Impact of Natural Fractures on Caprock Integrity in Steam Assisted Gravity Drainage

2020 ◽  
Author(s):  
Qiuguo Li ◽  
Jose Rivero
Keyword(s):  
Gravity Drainage ◽  
Natural Fractures ◽  
Steam Assisted Gravity Drainage ◽  
Caprock Integrity

Understanding the Thermo-Hydromechanical Pressurization in Two-Phase (Steam/Water) Flow and Its Application in Low-Permeability Caprock Formations in Steam-Assisted-Gravity-Drainage Projects

SPE Journal ◽  
2014 ◽  
Vol 19 (06) ◽  
pp. 1126-1150 ◽  
Author(s):  
Sahar Ghannadi ◽  
Mazda Irani ◽  
Rick Chalaturnyk
Keyword(s):  
Pore Pressure ◽  
Shear Failure ◽  
Thermal Recovery ◽  
Subcritical State ◽  
Gravity Drainage ◽  
Low Permeability ◽  
Steam Chamber ◽  
Steam Assisted Gravity Drainage ◽  
Caprock Integrity ◽  
Casing Failure

Summary Steam-assisted gravity drainage (SAGD) is one successful thermal-recovery technique applied in Alberta oil-sand reservoirs. When considering in-situ production from bitumen reservoirs, one must reduce viscosity for the bitumen to flow toward the production well. Steam injection is currently the most promising thermal-recovery method. Although steamflooding has proved to be a commercially viable way to extract bitumen from bitumen reservoirs, caprock integrity and the risk of losing steam containment can be challenging operational problems. Because permeability is low in Albertan thermal-project caprock formations, heating greatly increases the pressure on any water trapped in pores as a result of water thermal expansion. This water also sees a great increase in volume as it flashes to steam, causing a large effective-stress reduction. After this condition is established, pore-pressure increases can lead to caprock shear failure or tensile fracturing, and to subsequent caprock-integrity failure or potential casing failure. It is typically believed that low-permeability caprocks impede the transmission of pore pressure from reservoirs, making them more resistant to shear failure (Collins 2005, 2007). In considering the “thermo-hydromechanical pressurization” physics, low-permeability caprocks are not always more resistant. As the steam chamber rises into the caprock, the heated pore fluids may flash to steam. Consequently, there is a vapor region between the steam-chamber interface penetrated into the caprock and the water region within the caprock which is still at a subcritical state. This study develops equations for fluid-mass and thermal-energy conservation, evaluating the thermo-hydromechanical pressurization in low-permeability caprocks and the flow of steam and water after steam starts to be injected as part of the SAGD process. Calculations are made for both short-term and long-term responses, and evaluated thermal pressurization is compared for caprocks with different stiffness states and with different permeabilities. One can conclude that the stiffer and less permeable the caprock, the greater the thermo-hydromechanical pressurization; and that the application of SAGD can lead to high pore pressure and potentially to caprock shear, and to subsequent steam release to the surface or potential casing failure.

Predicting Geomechanical Dynamics of the Steam-Assisted-Gravity-Drainage Process. Part I: Mohr-Coulomb (MC) Dilative Model

SPE Journal ◽  
2018 ◽  
Vol 23 (04) ◽  
pp. 1223-1247 ◽  
Author(s):  
Mazda Irani
Keyword(s):  
Shear Zones ◽  
Thermal Recovery ◽  
Absolute Permeability ◽  
Test Facility ◽  
Gravity Drainage ◽  
Steam Assisted Gravity Drainage ◽  
Recovery Processes ◽  
Stress Changes ◽  
Caprock Integrity ◽  
The Impact

Summary In the steam-assisted-gravity-drainage (SAGD) recovery process, the injection of high-pressure/high-temperature steam causes significant stress changes at the edge of the heated zone or steam chamber. These stress changes include shear dilation, which can both enhance the absolute permeability and result in horizontal and vertical formation displacements. The importance of considering geomechanical effects in thermal-recovery processes has been extensively discussed in the literature, but the prediction and surveillance of the resulting effects, such as the impact on production enhancement and reservoir displacement, have in many cases been neglected. Furthermore, issues related to these geomechanical effects on thermal production have been the subject of considerable debate in the industry with no conclusive, meaningful assessments of the effect on reservoir deliverability and production, or of the associated risks that such geomechanical effects have on wellbore and caprock integrity. This study will focus on identification of the main findings from an extensive monitoring program conducted on the original SAGD pilot project conducted at the Underground Test Facility (UTF) in the late 1980s and a seismic program conducted during the last several years by an SAGD operator at a commercial thermal-recovery project. The measured displacements and identified dilation shear zones in these applications were compared with a Mohr-Coulomb (MC) dilative model. This paper illustrates some of the pros and cons of using such analytical models through comparison of the results based on field evidence of the dilation and shearing effects, and how these mechanisms affect both reservoir productivity (revenue) and wellbore and caprock integrity. Although the discussion on the geomechanical effects in thermal-recovery processes will no doubt continue, this study will provide field-supported results to illustrate both beneficial and potentially challenging impacts that these geomechanical effects can have in a thermal-recovery project.

scholarly journals Identifying Reservoir Features via iSOR Response Behaviour

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 427
Author(s):  
Jingyi Wang ◽  
Ian Gates
Keyword(s):  
Oil Sands ◽  
Gravity Drainage ◽  
Athabasca Oil Sands ◽  
Steam Chamber ◽  
Heterogeneous Reservoirs ◽  
Steam Assisted Gravity Drainage ◽  
Response Behaviour

To extract viscous bitumen from oil sands reservoirs, steam is injected into the formation to lower the bitumen’s viscosity enabling sufficient mobility for its production to the surface. Steam-assisted gravity drainage (SAGD) is the preferred process for Athabasca oil sands reservoirs but its performance suffers in heterogeneous reservoirs leading to an elevated steam-to-oil ratio (SOR) above that which would be observed in a clean oil sands reservoir. This implies that the SOR could be used as a signature to understand the nature of heterogeneities or other features in reservoirs. In the research reported here, the use of the SOR as a signal to provide information on the heterogeneity of the reservoir is explored. The analysis conducted on prototypical reservoirs reveals that the instantaneous SOR (iSOR) can be used to identify reservoir features. The results show that the iSOR profile exhibits specific signatures that can be used to identify when the steam chamber reaches the top of the formation, a lean zone, a top gas zone, and shale layers.

Dissolved Organic Matter in Steam Assisted Gravity Drainage Boiler Blow-Down Water

2013 ◽  
Vol 27 (7) ◽  
pp. 3883-3890 ◽  
Author(s):  
Subhayan Guha Thakurta ◽  
Abhijit Maiti ◽  
David J. Pernitsky ◽  
Subir Bhattacharjee
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Gravity Drainage ◽  
Blow Down ◽  
Steam Assisted Gravity Drainage

Investigation of Emulsion Flow in Steam-Assisted Gravity Drainage

SPE Journal ◽  
2013 ◽  
Vol 18 (03) ◽  
pp. 440-447 ◽  
Author(s):  
C.C.. C. Ezeuko ◽  
J.. Wang ◽  
I.D.. D. Gates
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Oil Recovery ◽  
Vital Role ◽  
Gravity Drainage ◽  
Steam Assisted Gravity Drainage ◽  
Emulsion Flow ◽  
Very High ◽  
Effective Representation

Summary We present a numerical simulation approach that allows incorporation of emulsion modeling into steam-assisted gravity-drainage (SAGD) simulations with commercial reservoir simulators by means of a two-stage pseudochemical reaction. Numerical simulation results show excellent agreement with experimental data for low-pressure SAGD, accounting for approximately 24% deficiency in simulated oil recovery, compared with experimental data. Incorporating viscosity alteration, multiphase effect, and enthalpy of emulsification appears sufficient for effective representation of in-situ emulsion physics during SAGD in very-high-permeability systems. We observed that multiphase effects appear to dominate the viscosity effect of emulsion flow under SAGD conditions of heavy-oil (bitumen) recovery. Results also show that in-situ emulsification may play a vital role within the reservoir during SAGD, increasing bitumen mobility and thereby decreasing cumulative steam/oil ratio (cSOR). Results from this work extend understanding of SAGD by examining its performance in the presence of in-situ emulsification and associated flow of emulsion with bitumen in porous media.

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