Abstract

Drilling, evaluating and completing two wells at angles in excess of 70 degrees required planning to account for the reduced along hole component of gravitational force. Drilling assemblies and their build up characteristics were affected and friction forces experienced by surveying and electic logging tools and perforating guns necessitated the use of the pump down technique. An S shaped hole allowed free fall below the shoe of the pump down string. The high angle adversely affected bore hole stability requiring higher mud weights to hold back the hole and hole condition was found to be more sensitive to changes in mud properties and to mud quality. A production test procedure and completion string were compiled and procedure and completion string were compiled and designed, neither of which made use of gravitational forces for wireline tool operation below 4,000 ft.

Introduction

In order to reach areas of the Aukfield not falling within the existing drainage pattern, Shell Expro embarked upon the drilling of 2 highly deviated offshore wells. A-03 and A-09, with a view to completion as single string oil producers. Auk-A is a small 12 slot steel platform located producers. Auk-A is a small 12 slot steel platform located in 280 ft of water in the central North Sea. Eight wells had then been drilled into various areas of the reservoir. The central North Sea Lithology is well known for its high content of both mud making and dispersible clays above 7,000 ft requiring a mud weight of some 12.5 pounds per gallon (ppg). Below 7,000 ft in the fractured pounds per gallon (ppg). Below 7,000 ft in the fractured Cretaceous and Permian evaporites (Fig. 1), losses had been experienced with mud weights in excess of 10.5 ppg necessitating the setting of a string of intermediate casing. In previous wells where the angles were less than 60 degrees it was possible to drill for and set 9 5/8 in. casing in the top chalk. However, with the long tangent sections in A-03/ A-09, the 9 5/8 in. was required higher necessitating a 7 in. liner in its place and a 4 1/2 in. liner across the reservoir section of Zechstein chalk and Rotliegend sandstone (Fig. 2).

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