Drilling, Completion, Isolation and Thru Tubing Re-entry of Multilaterals in Hard Open Hole Formations.
Authors: Durst Doug D. , Hart Shane P. , Brown W.H. , Norris Robert M. , Parker Robert D. 
Published: October 2008

In the Hassi Messaoud oil field of Algeria Sonatrach has been combining many new technologies in a re-entry well program that has substantially increased production. Some 600 of the vertically drilled wells are candidates for re-entry and rework to drill horizontal laterals, however to be eligible they must meet the following basic criteria which Sonatrach have established:They must be open hole completions.They must have been shut in for a long time - effectively since being drilled.

The zone of interest is the Upper Cambrian, an extremely hard and abrasive sandstone and quartzite formation which is extremely difficult to drill. Kicking off laterals in these reentry wells is therefore challenging and required the development of new tools in order to do so effectively. Additional challenges were posed by the requirements to be able to isolate the laterals, tie them back to the original cased hole and provide for thru tubing re-entry capabilities.

This paper addresses the milling, drilling and completion issues relevant to these wells and discusses the solutions arrived at. Using a typical well re-entry case history, it details the steps taken to create a TAML1 level 1 open hole multilateral completion. It will describe how a combination of liner hanger and inflatable packer technology, together with a large bore completion allowing for selective thru tubing reentry, has led to several successful installations with many more planned.

Introduction

Open Hole Multilaterals can be complex yet be well engineered to provide low risk system installation with full isolation between laterals, positive thru tubing re-entry capabilities and tie back to original drilled out cased hole. Kicking off the lateral legs in the abrasive sandstone and quartzite formations of the Hassi Messaoud field provided a real challenge which led to the development of a new exit mill to provide a quick rate of penetration with optimum ledge and geometry for the drilling bottom hole assembly. This facilitated the elimination of repeated mill and whipstock runs to get a proper lateral start. Using combined inflatable and liner hanger technology a very effective method is utilized too properly displace tailpipe cement, cement the anchor and safely hydraulically release the running/setting equipment. The large bore completion systems being installed allow for positive thru tubing, selective lateral re-entry into the respective lateral without having to ever remove the completion string. Unique to these applications is that the completion string is installed wholly within the newly drilled out open hole main bore and tied back to the original cased hole main bore. Installation of the completion string provides full isolation between each lateral. An engineered re-entry system, with sealable housing hardware, has been developed for open hole use, and is accurately placed across each of the two laterals. This provides a means for positive repeatable reentry into either lateral and/or selective or commingled production of each lateral.