be used for drilling evaluations and wellbore development plans. The effects of wellbore length and reservoir shape on the horizontal to vertical productivity index ratio were also analysed. The integrated model findings demonstrate the remarkable influence of these parameters on the horizontal wellbore performance, which will assist petroleum engineers to address a wide range of challenges involved in future wellbore development plans.In order to verify the accuracy of the developed integrated model, a series of core flood experiments were carried out and compared with CFD results. The results of the coal seam drainage model, perforated pipe and the horizontal wellbore performance study were further validated against existing theoretical/experimental pressure drop and productivity index models. It was observed that wellbore geometry can significantly influence flow resistance, and therefore its productivity. The integrated model also shows promising findings that provide an alternative solution for future experimental studies of wellbore/reservoir flow, by using this adaptable computer model.