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Energy Systems Division
Geothermal Materials Group
Sustainable Geothermal Well Cements for Challenging Thermo-Mechanical Conditions
This project is an international effort led by Brookhaven national Laboratory's Geothermal Materials Group. The project is conducted under the umbrella of Cofund GEOTHERMICA
To meet the targets, set in the Paris agreement, fossil fuels need to be replaced with other sources of energy. The supply of energy in the future is anticipated to come from a mix of various renewable sources. IPCC (2012) mentions geothermal energy as an energy source that could provide significant amounts of both electrical energy and heating and cooling (up to respectively 3% and 5% of the global demand in 2050).
By making geothermal wells durable and sustainable, the financial risks are reduced which makes investment in geo-energy more attractive. An important risk that needs attention is the behavior of cements under challenging geothermal conditions including high temperature variations subjecting casing-cement sheaths to thermal shocks, chemically aggressive environments and extreme temperatures of high-enthalpy wells. Expectations of long life-span of geothermal wells require addressing this risk with durable solutions. However, even for intermediate and low-temperature wells, common Ordinary Portland Cement (OPC) - based formulations are known to have problems with strong temperature variations causing severe thermal stresses and strains on cement. This results in cracks formation, which compromises zonal isolation, casing corrosion protection by cement and well-integrity in general. These conditions are specific for geothermal wells, so oil and gas cementing systems cannot be adapted without maturing and qualifying them under conditions of thermal and mechanical cycling loadings.
For extreme temperatures, the OPC-based systems are especially vulnerable to losing their integrity and cement-casing bond (thermal cycling further facilitates cement failure). A common oil-field solution of modifying cement slurries with organic additives to resolve these issues cannot be used under high-temperature geothermal conditions due to the lack of thermal and chemical stability of these additives. In the worst-case scenario failure of cement sheath can result in the loss of a well and significant environmental damage. Good candidates to mitigate possible cementing issues of geothermal wells are superheat- and thermal shock resistant cements (TSRC) as non-Ordinary Portland Cement system for extreme temperatures and temperature variations and an innovative tough OPC-based composite for low-to-moderate temperatures. Unlike OPC, the hydrated TSRC primarily consists of crystalline hydro-ceramic phase and amorphous inorganic polymer phase withstanding a heat temperature of 600oC. The thermal-shock tests demonstrated no noticeable change in cement strength while conventional high-temperature OPC-based samples disintegrated in the first 3 cycles. Furthermore, TSRC modified with self-healing aid showed outstanding strength-recovery properties under hydrothermal conditions at 300oC after imposed damage. Additionally, TSRC is strong-acid- and CO2 -resistant because of its low calcium content and the ability to sequester CO2 into stable crystalline structures.
By joining forces, the consortium will be able to evaluate and mature the available cement formulations to comply with the specific conditions of geothermal operations and to reduce the risks of wells failures. Modelling to obtain expected strains and stresses under the relevant environments and to define required mechanical properties, will be combined with optimization of formulations and extended characterization and evaluation of the cured cements under various temperature regimes. These will include the examination of super-critical temperature exposures and temperature/pressure cycling. To increase the maturity of the optimized composites the project will combine more fundamental small-scale experiments with large scale tests under relevant condition and numerical modelling. Where possible commercial products will be included in the research for comparison.
The TEST-CEM consortium combines scientific expertise with world-class experimental facilities and industrial partners that can provide an industry perspective. The involved research institutes have a long track record of working with cements for well engineering applications and bring in experience and expertise on the subjects to the project. Additionally, some of the experimental facilities that they have are unique and enable to significantly increase products maturity in a relatively short project. All partners have experience with international research projects which enables an effective collaboration to meet the objectives.