The piling design and construction cost is a major fraction of the total construction cost of an above-ground Steam Assisted Gravity Drainage (SAGD) gathering pipeline. Recently, there have been efforts to review the principle designs of the piling and possibly to reduce the associated costs.

In most common design practices for pilings design, the engineers use the sum of the loads caused by steam and production lines. Using the sum value can be considered a good engineering practice; however this can cause unnecessarily large pile sizes and therefore increased cost. Some of the case studies presented in this paper show that the sum value may not be necessary and that it is possible to maintain a safe design within the acceptable criteria by using a fraction of the sum value. For this study, several stress analyses on pipeline cases were modeled including various thermal scenarios and gradient directions.

In Alberta's SAGD projects, steam travels from the boiler source to the well heads through a trunk pipeline. It takes a few hours to a couple of days for steam to reach the well heads depending on the length of the pipeline. After this time period, the productions (bitumen and production gas) are extracted from the reservoir and travel to the production pads or interconnection pipelines.

As the steam and production travel along the pipeline a thermal gradient is generated and travels along the pipeline as well. In a typical production process, the piles are subject to thermal loads caused by the traveling steam and by the time that the steam reaches to well heads, the loads are in the equilibrium state.

After this, the hot productions (bitumen and associated produced gas) travel in reverse along a seperate pipeline. Due to the difference in period of traveling, the SAGD pipeline arrangement and pilings are not subject to receive the two maximum load waves caused by steam and production simultaneously and therefore it is possible to design the piles on a fraction of the total load amplitudes. These considerations have allowed us to review the design principles and conclude safe practice with respect to lowering the size and the cost of piles.

This paper explains that the current design philosophy tends to neglect some design elements such as thermal gradient direction and loading sequence on the piles. It reviews these factors and identifies room for improvement in piling design and cost saving with respect to constant, startup, shutdown and upset operating load conditions.

You can access this article if you purchase or spend a download.