Abstract

Steam-assisted gravity drainage (SAGD) is one of the successful thermal recovery techniques applied in Albertan oil sands reservoirs. When considering in situ production from bitumen reservoirs, viscosity reduction is necessary to mobilize bitumen thereby flowing toward production well. Steam injection is currently the most effective thermal recovery method. While steam flooding is commercially viable, condensation-induced water hammer (CIWH) resulting from rapid steam pocket condensation can be a challenging operational problem. In steam flooding, steam is injected through a well down to the reservoir, warming it to temperatures of 150ºC to 270ºC (302ºF to 518ºF) in order to liquefy the bitumen inside the reservoir (Garnier et al., 2008; Xie and Zahacy, 2011). The liquified bitumen then drains to a lower well through which it is produced to the surface. In this process, steam pockets can become entrapped in subcooled condensate inside either the injection or production tubing causing a rapid collapse of the steam pocket. This type of rapid condesation is commonly referred to as "steam hammer".

In this study three different scenarios are explored to better understand steam hammer situations in SAGD wells. These scenarios are: (1) at injectors or producers during the start-up phase (or circulation phase), (2) in the injection tubing during the injection phase, and (3) in the production tubing during the injection phase. Modelling each of these scenarios indicates that steam hammer occurrence is likely in two of the three scenarios but that its incidence can be mitigated. The likely scenarios for steam hammer occurrence are in either the injection or production tubing during the start-up phase, and the injection tubing during the injection phase. Steam hammer occurrences during the circulation period can be controlled by lowering the injection pressure and controlling water drainage into the reservoir. Flow shocks that occur as a result of Counter-Current Flow Limiting (CCFL) are very likely to take place in the injection tubing during the injection phase but can be controlled by injecting at a higher steam quality. The least likely scenario for steam hammer occurrence is in the production tubing during the injection phase. This is because the produced (or breakthrough) steam temperature would need to be more than 20ºC higher than the produced liquid temperature to initiate a water hammer condition.

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