This paper reports the field results obtained from application of a system that provides both pre-job modeling capabilities and real-time monitoring of maximum stress levels in the entire intervention stack, from the wellhead to the injector assembly.In addition, the paper documents the dynamic movement capabilities recently incorporated in the model and validation of the model calculations. Introduction Reference 2 discusses an intervention riser safety system which has become known as the ? (Zeta) Safety System.This paper documents further development and testing that has been done with this system.The system is composed of two basic components:?model - a numerical dynamic simulation model which models the stresses in an intervention stack.?gauge - a lubricator spool, instrumented with fiber-optic strain gauges, is placed in the intervention stack. It measures axial force, internal pressure, and bending moments in the spool. The initial coiled tubing (CT) field application of this safety system was performed to satisfy several primary objectives, including:Validation of modeled calculations versus field data measured by independent devicesSensitivity of the field stress measurements provided by the systemConfirmation that system design and calibration is sufficiently robust for routine field applications The ability to accurately model dynamic movement of two independent structures was driven by increased utilization of floating structures (TLPs and Spars) being deployed in deepwater projects.The tethered topside structure typically exhibits some amount of horizontal displacement in a figure-eight pattern as a result of wave motion, with the wellhead exhibiting a similar displacement pattern but with differing frequency and amplitude.The intervention stack may experience increased stress levels when each end of the rigid lubricator/riser assembly is attached to these two independently-moving bodies.A dynamic modeling capability incorporated in this model addresses these field conditions. In addition, offshore intervention stacks are becoming taller to accommodate offshore floating structure size, and often pass through multiple deck surfaces that constrain lateral stack movement.This can create a condition whereby conventional safety limits are exceeded.While counter intuitive, removal of lateral stack constraints may actually increase the safety of a given stack.Another finding is that the maximum stack stress may occur in situations where no CT hanging weight is applied to the stack. The pre-job modeling capabilities of the system are used to optimize intervention rig-up design and to determine the probability of exceeding pre-set safety limits during the operation.During the field operation, real-time stress values provided by the system enable informed decisions, rather than a judgment call, to be made if maximum stress levels are approaching unsafe limits.
TX 75083-3836, U.S.A., fax 01-972-952-9435.Abstract: Reverse circulation has always been viewed with some level of suspicion and reverse circulation with coiled tubing has often been avoided at all costs. Yet, results of over 1600 CT operations involving reverse circulating in Alaska's oil fields, with just a handful of failures, has proven reverse circulation to be a reliable procedure for a specific range of solids removal that is extremely effective in removing sand fill from wells with very large tubulars and in high deviations. Results from North Sea, Colombia, California and the US GoM are also included. This paper presents the basics of reverse circulation designed specifically for coiled tubing; including necessary surface equipment, BHA nozzle design, pump requirements, fluid rates, and procedures to reduce the potential for problems. The procedures and job overviews contained here were contributed during an ICOTA panel discussion on reverse circulating, held September 18, 2003, in Houston, TX.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA Tapered OD Coiled Tubing System (TODCTS) enabling the deployment of multiple outer diameter (OD) coiled tubing sections in a single string is being developed. 1 By employing larger OD tubing sections near the top of the string and smaller OD sections near the bottom of the string, the tension along the string length is reduced while maintaining sufficient flow capacity for well intervention operations. The TODCTS can enable intervention service in deeper wells or installation of multiple OD velocity strings with the diameters optimized based on well production requirements. This paper describes the development plan, system and component design, and the results of analyses and tests conducted to verify that the the tapered connector and surface equipment meets the requirements necessary to deploy the connector and adjoining strings of different ODs.
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