Study, Analysis and Methodology Involved in Frac String Rotation to Minimize the Axial Efforts to Enhance Monobore Completion Integrity and Accessibility to Streamline Frac Operations in Unconventional Wells of Abu Dhabi, UAE

Abstract

The purpose of this paper is to share the results and knowledge learned in implementing new procedure and techniques to rotate the 5-1/2", 26 PPF, T-95/P-110 Frac String (FS) during running into Unconventional wells. Developed by ADNOC Onshore ASR - UC Drilling Department at Abu Dhabi (U.A.E.) the novelty involves six (06) different technologies necessary to minimize axial buckling in the monobore completion while maximizing well accessibility and integrity during the Rigless frac operations. The 6 key enablers technologies employed to rotate the Frac String up to 30,000 pound-ft: Connection: strength to withstand rotation required to release the axial buckling.High Speed Reamer Shoe: open hole debris cleaning / obstruction removal.Bonded Ceramic Centralizers: providing 80% standoff, reducing the friction factor and removing the mud cake with the rotation.Casing Running Tool: designed to wash down and rotate FS during running.Rotating Tubing Hanger: enabling FS rotation using different techniques and design a new mechanism for it after landed and locked into the Tubing Head Spool.Rotating Cement Head: ability to rotate the FS while pumping cement and plugs simultaneously. Because of friction, sliding during running will result in helicoidal buckling of the FS that has a negative knock down effect on later completion operations / interventions and even in some cases not possible to reach the TD. The results of previous UC wells where FS was run in sliding mode revealed issues due to the helicoidal buckling of the FS impairing annulus / cement bond quality, creating tortuosity and altering the Internal Diameter (ID) leading to issues in accessing the well bore with the Plug and Perf tool for the fracking operations. The total depth for standard UC wells ranges from 16,000’ to 23,000’ MD with ± 12,500’ TVD and ± 8000’ MD 8"1/2 horizontal section dipping up to ±92° inclination for production reasons. Such profiles generate Friction Factor (FF) ± 0.5 in Open Hole. Based on performed simulations and depending on the well profile, surface torque required to rotate the string was between 25,000 to 30,000 pound-ft. This paper will describe and provide details on how the FS helicoidal buckling was minimized and its limitations overcome thanks to the six key enablers technologies devised by Onshore ASR - UC Drilling Department. It will also highlight other important added benefits such as mud cake removal, improved annulus geometry and cement bond.