Prospects for Assessing Enhanced Geothermal System (EGS) Basement Rock Flow Stimulation by Wellbore Temperature Data

Peter Leary, Peter Malin, Tero Saarno and Ilmo Kukkonen
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Peter Leary: Advanced Seismic Instrument & Research, 1311 Waterside, Dallas, TX 75218-4475, USA
Peter Malin: Advanced Seismic Instrument & Research, 1311 Waterside, Dallas, TX 75218-4475, USA
Tero Saarno: St1 Deep Heat Oy, Purotie 1/PL 100, 00381 Helsinki, Finland
Ilmo Kukkonen: Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland

Energies, 2017, vol. 10, issue 12, 1-33

Abstract: We use Matlab 3D finite element fluid flow/transport modelling to simulate localized wellbore temperature events of order 0.05–0.1 °C logged in Fennoscandia basement rock at ~1.5 km depths. The temperature events are approximated as steady-state heat transport due to fluid draining from the crust into the wellbore via naturally occurring fracture-connectivity structures. Flow simulation is based on the empirics of spatially-correlated fracture-connectivity fluid flow widely attested by well-log, well-core, and well-production data. Matching model wellbore-centric radial temperature profiles to a 2D analytic expression for steady-state radial heat transport with Peclet number P e ? r 0 ?v 0 /D (r 0 = wellbore radius, v 0 = Darcy velocity at r 0 , ? = ambient porosity, D = rock-water thermal diffusivity), gives P e ~ 10–15 for fracture-connectivity flow intersecting the well, and P e ~ 0 for ambient crust. Darcy flow for model P e ~ 10 at radius ~10 m from the wellbore gives permeability estimate ? ~ 0.02 Darcy for flow driven by differential fluid pressure between least principal crustal stress pore pressure and hydrostatic wellbore pressure. Model temperature event flow permeability ? m ~ 0.02 Darcy is related to well-core ambient permeability ? ~ 1 µDarcy by empirical poroperm relation ? m ~ ? exp(? m ?) for ? ~ 0.01 and ? m ~ 1000. Our modelling of OTN1 wellbore temperature events helps assess the prospect of reactivating fossilized fracture-connectivity flow for EGS permeability stimulation of basement rock.

Keywords: enhanced geothermal systems (EGS); crustal permeability; finite element flow modelling; crustal wellbore temperatures; wellbore injection; well logs; well core (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2017
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