Interactive Modelling of Multiphase Inflow Performance of Horizontal and Highly Deviated Wells

Abstract

SPE Members Abstract An interactive system for modelling of multiphase inflow performance of long, highly deviated and horizontal wells is presented. It's prime areas of use are design of well trajectories and completions, and evaluation of wells inflow performance including calculation of well indices for full reservoir simulation. Further, the system provides a basis for improved integration of the reservoir engineering and the well completion design. The reservoir pressure and multiphase flow distribution is modelled accurately using a finite element method combined with automatic local grid refinement around wells. A comprehensive multiphase wellbore flow model is available for accurate flow modelling in the wellbore. A well inflow model including a generalized formula for calculation of well indices of wells in arbitrary directions is proposed. Examples are given showing improved inflow performance calculations using the new well indices. Introduction Long, highly deviated or horizontal wells are increasingly being drilled and used throughout the world in general and in the North Sea in particular. Careful design of these wells are often crucial for successful performance since they in many cases are used to drain for example thin oil zones, wedge zones or marginal reserves. The well design relates to the well trajectory and the completion strategy, which both need to be assessed using a realistic reservoir model. Well trajectory design using reservoir simulation models, are often difficult and even impractical due to the complexity in constructing a realistic and accurate well trajectory and varying this systematically as a part of an optimization process. Examples of this are wells with varying dip, crossing geological layers at skew angles, and crossing the reservoir simulation grid at various locations and angles. Furthermore completion design is often performed on other simplified (homogeneous) reservoir models in order to determine the relevant completion type and parameters. In many cases new information during the drilling process makes it necessary to make new decisions concerning well trajectory and well completions on a short notice. This implies in turn that a model driven well design is not possible unless the models can be built, changed and run in a fairly short time. Compared to a vertical well, the inflow performance of a long, highly deviated or horizontal production well is generally more influenced by the pressure profile in the wellbore, being a function of friction pressure loss and gas slippage effects in the wellbore. These effects will in general be more significant for dipping or vertically undulating wells. They are, however, difficult to model this realistically in conventional reservoir simulators, due to lack of accurate well trajectory and inadequate wellbore flow modelling. Accurate modelling of both the well trajectory and the inflow performance is also often of major importance in the evaluation of a well's performance. P. 367^