Incoherent results of in-situ stress measurements and their implications in designing a crude oil storage caverns project are presented in this paper. Core-discing at depths corresponding to abnormally higher stress magnitude values were observed at the project site. It is brought to the notice that an optimistic assessment of in-situ stresses may result into costly design surprises during the excavation stage. Consideration of incoherency in the computed in-situ stress magnitudes and orientation resulted into lowering of the caverns level farther 5m from the surface than the design requirements as per the storage pressure. The paper also briefly outlines the project settings, fundamentals of crude oil storage projects in unlined mined caverns and in-situ stress measurements using hydro-frac technique. Impacts of in-situ stress regime on the caverns design is evaluated by using numerical modeling for which plain strain numerical models are prepared using a general purpose finite difference code, FLAC3D.
Indian economy is growing at a rapid scale and a growing economy has put pressure for increase in consumption for petroleum products. Majority of the Indian refineries are situated in congested urban sprawl above surface level where hardly any land can be spared to accommodate modern processing plants with higher storage capacities for crude and finished petroleum products. M/S Hindustan Petroleum Reserves Limited (HPCL), Mumbai has thus planned for storage of crude oil and finished products in unlined mined caverns at a floor depth of 55mfrom surface level with a planned capacity of 1.05MMT in 1.9 km long 11 caverns. The study conducted for requisite design by Central Institute of Mining & Fuel Research (CIMFR), India comprised of core drilling and logging, geophysical investigations, in-situ stress measurements, laboratory testing and numerical modeling to design the underground storage facility in unlined mined caverns.