Characterizing the Effects of Lean Zones and Shale Distribution in Steam-Assisted-Gravity-Drainage Recovery Performance

Abstract

Summary Performance of steam-assisted gravity drainage (SAGD) is influenced significantly by the distributions of lean zones and shale barriers, which tend to impede the vertical growth and lateral spread of a steam chamber. Previous literature has partially addressed their effects on SAGD performance; however, a comprehensive and systematic investigation of the heterogeneous distribution (location, continuity, size, saturation, and proportions) of shale barriers and lean zones is still lacking. In this study, numerical simulations are used to model the SAGD process. Capillarity and relative permeability effects, which were ignored in many previous simulation studies, are incorporated to model bypassed oil. Numerous ranking schemes are formulated to analyze various aspects of SAGD performance. A detailed sensitivity analysis is performed by varying the location, continuity, size, proportions, and saturation of these heterogeneous features. Lean zones and shale lenses (imbedded in a region of degraded rock properties) with different sizes and degrees of continuity are placed in areas above the injector, below the producer, or in between the well pair. It is noted that among numerous parameters that influence the ultimate recovery, remaining bypassed oil, chamber advancement, and heat loss, continuity and position of these features in relation to the well pair play a particularly crucial role. Neural network modeling is subsequently used for constructing data-driven models to identify and propose a set of input variables for correlating relevant parameters or measures, which are descriptive of the heterogeneity and properties of the shale barriers and lean zones, to recovery and ranking results. This work provides a guideline for assessing the impacts of reservoir and saturation heterogeneities on SAGD performance. A set of input variables and parameters that have significant impacts on the ensuing recovery response is identified. One can define readily the proposed set of variables from well logs and apply immediately in data-driven models with field data and scaleup analysis of experimental models to assist field-operation design and evaluation. One can also extend the approach presented in this paper to analyze other solvent-assisted SAGD processes.