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Article details: Ali, Farouq. “Thermal oil recovery – Will It Make a Comeback in Saskatchewan?” Petroleum Society of CIM, 95.116 (1995): 1-7.
Thermal Oil Recovery
The aim of this paper is to determine whether steam injection can be viable within the thin formations in Lloydminster (Saskatchewan), and if that turns out to be the case, to investigate the form that the steam injection method that should be taken. This investigation is necessitated by the drastic reduction in the volume of oil in Saskatchewan after the introduction of the CSS method during the 1960s. This change in the amount of oil occurred due to the depletion of the solution oil that was providing the drive.
The author points out that thermal methods can work in Saskatchewan’s relatively deep formations that are today dominated by horizontal wells as long as each thermal process is designed to suit the conditions of each specific field. Emphasis is on the need to evaluate various processes, including cyclic steam stimulation (CSS), electrical heating, and steam injection. The paper reviews steam injection projects using thermal recovery to determine the processes that work and those that do not.
The article reports that CSS was noted to be unsuccessful within thin formations but was successful in thicker sands. Many field tests produced unsuccessful results in regards to in situ combustion, though it was found to be successful in two cases. Steam-flooding was largely unsuccessful but some changes can be made to ensure its success in seemingly unfavorable conditions. The paper also highlights the extensive laboratory work that was carried out to create a better understanding of thermal processes.
Several benefits and limitations of steam injection are also highlighted. In terms of benefits, the author notes that the method has been a highly successful in heavy oil recovery, and that most of the oil production in North America is being undertaken using steam. Indonesia is identified as home to the world’s largest steam injection facility. However, steam injection technology is adopted using different approaches in different areas. A crucial observation is that some adjustments to the method have to be undertaken to make it work in certain areas, with a major contributing factor being reservoir response. This situation has greatly contributed to the evolution of the method.
Steam has numerous benefits according to this paper. To begin with, it is among the best heat carriers, and it contains a mix of latent and sensible heats. This characteristic makes it possible for a zone of constant temperature to be formed. Steam also exhibits the characteristics of a viscous fluid and has a favorable effective mobility ratio. This viscosity is helpful because any steam that advances ahead of main front easily condenses, thereby triggering a corrective mechanism on the front. As the amount of non-condensable gases within the steam-gas mixture increases, the effect of steam advances increases become less pronounced. Steam is also beneficial because it easily condenses into water, leading to a reservoir-flow method comprising of two components/phases: oil and water. It is also important that steam volume can be created particularly at the Lloydminster area in order to cover a large volume of rock. Additionally, steam tends to transfer heat to rock and fluids more efficiently than hot liquids. Even when steam segregates towards the upper parts of the formation, it tends to form a condensate that ultimately flows downwards. The desirability of this characteristic depends on the process being used. In steam injection, it is possible to derive numerous advantages from feature of steam.
Based on the analysis made in this paper, steam injection also has its limits. One of them is the increase in steam injection pressure at the point where liquid and vapor phases become identical. This means that the advantages of steam tend to decrease with an increase in steam injection pressure. Steam is often characterized by large levels of heat loss in areas with small thickness formation due to the transfer of a portion of heat into oil-bearing formations themselves. To deal with this problem, the rate of steam injection must be high enough. Additionally, small thickness formation renders steam less useful in places where a justification for the use of steam injection is provided a large spacing is being utilized, which in effect leads to prohibitive heat losses.
Regarding application in Saskatchewan, the author’s view is that steam can only be relied on in 5 percent of Saskatchewan’s reservoirs. However, the Lloydminster area has heavy oils whose favorable flow characteristics can allow the use of this method. In relation to this investigation, several issues arising from experimental studies relating to steam injection are highlighted. For instance, bottom water can affect steam injection while a 10 percent solvent slug can significantly improve oil recovery when steam injection is being used. Regarding horizontal wells, the author reports that a combination between a horizontal injector and a horizontal producer has been found to work in a most effective manner in all cases. In terms of steam override, the reported findings suggest that the length of a horizontal well becomes less beneficial as steam injection volume increases. Elsewhere, the changes that characterize multilayered formations have no significant impact in terms of changes in the effectiveness of steam injection, while using a water-flood before steam injection can be economical because of the reduction in investment.
In light of these findings, the author argues that two options are available in the use of steam injection in the area, and that determining the resource base is an important preliminary step. The first option involves directing heat placement to the center of the formation, while the second one involves directing the steam only towards the top section of the formation before facilitating downward drive. The option that is chosen depends on the process being used.
The conclusion arrived at in the article is that steam injection is a feasible method of thermal oil recovery in the Lloydminster area of Saskatchewan. However, some modification of the steam injection process (CSS) is necessary to take advantage of the low volume of steam that is economically injected into the thin, heavy formations. The author’s final remark is that laboratory experiments are a crucial source of information on how to modify the steam process.
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