Stress Concentration in Wellbore Zones at Underground Gas Storages
A. M. Svalov
Institute of Oil and Gas Problems, Russian Academy of Sciences, Moscow, Russia
Keywords: Underground gas storage, cement lining, destructive stress, wellbore reaming, spring centralizer
Abstract
The author studies stress concentration in wellbore zones during operation of underground gas storages. Numerical modeling yields that at the early stage of high-pressure injection of gas in underground gas storages, near the roof of a productive stratum, in rocks and in the cement lining, destructive shearing stresses arise, comparable with the injection pressure, which can induce the loss of tightness in the annular space. For preventing the loss of gas, it is proposed to ream the wells in the roof of a productive stratum and to install a spring centralizer at a certain place in the casing string. The nominal diameter of the centralizer should exceed the wellbore diameter. This can stop propagation of cement destruction. For decreasing the destructive stress intensity, it is advisable to round off corner zones while reaming within the interval of a productive strata.
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