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CO2-EOR, combined with multi-stage fractured horizontal wells has been considered as the most promising and environmentally-friendly technique for unlocking tight oil resources (Ghaderi et al., 2013). With more than 2,500 horizontal wells drilled into the Cardium formation within the Pembina field (CDL, 2016), adapting and utilizing existing wells and infrastructure for future CO2-EOR development is economically attractive. Nevertheless, the drilling, completion and hydraulic fracturing design and practices can vary greatly as a result of different geological conditions, operator preference and technology advancements through the years. This paper presents an effective workflow that selects hydraulically fractured horizontal wells suitable for CO2-EOR in consideration of both reservoir and completion qualities. The process of identifying refracturing candidates and potential risk associated with CO2-EOR performance is also developed. Two groups of parameters - the reservoir quality group (remaining oil in place, permeability, reservoir depth and a fluid type) and the completion quality group (well lateral length, well spacing, fracture spacing, SRV and a skin factor) - are first defined. A fully compositional simulator is applied to study the effects of these parameters on reservoir responses to CO2 injection. A Fuzzy Analytic Hierarchy Process (F-AHP) is then employed to rank candidate horizontal well pads for CO2-EOR. The ranking results and simulated oil recovery factor for each candidate show significant agreement. In addition, with the help of crossplots, the horizontal wells with below-average completion quality, but relatively good reservoir quality, are selected as refracturing candidates. A risk analysis reveals that the presence of conglomerate on the top of the Cardium formation plays a significant role, resulting in upward moving of CO2 and hence a lessened chance of contacting and displacing oil contained in the lower sands. Additionally, permeability heterogeneity has an adverse effect on CO2 sweep efficiency and can add uncertainty to the success of a recovery process. These factors should be further evaluated after the initial screening process. |
