Cyclic Loading of a Rock Mass for Underground Gas Storage Applications

The use of Underground Gas Storage (UGS) is expected to increase considerably in the near future due to various factors. Many of the UGS wells require sand control. Expandable Sand Screens (ESS) have many advantages as a completion option in UGS wells. But there has always been a concern on the effects on ESS due to cyclic loading. The paper deals with the changes in the borehole that would be caused during annual injection and production cycles from the storage reservoir. Specifically, the interest is in whether or not the deformation levels out to a constant or whether the damage continues evolving. Cycles can be either annual (production in winter / storage in summer) or far more frequent due to Peak shavering (production to cover peak usage, followed by top-up). Abaqus/Standard FEA Numerical modelling has been carried out on a rock sample with an 8.5" diameter wellbore that is lined with a 7" Expandable Sand Screen. The ESS was represented by a simple representation, a plain pipe, rather than a fully slotted system. The rock material has been assigned properties which weaken due to continuing cycles. Stresses were cycled to simulate a great number of years production and injection. The deformation of the ESS stabilised after a number of years. This shows that ESS is a viable completion option in UGS wells.