Modeling CHOPS Using a Coupled Flow-Geomechanics Simulator With Nonequilibrium Foamy-Oil Reactions: A Multiwell History Matching Study

Abstract

Cold Heavy Oil Production with Sand (CHOPS) has been widely and successfully applied for the last three decades in the Heavy Oil Belt region that straddles the provinces of Alberta and Saskatchewan in Canada. As its name suggests, the method relies on continuous production of sand to improve the recovery of oil from the reservoir. In CHOPS, a significant pressure drawdown around the wellbore is created by using progressive cavity pumps, which causes the loosely consolidated formation to fail, creating increased permeability channels, usually called wormholes, through which, a slurry-like mixture of sand, oil and water flows. Many attempts have been made to use conventional numerical reservoir simulators to model the CHOPS process. However, many of the commercial finite-difference reservoir simulators do not incorporate capabilities to model the complex geomechanical processes responsible for the failure of poorly consolidated formations in CHOPS. To circumvent these limitations, several approaches have been proposed. The most common relies on explicitly defining high permeability channels that radiate from the producing wells in an attempt to mimic wormholes created during CHOPS production. In this paper, we present a different, more rigorous approach that relies on the coupling of a finite-element geomechanical simulator with a finite-difference reservoir simulator. In the coupling process, the geomechanical simulator uses the pressure gradients calculated by the reservoir simulator to determine changes in the stress regime of the reservoir. In the case of CHOPS, these changes cause failure in the loosely consolidated formation, which in turn induces sand production with a corresponding increase in porosity and permeability. The new porosity and permeability values in the affected gridblocks are then fed back to the reservoir simulator, which is now capable of incorporating the effects of formation failure into fluid flow calculations. This process is then repeated at user-controlled intervals during the course of the simulation. The methodology has been validated by successfully history matching the production data from a section of a heavy oil field operated by Husky Energy in Western Canada. In this paper we compile the data integration efforts to create a coupled geomechanical model and the results of the history match.

Modelling of Cold Heavy Oil Production with Sand (CHOPS) using a fluidized sand algorithm

“…For example, Sawatzky et al [8] developed a sand failure mechanism that included kinetic reactions and foamy oil flow with sand transport. Another method that has been developed to model CHOPS alters reservoir properties near the wellbore to create an equivalent damaged (stimulated) zone to represent the effect of wormhole channels e.g., [19]. Istchenko and Gates [10] demonstrated another approach which is based on the concept of fluidizing sand grains which are transported along the wormholes from the reservoir.…”

“…Random walk algorithm to generate fractal wormholes (Yuen et al [14]), stress analysis and instability model of fluid and granular matrix flow (Geilikman et al [15]; Geilikman and Dusseault [16]; Wang and Chen [20]), and altering the absolute permeability and porosity in the region surrounding the production well (Denbina et al [17]; Sanyal and Al-Sammak [18]; Rivero et al [19]) are among the approaches used to model CHOPS process.…”

Well/Wormhole Model of Cold Heavy-Oil Production With Sand

“…The model is able to capture foamy oil flow through the use of kinetic reactions as well as the sand transport along the wormhole. One recently proposed CHOPS model uses an equivalent damaged zone to model the effect of several wormholes in a reservoir (Rivero et al 2010). This type of model captures the major CHOPS mechanisms of sand failure and foamy oil flow, but requires coupling with geomechanical models to adequately model sand failure in the reservoir and fails to generate enhanced-permeability zones that have the appearance of wormholes.…”

The Well-Wormhole Model of CHOPS: History Match and Validation

“…A recent approach presented by Rivero et al (2010) does not model individual wormholes, but uses an equivalent damaged zone to model the extent of growth of a wormhole network. The equivalent damaged zone is modeled as an increase in porosity of the zone growing radially from the wellbore due to plastic strain.…”