Coiled Tubing Operations From a Work Boat

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 141234, "Coiled Tubing Operations From a Work Boat," by N. Long, SPE, Brunei Shell Petroleum, and R. Raj, S. Srisa-ard, SPE, and N.H. Son, SPE, Schlumberger, originally prepared for the 2011 SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, The Woodlands, Texas, 5-6 April. The paper has not been peer reviewed.

Small offshore platforms have low deck-load capacity, and available deck space is insufficient for coiled-tubing (CT) workover operations. To find a solution to this issue, CT operations from a vessel were discussed and subsequently developed more than a decade ago. In 2002, the technique was refined substantially to improve safety and reliability, which allows well intervention from the deck of a floating anchored vessel. This technique uses a system that provides emergency CT disconnect and effectively compensates wave motion. 

Introduction

As with any mature oil and gas fields, maintaining and improving oil and gas production is considered part of production operations. Each year, Brunei Shell Petroleum typically selects a minimum of more than 60 wells as candidates for CT intervention. These candidates usually are distributed over 30 different offshore platforms. In terms of operational time, this intervention objective normally requires continuous activity for 7 to 8 months.

When studying the feasibility of conventional CT well intervention on a small production platform, there are normally three main issues to be examined. First, the platform deck area for placing equipment should be sufficiently large for placing CT equipment, pumping equipment, wireline equipment, and testing equipment, and for allowing equipment access spaces. Second, the platform crane must be able to lift equipment dynamically from a supply boat to the platform. Third, the production-platform structure must be strong enough to withstand the total weight of the CT equipment.

In Brunei, normally it is not feasible to place all the CT equipment on offshore production platforms because the decks of those platforms are too small. CT-intervention-work targets on three-leg platforms and four-leg platforms that have available deck space range between 214 and 1,905 ft². The maximum deck loads corresponding to these areas are in the range of 19 to 173 t. The installed crane on these platforms is primarily for lifting small loads, which are needed to support production operations. Therefore, the dynamic crane capacity is usually less than 5 t, and its boom length is approximately 15 ft.

CT well-intervention work commonly includes wellbore cleanout, wellbore mechanical-obstruction retrieval, sand control, adding perforations, and matrix acidizing. To cover all these types of work, the deck-space requirement for setting up equipment should be at least 3,500 to 4,000 ft² (or more) and deck-load capacity should be between 170 and 270 t.