Casing Mechanical Response to Reservoir Compaction Induced Loads in a Deep-Water Environment

The impact of the loads induced by reservoir compaction on the mechanical response of the casing were investigated for a study well located in a deep-water environment. The study reservoir is a highly porous sandstone with an average porosity of greater than 30%. A geomechanical analysis was carried out to calculate the compaction and subsidence along the study well due to reservoir depletion, followed by a well structural integrity analysis to assess the risks associated with the additional loads on the casing and completion system from the reservoir compaction. This was done for two cases based on the mechanical properties of the reservoir rocks, i.e. base and high cases. The reservoir compaction and overburden subsidence along the study well were calculated using an analytical approach based on the uniaxial compressibility of the reservoir rock. The loads and strains across each casing section were inferred from the vertical displacement obtained from the compaction and subsidence analysis. These are then compared against the yield strength of each casing section to obtain the safety factors from well model simulations. The minimum safety factors at discrete production time intervals were calculated from iterations of loads acting in each casing section. The results of the casing load analysis show that all sections except the lower completion section for the high case meet the design parameters over the production life of the well. Recommendations to mitigate the risk of lower completion failure are provided in the study. The impact of bottom hole temperature on the load scenarios was also considered. The thermal analysis shows only a slight decrease in the safety factors for each production scenario. The results of the analysis were used to optimize the casing design for the study well targeting a potentially highly compressible reservoir.