Further Advances In Slim-Hole Drilling
Authors: Eide Egil , Colmer R.A. 
Published: October 2008

Abstract Slim Hole Drilling(SHD) is being introduced in land and jack up based offshore operations to create more cost effective we//s. Over the last two years a number of innovative, technical approaches have been developed in order to improve the safety and drilling performance of floating operations. The paper describes the rig upgrades which have been carried out to introduce SHD on floating rigs particular attention being given to active heave compensation and kick detection. The impact of this equipment on the drilling operation has been briefly analyzed. It is concluded that it allows the drilling of slim hole wells success fully and safely from a semisubmersible.

The rig modifications will also be beneficial for other areas of the drilling operations. Based on specific needs the investment for some of the equipment can be justified due to improved overall operating performance. Although significant steps forward have been achieved over the last two years it is necessary that Drilling Contractors, Service Companies and Operators continue their co-operation in order to accelerate the upgrade of reliable equipment for the North Sea and other harsh offshore environments to progress application of SHD and consequent performance gains.

INTRODUCTION

Over the last few years a number of Shell Companies have gained experience with SHD which basically started in shallow land wells and expanded to deep land wells and horizontal wells [ref 1]. Encouraging results have been obtained with SHD at depths over 15,000 ft. which generated the idea to develop this technology further for exploration and appraisal activities on floating rigs in the North Sea.

The introduction of SHD on floating rigs raises some unique and particular issues in:heave compensationkick detectionwell evaluation/testing

It has become evident that more sophisticated technologies need to be developed to deal with the difficulties that will be encountered in this type of operation (Figure 1).

SLIMHOLE DRILLING IN SHELL EXPRO

SHD has been identified within Shell Expro's offshore operation as an area with potential for reducing exploration drilling costs and extending the drilling horizons. For high pressure deep drilling where casing string weights are fastly becoming the limiting factor, SHD is considered an attractive solution to keep the wells within the capacity of the current rigs. The challenges faced in Shell Expro's attempt to introduce SHD safely into the offshore floater drilling environment raise some unique issues particularly in heave compensation and kick detection.

It is important to understand what is meant by SHD in Shell Expro and what can be achieved by applying this technology. The exploration targets are planned to be drilled in 5 ¾ hole size with4 1/8" as contingency instead of today's 8 3/8" and 5 3/4" (Figure 2). SHDS contribution is shown in the following figures for a typical high pressure slimhole exploration well:rock volume to remove is approx. 1600 bbls or 32 %. less than in a conventional wellmud volume below seabed for the last section to be drilled is approx. 650 bbls or 52 % less than in a conventional welltotal casing weight more than 1,000,000 pounds or 36%.less than in a conventional well