Design Methodology and Operational Practices Eliminate Differential Sticking

Abstract

This paper discusses a successful initiative begun six years ago to eliminate differential sticking across global operations. In the five year period from 2004 through 2008, there were only 3 differential sticking events in 3,476 wells drilled with the recommended practices. There were an additional 17 sticking events with designs that did not conform to recommended practices, and 14 of these were freed. The drilling environment was diverse. Overbalances in excess of 1,000 to 2,000 psi were common in multi-darcy rock and high angle, and depleted reservoirs have been drilled with overbalance as high as 7,800 psi in vertical wells. The early focus of the Stuck Pipe Avoidance practices was the elimination of differential sticking. However, some level of sticking occurs routinely in drilling operations and these events only become problematic if the force required to initiate pipe movement exceeds what can be delivered to the stuck point. It is now accepted that sticking cannot be prevented and that elimination of sticking is not a proper design objective. The philosophical objective has now shifted from elimination of sticking to "maintaining conditions that allow the pipe to be pulled free," assuming that it will become differentially stuck. The desire to maintain this ability to move the pipe has required the implementation of a range of practices, some of which were not common in the industry. Changes were made in bottomhole assembly (BHA) design, fluid design, real-time cake shear strength recognition, and real-time cake remediation practices. A finite element (FE) model was also applied to redesign new systems or applications that lie outside the operator's previous experience. The stochastic model predicts cake growth and sticking force and the probability that it will be possible to deliver a force that can free the pipe for any given still-pipe time. The model inputs were calibrated through pullout tests with a variety of fluids to determine mechanical cake strength properties, the rate at which those properties develop, changes in the pressure transient through the cake as it matures, and the cake contact areas and geometry at any point in time. Engineering and operations training also contributed greatly and allowed relatively uniform implementation to be achieved across a large, globally diverse operation in less than one year. A small number of non-compliant designs continued to be used and these contributed greatly to the incidence of stuck pipe in the first three years. Last year, there was only one incident of stuck pipe with a non-compliant design. The paper describes the underlying sticking concepts, the engineering design and field practices used, the modeling capability, and the field results.

Mudcake growth: Model and implications

“…This trend resembles earlier experimental studies (Annis and Monaghan 1962, Reid et al 1996, Sherwood 1998). Indeed, minimal time is recommended to reduce stuck pipe complications (Dupriest et al 2011).…”

Using Wireline Standoffs (WLSOs) To Mitigate Cable Sticking

“…For wireline operations, breaking free is provided in the axial direction only, by pulling or jarring. It has been suggested from extensive laboratory tests that material failure commonly dominates the freeing action as opposed to overcoming static friction forces (Dupriest, Jr, & Ottesen, 2011). • is the sum of cake shear strength distribution in 3D (away from the sandface, around the contact arc with the object, and along the object length, if not perfectly parallel to the borehole wall).…”

“…A focus on cable sticking mitigation is therefore warranted, with the goal of minimizing the overall sticking risk, reducing NPT from fishing, and matching the other recent developments and innovations in wireline conveyance. Differential sticking mechanisms and modeling It should be noted at the outset that this paper does not explore the complex science of mud cake generation, composition, and sticking capacity, which has been studied in great detail by others (Dupriest, Jr, & Ottesen, 2011;P. Isambourg, 1999;Reid, et al, 1996).…”

Practical Guide to Lost Returns Treatment Selection Based on a Holistic Model of the State of the Near Wellbore Stresses

“…-Maintain high fluid loss through intense monitoring program. -Employ practices to prevent differential sticking (Dupriest et al 2010). -Barite is the primary blocking agent.…”