Out of the Box or Back to the Basics: A Case History of Retrieving Stuck Coil Tubing

Abstract

Abstract A high-profile and major contributor exploratory well was at the verge of being a work-over candidate due to badly stuck coil tubing (CT) inside wellbore during routine well intervention operations. The situation got even worst when pin hole was established in CT string inside wellbore. The conventional and primary mechanism to release such CT is to operate hydraulic disconnect, which is an integral part of bottomhole motorhead assembly (MHA), by means of applying desired differential hydraulic pressure however, presence of pin hole restricted the desired differential pressure to communicate at motorhead assembly and to operate it. This work highlighted the importance of "back to the basics" phrase when conventional operating procedures failed to be executed and hence termed as "out of the box solution for coiled tubing retrieval". The method proposed in this work can be used by oil and gas professionals as the last resort to retrieve stuck coil tubing with complications like pin hole and failed hydraulic activation mechanism which will certainly avoid major cost exposure and operations complexities associated with rig assisted work-over. In order to activate the hydraulic disconnect inside motorhead assembly of stuck coil tubing, depth of point of communication was estimated, inside volume of coiled tubing upto point of communication was calculated, additional pressure requirement to operate motorhead assembly was identified and heavy mud was pumped at a very slow rate in order to create hydraulic imbalance across coil tubing. Additional pressure due to hydraulic imbalance across coiled tubing was not sufficient to operate motorhead assembly therefore once the heavy mud reached point of communication; by calculation; high pressure pumping was performed in order to give high pressure pulses to motorhead assembly with a hope to activate and release it. All the theoretical calculations and planning based on above went as per plan and coiled tubing was successfully released. The proposed principle of stuck Coil Tubing retrieval is new to oil industry as no literature has been found related to it. It not only saved a high profile well from expensive work-over operation but also the reputation of the exploration and production and service companies involved. The novel approach presented in this paper is inherited from the concepts of fluid mechanics and has been successfully implemented. This methodology has all the merit to be included in the International Well Control Forum (IWCF) as the well control methodology for the stuck coil tubing with pinhole deeper into the well.