Field-Scale Deformation Analysis of Cyclic Solvent Stimulation in Thin Unconsolidated Heavy-Oil Reservoirs With Developed Wormhole Network

Abstract

Summary With the current interest in exploiting thin unconsolidated heavy-oil reservoirs, cold heavy-oil production with sand (CHOPS) can be considered to be a promising primary-recovery technique. However, it offers low recovery factors (~5-15%) and creates a complex network of high-permeability channels known as workholes, while simultaneously changing formation compressibility and in-situ stress conditions. Eventually, development of such a network would lead to a softer layer within the shallow unconsolidated reservoir, which can carry less of the overburden stress. Further development of such reservoirs is usually achieved through enhanced-oil-recovery (EOR) applications in the form of cyclic solvent stimulation within an economic framework. Cyclic loading and unloading of this EOR technique make it even more difficult to predict the recovery performance. In this study, a 3D geomechanical model was used to calculate the stress distribution in a history-matched field in Alberta with 15 producers. The fractal patterns generated from the diffusion-limited-aggregation (DLA) algorithm were used to represent the wormhole network with different strength properties. Foamy behaviour of heavy oil was modelled with the help of a set of kinetic reactions. The hydro-geomechanical model was then used for field-development planning, reservoir management, and assessment of near-wellbore regions during cyclic injection and production. The fieldwide deformation and stress changes were analyzed in deep overburden, caprock, and reservoir to show the influence of local stress orientations in soft and stiff layers. Next, we considered a sector model with a single well. The model introduced was used to assess EOR processes with different solvent streams. While light hydrocarbon components help to repressurize the formation, the heavier components seem more effective in heavy-oil dilution. This occurred while stress arching redistributed the cyclic injection/production-induced stresses to flow around soft inclusions. Although it is difficult to obtain data to calibrate the 3D hydro-geomechanical model, it allows for reliable investigation of reservoir performance and provides deeper insight than does the use of flow simulation alone. The assessment of the potential of geomechanics can ascertain whether a more-detailed modelling is necessary.