The GeoWell project has received funding from the European Union’s

Horizon 2020 research and innovation programme under grant agreement

No 654497

The DEEPEGS project has received funding from the European Union’s

Horizon 2020 research and innovation programme under grant agreement

No 690771

Innovative design of high temperature geothermal wellsIngolfur Thorbjornsson

Head of Geothermal Engineering

Iceland GeoSurvey

Reaching deeper – higher temperatures – harsh chemistry

Simplified model of high temperature system with two feed zones

Temperature rise - thermal expansion

Mitigation of thermal expansion in surface equipment by using thermal expansion loops is common practice in geothermal fields

Designed to prevent damages and displacement of the pipes

Geothermal Well reaching 2-4 km down is drilled and cemented in place – no compensation for thermal expansion??

Same physics applies for materials on surface as downhole

Photo: Gunnar S. Kaldal

High Temperature - Thermal expansion damages of Casing during warm up

Photo: ISOR HS-ORKA Photo: Thorbjornsson

Due to high axial load, the constrained casing either collapse – bulge, or deform locally

And if the need for cooling the well down!

Coupling failures due to high tensile load during cooling from deformed casing segment

Photo: ISOR-IDDP1Photo: ISOR-IDDP1

Flexible couplings

• Allow displacement that compensate for

thermal expansion of the casing

• Stress in the casings will be within the elastic

range

• No plastic strains are therefore generated

• If wells need to be shut-in or quenched with cold

water for maintenance, no axial tension is

generated if the well cools down again

Mitigation

• The Flexible Coupling is designed according to applicable standards, API (American Petroleum Institute) and ISO standards

• Designed with conventional API BTC threads

• Made of L80 material (for K55 and L80 casings)

• Allows clearance for cementing

Flexible couplings

Mitigation

Flexible couplings – function

LT

~12m

• Casings with Flexible coupling are run in hole

with same procedure as normally done

• The couplings remain in their open position

during casing installation

• The gap length LT is fixed for design

temperatures in each case

• When the casing warms up it expands and the

Flexible couplings close without generating

plastic strains in the casing

Main load cases of couplings

• Installation:

• make-up torque

• axial tension (self weight)

• Operational:

• axial compression due to thermal expansion

• axial tension due to cooling

• burst and collapse pressures (radial and hoop loads)

• additional bending

• The Flexible Coupling is designed so that when the casing expands thermally it reaches 70-80% of casing material yield strength without generating plastic deformations

σb-σb

σth

σw

σth

Flexible couplings – Designed and tested

Testing of Flexible Couplings

Testing results:

Tight up to 110 bar (with pressurized water, open position)

Can hold load up to 3000 KN (as build)

Sliding not affected by bending

Sliding force constant with repeatable sliding.

In total 4 full size 9,5/8 Flexible Couplings tested

Photo: Thorbjornsson

Photo: Thorbjornsson

Conclusion

✓ Current design standards for casing design do not prevent plastic deformation of casings due to thermal expansion

✓ Flexible Couplings for high-temperature geothermal wells aim to eliminate these forces by allowing displacement of every casing segment (~12m)

✓ Flexible Couplings have been in development in the EU funded H2020 project GeoWell (and further developed in H2020 project DEEPEGS)

✓ It is our hope that the new solution, Flexible Couplings, can in part solve problems involved in designing and drilling for geothermal wells, conventional as well as high temperatures

Photo: Gunnar S. Kaldal

THANK YOU

www.isor.is