A Simulation Study of a Cyclic Steam Stimulation Pilot in a Deep Carbonate Heavy Oil Reservoir in Oudeh Field, Syria

摘要

The Oudeh Shiranish reservoir in Syria contains 5.1 billion bbls of 12-16° API crude oil. However primary recovery factor is estimated to be only 5 to 7% of the original oil in place. To increase oil recovery, waterflood, VAPEX, microbial treatment and cyclic steam stimulation (CSS) were examined. Eventually, CSS was selected for a pilot test despite the depth of the reservoir, approximately 1600 meters, was deeper than most successful CSS projects in the world. The CSS pilot was implemented in September 2006 and suspended in November 2009. The project expanded from 2 to 24 wells. Low steam quality at the bottom of the well proved to be the most prominent challenge due to a combination of heat loss in the wellbore and relatively low steam injectivity. Only hot water reached the bottomhole when steam was injected through casing. Injection into tubing improved steam quality. Vacuum insulated tubing (VIT) produced the best, increasing steam quality to between 20 and 40% at a wellhead steam quality of 80% and an injection rate of 200 m~3 CWE/day. The high pressure required to inject into the Shiranish reservoir at close to or higher than initial reservoir pressure conditions means that the latent heat of vaporization is low, compared to the typical CSS injection pressure, resulting in a less effective heating process. In the study, a new thermal simulation model was developed to examine history-matching parameters, match the well and pad performances and optimize operations if the pilot were to be continued. Excellent history matches were achieved. Forecast indicated that Shiranish CSS performance was positive and could increase oil recovery by up to 100% over cold production.