| Title | Modeling of Coupled Flow, Heat and Mechanical Well Integrity During Variable Geothermal Production |
|---|---|
| Authors | Jonny RUTQVIST, Lehua PAN, Mengsu HU, Quanlin ZHOU, Patrick DOBSON |
| Year | 2018 |
| Conference | Stanford Geothermal Workshop |
| Keywords | Modeling, well integrity, thermal expansion, variable production, thermal pressurization, stress |
| Abstract | We investigate the effects of steady and variable geothermal production on mechanical well integrity issues using coupled modeling of flow, heat and mechanical responses in the well assembly. The coupled modeling is based on linking the T2Well reservoir-wellbore simulator with the FLAC3D geomechanical simulator and a detailed discretization of the well assembly, including casing, cement, wellbore, host rock, and their interfaces. We tested the applicability of this model by conducting a series of simulations of generic steam-dominant and liquid-dominant systems of both steady and variable geothermal production. The modeling shows that the highest thermal perturbation, ∆T, occurred in the case of a steam-dominant system in the shallow formations beneath the ground surface near the production well. In this zone, the temperature increases quickly with production, and decays quickly when the production rate is reduced during variable or flexible-mode operation, with the highest cyclic increase and decrease of temperature. Moreover, temperature increases in the cement behind casing causes pressure increases due to thermal pressurization. These temperature and pressure changes can cause non-linear mechanical responses that are dependent on the thermal expansion of the different components of the well assembly and include effects of potential frictional sliding at interfaces and material yielding. In the current analysis, we found that temperature changes during the initial start-up of production could cause cement failure in the shallowest parts of the well both in tension and compression. The coupled T2Well-FLAC3D model can be applied to better quantify these effects for safe and sustainable production, both for base-load and flexible production modes. |