This document summarizes a presentation on evaluating geothermal formations. It notes that while the Netherlands produces significant energy from gas, reserves are declining so geothermal is an important potential replacement. However, geothermal prospects are less explored than gas-bearing areas, leaving greater uncertainty. Detailed logging can identify productive fracture zones within wells, allowing optimized completions. Well steering guided by logs may increase production by targeting thicker reservoir sections. Simulation shows a 5% increase in net-to-gross or permeability from such practices could yield hundreds of kilowatts more output. Further formation evaluation applying oil and gas principles could better characterize geothermal reservoirs.

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Geothermal Formation
Evaluation
November 30, 2018
3rd TU Delft Geothermal Get Together
Tom Bradley, Senior Geoscience Advisor
Baker Hughes, a GE Company
Tom.Bradley@bhge.com

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The Future in the Netherlands
November 30, 2018 2
• We produce and use a lot of energy, much of it gas
• Groningen is closing with 50+ years reserves still left in ground
• We need to replace that energy
• Dutch government push for renewables, including geothermal
• Currently 18 geothermal projects
• Potential for 700+ projects in the next 30 years

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A Geothermal Doublet – What’s Important?
November 30, 2018 3
Property What do we want? Why?
Temperature Higher is better More heat produced
Permeability Higher is better Greater flow, more heat production
Effective porosity Higher is better More surface area, more heat transfer
Fractures More open fracturesis
better
More surface area, better permeability, greater flow, more
heat
Is there anything else?
Property Why?
Lithology and geochemistry Different lithologies behave differently with injection = scaling potential,
pore plugging
Formation water Dissolved solids, scale (radioactive?) and corrosion
Formation and reservoir
structure
Is the well in the optimal position? Better location = better flow = more heat.
Is the injected water going where you think it is?
Geomechanical properties Rock strength, fracture strength. Subsidence and seismicity, wellbore
stability
And more?……… What else don’t we know?

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How Well Do We Know The Subsurface?
November 30, 2018 4
NLOG Database
• Record of all subsurface information in NL
• All data older than five years in public
domain
• Very comprehensive database

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How Well Do We Know The Subsurface?
November 30, 2018 5
NLOG Database
• Record of all subsurface information in NL
• All data older than five years in public
domain
• Very comprehensive database

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How Well Do We Know The Subsurface?
November 30, 2018 6
NLOG Database
• Record of all subsurface information in NL
• All data older than five years in public
domain
• Very comprehensive database
• BUT
• Data concentrated in oil and gas areas
• Data in Geothermal plays is rather old
(1900’s to 1980’s) and limited
• Geothermal prospects are ‘dry’ for oil and
gas! No recent exploration or data.
• Lots of uncertainty

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How Well Do We Know The Subsurface?
November 30, 2018 7
Subsurface acquisition – Logging (Wireline/LWD)
• Limited – Gamma Ray, occasionally resistivity, identify formation tops for stopping
• Porosity, permeability inferred from other data – not measured
Well Tests
• Bulk measurement of flow
• Doesn’t say where flow is coming from
What do we acquire today in a geothermal well?
Implications?
• High local uncertainty on formation properties

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Where’s the flow coming from?
November 30, 2018 8
• Fractured carbonate geothermal well –
110m open hole interval
• Nuclear Magnetic Resonance (NMR) and
acoustic logs run in open hole for porosity
determination
• Assumed majority of interval will flow
An Example

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Where’s the flow coming from?
November 30, 2018 9
• Production logs (spinners, pressure,
temperature) run in open hole for flow
identification
• Very few intervals actually flow?
• Why?
An Example

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Minor Inflow through fracture at xx55m
November 30, 2018 10
Borehole
Anisotropy Deep Shear
Imaging
Production logs
20m

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Significant Inflow through fracture at xx35m
November 30, 2018 11
Borehole
20m

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3D near wellbore visualisation
November 30, 2018 12
• Near wellbore visualisation using
wireline acoustic data
• Fracture plane orientation can be
visualised

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Where’s the flow coming from?
November 30, 2018 13
Certainly not the whole reservoir!
• Total well flow coming from only two very short intervals
• Implications?
• Can a more optimal completion be used? – cost savings
• Can the well be steered into the fractured zones? Better production? Economic
benefits?
• What if these two intervals scale up?
• What else? Excess pressure drawdown, solids production, ESP wear?

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Targeting the most productive zones
November 30, 2018 14
• Sand-shale sequence
• Well steered using porosity logs
(e.g. deep azimuthal resistivity,
azimuthal density, Nuclear Magnetic
Resonance)
• Stay in most productive
(porous/permeable) zone.
• Initial target 400m sand (based on
seismic)
• Final achieved sand 460m
15% increase!

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Can steering a well really give value?
November 30, 2018 15
DoubletCalc Example
• TNO example DoubletCalc scenario
• Base case calculation – 0.8 net to
gross
• What if we steered well to improve
net-to-gross by 5%?

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DoubletCalc – Base Scenario
November 30, 2018 16

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DoubletCalc – 5% increase in Net to Gross by Steering
November 30, 2018 17

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5% Net to Gross increase = 440kW (5.3%) power increase at P50
November 30, 2018 18
8.33 MW 8.77 MW
+500kW = ?

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Not Just Net-to-Gross
November 30, 2018 19
5% increase in permeability gives further 300kW output
9.07 MW

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Conclusions
November 30, 2018 20
• Current application of FE to Geothermal is limited
• Well established O&G FE principles equally applicable to Geothermal
• Additional direct measurement of certain key properties would be very beneficial
• Potential to increase heat production and cost savings through efficiency of prospects