Abstract

This paper details a coiled tubing perforating campaign conducted in New Zealand, during the first half of 2006.

Coiled tubing has been used for deploying perforating guns for many years now. The challenge with this type of work, is first designing a coiled tubing string which can push and pull long gun lengths along highly deviated wells. Secondly, a method of retrieving (and deploying) the guns against a high wellhead pressure is required. In this instance, down hole isolation valves could not be used. Instead, a pressure deployment system was utilized.

The length of perforating guns run during this campaign is extreme, but not unique[i]. The use of pressure deployment systems is also not unique[ii]. The combination of these factors along with the facts that this is a very remote operation (with regard to oilfield manufacturing and supply), that much specialized equipment needed to be fabricated (in a market cycle where all equipment deliveries see long lead times), and that the operation must take place in a seismically active area, all combine to make this a very challenging project.

This paper lists observations taken from the project that may prove useful to future campaigns of a similar nature.

Introduction

The upstream oil and gas industry is not generally noted for its picturesque, pleasant locations. More common associations might be baked dry deserts, thick jungles or even civil war zones. However, New Zealand offers many geographically beautiful locations, one of which is the site of this challenging coiled tubing campaign.

The location is just north of the town of New Plymouth, on the west coast of the North Island of New Zealand. Specifically, the coiled tubing operation was sited immediately adjacent to the coast, bounded by the Tasman Sea to the West, Mount Egmont providing the backdrop to the East. On a clear sunny day, the vistas are spectacular, although those vistas come with a price, high coastal winds and the potential for seismic activity (Mount Egmont is a volcanic mountain).

The coiled tubing work described in this paper involves three newly drilled wells, drilled from the coastline but extending far under the adjacent sea. The deepest well has a measured depth of 7.4km, stepping out some 5.7km with a true vertical depth of 3.6km. The wells were completed with 5½″ by 5″ completion strings and 5″ liners.

The principal task for the coiled tubing was to perforate the wells, perforating long intervals in a single fire, firing the guns underbalanced and retrieving the guns against a live wellhead. Secondary tasks included preparing the well for the perforating run, including depth correlation logging runs, production logging and down hole sample runs.

At the time of writing this report, the first two wells have been successfully perforated and are flowing strongly. This paper details the operational history, highlighting issues that offer learning points for future campaigns.

Objectives

The technical objective was to perforate at an accurate depth, in the underbalanced condition. The softer but equally important objective was to complete the work with minimal environmental impact, particularly with respect to noise and light spill, working within a strict health and safety operating envelope.

Table 1 lists the perforating guns lengths planned for each of the three wells. The guns ran were 2¾″, 60 degree phasing six shots per foot, deep penetrating charges.

Table 1

Table 1 Gun assembly lengths

Well Number Gun Assembly Length (m) 
672 and 93 (two runs) 
645 
710 
Well Number Gun Assembly Length (m) 
672 and 93 (two runs) 
645 
710 

Well Details

Three land wells are the subject of this paper. The wells are all drilled and completed in a similar manner. Their measured depths vary from 6,400m to 7,400m, all with a 60° sail angle and an 82° to 90° reservoir section. The true vertical depth is of the order of 3,600m with a bottom hole temperature of 120°C.

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