Development of Numerical Simulation Capabilities for In Situ Heating of Oil Shale

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1 Development of Numercal Smulaton Capabltes for In Stu Heatng of Ol Shale Sharad Kelkar, Rajesh Pawar Los Alamos Natonal Laboratory Nazsh Hoda, Chen Fang ExxonMobl Upstream Research Company Presented at the 32 nd Ol Shale Symposum, October 15-17, 2012, Colorado School of Mnes, Golden, CO, USA.

2 Full physcs modelng of n stu heatng processes s challengng Mmckng n stu heatng processes requres coupled thermal, mechancal, chemcal, and multphase flow modelng Toe Connector Well Producton Wells Process Heater Wells Heatng Element Heat transport Pyrolyss Creaton of flow pathways by flud generaton Mgraton of generated fluds Electrcally Conductve Materal Conductve Heatng and Ol Shale Converson 2

3 3 Each aspect of ol shale smulaton physcs s complex n ts own rght Thermal modelng Chemcal modelng Mechancal modelng Multphase flow Q T T C t T C p p + = + ) ( ) (. ) ( κ U ) exp(, 1 RT E A f c f r a N j j = = = γ T + = = + α σ C ε F σ 0, - ρg) µ P k r = ( K q

4 Ol shale smulator s feature lst s extensve owng to complex propertes of ol shale Beddng plane Thermal and mechancal propertes depend on temperature Transversely sotropc thermal and mechancal propertes Typcally, rock s non-porous and mpermeable Fractures Pyrolyss Strong flow-mechancs couplng requred to capture porosty/permeablty creaton durng pyrolyss and by rock falure 4

5 LANL s FEHM smulator s an deal sprng board for ol shale smulator development FEHM: Fnte Element Heat and Mass Has the coupled thermal-flow-mechancs smulaton capablty applcable to elastc response Control volume-fnte element (CVFE) approxmaton: Control volume for mass/energy balance Fnte element for stress FEHM has been verfed through extensve applcatons: Groundwater modelng Contamnant transport and reactons Methane hydrate reservor producton CO 2 sequestraton Geothermal 5

6 Developng new thermal-hydrologcal-mechancal-chemcal (THMC) modelng capabltes n FEHM Thermal: Ansotropc, temperature-dependent thermal propertes Hydrologcal (multphase flow): Black ol model: accounts for water bolng EOS based propertes Mechancal: Ansotropc, temperature-dependent mechancal and fracturng propertes Plastc/elastc deformaton models Stress-dependent changes n porosty and permeablty Chemcal: Kerogen converson nto ol/gas/coke and subsequent reactons User-specfed stochometry and knetcs 6

7 Benchmarked new temperature dependent thermal and mechancal property varaton capabltes aganst Abaqus Problem descrpton: Heater Q: 4 kw Parabolc heat dstrbuton No heat flux condton Temperature dependent thermal and mechancal propertes No pyrolyss Thermal propertes Mechancal propertes Heater 328 OB 450 Mahagony: 100 UB: 450 7

8 FEHM and Abaqus results compare well!! Results compare well Thermal softenng of rock mpacts stress evoluton n the heated zone 8

9 Benchmarked FEHM s new multphase flow and kerogen converson capabltes aganst CMG s STARS Problem descrpton: Heater: Q = 0.7 kw Permeablty, K = 10 md Porosty, φ = 0.3 Sw = 0.1, S Kerogen = 0.9 P Intal = P BHP = 0.1 Mpa Rxn: Kerogen Ol + Gas + Coke Ol Gas + Coke 1 m Heater Z Y X 10 m Producer 90 days Presence of water mpacts thermal conducton and, as a consequence, converson extent 9

10 Implct-couplng requred to model steep changes n rock propertes and tme- scale separaton Physcal phenomena take place at very dfferent tme-scales Kerogen converson and permeablty/porosty enhancement: on the order of hours Tme scale of flow: on the order of days Steep changes n materal propertes wth tme Mechancal propertes (Young s modulus and thermal expansvty) show nonlnear temperature dependence. Enhancement n permeablty takes place at a very small tme scale Large varatons n flud pressure, temperature, saturatons, and stresses Wth explct couplng, very small tme step needed to model steep changes; mpractcal for commercal scale smulaton. 10

11 Implct-couplng: Formulaton Thermal and multphase flow problem solved on a control volume (CV) Stress calculatons done on a fnte element mesh Mappng between CV node and fnte element node q u j k F u j k = = K j γ 1 N j j e ρ ( A µ elements j j / l F σ j e Dervatve of mass flux term wth respect to dsplacements j j e e ) ( P 1. Ve j gp F P ) u k J D B I K j : Absolute permeablty γ j : Relatve permeablty F j : Effectve permeablty P: Pressure u k : Dsplacement σ e : Average stress tensor V e : volume of element A j /l j : rato of area to length J: Jacoban ρ/µ: Rato of densty to vscosty D, B, I: stress-stran, stran-dsplacement, and dentty matrces 11

12 Implct-couplng shows sgnfcant computatonal advantages over explct-couplng Problem descrpton: 5 DOF per node: dsplacements, temperature, and pressure Intal Permeablty = 1 µd, Porosty = 0.2 Young s modulus = 10 GPa Posson s rato: 0.25 Water njecton rate: 0.04 kg/s Temperature: 25 0 C Flud Compressblty = 100 x water Permeablty generaton because of pore pressure buld-up Water Injecton Fxed P Permeablty Factor 1000 Pore Pressure Implctly-coupled model needs only 12 Newton-Raphson teratons compared to 42 needed by explctly coupled smulator. Explct method does not converge for tme step > 2x10-3 days, however, mplct s stable for tme steps beyond 1 day 1 12

13 New THMC modelng capabltes n FEHM enable comprehensve modelng of n stu converson processes Ø New thermal-hydrologcal-mechancal-chemcal (THMC) capabltes have been developed n FEHM to numercally smulate n stu converson processes Ø Some THMC modelng capabltes extensvely benchmarked aganst CMG s STARS and Abaqus Ø Implct-couplng between flow and mechancs crtcal to model steep changes n propertes, especally for commercal scale smulatons. Ø Future developments nclude: - Extend the mplctly coupled code to multphase flow accountng for kerogen converson - Extend mplctly-coupled code to account for plastc deformaton 13

14 Acknowledgments Ths work was conducted under the collaboratve research and development agreement between LANL and ExxonMobl URC The mplct-couplng capablty developed n FEHM was funded through US DOE s Carbon Sequestraton Program ExxonMobl Ol Shale Team: Sandra Hopko, Mchele Thomas, Wllam Symngton, Mchael Ln, and Pengbo Lu LANL Ol Shale Team: Chrs Bradley, Doran Greenng 14