SAGD Performance Optimization Through Numerical Simulations: Methodology and Field Case Example

Abstract

SAGD is a very promising recovery process to produce heavy oils and bitumen resources. The method ensures both a stable displacement of steam and economical rates by using gravity as the driving force and a pair of horizontal wells for injection/production. After several years of small scale field tests (pilots), the method is now considered as mature and large scale projects are scheduled in a near future (in Canada for instance). Nevertheless, both technical and economical success of the process require a satisfactory development of the steam chamber, which can be achieved by well monitoring (i.e. steam trap control). This paper presents a general methodology based on numerical investigations to obtain and maintain an optimized development of the chamber throughout the production life of the wellpair. First, the methodology is explained on a synthetic case and applied to a real field case example. Field data are first history matched with the model and then the proposed approach is used to evaluate how the oil production could have been enhanced and optimized further. It is shown that an optimized steam chamber development is obtained by adjusting the steam injection rate to the potential of the reservoir (fluids and geology) and by monitoring the production rate during the process/operations to keep the steam chamber as large as possible but away enough from the production well to prevent any steam breakthrough. The results are in good agreement compared with Butler's analytical model (oil rate and steam chamber shape). A very good history match is obtained in the field case example. The proposed methodology shows that oil production rate can be doubled when injection/production rates are adapted to the SAGD reservoir potential. Introduction SAGD principle In one decade, SAGD process has turned out to be the most promising strategies to develop huge heavy oil and bitumen accumulations [1,2,3,4,5,6]. Like the conventional thermal processes (steam stimulation, steam injection,...) [1,7], this method aims at reducing oil viscosity by increasing the temperature. In the SAGD process, this is achieved by drilling a pair of horizontal wells. Typically, the two horizontal drains are located at short distance one above the other (Figure 1). Steam is injected into the upper well and hot fluids are produced from the lower well. This progressively creates a chamber, which develops by condensing steam at the chamber boundary and giving latent energy to the surrounding reservoir. Heated oil and water are drained by gravity along the chamber walls towards the production well [1]. The strength of SAGD is to merge a stable displacement of oil by steam with high production rates. The first feature is achieved by using gravity drainage as the only driving force. Whereas gravity drainage gives rise to poor production rates with conventional wells, some good productivity can be obtained with the use of horizontal wells. SAGD process obviously benefits from the recent and impressive progress drilling technology and development of specific tools enable to make possible accurate well pair placement and roughly constant inter-well spacing [8].

Transformation of Resources to Reserves: Next Generation Heavy-Oil Recovery Techniques

“…The lower production well is operated with steam trap conditions to avoid excessive steam production. This steam trap control is achieved in the simulation by setting production temperature 18°F below steam temperature and establishing a liquid leg above the producer (Edmunds, 1998;Egermann 2001). The simulation runs are terminated after 10 years of production.…”

Application of the SAGD to an Iranian Carbonate Heavy-Oil Reservoir

“…On the economic standpoint, SAGD is thus very interesting because it combines high flow rates due to horizontal wells and favorable energy balance Moreover; expected oil recovery is in the range of 50 to 75 %. [14,15] However, to be efficient, SAGD requires a production monitoring to systematically adjust well parameters in order to optimize the steam chamber development during the operating life of the pair. The main problem is that the steam chamber capacity to drain heated bitumen downwards continuously changes and so is the optimum set of parameters to pilot the pair.…”

Model-Based Adaptive-Predictive Control and Optimization of SAGD under Uncertainty

“…Considering that about 70% of the world oil reserves correspond to heavy oil, extra-heavy oil and bitumen (Alboudwarej et al 2006), thermal recovery methods should play a key role in satisfying such demand. Among these recovery methods, steam-assisted gravity drainage (SAGD) has shown the potential to achieve recovery factors in the range of 50% to 75% (Egermann et al 2001). Fig.…”

“…The former requires strategies for subcool control so that the liquid does not accumulate over the producing well but neither is steam produced (Edmunds 1998), while the latter accounts for economic and efficiency issues such as operating costs, oil prices and steam-oil ratio (SOR). Subcool makes reference to the difference between the saturation temperature and the actual temperature of water at the producer; on the other hand, SOR represents the volume of steam necessary to produce one volume unity of oil and is a measure of recovery efficiency (Egermann et al 2001).…”