Exploration • Drilling • Field Services
63 per cent to 65 per cent is not recoverable at present by using traditional recovery methods. Tere are three methods of EOR:
● Termal recovery/steam injection. ● Chemical injection / polymer injection. ● Gas injection: natural gas, carbon dioxide, nitrogen.
EOR techniques are applied to: ● Decrease the viscosity difference between the oil and water phases.
● Reduce interfacial forces holding the oil in pores within the rock formation.
● Modify the reservoir and oil properties to make the oil more easily released and produced, that is improve sweep efficiency.
Termal EOR employs high pressure steam or in some cases in-situ combustion. Tis technique is favoured for the displacement of heavy oil. Chemical EOR involves injection of interfacial
active components, such as surfactants, polymers and alkalis. Te mechanism of oil displacement is obtained through the creation of ultra-low surface tension. Gas injection, the most-widely used approach
today, utilises high pressure carbon dioxide, nitrogen or hydrocarbon gas to generate miscibility, thus increasing oil volumes and decreasing oil viscosity. Tere are a number of advantages associated with the adoption of EOR techniques; not only can EOR prolong the life of a depleting field by up to 30 years when correctly employed on proven reserves, but it can also save the costs of finding a replacement field. As many fields around the world are starting to reach the end of their productive life, EOR represents the solution to sustain production levels and meet the increasing demand for oil.
First trials Te first export of Omani oil took place on 27 July 1967. Initially oil production rose steadily to 341 000 barrels per day in 1975 and in 1984 the average daily production reached 400 000 barrels a day. However, aware of the low recoverability factor of its fields due to a complex geology, Petroleum Development Oman (PDO) – the largest oilfield operator in the Sultanate – started a series of EOR trials in 1986. Te trials proved successful and Oman moved swiftly to implement EOR, boosting production to 714 300bpd in 2008 before enhanced oil recovery methods were implemented and to a current level of nearly 900 000bpd with EOR techniques. EOR projects commonly yield between 5-15 per cent incremental reserves and PDO expects its EOR projects to contribute around
35 per cent of its total production by 2020. For this reason Oman is seen by many as pushing the limits of EOR technology.
Steam injection Qarn Alam is the world’s first full field EOR project and also the largest of its kind in the world. A sophisticated EOR technique called thermally assisted gas oil gravity drainage (TAGOGD) is employed due to characteristics of the fractured carbonate reservoir where the oil is highly viscous and a very low percentage of recovery is feasible by conventional oil extraction method. Te US$1.2bn facility comprises a water
treatment plant producing 24 000 tonnes per day of boiler feed water, using reverse osmosis and a steam generation facility producing 18 000 tonnes per day of steam, using heat recovery steam generators (HRSG). Te application of EOR is adding 60 000 bpd, and 1.2MMSCMD of gas to the original output.
Polymer injection Marmul field is located in south Oman. Marmul field is characterised by heavy viscous crude that is difficult to extract by traditional recovery methods. Te reservoir has a viscosity of around 90Cp. To improve the reservoir’s sweep efficiency, water is viscosified by the addition of polyacrylamide polymers and then injected in the reservoir through polymer injection wells. Te polymer flooding at Marmul field will add a further 8000 bpd. Te implementation of this technique will lead to an estimated 10 per cent to 15 per cent increase in recovery levels from the Marmul reservoirs. ●
Enter 23 or ✔ at
www.engineerlive.com/iog
Vinod Shah is Managing Director, Mott MacDonald & Company LLC, Sultanate of Oman.
www.mottmac.com
www.engineerlive.com 23
Fig. 2. View of the Marmul polymer injection facility.
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