Abstract
Loss of steam quality and energy in steam injection wells is a key component in the design of steam-based thermal operations. These operations are increasingly employing more sophisticated wells that have longer trajectories with multiple control points. Reservoir simulation of thermal fields requires high accuracy in thermal boundary conditions for all wells, and conductive heat loss often plays a large role in overall energy conservation. Thermal injection wells are usually modelled only in the reservoir where injection enthalpy and steam quality at the bottom hole depth are estimated. In this paper, an examination is made of the benefits of modelling conductive heat and quality loss through the upper formation as part of the overall field simulation.
A comparison is made between the use of analytic models for heat and quality loss through the overburden based on work by Ramey and Satter, and a multisegment thermal well model that is segmented from the surface through the overburden and to the top of the oil-bearing formation. The analytic models of heat and steam quality loss are based on steady-state wellbore flow and conductive heat loss to the overburden. A more detailed representation of wellbore physics and control is available with the multi-segmented steam injection well model, including conductive heat transfer between the wellbore tubular and overburden or reservoir, a user-specified nodal resolution, a multiphase flow model that includes unequal phase flow rates of steam and condensate, the ability to correctly model the phase change of steam vapour to condensate as it flows downward from the surface, and an implicit coupling to the reservoir. Limitations of the analytic and segmented models are discussed including accuracy differences and instances when one or the other models may not be appropriate.
