Energy Balance in Steam Injection Projects: Integrating Surface-Reservoir Systems

摘要

Steam injection projects consume considerable amounts of energy to generate steam. Understanding where the heat goes at various times and places during the process provides the means to improve the performance of a project. Enhancements can be achieved integrating an energy balance analysis from the steam generator through the injection network, the reservoir, the producing network and the journey of the produced fluids to the separator. This investigation presents a workflow to analyze the integration of surface and reservoir systems for a Steam Assisted Gravity Drainage (SAGD) project, to properly estimate energy transfers in the various components of the system thus providing information to improve project planning and enhance both the oil recovery and the economics of the project. The elements considered in the systems were: boiler, heat exchanger, steam trap, steam injection and well networks, reservoir heat usage, heat losses to the over- and under-burden, production wells and surface networks. Parameters such as completion schemes, artificial lift and boiler-wellhead distances were also analyzed. Results show that surface-reservoir integration, using reservoir and network simulators, is a powerful tool to estimate heat losses in steam injection projects, helping to understand and successfully optimize their performance. The integration allowed the detection of steam quality variations at injection wells at various times during the process as a function of injectivity changes. Adequately insulated production wells under certain circumstances could produce under natural flow for some FAJA types of reservoirs. However, artificial lift methods had to be incorporated into other completion schemes to compensate for high heat losses and their correspondent increased oil viscosities that imposed higher pressure drawdowns in the production and surface gathering networks. The SAGD processes analyzed were energy efficient in spite of retaining in the reservoir less than a third of the energy from the steam. In all the scenarios, oil production was considerably greater than the fuel consumed to generate steam. The paper shows how the analysis of steam injection processes integrating surface, well and subsurface mechanisms allows the identification of critical components of heat losses to optimize the design and operations to maximize oil recovery and reduce energy consumption.