Understanding the Steam-Hammer Mechanism in Steam-Assisted-Gravity-Drainage Wells

Abstract

Summary Steam-assisted gravity drainage (SAGD) is one of the successful thermal-recovery techniques applied in Alberta oil-sands reservoirs. When considering in-situ production from bitumen reservoirs, viscosity reduction is necessary to mobilize bitumen, thereby flowing toward the production well. Steam injection is currently the most effective thermal-recovery method. Although steamflooding is commercially viable, condensation-induced water hammer (CIWH) resulting from rapid steam-pocket condensation can be a challenging operational problem. In steamflooding, steam is injected through a well down to the reservoir, warming it to temperatures of 150 to 270°C (302 to 518°F) to liquefy the bitumen inside the reservoir (Garnier et al. 2008; Xie and Zahacy 2011). The liquefied 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 the production tubing, causing a rapid collapse of the steam pocket. This type of rapid condensation 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 at injectors or producers during the startup phase (or circulation phase), in the injection tubing during the injection phase, and in the production tubing during the injection phase. Modeling each of these scenarios indicates that a steam-hammer occurrence is likely in two of the three scenarios, but that its incidence can be mitigated. The likely scenarios for a steam-hammer occurrence are in either the injection or the production tubing during the startup phase, and in 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 countercurrent 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 a 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 20°C higher than the produced-liquid temperature to start a water-hammer condition.