Challenges of Traditional Premium Connections for Geothermal Wells
Governments around the world are addressing climate change by focusing on setting and achieving net-zero carbon emission targets. Green energy plays a key role in achieving those targets.
One technical option has the potential to provide a vast amount of energy with very low environmental impacts: geothermal wells.
But there are significant challenges. Creating high amounts of energy from geothermal resources often requires high temperatures. These resources are known of its high corrosive environments. The resulting harsh environment in high-temperature geothermal wells can pose a significant challenge to casing integrity.
Traditionally, casing strings are one of the most important barriers supporting the wellbore. However, casing strings are particularly vulnerable to damage in these harsh environments. Casings are exposed to complex combined loading conditions such as axial load, and internal and external pressures.
For geothermal wells, the casing is not only exposed to traditional loading, but they are also exposed to thermal stresses. These stresses cause degradation of mechanical properties of casing materials at elevated temperatures.
As a result, designing casing strings specifically for geothermal applications becomes increasingly complex.
C-FER Yourself
Learn more about this topic in the paper, “Feasibility Study of Premium Casing Connection with Titanium Alloy for High-temperature Geothermal Applications,” developed for the 2022 SPE Thermal Well Integrity and Production Symposium.
The paper provides a reference for high-temperature geothermal and thermal well operators who are considering alternative materials to improve casing integrity.
Alternatives to Oil Country Tubular Goods (OCTG) Materials for Geothermal Applications
Titanium alloys have been shown to have great corrosion resistance in geothermal wells. However, there hasn’t been much investigation of the structural performance, and sealability of titanium alloy casing connections. C-FER Technologies used Finite Element Analysis (FEA) to conduct an engineering feasibility study to evaluate the sealability of a premium casing connection with a proprietary titanium alloy material. For this study, coupon tests were performed to characterize the temperature-dependent mechanical response of the titanium alloy. C-FER then applied thermal cycle loading commonly found in geothermal well conditions to the FEA model to quantitatively evaluate the connection sealability performance. The titanium alloy connection model was then compared to the same connection design with L80 material that was previously qualified by full-scale physical testing.
How did the titanium alloy connection measure up?
The titanium alloy connection showed a much more stable sealability response when compared to the L80 connection throughout the thermal cycles. This superior performance was primarily attributed to the:
- elastic response of the pipe body,
- relatively low thermal stress, and
- minimal plastic deformation within the connection.
Preliminary physical make-and-break test results were also shown to demonstrate the galling resistance of several connection types made of the titanium alloy.
What’s next for titanium alloy connections for geothermal applications?
The engineering study established a strong technical basis for further development of casing and premium casing connections with titanium alloys for challenging high-temperature geothermal well applications.
Based on the learnings and outcomes of this study, C-FER recommends the following next steps for further designing and qualifying titanium alloy premium connections:
- Advanced coupon tests to establish an in-depth understanding of the effect of strain rate on the mechanical properties of the titanium alloy.
- A carefully designed and executed full-scale connection test program to evaluate connection performance in terms of galling resistance, sealability and structural capacity for geothermal applications.
Kelly Piers, MSc, PEng.
Principal Engineer, Business Development & Strategic Initiatives
Kelly Piers is a Principal Engineer at C FER Technologies. In this position, Kelly works on strategic and business planning for C-FER and focuses on identifying, developing and implementing C-FER’s strategic diversification objectives, working with a number of industry associations in Alberta and across Canada.
