Cyclic Steam Stimulation (CSS)
Definition - What does Cyclic Steam Stimulation (CSS) mean?
Cyclic steam stimulation (CSS) is a petroleum extraction technique. It uses hot steam injection into heavy-oil reservoirs or oil-sands deposits, through a common wellbore, used for injecting hot steam downward and extraction of oil through pumping upward, in cycles.
The production cycle of a CSS technique consists of the following stages:
- Injection stage for heating and thinning the oil in the deposit.
- Soaking stage, allowing the separation of oil from other ingredients, allowing reservoir pressure to build.
- Extraction by natural flow and also by forced pumping.
This is also sometimes referred to as huff and puff technique.
The study of the CSS technique is important because:
- It is widely used for petroleum extraction from oil sands and reservoirs with very heavy crudes, in California, Alberta (Canada) as well as other places.
- There is flexibility of using the same wells for steam flooding technique, at a later stage.
Petropedia explains Cyclic Steam Stimulation (CSS)
The Cyclic steam stimulation technique is found to be efficient and effective in the initial cycles. However, its limited recovery of nearly 20% of the potential Original Oil in Place (OOIP) is unfavorable as compared to the SAGD (steam assisted gravity draining) process, which has a recovery rate of around 50% of Original oil in place.
The process has been developed and adopted in California since early 1950's. In this process, initially, the superheated steam is injected at a high pressure, at temperatures ranging between 300 to 350 degrees Celsius, continuously for a few weeks depending on the nature of the reservoir or sand oil deposit. When the steam injection is stopped, the formation soaks the heat for a few days, allowing the heavy matter to separate from the heated lighter oil of lower viscosity, thus enabling natural extraction of oil due to the reservoir pressure and additional pumping when required. The main disadvantage of this method is the added cost of steam generation at a very high temperature. Superheated steam is injected again when the production falls due to the cooling of the formation, thus restarting a new inject-soak-produce cycle.