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A metal-to-metal sealing expandable liner hanger (ELH) was designed for high pressure/high temperature (HPHT) applications [1]. It has been proven to be very robust for geothermal applications in deep well simulator testing, with temperatures up to 575°F. A potential scenario when using this ELH for geothermal applications is that fluid could be trapped between the expanded hanger and casing ID. The trapped fluid can induce a pressure change from a significant temperature rise because fluids typically have much higher thermal expansion coefficients than metals. When the temperature rises, the trapped fluid can generate significant pressure between the hanger and the casing. On the other hand, the volume change on the cavities can reduce the trapped pressure if the temperature change is not large enough and may help to increase anchoring capacity. The full fluid-structural interaction needs to be considered to accurately evaluate the effect of trapped fluid on expandable liner hanger performance. This paper illustrates how a surfaced-based fluid cavity finite element model can be utilized to simulate fluid-structural interaction between the structure and the trapped fluid [2, 3]. The model accounts for the coupling between the deformation of the surrounding structure and the pressure from the trapped fluid acting on the structure. This methodology was applied to investigate the effects of trapped fluid on the ELH performance when subjected to high pressure/high temperature applications. With a specific well condition in consideration, it was observed that: 1) the pocket (cavity) pressure after expansion was lower than the hydrostatic pressure, as per design intention; 2) the net effect was that the hydrostatic pressure squeezed the hanger which improved the ELH hang weight capacity. In the extreme well conditions where the trapped fluid pressure may reduce the hanger anchor capacity, a novel design concept was developed to mitigate trapped fluid pressure effect. |
