A laboratory method of freeing differentially stuck pipe with shear has been used to rank different mud types. This highlights the effect of minor changes in mud chemistry and enables speciality additives such as lubricants to be assessed. The influence of mud type, mud circulating conditions and time of filtration on sticking tendency is also discussed.
Tests reported here were carried out at a pressure of 100 psi and ambient temperature. A new apparatus which more accurately simulates downhole conditions has now been constructed.