The Viking reservoirs of west-central Saskatchewan contain a large number of light oil resources, of which only approximately 10% is considered recoverable. Oil production is hindered by (a) permeability damage due to clay swelling and migration during water injection and (b) organic solid (asphaltenes/wax) precipitation due to pressure and temperature variations. The Saskatchewan Research Council conducted laboratory experiments to evaluate and address these problems. Reservoir cores were tested for permeability damage measurements using both injection and produced brine. Different additives [i.e., potassium chloride (KCl) with/without hydrochloric acid (HCl), commercial clay stabilizers, liquid CO2, and isopropyl alcohol] were assessed as permeability remedies. The results showed that injection brine caused greater permeability damage than produced brine. KCl solutions preserved permeability, whereas KCl acidized with HCl appreciably improved it in one core. None of the used commercial additives significantly improved permeability. Injection of liquid CO2 and isopropyl alcohol caused encouraging permeability improvement in some cores. Wax precipitation tests were carried out on both dead oil and live oil samples. It was found that precipitation occurred in the dead oil even at the reservoir temperature of 22 °C. Filtration tests demonstrated that the live oil was much less sensitive to wax precipitation than the dead oil.
The Viking horizon of the Kindersley area of west-central Saskatchewan contains an estimated 300?106 m3 initial oil in place (IOIP), of which only about 10% is deemed to be recoverable(1). The Saskatchewan Research Council (SRC) carried out an experimental study aimed at evaluating and solving two major problems that hinder effective oil production in the Viking reservoirs of west-central Saskatchewan: permeability damage due to water sensitivity of the formation and organic solid precipitation due to pressure and temperature change.
Most of the Viking oil reservoirs are thin, with net pays from 2.0 to 5.4 m, and produce from depths between 640 and 750 m. The reservoir temperatures are around 23 °C, and the discovery pressures are approximately 6.4 MPa. The oil generally has densities between 840 and 870 m3/kg (37- 31 °API) and formation volume factors of about 1.1 m3/m3. Figure 1 shows a detailed map of well locations in Kindersley area in Saskatchewan. It is seen that most of the wells produce oil at rates below 1 m3/d (yellow), whereas a number of wells produce more than 10 m3/d (black).
The Viking reservoirs are sandstone of Lower Cretaceous age that was deposited in a shallow marine environment(2). The reservoir rocks have variable lithology, and are from mid- to poorly consolidated and contain movable and swelling clays, such as kaolinite and montmorillonite(3,4). Due to the presence of these clays, the formation is sensitive to fresh water and this has hampered efforts to improve oil recovery by waterflooding. Organic (waxes and/or asphaltenes) solid precipitation is another major factor hindering oil production. This solid removal is costly because it requires periodic workovers as well as disruption to well flow. Consequently, productivity will be greatly improved if these two problems are alleviated or solved.
