A Comprehensive Review of Differential Sticking, Spotting Fluids, and the Current Testing and Evaluation Methods

Summary Differential-pressure pipe sticking is one of the biggest problems encountered during drilling and also one of the leading causes of high nonproductive time. It usually occurs in permeable or depleted formations due to the cession of drillstring movement to connect a new pipe, make a trip, overcome a drilling problem, etc. As the drillstring becomes stationary, it gets embedded into the filter cake because of the pressure difference between the formation and the wellbore, and also due to the high filtration in the presence of a high permeable zone. The sticking bonds created in the pipe/filter-cake interface due to the combined action of adhesive and cohesive forces acting in the vicinity of the sticking zone prevent any movement of the drillstring in the wellbore. Therefore, the driller is unable to rotate or reciprocate it without releasing it by mechanical or chemo-mechanical actions. The industry uses various spotting fluids to recover a differentially stuck pipe as soon as possible as any delay may lead to an increasingly complicated rescue operation with the possibility of abandoning the well in extreme conditions. Therefore, the selection of a suitable spotting fluid that is compatible with a particular mud composition is very important to improve the success rate of a rescue operation. Use of an incompatible spotting fluid, instead of helping in recovering a stuck pipe, may lead to disastrous conditions. There are other factors that can aggravate the recovery of a stuck pipe significantly. Therefore, understanding the root causes of this problem, the conditions that lead to this problem, and the working mechanism of various spotting fluids along with their application domains, are very important for prevention, remediation, and improving the ease of recovery of stuck pipe. This paper provides a comprehensive review of pipe sticking problems with emphasis on differential pipe sticking encountered while drilling and the various spotting fluids used to recover a stuck pipe. The paper further discusses the current testing and evaluation methods used for screening, testing, and evaluating spotting fluids to select the superior and reject the inferior along with their advantages and disadvantages. Finally, a recommendation is made to improve the testing and evaluation method and overcome the limitations of conventional methods and apparatus.