Definitive Method of Flow Analysis of Surface Pipeline Networks

Abstract

Abstract The producing wells and the surface pipeline network comprise a dynamic system. Flow rate changes in the individual wells affect the flow in the pipeline network and the fluid distribution among the gathering stations and, vice versa. Many times, the surface network is constructed responding to the necessity of merely connecting the wells to the separators or gathering stations without accounting for the impact that dramatically increased or decreased well flow rates may have. Nevertheless, in the life span of a reservoir, the hydrocarbon production may be substantially altered owing to several processes that may take place, such as fracturing, or gas/water injection. Thus, it is imperative that the surface pipeline network be effectively designed to ensure an unobstructed production regardless of the well flow rates. It is readily acknowledged that a computational tool is needed to perform a hydraulic analysis of the pipeline network for any set of flowing conditions. An iterative algorithm is developed for the quantitative analysis of any surface pipeline network configuration. Pipe gas flow under isothermal conditions is studied. The algorithm uses the minimal information that is commonly available for a surface pipeline network, namely the well mass flow rates, the temperature and molecular weight for the well pipes, the chokes pressures, the gathering stations pressures and the geometric characteristics of the pipes, and does not require the knowledge of the location of the split nodes. It calculates the mass flow rate, temperature and molecular weight in each pipe of the network as well as the nodal pressures. It also derives the flow direction in each pipe identifying the location of the split nodes. The algorithm incorporates an approximation scheme used for large and complex network configurations. The scheme is validated through mass balance and pressure drop tests. The algorithm is a generic tool of network analysis as it can be modified to account for liquid or two-phase flow in the pipes. Application of the iterative algorithm indicates a notable accuracy (the absolute error in calculating mass flow rates and nodal pressures is less than 1%).