SLIDE 1
Outline
- Introduction and background
- Modeling approach: discrete element model
- Review of mechanical properties of oil shale as function of
grade and temperature
- Model calibration
- Results and discussion
Modeling of Mechanical Interactions of Proppant and Hydraulic - - PowerPoint PPT Presentation
Modeling of Mechanical Interactions of Proppant and Hydraulic - - PowerPoint PPT Presentation
Modeling of Mechanical Interactions of Proppant and Hydraulic Fractures for In-situ Retorting Hai Huang Shouchun Deng Thomas Wood Carl Palmer www.inl.gov Earl Mattson Energy Resources Recovery Idaho National Laboratory Outline
SLIDE 2
SLIDE 3
Background
- Various in situ approaches require hydraulic fracturing &
proppant filling
– To facilitate flow of hydrocarbon fluids – Some approaches require connectivity of proppants, i.e., Electrofrac (ExxonMobil)
- Need better understanding of mechanical interactions
between shale and proppants under in situ conditions
– Stress focusing – Proppant embedment – Deformation of fracture walls – Changes of fracture aperture as function of stress and temperature
SLIDE 4
Objectives
- Quantify proppant embedment as function of:
– Proppant size – Modulus of shale – Confining stress – Temperature – Elastic vs plastic deformation
- Evaluate performance of hydraulic fracture:
– Stress-dependence of fracture aperture – Evolving porosity in propped fracture – From evolving aperture/porosity to predict permeability of propped fracture: Carman-Kozeny, for example
SLIDE 5
Modeling Approach: Discrete Element Model
σ
y
ε
ε
- Particles interact through bond.
- Bond can be broken if shear stress
and/or tensile stress in bond exceeds threshold (i. e., critical tensile/shear stress).
- Repulsive & fraction forces between
grains in contact after the bond is broken
- Plasticity was triggered if either grain
- r bond compressive deformation
exceeds elastic limit: a simple ideal plasticity model
- The particles will be marked for
undergoing plastic deformation.
SLIDE 6
Mechanical Properties of Oil Shale at High Temperatures
Source: Eseme et al., 2007, Oil Shale
SLIDE 7
Mechanical Properties of Oil Shale at High Temperatures
Source: Eseme et al., 2007, Oil Shale
SLIDE 8
DEM Model Calibration For Oil Shale at High Temperatures
Critical strain for plasticity 0.004 0.015
SLIDE 9
DEM Model Calibration For Oil Shale at High Temperatures
"
SLIDE 10
Conceptual Model
Model domain Periodic BC Periodic BC Hydraulic fracture filled with proppants
Representative of physics and in situ condition
Two types of proppant used: 20/40 and 40/70 (US mesh sizes)
SLIDE 11
Simulation Results: 150°C, 20/40 proppant
1470 psi (10.1MPa) Linear elastic 5390 psi (37.2MPa) Right before peak stress 6860 psi (47.3MPa) After peak stress
SLIDE 12
150°C, 20/40 proppant-development of plastic zone
1470 psi (10.1MPa) 5390 psi (37.2MPa) 6860 psi (47.3MPa)
SLIDE 13
Comparison at 150°C between 20/40 and 40/70
1470 psi (10.1MPa) 5390 psi (37.2MPa) 6860 psi (47.3MPa)
SLIDE 14
Comparison at 150°C between 20/40 and 40/70
1470 psi (10.1MPa) 5390 psi (37.2MPa) 6860 psi (47.3MPa) 20/40 40/70
SLIDE 15
Simulation Results: 300°C
870psi (6MPa) 2900psi (20MPa) 4350psi (30MPa) 4640psi (32MPa) 20/40 40/70
SLIDE 16
- Larger proppant lead to larger aperture reduction
Fracture Aperture Reductions
150C 300C
SLIDE 17
Discussions
- DEM model is appropriate approach for modeling
proppant-shale interactions in hydraulic fractures
- The credibility of model predictions, i.e., stress focusing,
proppant embedment and aperture reduction, is determined by the availability of mechanical test data.
- A great need to fully characterize mechanical behaviors of
- il shale as function of temperature, grade and conversion
degree.
- Need to consider effect of fluid pressure inside the