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Technical Committee Production Engineering

Workover fluid for lowered reservoir pressure: Requirements on elasticity, rheology and phase behaviour of a liquid crystalline surfactant plug for the shut off of boreholes - Feasibility study -

In this work we consider the possibility to shut off a gas well for workover by using a surfactant liquid crystalline phase as a plug. The requirements concerning the structural stability and the phase behaviour of the surfactant system are exposed and are compared with known experi-mental facts.

These requirements and the expected behaviour of surfactant liquid crystals are discussed in detail for the operational steps which are involved. This covers the filling of the borehole with a flowable surfactant phase and its possible invasion into the formation, the conversion into a liq-uid crystalline plug, its subsequent loading with a water column in the borehole, and the removal of the plug after the workover.

To apply this method, a series of open question would have to be settled experimentally. The largest obstacle, however, are the low yield-stress values which have been measured for sur-factant liquid crystals so far. They fail to meet the requirements by at least one order of magni-tude. Using such systems to improve the water-sealing properties of a chalk-plug has a good chance of success.

Th. Hofsäss
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