Casing Corrosion Evaluation Using Wireline Techniques
Authors: Dennis Bob 
Published: March 2010

Abstract
Corrosion control in the oil industry is a matter of economics. Up to 1% of the over-all operating costs could be saved through corrosion management. All too often, this is not considered and corrosion monitoring only occurs on a need to know basis, after an unscheduled shutdown or actual casing failure. Corrosion management involves casing inspection and periodic monitoring, corrosion rate prediction and cathodic protection evaluation. Today's corrosion wireline logging tools offer a technique to predict and detect potentially disastrous corrosion problems. Current wireline measurements utilize electromagnetic, flux leakage, ultrasonic and mechanical techniques. They can predict, detect and delineate corrosion in the form of metal loss, holes, pits, and mechanical deformation. Furthermore, external problems can be distinguished from internal ones, These measurement systems will be briefly described along with examples of multiple measurement diagnostics.

Introduction
Corrosion control in the oil industry is essentially a cost containment exercise; the likely cost of a failure being balanced against the expenditure on a corrosion control program. The oil and chemical processing industries, which have to live with their corrosion problems, have a better record of corrosion control than most. In oil production, some 3% of the over-all operating costs can be attributed to corrosion. Up to one third or this could be saved through a planning scheme involving corrosion detection, evaluation and management in downhole casings. This generally involves three areas: casing inspection and periodic monitoring, corrosion rate prediction and corrosion protection evaluation. These can be accomplished through the application of current wireline measurements in addition to corrosion protection techniques.
All too often, corrosion is not considered during the planning stages of a field. Most corrosion programs result from an adverse inspection report, an unscheduled shutdown or an actual failure. Cathodic protection systems of both surface and downhole tubulars are becoming the only realistic solution to a field's corrosion problems.
Simply pm, monitoring casing corrosion is a function of dollars and cents. Today's corrosion logging tools offer oil companies the best chance of detecting and correcting the potentially disastrous effects of corrosion. These wireline measurement systems consist of three basic principles.

Electromagnetic Tools

Cathodic Protection Profile Tool
Location of anodic corrosion cells - a device to evaluate external casing corrosion cell activity and determine cathodic protection needs.

Flux Leakage Tool
Localized corrosion - a high resolution flux leakage and eddy current multi-pad device to evaluate the extent of internal and external localized pitting and holes.

Multifrequency Electromagnetic Thickness Tool
General wall loss - electromagnetic device which determines wall thickness, inner diameter and casing wall electromagnetic properties measurement.

Ultrasonic Tools

Acoustic Corrosion Tool
General wall loss - an acoustic device which determines wall thickness, inner radii and internal roughness, using eight fixed ultrasonic transducers.

Borehole Televiewer
Casing wall imaging - a high-resolution acoustic imaging device to evaluate internal surfaces and determine pipe geometry.

Mechanical Tools

Mechanical Calipers
Inner wall loss - a multifingered mechanical caliper system with, 16 to 60 fingers to evaluate inner pipe wall for wear or deform