Modifications to Butler Theory for Geomechanical Effects at the Edge of SAGD Steam Chamber. Part I: Drained Condition

Day 2 Tue, December 09, 2014

Ghannadi

2014

Self Cite

In Part 1 of this study (SPE 165457-MS) a permeability enhancement at the edge of steam chamber where the oil sand has been sheared under thermal stimulation was described and an increase in oil drainage rates was calculated for different conditions. Finally, a modified Butler's Theory that includes geomechanical effects was described.Since heat transfer mechanisms are pivotal to the SAGD process and there are some doubts on the behaviour of the undrained zone at the edge of SAGD steam chamber in this study thermodynamics of undrained zone is discussed and new mechano-thermal equations are described. At the edge of steam chamber heat energy is transferred from steam to reservoir, reducing the viscosity of the bitumen, which flows under gravity toward a horizontal production well. Some of the heat transferred into the reservoir is used to increase the temperature of the reservoir, and some is stored as strain energy associated with the thermal stress field. The classical approach to exploring heat transfer studies in the SAGD industry is designed to satisfy only the "conservation of energy". Therefore, there is a lack of understanding of strain energy absorbed within the reservoir, and its effect on temperature variation inside the reservoir. The aim of the present work is to introduce a thermodynamic model to explore the effects of strain energy on temperature within the reservoir. This study explores the negative effect of developed stress field on heat transfer normal to the steam chamber interface. The novelty of this approach is the fact that it fully honours the energy equation. This study suggests the strain-energy number (N ⌬ ) as a new dimensionless number representing an importance of the strain energy effect on the temperature profile within the reservoir. The results obtained from this study reveal that it is suitable to use Butler's theory and to exclude the strain energy effects in heat transfer in the SAGD process. This study uses both thermodynamic approach and pressure front evaluation to argue the current practice of suggesting no permeability enhancement occurrence beyond the 12 m from the steam interface suggested by Li et al. (2004) based on the bitumen viscosity greater than 20,000 cP. This study proposes using one tenth-length of pressure front for drained zone which is beyond the temperature front advancement. Knowing that the shear is mostly induced within temperature front, geomechanical effects within the reservoir can be studied suggesting drained condition.

Section: Analytical Model Assumptionsmentioning

confidence: 99%

On Thermodynamics of Undrained Zone in SAGD Process

Day 2 Tue, December 09, 2014

Ghannadi

2014

Self Cite

Drained/Undrained Zones Boundary in Steam-Assisted Gravity Drainage Process

Gates

2015

All Days

Li et al. (2004) described three zones at the edge of steam chambers based on drainage conditions: 1. drained, 2. partially drained, and 3. undrained. In the drained zone, the pore pressure is controlled by injection pressure and fluid mobility within this region is sufficient to drain additional pore pressures due to shear dilation and pore fluid thermal expansion. The undrained zone lies beyond the partially drained zone and extends to virgin reservoir far beyond the chamber. In this zone shearing behaves under undrained condition; by this they mean no volume change occurs but shear lead to changes in pore pressure. Li et al. (2004) proposed that the boundaries of these zones are based on bitumen viscosity which relates to the temperature distribution beyond the steam interface. Since drained/undrained conditions impact the geomechanics at the edge of the chamber, we investigate whether Li et al.’s assumption that there is no volume change within the sheared zone is correct and is supported by field data. Here, we establish the physics associated with the undrained zone at the edge of SAGD steam chamber and explore the pressure front versus temperature front of different oil sand field projects. The results reveal that the drained zone governed by pressure front advancement is greater in extent than the sheared zone.. The thermodynamics of the undrained zone is discussed to derive a new theory for mechano-thermal phenomena at the edge of the chamber. The results from the theory show that the drained zone extends beyond the temperature front and thus, from a geomechanical point of view, the system solely consists of the drained and partially drained zones.

Drained/Undrained-Zones Boundary in Steam-Assisted-Gravity-Drainage Process

Gates

2016

SPE Journal

Summary Li et al. (2004) described three zones at the edge of steam chambers on the basis of drainage conditions: drained, partially drained, and undrained. In the drained zone, the pore pressure is controlled by injection pressure, and fluid mobility within this region is sufficient to drain additional pore pressures because of shear dilation and pore-fluid thermal expansion. The undrained zone lies beyond the partially drained zone and extends to virgin reservoir far beyond the chamber. In this zone shearing behaves under undrained conditions; by this, Li et al. (2004) mean no volume change occurs but shear lead to changes in pore pressure. Li et al. (2004) proposed that the boundaries of these zones are dependent on bitumen viscosity, which relates to the temperature distribution beyond the steam interface. Because drained/undrained conditions affect the geomechanics at the edge of the chamber, we investigate whether the assumption of Li et al. (2004) that there is no volume change within the sheared zone is correct and is supported by field data. Here, we establish the physics associated with the undrained zone at the edge of steam-assisted gravity-drainage steam chamber and explore the pressure front vs. temperature front of different oil-sand field projects. The results reveal that the drained zone governed by pressure-front advancement is greater in extent than the sheared zone. The thermodynamics of the undrained zone are discussed to derive a new theory for mechanothermal phenomena at the edge of the chamber. The results from the theory show that the drained zone extends beyond the temperature front and thus, from a geomechanical point of view, the system solely consists of the drained and partially drained zones.