Bottom water coning has a detrimental impact on the performance of steam assisted gravity drainage (SAGD) causing reduced oil mobility around the producer. It, also, leads to higher steam to oil ratio (SOR). Produced water chlorides concentration can be used as an indication and quantification tool for bottom water coning analysis. The chlorides material balance for bottom water coning analysis depends upon connate water saturation and the concentrations of chlorides in connate water, bottom water and produced water along with the water cut of produced emulsion. Most oil sands are water wet but wettability changes with high steam temperatures and almost all the connate water is drained because of steaming. The safe produced water chlorides concentration, at which no bottom water is produced, depends mainly upon connate water saturation and its chlorides concentration besides water cut and oil saturation. Therefore, careful sampling and laboratory procedures for connate water chlorides measurement is vital in bottom water coning analysis.
The mechanical extraction device (referred to as the plunger) was developed mainly to facilitate the recovery of heavy oil and bitumen samples from oil sands cores. In this study, the plunger technology is employed in order to recover water samples to enable measure connate water chlorides PPM (concentration in parts per million). The measured connate water chlorides are also corrected for drilling fluid invasion. A new material balance for bottom water coning analysis is established based on different connate water and bottom water chlorides concentrations and drainage patterns of connate water and oil saturations. The new material balance is used to determine the safe chlorides concentration and applied to bottom water coning analysis in the field application at Leismer SAGD project.
Since, the earlier study assumed the same chlorides concentrations of bottom water and connate water, the new measurement technique of chlorides concentration of connate water has led to a better material balance calculation for bottom water coning and data analysis. The new material balance has led to a lower safe chlorides limit. It has, also, helped better optimization of steam chamber pressure and steam injection strategy to avoid negative impacts of bottom water conning to enhance oil production and lower SOR at Leismer.