Rotary Drilling at st1 Deep Heat

By Peter Malin, SMU Adjunct Faculty

Peter Malin, an Adjunct Faculty in the SMU Huffington Department of Earth Sciences provided this update on the st1 Deep Heat project in Espoo, Finland.  Peter’s company Advanced Seismic Instrumentation & Research (ASIR) is providing seismic monitoring for the project.

In September 2017 drilling recommenced on the st1 Deep Heat Project in Finland.  Well OTN-III, which had been drilled to 4,500 m using air drilling, switched to water drilling.   Over the course of 60 meters, 3 drill bits were consumed.  The decision was made to switch to rotary drilling.  Rotary drilling commenced and a “J” incline to 35° began.

Aerial photo of st1 site with drilling rig in the center.
Aerial photo of st1 site with drilling rig in the center.

At 5,020 m, with an inclination of 20°, a fault zone was encountered.    The fault zone caused a 3 week delay in drilling as the drill bit became stuck several times.  After the drill bit was freed the first time a Jar device was attached to help release the bit on subsequent occasions.  During this process the well was cemented and re-drilled at least 6 times.

During one of the recovery efforts for the drill bit an earthquake occurred.  The ASIR team recorded the earthquake on their subsurface equipment with a magnitude of -0.8 to -1.

Map of the st1 site with seismic stations shown as dots. Star is the drill site.
Map of the st1 site with seismic stations shown as dots. Star is the drill site.
Seismic event at st1 following a "Jarring", magnitude about -1. About 1 second of 3 component seismograms, vertical, east and north for the following stations: RUSK, LEPP, ELFV, TVJP, MUNK.
Seismic event at st1 following a “Jarring”, magnitude about -1.  About 1 second of 3 component seismograms, vertical, east and north for the following stations: RUSK, LEPP, ELFV, TVJP, MUNK.

After making it through the fault zone, rotary drilling continued.  The well is currently at 5,200 m with an inclination of 30°.

The next step is logging of the well from 3,500 m to 5,200 m followed by continued drilling at the 30° incline.  The goal is to drill to 6,200 m.  Stimulation at 6,200 m is scheduled for December 2017 or January 2018.

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