Innovative Retrievable Lock Mandrel Extends Monobore-Completion Potential
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 121548, ’Innovative Retrievable Lock Mandrel Extends Monobore Com pletion Potential,’ by Francois G. Millet, SPE, and Pierre-Arnaud Foucher, Geoservices Equipements; Paul Helderle, E.W.E.; Dedi K. Djunaedi, SPE, Vico Indonesia; and Pierre Petel, SPE, PT Welltekindoo Nusantara, originally prepared for the 2009 SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, The Woodlands, Texas, 31 March-1 April.
Monobore completions are an efficient way to exploit multilayer reservoirs. During the life of a field, targeted layers can be opened or closed to optimize hydrocarbon production and avoid undesirable fluid entry. For these cases, nippleless retrievable bridge plugs often are required to isolate a specific reservoir. However, tools currently available fail as a result of their traditional rubber sealing element. To solve these problems, a tool has been developed that is based on a segmented sealing ring that expands by the mechanical displacement of blocks.
Introduction
Since 1990, tiny pay zones have been produced cost effectively by commingling through cemented liners or tubing perforated “on demand” to optimize hydrocarbon production. Progressively, the conventional landing nipple has been eliminated from completion architecture as the number of producing layers has increased to as many as 70. This evolution also has been motivated by the need for first-class reliable liner cementations with optimal wiper-plug efficiency. This architecture also permits more-reliable exploitation of multizone wells (including high-temperature reservoirs) by avoiding wire tracking of landing-nipple sealbores and rubber-seal-based completion packers.
Sealing-Element Limitations
Many trials of adapting conventional completion packers have been performed, with irregular results. Operators know that all available lock mandrels often fail because of their massive rubber sealing-ring element(s) that.
Swell under the effect of temperature and gas, and only sometimes set.
Must be highly stressed to seal against the walls of the borehole and the lock-mandrel ring, while having a low expansion ratio to prevent the gasket from suffering from creep.
Swells and hardens to become irreversibly deformed, which prevents it from being retrieved easily.
Both downhole conditions and duration are therefore conditioning the irreversible deformation of the rubber and consequently the retrievability of the current designs. Relative axial displacements of the anchoring slips and the sealing ring also make the mandrel difficult to unset.
Different attempts have been made to solve these identified problems, but they were not able to correct them all at the same time with a simple versatile tool that fulfils the various needs of drilling, production, and well servicing.
Kinematic-Seal Concept
To surmount these limitations, the unidirectional blowout-preventer seal-ram proven concept has been extrapolated in two dimensions by dividing the traditional rubber packoff ring into an assembly of paired tapered blocks.