|Publisher||American Petroleum Institute||Language||English|
|Content Type||Conference Paper|
|Title||Oil-well Casing Corrosion|
|Authors||R. H. Goodnight, Pan American Petroleum Corp.; J P Barret, Pan American Petroleum Corp.|
|Source||Drilling and Production Practice, 1956|
|Copyright||1956. American Petroleum Institute|
Information is presented to outline the major causes of both internal and external corrosion and the possible damage that could occur as a result of this action The use of a volatile inhibitor to control internal corrosion is proposed in those cases where it is impractical to use a packer to seal the tubing-casing annulus The use of internally coated casing may become effective with the development of more suitable coating materials and method of application. Control of external corrosion on well casing caused by bacterial activity, electrolytic effects, or acid water attack, by cathodic protection is proposed Protection from external corrosion on new wells by the use of coatings plus cathodic protection is suggested
There have been widely separated views on the matter of corrosion prevention as practiced by the pipeline and production companies Pipeline people generally coat their lines, wrap them, and even give them extra mechanical protection in rocky country Cathodic-protection systems are installed and frequent inspections are made to determine if corrosion is being controlled All of this is on lines which can be dug up and repaired at a relatively low cost
On the other hand, production people have installed thousands of miles of bare vertical pipe-lines No protection has been supplied against external corrosion, and in many cases, no measures are taken to prevent internal chemical attack
Casing has failed rapidly in many areas as a result of either internal or external corrosion Casing strings in a number of fields have been perforated by internal attack in as little as six years, whereas in other fields, failures have resulted from external attack in a like period. Typically, a number of wells in the same field are affected Repairs of casing failures are extremely costly and tests for determining corrosion of casing are not well-developed
The oil industry's investment in oil-well casing is well over $5 billion The yearly increase in this investment is over $85 million The cost of corrosion-mitigation measures becomes relatively cheap when one considers that uncontrolled casing corrosion result not in the loss of the casing but also in the interruption of production, and may result in loss of the well, or even permanent damage to the reservoir.
Although internal corrosion of the casing surfaces can be caused by carbon dioxide, hydrogen sulfide, and organic acids known to be responsible for tubing corrosion, production techniques modify the opportunity for attack In general, the main cause of internal attack is hydrogen sulfide The general mechanism for this attack may be expressed as follows(Formula is available in full paper)
As this reaction is primarily one of acid attack, carbon dioxide, when present, accelerates the reaction by increasing the total acid present. The iron sulfide formed sets up a galvanic cell in which the steel pipe becomes the anode This reaction is generally assumed to be responsible for the deep irregular pitting observed in sulfide corrosion.
|File Size||757 KB||9|