In steam injection processes such as steam flooding, SAGD, or huff & puff, the selection of the injection tubing is an important factor that determines the steam quality downhole. For example, insulated tubing will decrease the heat loss in the well. The tubing dimensions also have an impact on the process. The objective of this study is to evaluate how the combination of superior thermal performance and down-sized injection tubing can improve the steam quality downhole.
A detailed analysis of steam flows was performed for a project in the Middle East to quantify the effect of thermal performance and tubing size on steam quality downhole. Using a steam flow analysis model, different tubing size and thermal insulation performance combinations were compared for the same well. The thermal performance (Overall Heat Transfer Coefficient) of different types of insulated tubing was confirmed with a field trial by the operator prior to use as input into the model. The output of the model is the quality, temperature, and pressure of the steam as a function of position in the well, including the downhole conditions.
Unsurprisingly, the results of the study show that to get the highest steam quality downhole, the best thermal performance is required. It was also found that, with the best thermal performance, downsizing the tubing can have a positive effect on the economics of the system. Conversely, it was found that, using tubing with relatively poorer thermal performance, downsizing the tubing was not practical. The results were used by the operator to select the type and size of tubing for its new injector wells.
With the analysis now complete, the steam wells in the studied field are being modified according to the study recommendations. Vacuum-Insulated tubing is being replaced with a design with improved thermal performance and the tubing size is being reduced. The result is a system with decreased, overall costs and increased downhole steam quality.