THE EFFECT OF IMPOSED ELECTRICAL-CURRENT ON TORQUE RELEASE AT THE METAL-MUDCAKE INTERFACE

Differential sticking arises in drilling operations when the drillstri ng embeds into a layer of mud on the borehole wall. The present work i s aimed at proving the concept of an unconventional method of releasin g the drill string, namely, the application of an electrical current. An instrument has been designed and constructed to measure the slippag e torque at the interface between a steel disc and a filtercake prepar ed from a model aqueous drilling mud. Experiments have demonstrated th at a cathodic current of 1 mA cm(-2) reduced the slippage torque by ab out 50% with both mild and stainless steel. The same effect was obtain ed galvanically, using a magnesium sacrificial anode connected to the steel, thus dispensing with the need for an external power source. It is hoped that this effect could be used to inhibit differential sticki ng in aqueous drilling muds, as well as offering a fast method of stuc k pipe release.