The SAGD process can be defined to have three sequential phases to its operating mode, namely: startup, SAGD mode and wind-down. The startup phase most commonly has the shortest operating period, yet it has significant influence on the success of the subsequent operating modes. Historically, there are two primary means to achieve startup of a SAGD well pair and are commonly referred to as circulation and bullheading. The circulation process was employed at the Grand Rapids SAGD Pilot on Well Pair 1 and Well Pair 2 in 2010 and 2012 respectively.
The circulation process is complex to optimize from a heat transfer perspective. Parameters such as well length, tubular sizing, steam injection rates, steam injection pressures, steam blanketing, and reservoir dynamics all influence the performance of the process. Transient reservoir simulation models with fully coupled well and reservoir grids are required to effectively model the process, relying on key inputs from field data to calibrate models. Typically, the objectives of circulation are to achieve a uniform heating profile along the entire length of the lateral portion of the SAGD well pair and establish fluid transmissibility between the injector and producer.
A study on startup methods was conducted with the intent of optimizing temperature conformance, thermal efficiency and circulation time. The study generated several alternative startup designs, many of which employ insulated tubing strings and varied operating conditions to optimize heat exchange and energy efficiency. A field based trial was conducted using the closed circuit startup design (Canadian patent pending) at the Grand Rapids SAGD Pilot in 2015. Results of the study and field trial suggest that the closed circuit design offers several advantages; it is a thermally efficient, able to operate at higher temperatures, can use less steam per well pair, is scalable up to 1,200 meter long laterals, and can achieve excellent thermal conformance during startup.
The findings of this field based investigation add to the knowledge base related to startup techniques and well conformance. The closed circuit technology employed at the Grand Rapids SAGD Pilot is an innovative startup design that may be used in other heavy oil and oil sands reservoirs to enhance startup and promote recovery.