Heat Conduction Modeling Tools for Screening In Situ Oil Shale Conversion Processes

Transcription

1 Heat Conduction Modeling Tools for Screening In Situ Oil Shale Conversion Processes William A. Symington, P. Matthew Spiecker 28 th Oil Shale Symposium Colorado School of Mines October 14, 2008

2 In Situ Oil Shale Screening Calculations Address the Most Critical Aspects of the Process Physics Full Physical Problem Thermal conduction and advection Coupled geomechanical model for predicting permeability creation Kinetic model of kerogen chemical decomposition Secondary cracking of oil to lighter hydrocarbons and coke Multiphase fluid flow of oil, gas, and water Multicomponent hydrocarbon phase behavior model Electrofrac Process Schematic Screening Calculations Thermal Conduction Kinetic model of kerogen chemical decomposition

3 Screening Tools Utilize Linear Heat Conduction Theory and Basin Modeling of Source Rocks 2c 2b Linear Heat Conduction Theory 2a z Rectangular solid heated by T degrees at time, t = 0 y x = T T 0 where : T f ( x, t) = g( y, t) = h( z, t) = Basic Initial alue Problem (*) f ( x, t) g( y, t) h( z, t) a x a x erf ( ) erf ( ) 2 α xt 2 α xt b y b y erf ( ) erf ( ) 2 α yt 2 α yt c z c z erf ( ) erf ( ) 2 α zt 2 α zt Arbitrary heat sources modeled as time sequences of a basic initial value problem. Complicated heating programs can be treated as a series of heaters turned on/off. Basic anisotropy can be included. Calculations done only at sites of interest. Basin Modeling of Source Rocks Can use end member source rock types or measured kinetics. Simplified chemistry model. Kerogen Oil Gas Coke Oil Gas Coke First order reaction kinetics. Percent grams/gramotoc Example Activation Energy Spectrum dk dt = A i f i e Ea i RT Kcal/mole Example Calculated Yield 3 degc/ma 50 degc/yr 100 degc/yr Degrees, C (*) Analysis of Heat and Mass Transfer, 1972, Eckert, E. R. G. and Drake, R. M.

4 Screening Calculations Follow a Generalized Procedure Describe heating scenario as a set of rectangular volumetric heaters. Include all heaters with an impact on the zone of interest. Superpose heaters to calculate temperature history at points of interest. Temperature Temperature Time, yrs Sum up total oil & gas generated. Compare to heat energy input. Fraction of Kerogen Converted Convolve thermal histories with basin modeling source rock model to calculate oil & gas generation history. Use full math model or relate fractional conversion to maximum temperature reached. 2.5 years 5 years 10 years Ea dk i RT = A fi e 1.0 dt i Fraction Converted Example Fractional Conversion degrees, C

5 Screening Calculations Follow a Generalized Procedure Describe heating scenario as a set of rectangular volumetric heaters. Include all heaters with an impact on the zone of interest. Superpose heaters to calculate temperature history at points of interest. (Based on Green River Oil Shale) Heat Capacity 0.3 (BTU/lbºF) 0.3 Thermal Conductivity Temperature 25 (BTU/dayftºF) 25 Density 137 (lb/ft 3 ) 137 Thermal Diffusivity 07 (ft 2 /day) Temperature window for conversion at Fraction of Kerogen Converted 180 ºF/year (ºF) Oil Shale Richness 30 (gallons/ton) Sum up total oil & gas generated. Compare to heat energy input. Electrofrac Screening Analysis Parameters Temperature Time, yrs Convolve 07 thermal histories with basin modeling 500 to 615 source rock model to calculate 500 to 615oil & gas generation history. Use full math model or relate fractional 30 conversion to maximum temperature reached. = A f i e 2.5 years 5 years 10 years 1.0 dk dt i Ea i RT Fraction Converted Example Fractional Conversion degrees, C

6 Electrofrac Fractures are Parsed into Small Uniform Heaters for Screening Tool Application Process Schematic Geometric Process Parameters Fracture height Fracture spacing Heat Generation Mimics Thickness oltage in a Long Fracture is Nearly Linear Permits a 2D Treatment of Heat Transfer (dimensions in feet) Distance from tip Distance from tip Thickness distance distance from from tip tip Fracture Slivers with Uniform Heat Generation Heat Generation

7 2.5 years 5 years 7.5 years 10 years Temperature Fraction of Kerogen Converted 1.0 ºF 50 ft iew Direction Case Specifics Screening Tools Permit Evaluation of Overall Process Effectiveness : 150foot fracture height, 5year heating program sufficient to convert 200 feet of oil shale, 100foot fracture spacing. : Ratio of oil shale actually converted to the oil shale that could be converted by the heat input (59% for this case)

8 Screening Tools Can Consider Numerous Cases, arying Multiple Process Parameters Fiveyear Heating Program 150foot Fracture Height

9 Screening Tools Can Consider Numerous Cases, arying Multiple Process Parameters TiptoTip Fracture Height 100 Feet 150 Feet 200 Feet 250 Feet Heating Program Length 3 years 7 years 5 years

10 2.5 years 5 years 7.5 years 10 years Temperature Fraction of Kerogen Converted 1.0 ºF 50 ft Screening Tools Indicate Multiple Layers of Electrofracs Improve iew Direction Case Specifics (*) : 150foot fracture height (2 layers), 5year heating program sufficient to convert 325 feet of oil shale, 120foot fracture spacing. : 74% (*) ExxonMobil s Electrofrac Process for In Situ Oil Shale Conversion, 2006, Symington, et. al.

11 Screening Tools Indicate Multiple Layers of Electrofracs Improve Case Specifics (*) : 150foot fracture height (2 layers), 5year heating program sufficient to convert 325 feet of oil shale, 120foot fracture spacing. : 74% Temperature iew Direction ºF 1.0 Normalized Hydrocarbon Generation Total Generation Generation Rate 2.5 years 5 years 7.5 years 10 years End of Heating Time, years Fraction of Kerogen Converted 50 ft 1.0 (*) ExxonMobil s Electrofrac Process for In Situ Oil Shale Conversion, 2006, Symington, et. al.

12 Screening Tools Can Assess Severity of Process Imperfections Example: Fracture Placement is Relatively Insensitive to Minor Errors in Fracture Placement ºF Spot on 15foot miss 30foot miss Temperature after Fiveyear Heating Program 100 ft 45foot miss 60foot miss ertical Offset, ft

13 Screening Tools Can Assess Resource Suitability for In Situ Processes Rundle Example Rundle Location Rundle Essooperated asset, originally acquired in Extensional halfgraben with probable recent compressional reactivation. Historically considered a candidate for mining and surface retorting. Attention focused on Kerosene Creek Member. Screening tools used to evaluate in situ potential of deeper Brick Kiln and Ramsay Crossing Members. Rundle (*) Geologic Map KC N TE C A SW meters MC BK WESTERN kilometers Southwest Northeast Cross Section AA RL KC TE A TE THE?? MC HC FAULT BK BK NARROWS URX URX CURTIS ISLAND LRX UTG LTG UTG LRX BK MO Tertiary Narrows Beds (MidLate Eocene) meters Rundle Stratigraphy Quaternary Curlew Formation Rundle Formation Worthington Formation Palaeozoic? Kerosene Creek Telegraph Creek Munduran Creek Humpy Creek Brick Kiln Ramsay Crossing Teningie Creek Monte Cristo NE (*) Cyclic Depositional Sequences in the Rundle Oil Shale Deposit, 1983, L. Coshell

14 Rundle Screening Study Considered Multiple Electrofrac Heater Arrangements Study focused on application of Electrofrac to Rundle Brick Kiln and Ramsay Crossing Members. Shallow depth and recent compressional tectonics indicate beddingparallel fractures are likely. Screening study varied numerous parameters. Fracture size Heating duration Fracture spacing Physical properties Screening Analysis Physical Parameters Electrofrac Screening (Green River) Rundle Screening Heat Capacity (BTU/lbºF) Thermal Conductivity (BTU/dayftºF) Density (lb/ft3) Thermal Diffusivity (ft2/day) Temperature window for conversion at 180 ºF/year (ºF) Oil Shale Richness (gallons/ton) InPlane Fractures Fracture Width ertical Spacing Geometry Heat input Horizontal Spacing Staggered NonOverlapping Fractures Staggered Overlapping Fractures 500 to to to 22 Horizontal Spacing

15 Overall Process Effectiveness Depends Most Strongly on Extent of Heated Interval Staggered, overlapping fractures are highly efficient. Highest efficiencies occur when heating the entire Brick Kiln to Lower Ramsay Crossing interval. Lower thermal conductivity limits vertical spacing. Rundle s higher heat requirement (relative to Green River) may be offset by higher heating efficiency. Seven Layers of 150foot Staggered Fractures (Suitable for Brick Kiln to Lower Ramsay Crossing) 1 60 ft 75 ft 45 ft Heating Program 0 3 years 5 years 7 years 90 ft Fracture Spacing Three Layers of 150foot Fractures (Suitable for Brick Kiln Member) InPlane Fractures Staggered NonOverlapping Staggered Overlapping Heating Fracture Program Spacing 3 yrs / 45 ft 5 yrs / 45 ft 7 yrs / 45 ft 3 yrs / 60 ft 5 yrs / 60 ft 7 yrs / 60 ft

16 Heating the Brick Kiln / Ramsay Crossing Interval Provides a High Case Specifics: 150foot fracture width (7 layers), 5year heating program sufficient to convert 400 feet of oil shale, 60foot vertical fracture spacing. : 94% iew Direction Temperature 2.5 years 5 years 7.5 years 10 years ºF 12.5 years 15 years 50 ft Fraction of Kerogen Converted 1.0

17 Heating the Brick Kiln / Ramsay Crossing Interval Provides a High Case Specifics: 150foot fracture width (7 layers), 5year heating program sufficient to convert 400 feet of oil shale, 60foot vertical fracture spacing. : 94% iew Direction Temperature ºF Normalized Hydrocarbon Generation 1.0 Total Generation 2.5 years Generation Rate 5 years 7.5 years 10 years 12.5 years 15 years 50 ft End of Heating Time, years Fraction of Kerogen Converted

18 Heat Conduction Modeling Tools for Screening In Situ Oil Shale Conversion Processes Screening tools based on linear heat conduction and basin modeling source rock calculations provide useful estimates of process effectiveness and resource suitability. For in situ process development work, screening tools can: Estimate process conversion. Examine impacts of process parameters such as heating geometry, size, spacing, total heat input, and heating duration. Assess process sensitivity to implementation problems such as imperfect heating geometry or performance. For resource assessment work, screening tools can: Estimate the resource suitability for in situ processing. Examine the impact of rock physical property variations.