With SAGD operations, it is often inevitable to have shut-in time and turnaround periods because of facility, operation, and supply issues. During these shut-in periods, the gravity drainage of cooling bitumen and steam condensate continuously raises the liquid level over the production well. Therefore, the producer downhole temperature keeps decreasing. This situation makes the restart more difficult. Sometimes even if there is no shut-in, the production well also becomes cold after it is converted from circulation to Full SAGD. This paper classifies the SAGD operation modes into three categories, including Full SAGD, Semi-SAGD, and Partial SAGD. In Partial SAGD, the injector return is shut-in while steam injection continues in the long tubing or in the short tubing and annulus of the injector. The producer is operated with the appropriate steam injection rate to the long tubing. Numerical simulation results associated with Partial SAGD effect are presented. In addition, Partial SAGD applications in Jackfish SAGD project are also discussed.
Up to the end of 2008, the number of commercial Steam-Assisted Gravity Drainage (SAGD) projects in Alberta has increased to 18 and 13 of them are on production (ERCB, 2008). As more projects come on stream, there is increased opportunity to gain valuable experience and improve SAGD performance. The typical SAGD process uses two parallel horizontal wells. The upper well is the steam injector and the lower well is the bitumen producer. It is common that the producer is completed with two tubing strings; a short tubing (ST) string landed at the heel and a long tubing (LT) string landed at the toe. For the injector, there are different completion designs. In the Jackfish project, dual tubing completions for both injector and producer are used and this completion style is considered in this paper.
Operations at a SAGD project are often interrupted artificially by a number of issues associated with facility and material supply. During these shut-in periods, the steam chamber inside the reservoir becomes smaller. Cooling bitumen and steam condensate continuously raise the liquid level above the producer. Sometimes, even though there is no shut-in, either the whole horizontal section or just part of the producer becomes cold so that no effective production occurs. Figure 1 shows a typical producer response in the Jackfish SAGD project under these circumstances. Wells with dual tubing completions have the flexibility to adjust the injection and production to remedy this situation. This paper will describe and classify the options which are available to make the adjustment. Reservoir simulations with discretized well bore models are conducted to investigate the effect of some adjustments on SAGD performance. Field cases from the Jackfish SAGD project are also presented to illustrate the application result.
Full SAGD mode is started after the steam circulation period. The SAGD operation modes can be classified into three major categories based on the steam injection and bitumen production options. The three categories are Full SAGD, Semi-SAGD, and Partial SAGD.
