Enhancements to an Online Steam Analyser for Thermally Enhanced Heavy Oil Recovery
Canada’s oil reserves are primarily located in the oil sands of Northern Alberta. Steam Assisted Gravity Drainage (SAGD) is the dominant enhanced oil recovery technology used for in-situ oil sands operations. High pressure steam is continuously injected into an upper wellbore to heat the oil and reduce its viscosity, causing the heated oil to drain into the lower wellbore, where it is pumped out. In 2015, thermal oil production in Canada reached 1.2 million barrels per day (bpd) requiring about 2 billion kg per year of steam from approximately 191 steam generators. The burning of natural gas to generate steam contributes to approximately 11% of Canada’s total GHG emissions.
Steam quality is a measure of vapor to liquid portion in the steam. The actual “heat” or energy that is desired for production resides in the vapor portion and therefore, the maximum steam quality is desired to most efficiently produce heavy oil. In heavy oil operations, the maximum steam quality allowed is 80% for Once Through Steam Generators (OTSGs) – the most common technology used in the oil sands. Above 80%, deposits from treated recycled produced water form on the OTSG tubes, hot spots are generated and the tubes rupture leading to expensive down time.
Presently, steam quality is measured manually which means periodicity and delays between measurements and potential corrective actions. An online steam quality analyser would allow producers to operate OTSGs more efficiently and increase steam quality. Recognizing the need, Petroleum Technology Alliance Canada (PTAC) proposed the project “Enhancements to an Online Steam Analyser for Thermally Enhanced Heavy Oil Recovery” for ecoEII funding. The Project was awarded $1M to test and demonstrate the performance of a steam quality analyser in conditions representative of oil sands operations. The Project builds on prior proof of concept work performed by PTAC’s partners Luxmux and Agar - a bench scale steam quality analyser unit incorporating Luxmux’s photonics laser sensor was designed, built and tested to prove that optical measurement of steam quality using photonics was possible.
A dual boiler system was needed to facilitate the testing of the steam quality analyser under conditions representative of oil sands steam operations. Design of the dual boiler system involved the creation of Process Flow Diagrams (PFD) and Process and Instrumentation Diagrams (PID), as well as the specification of flow parameters, operating parameters and additional metrics required by the system to validate steam quality. The boiler system incorporates two chambers 8” in diameter and connected at the top with 2” pipe, a globe valve and orifice nozzle. The left chamber is the “receiver” and the right chamber is the “boiler”, as it is the main source of steam. The boiler chamber’s function is to generate saturated steam (100% steam quality) at the temperature of 343°C and pressure of 14,824 kPa(g). The receiver chamber’s function is to receive the steam coming from the boiler via the top pipe and initiate condensation, since it is at a lower temperature and pressure (300°C and 8,584 kPa(g), respectively). During natural condensation, a fine cloud of wet steam will develop in the top part of the receiver chamber. The steam cloud is ideal for testing and calibrating the steam quality sensor.
Once initial design was completed, materials were purchased and then a hazard and operability study (HAZOP) was conducted to identify and evaluate problems that may represent risks to personnel or equipment. HAZOP identified areas for improvement and modifications were made to the boiler design. Once HAZOP was successfully completed, construction began. The boiler system was successfully commissioned and preliminary performance testing began in July 2016. The steam analyser was tested under conditions of static steam and in the dual boiler system. Moreover, tests were conducted to determine the impact of steam contaminants on the performance of the steam analyser.
Benefits to Canada
Wide scale deployment of online steam quality analysers in the oil sands industry will enable producers to operate steam generators at greater efficiency, thereby reducing GHG emissions and water consumption.
Testing is continuing to further improve the efficiency of the dual boiler system and performance of the steam quality analyser. A robust data set is required to secure field testing sites at operating oil sands steam plants.
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