Steam-Oil Ratio

The steam-oil ratio is the measurement scientists and engineers use to quantify the efficiency of enhanced oil recovery (EOR) processes which use various forms of steam injection. The ratio compares the volume of steam used to produce a barrel of crude oil. Lower ratios will indicate more efficient processes. As technology improves, less steam is required to generate a barrel of oil.

The steam-oil ratio helps standardize guidelines for efficiency in oil recovery and production. The ratio shows how well a specific steam process works compared to others. For example, a steam-oil ratio of 4.5, indicates 4.5 barrels of water converted to steam to produce one barrel of oil. This method is more efficient than one with a ratio of 6.5 as less steam is required to recover the same amount of petroleum. Lower steam requirements indicate a lesser cost of production.

Two enhanced recovery processes for using steam to recover oil include the cyclic steam simulation technique and the steam-assisted gravity drainage technique. Oil companies utilize these processes in areas where oil may be difficult to retrieve or located deep below the surface.

• The cyclic steam simulation technique injects steam into a well containing a heavy oil reservoir. Heavy oil is very thick and dense. The addition of steam makes the heavy oil less viscous facilitating recovery from the well. This technique requires the conversion of between three to eight barrels of water into steam for the recovery of one barrel of crude oil. The cyclic steam-oil ratio is between 3/1 to 8/1.
• The steam-assisted gravity drainage technique (SAGD) requires drilling two horizontal wells near an oil reservoir. One well sits above the oil reservoir, and another horizontal well sits below the pool of oil. The injection of steam into the top well heats the heavy oil below, reducing its viscosity. Gravity allows the less viscous oil to fall into the well drilled below the reservoir where pumps take it to the surface. This technique generally requires the conversion of between two to five barrels of water into steam for the recovery of one barrel of crude oil. The SAGD steam-oil ratio is between 2/1 to 5/1.

In comparison, the steam-assisted drainage technique is usually considered more efficient in maximizing productivity and reducing costs.

It’s important to note, however, that steam injection may not be economical unless used in vast oil fields. This economical factor is due to the potentially high, upfront capital costs to move equipment into the area and the cost of fuel, which is often natural gas, used to heat water into steam.