//

Subscribe to our newsletter to receive the latest news and events from TWI:

Subscribe >

S4CE Project: Condition Monitoring of Geothermal Casings

Use of Acoustic Emission technology for condition monitoring of geothermal casings subjected to fatigue and fracture loads

Increasing the amount of renewable energy captured from geothermal fields while ensuring the structural integrity of the wells has become very important in recent years. Casings are essentially large diameter pipes that transport high temperature and corrosive geothermal fluids from several kilometres beneath the ground to the surface.

Structural monitoring (SM) of such casings using acoustic emission (AE) methods is very promising, mainly due to the reduced costs and early detection capability of flaws in the casing material.

TWI has been a major partner in a large international consortium involved in the EU-funded Science for Clean Energy (S4CE) project.

Project background
Early detection of initiation and deterioration of defects in geothermal casings in operation can be very challenging with traditional techniques. Difficulty in getting access to the location of the defect, high temperatures and pressures, and the presence of very corrosive environments are all adverse factors. AE can potentially overcome all of these major challenges as it is, in principle, using a microphone attached to the external surface of the casing above the ground to monitor and analyse the sound signals that travel through the material.

Figure 1. Experimental setup of casing under fatigue resonance loading in air with AE monitoring system installed
Figure 1. Experimental setup of casing under fatigue resonance loading in air with AE monitoring system installed

Work Programme
TWI developed an AE system with sound sensors, data logging, and signal analysis software for the detection of crack initiation and propagation in typical geothermal casing material. The material was subjected to fatigue resonance testing (Figure 1) and fracture toughness testing (Figure 2). The main objective was to compare the capability of the AE method of detecting crack initiation and propagation with the traditional fatigue and fracture toughness techniques and associated measuring devices.

For the fatigue resonance testing, a full-length casing was pressurised internally with water. A sharp starter notch was machined on the external surface and cyclic loading was applied at the ends of the casing. For fracture toughness testing, customised single edge notch bend (SENB) specimens were extracted from the casing. The geometry of the specimens was modified using electron beam (EB) welded extensions, in order to allow the attachment of the AE sensors. Single specimen unloading compliance fracture toughness testing was conducted in air at room temperature. Resistance curves were generated showing the toughness of the material as a function of crack growth.

 

Outcome
TWI developed software and analysed the acoustic signals to filter out the “noise” during the tests. The AE method detected both crack initiation and crack propagation events earlier than the traditional strain and clip gauges used in the tests.

 

The S4CE project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 764810.

Figure 2. Experimental setup for validating the AE method using customised fracture toughness testing SENB specimens
Figure 2. Experimental setup for validating the AE method using customised fracture toughness testing SENB specimens
Media /

Related Insights

View all insights
}