BULETINUL Universităţii Petrol – Gaze din Ploieşti Vol. LXVI No. 1/2014 79 – 84 Seria Tehnică A Probabilistic Method to Estimate the Initial Oil Rates of the Horizontal Wells Stimulated by Steam Marian Irimia*, Iulian Nistor ** * Ph.D. student - UPG, SPE International Member, OMV Petrom S.A., Romania e-mail: marian.irimia2@petrom.com ** SPE International Member, Universitatea Petrol-Gaze din Ploieşti, Bd. Bucureşti 39, Ploieşti e-mail: nistor@upg-ploiesti.ro Abstract To accelerate the oil production and increase the recovery factor for heavy oil reservoirs, since 1992, in the world is often used the SAGD method (SAGD – Steam Assisted Gravity Drainage). This method, which was not applied for Romanian oilfields, it’s an advanced kind of stimulation using steam. In fact, a pair of horizontal wells are drilled into the reservoir, one few meters above the other one. In each well pair, steam is injected into the upper well, to heat heavy oil, which allows it to flow into the lower well, where it is pumped to the surface. It’s known that in Dealu Batran, an old Romanian oil field there is a heavy oil reservoir located Drader II, where natural drive mechanism is associated with a thermal method (continuous steam injection) to increase recovery factor. Taken into account the positive effect of seam in this zone and the fact that there is an area where cannot be applied this process because of any surface restrictions, the possibility of applying and implementing SAGD has been researched. One of first steps was to estimate one hand the initial oil rate for a horizontal well produced without steam and on the other hand the initial oil rate in case the well will be stimulated by steam. Based on Butler and Joshi equations and playing with any uncertain parameters as permeability, effective thickness, horizontal length, oil viscosity there were established a range of initial oil rates in both cases. Key words: oil, heavy, steam, horizontal wells, initial oil rates, SAGD. SAGD – Steam Assisted Gravity Drainage In the SAGD process, two parallel horizontal oil wells are drilled in the formation, one about 4 to 6 meters above the other (fig. 1). The upper well injects steam, and the lower one collects the heated crude oil or bitumen that flows out of the formation, along with any water from the condensation of injected steam. The basis of the process is that the injected steam forms a "steam chamber" that grows vertically and horizontally in the formation. The heat from the steam reduces the viscosity of the heavy crude oil or bitumen which allows it to flow down into the lower wellbore. Solvents like butane are used to help to reduce the viscosity of the petroleum. The steam and gases rise because of their low density compared to the heavy crude oil below, ensuring that steam undefined is not produced at the lower production well. The gases released, which include methane, carbon dioxide, and usually some hydrogen sulfide, tend to rise in the steam chamber,