Kinetics of Fluid Phase Behavior Changes: A Critical Uncertainty for Offshore Field Development

Abstract

Abstract With increasing pressure on project costs, accepting uncertainty is increasingly less viable for offshore field developments. An urgent issue that affects conventional and novel technologies across the production landscape is that of the kinetics of fluid phase behavior changes. Be it pressure boosting using electrical submersible pumps (ESPs) or separation with novel compact separators, the rates of gas dissolution and evolution are a critical uncertainty. PVT laboratories today report fluid properties at equilibrium points, with a prevailing unwritten assumption that the system can achieve the new phase equilibrium either instantaneously or at a time scale that is negligible when compared with production system residence time scales. However, even anecdotally, many in the industry understand this assumption to be optimistic and recognize there is a kinetic process that must occur to achieve the new equilibrium state. Fluid property measurements – kinetics included – are highly valuable to a variety of disciplines: research engineers, process engineers, flow assurance engineers, and more. To effectively apply fluid property measurements to field development activities, each engineer must have a quantitative understanding of the data uncertainties. The kinetics of fluid phase behavior changes are, however, often overlooked; nearly all industrial process simulators apply equilibrium models, regardless of whether the system has achieved the equilibrium state. As the industry drives towards more challenging offshore fields and focuses on simplifying designs, reducing size, and reducing costs, the result is an increasing risk of consequences due to incomplete evolution or dissolution of gas. Engineers currently have no tools available to predict or estimate the rate at which the gas will evolve from or dissolve into solution. This unknown propagates to potential issues in a variety of applications, including design and optimization of artificial lift systems, design and operation of electrical submersible pumps, subsea or topsides pumping, compact separations, and more generally gas-liquid separations. In this paper the authors share insight and information about challenges in design, development, operation and troubleshooting with regards to the uncertainty in the kinetics of fluid phase behavior. Discussion also covers the value in developing an alternative fluid property measurement for quantifying and predicting the rates of gas evolution and dissolution.