Upstream Research ExxonMobil’s Electrofrac ™ Process for In Situ Oil Shale Conversion William A. Symington, David L. Olgaard, Glenn A. Otten, Tom C. Phillips, Michele M. Thomas, Jesse D. Yeakel 26 th Oil Shale Symposium Colorado School of Mines October 17, 2006 Colorado Energy Research Institute 26th Oil Shale Symposium October 16-18, 2006
Electrofrac Upstream Research Oil Shale Conversion via Electrically Conductive Fractures • Early screening research indicated: Production wells � In situ methods preferred. � Heat conduction is the best way to “reach into” oil shale. + - + � Linear conduction from a planar heat V source is more effective than radial conduction from a wellbore. • Electrofrac concept is applicable with either vertical or horizontal fractures. • Conductant electrical resistivity: � high enough for resistive heating. � low enough to conduct sufficient current. • Electrofrac research has focused on critical technical issues: � Identification of conductant. Conductive heating and � Maintaining electrical continuity. oil shale conversion � Expulsion under in situ stress. � Completion strategy for effective heating. Hydraulic fractures containing electrical conductant Colorado Energy Research Institute 26th Oil Shale Symposium October 16-18, 2006
Electrofrac Laboratory Research has Upstream Research Focused on Critical Technical Issues Hydrocarbons Expelled Core-plug-scale experiments demonstrate: under Stress 20/40 Mesh Proppant • Calcined coke is a candidate conductant. • Electrical continuity is not disrupted by kerogen conversion. • Hydrocarbon expulsion under in situ stress. Modeling indicates: • Volume expansion is a large potential drive Calcined Coke mechanism. • Fractures will generally be vertical. • Longitudinal fractures heat effectively. Electrical Continuity Undisrupted by Kerogen Conversion Temp, ºF Effective Heating from Longitudinal Fractures #170 Cast steel shot Colorado Energy Research Institute 5 years 10 years 26th Oil Shale Symposium October 16-18, 2006
Identification of Conductant Upstream Research Calcined Petroleum Coke is a Candidate Electrofrac Conductant Coke Resistivity is Temperature Insensitive • Physical properties (density, particle size) Normalized Resistivity ( ρ / ρ 25ºC ) 2 similar to fracture proppants. 1.8 Normalized Resistivity EF135 • Electrical resistivity in desired range and 1.6 EF136 temperature-insensitive. Resisitivity should 1.4 1.2 be controllable by calcining process. 1 • Chemical stability up to calcining 0.8 temperature. 0.6 • Readily available. Current uses are - 0.4 0.2 – Carbon anodes for aluminum smelting. 0 – Anode beds for cathodic protection. 0 100 200 300 400 500 600 700 800 – Packing for industrial electrical grounding. Temperature, degC Calcining Temperature Controls Resistivity 0.13 TE-315 0.12 TE-315 Resistivity, ohm-cm TE-316 0.11 TE-317 TE-431 0.10 0.09 0.08 0.07 20/40 Mesh Frac Proppant Calcined Coke 0.06 1150 1200 1250 1300 1350 1400 1450 1500 1550 Colorado Energy Research Institute Calcining Temperature, degC 26th Oil Shale Symposium Data from Hardin, et al, 1992 October 16-18, 2006
Maintaining Electrical Continuity Particle Embedment Does Not Disrupt Upstream Research Continuity in Core-Scale Experiments • Stress applied with hose clamps to achieve electrical continuity. • Sample heated externally to Calcined petroleum coke or #170 cast steel shot (0.02 inch) 360ºC for 24 hours – 90% packed in 1/16 inch deep tray uniform conversion achieved. • Although embedment occurred to a minor degree, electrical continuity was not disrupted. 1/16 inch h c n i 1 Colorado Energy Research Institute 26th Oil Shale Symposium October 16-18, 2006
Maintaining Electrical Continuity Simulated Electrofrac Heating Circuit Upstream Research Undisturbed by Kerogen Conversion #170 Cast steel shot Photomicrograph section Photomicrograph under Fluorescent Light Experiment Summary Epoxy-Filled Fractures • Heated with 20 amps for 5 hours Spent Oil (~60 W). Circuit not disrupted by Shale rock alteration. • Internal measured temperature reached 268ºC. Estimated fracture temperature of 350-400ºC. Fracture Face • Thermal expansion caused fractures in the sample. • Recovered 0.15 mL of oil. 3 mm Steel Balls Conversion Initial Unaltered Zone Conversion Colorado Energy Research Institute Oil Shale Zone Spent Oil Shale Thin Section 26th Oil Shale Symposium Showing Porosity (blue) October 16-18, 2006
Expulsion Under In Situ Stress Upstream Research Experiments Demonstrate Expulsion of Hydrocarbons Under Stress • Stress is applied in axial direction, strain is inhibited in lateral directions. • Experiments under stress recovered 21 to 34 gal/ton from 42 gal/ton samples. Oil shale inside Berea cylinder - jacketed and clamped High temperature (Inconel) springs provide axial load. Gold foil records maximum spring deflection. Colorado Energy Research Institute 26th Oil Shale Symposium October 16-18, 2006
Expulsion Under In Situ Stress Upstream Research Volume Expansion Provides a Large Potential Drive Mechanism • Product compositions derived from MSSV (micro-sealed spherical vessel) pyrolysis experiments. • Equation-of-state model used to calculate expected density and phases at typical Electrofrac conditions. 1 Ton of Green River Oil Shale (22% TOC, 42 gal/ton) Pressure, psi Phase Diagram 4000 7.2 ft 3 mineral t n i o p e l b b 2.9 ft 3 coke u 3000 B Electrofrac P/T 25% vapor 9.4 ft 3 HC vapor 7.2 ft 3 mineral Dew point r 2000 o p a v % 0 5 8.1 ft 3 kerogen 6.6 ft 3 HC liquid 1000 75% vapor 15.3 ft 3 total 26.1 ft 3 total Before Conversion After Conversion @ 2400 psi, 750ºF Temperature, ºF 0 (without liquid cracking to gas) 0 200 400 600 800 1000 Colorado Energy Research Institute 26th Oil Shale Symposium October 16-18, 2006
Completion Strategy for Effective Heating In Piceance Basin, Electrofrac Heating Upstream Research Fractures will be Dominantly Vertical Oil shale outcrop Present day surface Geomechanical Model Calibration Oil shale Location A Wasatch σ vertical Mesa Verde σ east-west σ north-south N o Elevation → r 5 miles t Humble tests (1964) constrain h horizontal/vertical transition Fracture Orientation Transition Elevation Stratigraphic Markers Fracture jobs constrain Higher Lower minimum principle stress Borehole ellipticity/breakouts constrain stress difference Stress → Colorado Energy Research Institute 26th Oil Shale Symposium October 16-18, 2006 Symington, W. A. and Yale, D. P, 2006, ARMA GoldenRocks Conference
Completion Strategy for Effective Heating Preferred Process Geometry Relies on Upstream Research Vertical Electrofrac Heating Fractures • Heating wells drilled horizontally, Production wells perpendicular to direction of least principle in situ stress. + - + • Vertical longitudinal fractures filled V with electrically conducting material. • Electrical conduction from the heel to the toe of heating wells. • For reasonably spaced fractures, induced stresses should not alter the least principle in situ stress direction. • Multiple layers of heating wells may be stacked for increased heating Conductive heating and efficiency. oil shale conversion Hydraulic fractures containing electrical conductant Colorado Energy Research Institute 26th Oil Shale Symposium October 16-18, 2006
Completion Strategy for Effective Heating Modeling Optimizes Heating Efficiency Upstream Research Process Schematic Thermal model view direction Simulation Case Selected as “Typical” – 150 foot fracture height, 5-year heating sufficient to convert 325 feet of oil shale, 120-ft frac spacing, 74% heating efficiency Temp, ºF 300 ft 100 ft 2.5 years 5 years 7.5 years 10 years 100 ft Colorado Energy Research Institute 26th Oil Shale Symposium October 16-18, 2006
Electrofrac Upstream Research Oil Shale Conversion via Electrically Conductive Fractures ExxonMobil’s Electrofrac research has focused on critical technical issues. Research highlights include: • Laboratory experiments demonstrating – � Calcined petroleum coke is a suitable Electrofrac conductant. � Electrical continuity is unaffected by kerogen conversion. � Hydrocarbons will be expelled from heated oil shale even under in situ stress. • Modeling including the following – � A phase behavior model showing volume expansion is a large potential drive mechanism for expulsion. In situ oil shale can expand by 70% upon kerogen conversion. � A Piceance Basin geomechanical model showing the stress state of the Green River oil shale favors vertical fractures. � Heat conduction models showing that several fracture designs can deliver heat effectively. A “typical” case requires one Electrofrac heating well every 1.5 acres. Colorado Energy Research Institute 26th Oil Shale Symposium October 16-18, 2006
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