A New Approach to Monitor Tubing Limits

摘要

This paper presents a new approach to monitor coiled tubingrntension and pressure limits during operation. Thernconventional way to monitor the tubing limits in real time isrnthrough monitoring the section right below the stripper. Itrnworks well for a single-wall tubing string operating in arnshallow well with low wellhead pressure. For high-pressurernwells, deep wells or high deviation wells, this becomesrninadequate because the critical section may not be at thernsection below the stripper. Instead of monitoring the tubingrnlimits at a specific section (such as the section below thernstripper), the model presented herein dynamically tracks andrnmonitors the critical section of the tubing during operation.rnOur approach starts with a new way to express the tensionrnand pressure limit curve of the coiled tubing. The use ofrneffective force to generate the limit curve facilitates the task tornidentify the critical section of the coiled tubing duringrnoperation. To identify the critical section, the distributions ofrntubing force and pressure difference along the coiled tubingrndownhole are calculated during the operation. Thisrninformation is used to calculate the safety factor along therncoiled tubing string, from which the critical section isrnidentified. A software based on this approach has beenrndeveloped, which allows operators to dynamically track andrnmonitor the critical sections during operation. By couplingrnwith surface measurements (such as ovality) in real time, itrnsignificantly improves operators’ ability to monitor tubingrnlimits.