How to Keep Tubing Sealed in Packers

Abstract

In many oil, gas, and injection wells. a string of tubing, sealed at itslower end in a packer, is used to isolate tubing pressures and fluids from thecasing. In multiple completions, two or more tubing strings are used to isolatezones. This paper presents a means of determining the best way to initiallyland the tubing in the packer to compensate for future anticipated wellconditions. The equations in this paper were developed in a previous publication andhave been successfully applied to over fifty critical wells in the UnitedStates, Canada, and Europe. Many of these were deep, high-pressure, high-temperature, high-cost wells in which it was imperative that atubing-to-packer seal be maintained during all completion, remedial. andproducing operations. In some of these wells, it was important to keep thetubing as straight as possible to facilitate future wire line work. The conditions of these wells have been grouped and tabulated so the readercan see some of the practical applications of the paper. Introduction The bottom of a string of unanchored tubing in a rod-pumped well moves up onthe upstroke and down on the downstroke. In addition, the tubing graduallyelongates until the well reaches pumping equilibrium. Disregardingrod-to-tubing friction, vertical movement is caused by pressure and temperaturechanges acting on the entire tubing string. Knowing tubing and casing size, initial and final fluid densities and levels, and initial and final tubingtemperature, it is possible to calculate the extent of these verticalmovements. Rod-pumped wells are generally familiar to the reader and are mentioned herebecause the freely hanging tubing string reacts in exactly the same manner tochanges in well conditions as does a string of tubing sealed, at its lower end, in a packer which permits free seal movement. A packer, however, may be setmuch deeper than a pump, and not only is a longer string of tubing exposed tothese changes but the changes may also be much more severe. Consequently, theamount of vertical movement is usually much greater.

Workflow to Evaluate Maximum Allowable Treating Pressures, Tubing Movement, and Tubular Limits for Deepwater Subsea and Dry-Tree Fracpacks

“…The deepwater fracpack tubing movement is based on a theory that has been used for decades (Logan 1963;Lubinski et al 1962). Injection down the work string and into the formation will change the wellbore pressure and thermal conditions; these circumstances will cause the work string to either shorten or elongate.…”