CSS - Canada's Super Strategy For Oil Sands
Authors: Ali S.M. Farouq 
Published: March 2010

The oil sands of Alberta represent a resource nearly as large (363x109 m3) as the world's conventional oil in place (about 450x109 m3; reserves 160x109 m3). Development of this resource to commercial production has been costly and time consuming. There are now at least two commercial in-situ projects - in Cold Lake and Peace River - producing over 10.000 m3/day of bitumen. Several pilots operations, such as UTF and HASDrive in Athabasca, are testing new technologies. We shall briefly talk about one of the commercially successful in-situ recovery methods - CSS, or Cyclic Steam Stimulation.

CSS, as employed in Cold Lake, is quite different from the similar process (we'll call that conventional CSS) known variously as cyclic steaming, steam soak and huff n'puff in California, Venezuela, Indonesia and other heavy oil areas. Even there, the basic process varies from field to field because the reservoir drives and oil viscosities are different. CSS in the oil sands of Alberta has evolved over more than 30 years, based on steam parting in response to the peculiar reservoir conditions. rather than any ground-breaking innovation. Various papers have described CSS in other areas (e.g., Towson and Khallad's(1) paper on the Athabasca operations), but we shall primarily talk about the Cold Lake CSS. First let's look at conventional CSS as a basis for comparison.

TABLE 1: Cold Lake project - phases 5 and 6 average performance forecast by cycle per well (from Esso's Application to ERCB, January 1985). (Available in full paper)

Conventional CSS

Conventional CSS is a field process discovered (Western Venezuela, 1959) and developed in the field. Experience in a given area is the key factor for success. The basic process is simple: steam is injected for two to three weeks, the well may then be shut in for a few days (soak period), after which it is put on production. The ensuing production is many times greater than the pre-stimulation rate, and even though production decline starts almost immediately, the rate may still be economic after six to 12 months.

When the oil rate declines to a low level, the whole cycle - injection, soak, and production - is repeated, and this may be continued as many times as is economical. In some operations in California, more than 20 cycles have been conducted.

The key performance index is the oil steam ratio (OSR), defined as the volume of oil produced per unit volume of water injected as steam (at standard conditions). The energy break-even OSR is about 0.07).

The chief attraction of the process is quick payout: oil production starts within weeks, and also at a high initial rate. Notice that, as described above, conventional CSS is a single well operation, draining the oil in the circular hot zone formed during the injection portion of the cycle. Typically, the total oil produced declines from cycle to cycle, whereas the volume of water increases, as if the volume affected is only the original hot zone. How far this is the case would depend on many factors: oil viscosity, well spacing, shape of the hot zone, formation properties, geological factors, and particularly the reservoir drives.