Abstract

As the number of deepwater installations increase, so will the number of coiled-tubing (CT) operations that are needed to support these deepwater fields. This need will grow significantly as rigs on spar platforms and tension leg platforms (TLP) are eventually demobilized for work on new installations, leaving CT as the most economical option for performing future well maintenance on these platforms.

The need to operate without a rig is a critical factor in the success of future coiled-tubing work in the deepwater environment. Rigless operation is complicated by the fact that each platform type has its own unique heave-compensation issues that must be addressed for an effective CT operation to take place.

An additional challenge to deepwater CT operations has been the assembly and installation of tension lift frames or heave-compensated jacking frames. This equipment is typically cumbersome and time-consuming to install and has many safety-related risks associated with the installation of coiled-tubing components.

A new coiled-tubing heave-compensation system has been created to address issues associated with rigging up and operating coiled tubing on deepwater installations. This system was designed with particular focus on operational safety and efficiency to meet the complete range of floating platform coiled-tubing deployment scenarios. There are three primary modes of operation. As a stand-alone system, it can operate as a heave-compensated jacking frame; with a rig, it can operate as a standard tension lift frame or as a self-compensating tension lift frame. The adaptive heave-compensation system uses automated process control to maintain wellhead loads within the American Petroleum Institute-specified allowable stress limits. A specially designed proprietary titanium flex joint incorporated in the system reduces the effect of lateral loads and bending moments transmitted to the wellhead.

The total heave-compensation package is composed of three skids (injector tension frame, blowout preventer (BOP) tension frame, and hydraulic power unit). The injector, gooseneck, and all well control equipment come preassembled within the injector and BOP tension frames. This improves the overall efficiency of the rig-up and eliminates most safety issues associated with the rig-up/rig-down process. The heave-compensation system not only improves the efficiency of the rig-up process but also makes tool changeouts more efficient.

The initial field test data and the associated job case history establish the benefit that this new heave-compensation system has brought to the deepwater market.

Introduction

In April of 2002, at the request of several deepwater operators, a newly initiated study focused on improving the performance of coiled-tubing surface equipment to meet the growing demands of the deepwater market. There was a need for a new type of heave-compensation system that would allow horizontal and angular movement of wellheads on TLPs. The added capability to perform coiled-tubing work outside of the rig or even without the rig while mitigating the stress on the wellhead connection was also desirable. An improved system would address heave issues on multiple types of platforms including spars, semi submersibles, drill ships and TLPs.

Understanding the value to the future of deepwater coiled-tubing operations, it was decided to pursue a heave-compensation system design that could meet the demands of wellhead movement on TLP platforms. The new system represents a complete solution for addressing heave complication issues on spars, semi submersibles, drill ships and TLPs.

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