Thermal Techniques For The Recovery Of Heavy Oil In Sudan: Current And Future Trends

Heavy oil reserves are estimated to take 40% of Sudan's total reserves. Because of high oil viscosities in such reservoirs, fluid drives are inefficient and production rates are uneconomical. Thermal enhanced oil recovery (TEOR) is the best technique for maximum ultimate oil recovery of these reservoirs. The first field-scale cyclic steam stimulation (CSS) experiment of Sudan was applied in FNE field. In this paper, the successful CSS case is reviewed and those processes which are of practical importance in heavy oil reservoirs are discussed. In view of higher viscosities and consequently lower oil rates and envisaged meager primary recovery of around 18-20%, plan is made for CSS application early to overcome the resistance to flow and maximize the recovery. Wells have been completed with heat compatible casing and cement. Steam quality of 75% was injected for 6-12 days and wells were subjected to soaking of 3-5 days. Putting on production an improvement of three to five folds has been realized compared to primary production and first cycle is sustaining more than twelve months. Actual results are better than predicted in simulation studies with lower steam intensity of 120 m(3)/m compared to planned 160 m(3)/m. CSS is a conventional method for developing heavy oil reservoirs, new techniques, including steam flooding, in-situ combustion and steam assisted gravity drainage (SAGD) were developed to improve heavy oil recovery in recent years. The other part of this paper introduced the develop status, the mechanisms and the characteristics of these techniques. The investigation indicates that with the development of science and technology and increasing requirement on environmental protection, these techniques will be the main techniques for heavy oil development in Sudan.