ABSTRACT:

Rock salt formations are a common reservoir seal worldwide with excellent sealing capacity. Restoring the sealing capacity of rock salt caprocks penetrated by wells using the same rock salt as plugging material is therefore an attractive, safe and environmentally friendly option. The concept is based on the removal of a section of casing over a part of a formation consisting of rock salt and creation of a sealing well barrier (plug) by the creep of rock salt. Geomechanical numerical simulations were conducted to estimate wellbore closure times for a range of conditions representative of the Zechstein evaporites overlying Rotliegend reservoirs in the Northwestern Europe. Results showed that the salt creep largely depends on the salt properties, differential stress and in-situ temperature. Estimated closure times of a reamed interval, for the maximum underbalance, were in the range of a few weeks for a depth of 3100 m, a few months for a depth of 2500 m and a few years for a depth of 2000 m. Reamed intervals should be at least 10 m long to avoid slowing down the process of creep that occurred for shorter reamed intervals.

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