Dynamic Steam-Trap-Control Simulation Technique: Formulation, Implementation, and Performance Analysis

Abstract

Summary Steam-trap subcool is a technique that is used to maintain the energy efficiency of the steam-assisted-gravity-drainage (SAGD) process by most heavy-oil producers in Canada. The concept is rather simple (i.e., create a liquid pool around the production well to prevent steam from escaping from the steam chamber into the production well). A numerical steam trap based on a thermodynamic approach was implemented by Edmunds (2000), and it has been used in simulations with different types of wellbore models in commercial codes. In this approach, a thermodynamic relationship is solved as a well-residual equation to guarantee that the bottomhole temperature (BHT) is less than the saturation temperature of water at the hottest location along the wellbore. The location of the hottest spot along the wellbore is static in time. Steam trap is a dynamic process, and inflow temperatures can vary significantly along the wellbore according to the local fluid and rock properties along the well. It is highly possible that the location of the hottest spot along the well changes frequently with time during the SAGD operation. In this study, the simulation of a dynamic steam-trap-control technique is provided. The location of the hottest spot along the wellbore is scanned at every timestep. Severe numerical instabilities are observed when the thermodynamic approach is used. A new constraint based on the total production rate at reservoir condition is introduced. Details of the mathematical formulation and the numerical behavior of the new method are discussed in this paper. Several real field models with different wellbore designs (multiple tubing strings) are simulated, and the results of the new approach are compared with the thermodynamic approach. Simulation results show that the numerical performance of this new approach is significantly more stable. We also compared the run time of simulation between cases with new well constraint and thermodynamic steam-trap control, and results show a significant improvement in simulation run time.