Stuart R. Keller

Improved Method for Use of Chelation to Free Stuck Pipe and Enhance Treatment of Lost Returns

This paper describes how intentionally increasing the permeability of a non-aqueous fluid (NAF) filter cake can enhance treatments to free differentially stuck pipe and recover from lost returns. NAFs are well known for their ability to deposit thin, low-permeability filter cakes that reduce the risk of differential sticking. Yet, differential sticking still occurs and techniques to free the pipe have largely been ineffective. In addition, lost returns in NAF continue to be one of the industry’s most difficult and expensive problems to solve. The operator has developed an improved technique to increase the permeability of a NAF filter cake. The technique involves locally soaking the cake using a combination treatment that first conditions the cake and then removes a significant amount of the weighting material. Laboratory experiments have shown the technique can increase cake permeability by more than 850 fold. There are at least two applications for this treatment. In the first, a pill is spotted across pipe segments (e.g., drill collars) believed to be differentially stuck. By increasing the cake permeability, pressure is allowed to penetrate the cake underneath the pipe, allowing it to more easily become free. Dissolving barite also reduces the shear strength of the filter cake, which may also facilitate freeing stuck pipe. A second application is to enhance the performance of high fluid loss lost circulation material (LCM) treatments after NAF has damaged the fracture face permeability. Increased permeability enhances loss of the LCM carrier fluid and development of the immobile mass required to stop the growth of the fracture induced during lost returns. Formation integrity can then be rebuilt using rock mechanics-based