The performance of steam assisted gravity drainage (SAGD) depends, mainly, upon reservoir characteristics e.g. porosity, permeability and heterogeneity, well bore hydraulics e.g. steam quality, the length and size of wellbores and operational parameters e.g. reservoir and wellbore subcools. However, in reservoirs with underlying bottom water, the performance of SAGD depends on vertical offset between bottom water and producer and pressure differential between bottom water pressure and bottom hole flowing pressure of the producer. Bottom water can act as a heat sink is a known fact, therefore, it can affect project oil rate, steam rate, steam oil ratio (SOR) and, ultimately, the economics of the project. Bottom water can affect heat transfer within reservoir by the injected steam in case of water coning or steam loss to the bottom water. Produced water chlorides concentration (PPM) is an important indication of bottom water coning because of difference in the chemistry of injected steam and bottom water. The chlorides material balance depends upon water saturation in bitumen zone (connate water), formation water chlorides concentration, produced water chlorides concentration and water cut. This study will shed light on significant impact of bottom water coning on SAGD performance through reservoir simulations. It will, also, describe contribution of each of the aforementioned parameters (water saturation in bitumen zone, formation water chlorides concentration, water cut and produced water chlorides concentration), which is very significant, on chlorides PPM material balance for bottom water coning analysis. And it will, also, describe how the safe limit of produced water chlorides PPM (produced water chlorides PPM at which no bottom water is produced) is affected by each of these parameters.

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.

The depositional environment at Statoil's Leismer SAGD demonstration project is dominated by a fluvial-deltaic system with complex geological features which present challenges for SAGD operations. An efficient monitoring tool that could combine geoscience data with production knowledge is vital for optimizing SAGD operational strategies. Time lapse (4D) seismic survey is one such monitoring tool. It can be integrated with wells and production data to prepare and optimize operational strategies. The pattern of growth of steam chamber is critical for well performance optimization. Steam chamber development dictates which reservoir areas are using heat efficiently and contributing to drainage of bitumen and increased production. At Leismer, two 4D monitor seismic surveys have been conducted since the start of operations. The 1st monitor was acquired in 2012 to observe one year of SAGD performance and the 2nd monitor in 2013 to observe the performance after 2 years of operation. These surveys have been used to identify challenges to maximizing well pair productivity. Of primary concern is the effective distribution of steam along the entire horizontal section of the SAGD well pair. Other 4D monitoring benefits include, monitoring subcools with respect to reservoir heterogeneities, bottom water communication, steam chamber coalescence, baffle or barrier to steam chamber growth identification. In this study, examples are presented to show how combining production and 4D seismic data has contributed to well pair optimization. Communication with bottom water in the early stages of SAGD, while rare, occurred in specific Leismer well pairs – analyses of production data combined with 4D seismic data helped identify steam loss into bottom water which drove steam injection strategy and improved well productivity. Another Leismer example shows how 4D seismic has been used to confirm a low reservoir roof at the toe of a particular well pair. This knowledge drove a change in injector well completion to optimize production. In the final example, it is shown how 4D seismic has helped analyze and confirm well conformance (heat distribution along SAGD well pairs) which is critical for uniform steam chamber development. Based on Statoil's Leismer experience of applying results of 4D seismic analyses for well optimization, it can be concluded that 4D seismic has proven to be a very useful and value adding monitoring tool.