Practical Considerations of Reservoir Heterogeneities on SAGD Projects

Abstract

Abstract SAGD has been implemented through a variety of different operating schemes. Determining the optimum and cost-effective strategy poses the greatest challenge to any SAGD reservoir. In addition to average rock quality, reservoir heterogeneities have a deep impact in steam chamber development and the overall volumetric sweep. This paper examines two well pairs in the Surmont pilot project. From this analysis and general experience, the following critical factors must be considered when optimizing SAGD operating strategies:Getting enough heat close to the producerAccounting for areal (lateral) heterogeneityIdentifying shale extent and its effect in partially retarding steam chamber height growthDetermining the effect of water saturation and assumed irreducible water saturationUnderstanding that permeability is often higher than air permeability most likely due to dilation effects This paper also addresses potential geological risk through analogy and the amount of heterogeneity that must be accounted for when developing a representative simulation. Introduction There is great emphasis on developing cost-effective strategies for the production of large heavy oil and bitumen reserves located within Western Canada and worldwide. Steam-assisted gravity drainage (SAGD) has been proven effective on both a laboratory scale and field-level. Recent advances in directional drilling and measuring while drilling (MWD) technologies have allowed for improved wellbore to reservoir contact, thereby enabling higher sweep efficiencies. This is essential in maximizing the reserves and accounting for complexities including reservoir heterogeneities. Steam chamber growth rates and shape must be adapted to particular characteristics of the reservoir. Key components that may not promote ideal growth behavior are:–Permeability (both areally and vertically) distribution–Water saturation heterogeneity and characteristics (irreducible versus connate)–Viscosity variation–Injection/producer locations and separation distance (standoff distance)–Solution gas effects–Geomechanical effects The applicability of conventional waterflood analyses is insufficient because of the high compressibility of the steam zone and water condensation. SAGD is an energy-intensive process where steam is required to reduce the viscosity to the point when oil can flow. For this reason, thermal recovery becomes more challenging as more complexities are introduced. Therefore, common production techniques may not be advantageous in particular reservoirs as problems can easily be compounded. The approach to SAGD simulation varies as heterogeneity changes. To illustrate this point, analysis of different well pairs with different degrees of heterogeneity was performed.