Abstract:
Sanding onset and sand production rate in non-isothermal conditions are of interest both for post-Cold Heavy Oil Production with Sand (CHOPS) and thermally related (Enhanced Oil Recovery) EOR processes for sand control and optimized production purposes. Critical drawdowns with different sanding criteria representing different types of formations or failure mechanisms are presented based on fully a coupled geomechanics model under a uniform in-situ stress and non-isothermal conditions. Comparisons between validated isothermal conditions and those of heated/cooled formations are made. Sand production rate after the onset of sanding is also calculated and two different formulations defined by sanding zone change and displacement at the wellbore wall for an open hole case are developed and used.
Introduction
Differential temperatures applied between a wellbore and found in the far field, impose a non-isothermal condition in energy producing formations. Both formation mobility and skeleton deformation may induce incremental flow and possible formation failure leading to either wellbore collapse or sanding issue at the same time. These effects can be a major concern for well completion, as unwanted sand may be triggered, attempting to improve the production in petroleum engineering. As a possible post-CHOPS production strategy by heating the formations up, sanding may be purposefully mobilized for permeability enhancement and for better steam circulations. A combination of viscosity reduction and formation permeability increase, mobility change, is intuitively desirable for production enhancement in those mature EOR processes. Although extensive sanding related studies has been reviewed by Veeken et al 1992, thermally related reports on sand prediction and sand rate calculations are rare and quite limited (Wang, 1998). Thermal coupled geomechanical related studies seem to heavily be focused on wellbore stability and fracturing issues (McTigue (1990), Kurashige (1989), Wang & Papamichos (1994), Wang & Dusseault (1995), Settari & Walters (2001)). Part of the reasons for the lack of the related studies on sand production with thermal effects may be due to the fact that the conventional thermally related EOR processes are combined with a strict sand control strategy. Furthermore, a complete fully coupled thermal-geomechanics-flow framework is rather complex and poses great challenge mathematically.
CHOPS has been applied in Alberta and elsewhere for those intermediate heavy oil reservoir. About 8-15% recovery rate by the current CHOPS completion (Smith, 1988) pushes us to search a post-CHOPS strategy to produce additional oil after a preliminary production. Field experiences and our intuition with a combined CHOPS-thermal method indicate that incremental oil can be produced by reducing oil viscosity and introducing sanding related permeability enhancement. Furthermore the steaming circulation process may be enhanced once wormholes or high permeability zones are generated and thermal effect may further improve sanding processes. In this study, a general thermal-geomechanics-fluid coupling procedure is reviewed. Three possible sanding mechanisms are identified, reflecting different sand failures mechanisms, and the corresponding critical drawdowns are derived. Both critical producing drawdowns and sand rate subject to different wellbore temperatures are calculated, respectively.