Oil Measurement in SAGD Steam Generation
The steam injection enhanced oil recovery method used primarily in Alberta, Canada, also known as Steam Assisted Gravity Drainage (SAGD), pushes energy in the form of steam into the formation to liquefy very heavy oil known as bitumen so it can be recovered and lifted to the surface. This method causes the continuous release of water soluble organic material more commonly known as WSO’s into the produced water. The injected steam is recovered and recirculated for process efficiency and water conservation. In traditional industrial steam recycle processes the free oil concentration must be below 1 part per million to prevent boiler and other component fouling. Detection of oil with an on line fluorescence monitor at this concentration can achieve reliable protection for the boilers or boiler feed water pretreatment systems. In SAGD operations, the fluorescence response of the WSO’s is similar to bitumen. Because the fluorescence signal of the WSO’s is significantly higher than the bitumen, operators must have a reliable measurement method for Free Oil to protect the Once Through Steam Generators (OTSG). A study was conducted to find a viable solvent extraction procedure which would extract and measure the free oil from samples of produced water and which would leave the WSO’s behind. Measurement of the bitumen in the extracted solvent provides the needed process information to protect the OTSGs in the SAGD plants. Determining an effective solvent to accomplish this was important because the bitumen is not readily extracted from the produced water in commonly used solvents such as Hexane. Field experience has shown that toluene is a more effective solvent than hexane at extracting the bitumen from the produced water.