Geothemal energy is used for heating, cooling or conversion to other energy sources. This geothermal energy is obtainable near the earth surface in places like Iceland or New Zealand. However when not readily available one has to drill into the earth crust to reach for this energy. The deeper one gets the higher the water temperature and, due to the hydrostatic force, also the higher the pressure. Temperatures of up to 300 °C and pressures over 1000 psi may be encountered in practice.
In order to be able to extract the energy (heat) in an economical effective way, it is essential that in the underground layers a circulation of water over large distances can be established. Only then the water will be heated to sufficient high temperature without (premature) cooling of the well. For this it is required to inject and extract the water in and out specific selected (porous) geological layers or fractures. This can be done by using a technique which is also used in the oil- and gas industry under the name of “zonal isolation”. This is however, using conventional techniques, a very costly operation. By applying elastomeric seals, these costs can be reduced significantly. However, the extreme conditions for high performance geothermal applications are at the edge of what technological can be accomplished using elastomers. This requires an optimal design of the seals. A typical elastomeric seal consists out of layers of elastomers with different properties. Density, strength, moduli are a few examples of the parameters that vary between the layers. It is important to have a clear understanding of the effects that the external forces have on these multi-layered systems in order to be able to optimize the design.
The goal of this study is to develop a Finite Element Model (FEM) of a typical seal that can be used as a tool in the optimization process of seal design and compound development.
The graduate student will identity and investigate all relevant parameters. Relevant for the mechanical modelling of the functioning of the seal as well as relevant for the model as a tool in the design optimization process for which it is meant to be used:
- Investigations into properties of multi-layered rubber
- Investigation into geometrical shape(s) of activated seal
- Investigation of load case
- Investigation of fail mechanism
- Analyses of the design optimization
Fig. 1 Typical seal configuration
On basis of the collected data the graduate will define a typical seal configuration with the basic load model. On basis of that a FEM model will be established by which the design and material development can be optimized with respect to the mechanical performance of the seal. The model should :
- Describe the distribution of the relevant forces in relation to the applied pressure difference over the seal on bases of a typical seal geometry and given material properties
- Describe the deformation of the seal in relation to the distribution of these forces
- Calculate the maximum pressure difference the seal can withstand given specific material properties
The maximum pressure difference the seals can withstand can be tested (at elevated temperatures) in the Pressure Integrity Test (PIT) unit at Ruma. This allows for partly validation of the FEM model. The graduate will determine the seal configuration that will suite this purpose best and determine the test conditions. Ruma will perform the test and supply the test data.
The graduation report should contain clear an precise description of the:
- The mechanical modelling the FEM model is based upon
- The assumptions, simplifications and limitations that are applicable
- The accuracy, reliability and limitations of the FEM model as a design tool
A preliminary planning for the work described above is given in fig. 2. This planning is based on a nine month graduation project. If necessary the planning can be shortened by omitting the validation testing part.
Define typical seal configuration with basic mechanical load model
Establish FEM model
Define validation test
Evaluation and report
Fig. 2 Estimated planning of the project