Steam Assisted Gravity Drainage (SAGD) is an enhanced oil recovery process wherein a long horizontal steam injection well is located above a long horizontal production well. Injected steam forms a steam chamber above the SAGD well pair, heating the reservoir rock and reservoir fluids. Heated oil (or bitumen) plus condensed steam flow down the sides of the steam chamber towards the production well. The condensed steam and bitumen are then lifted to surface with a downhole pump or by gas lift. Due to a rapidly increasing number of SAGD well pairs, Suncor required a tool that could accurately model these challenging thermal production wells.
Nodal analysis for well performance is based on the principle that reservoir inflow and wellbore outflow can be independently characterized as functions of flow rate and pressure. Nodal analysis is used to design new wells and optimize production or injection on existing wells. Wellbore simulations are cheaper than instrumentation, meters or single well tests. Well evaluation software is the most popular engineering package in Suncor's production engineering toolkit because it is very accurate and easy to use. Over the past few years Suncor worked with their software provider to develop nodal analysis for SAGD production wells. Suncor can now model SAGD producers with electric submersible pumps (ESPs) and gas lift with a high degree of confidence.
The new SAGD nodal models quite closely match production rates, plus surface and downhole pressure and temperature data. Reliable and rigorous SAGD nodal models enable improved decisions with respect to SAGD field development and production optimization. Nodal analysis can be used as a predictive tool for production optimization, or for a better understanding of what is happening downhole with respect to temperature, pressure, and flow distribution within the wellbore.
This paper is a logical continuation of SPE 170054, Nodal Analysis for SAGD Production Wells with ESPs (ref 1). The main difference between modeling wells with gas lift rather than mechanical lift is that the gas lift models also account for steam lift. Steam lift occurs when some of the produced water (PW) in the emulsion flashes to steam as pressure is reduced. The resulting vapour significantly augments gas lift and reduces lift gas requirements.