Stuck pipe caused by differential sticking in horizontal wells is a problem that can result in the loss of tools in the hole, non-productive time (NPT), side tracks and even total loss of the well, with the consequence of significant cost increase for wellbore construction.
A differential pressure that pushes a drill string into the filter cake of a permeable formation causes differential sticking. It is typically remediated by pumping spotting fluids that are designed to break down the filter cake and reduce the bond between the filter cake and the pipe.
When drilling heavy crude oil reservoirs, conventional spotting fluids often fail to free the stuck pipe, because the filter cake is covered with heavy crude oil, which prevents the spotting pills from achieving good diffusion through the filter cake.
Additionally, these conventional spotting pills contain solids that cannot be easily removed from the production section when the well begins production.
Eventually, the solids would damage to the formations of interest. For this reason, a viable alternative was evaluated that could effectivety remove differential stuck pipe, and minimize potential formation damage.
To achieve this objective, a spotting fluid was formulated with a surfactant package that produces very low interfacial tension, enables high oil-cleaning capacity and easily removes heavy crude oil. This formulation is a solid-free fluid, formulated without acid. The mechanism to eliminate the bond between the pipe and filter cake is a diffusion process and solubilization of the heavy crude oil into the microemulsion, leaving the filter cake very porous, achieving quick release of the stuck pipe string. The fluid is mixed at the rig, using conventional equipment, and pumped downhole using standars rig pumps.
This paper discusses the use and operational procedures for application of this novel spotting fluid for cases of differential sticking occurring while drilling heavy crude oil reservoirs. Currently, the new spotting fluid has been applied in eight wells, with successful release of differential sticking in the reservoir zones during drilling of horizontal sections.