1.1 Introduction

We begin with a chapter on the usual obligatory information for a book on oil-field casing. The real book starts in Chapter 2, but in the rare case that the subject is totally new to you, you will find a rudimentary coverage of what casing is in this chapter. The steel tubes that become a permanent part of an oil or gas well are called casing, and the tubes that are removable, at least in theory, are referred to collectively as tubing which are not covered in this book. Oil-field casing is manufactured in various diameters, wall thicknesses, lengths, strengths, and with various connections. The purpose of this text is to examine the process of selecting the type and amount we need for specific wells. But first, a question: What purpose does casing serve in a well? There are three:

It is as simple as that, though we could list many subcategories under each of those. Most are self-evident. Additionally, there are some cases where the casing also serves a structural function to support or partially support some production structure, as in water locations.

1.2 Setting the Standards

By necessity oil-field tubulars are standardized. Until recent times, the standards were set by the American Petroleum Institute (API) through various committees and work groups formed from personnel in the industry. Now, the International Organization for Standardization (ISO) is seen as taking on that role. Currently, most of the ISO standards are merely the API standards, but that role may expand in the future. In this text, we refer primarily to the API standards, but it should be understood that there are generally identical standards, and in some cases more advanced standards, under the ISO name.

It is important that some degree of uniformity and standardization is in force and that manufacturers be held to those standards through some type of approval or licensing procedure. In times of casing supply shortages, a number of manufacturers have entered the oil-field tubular market with substandard products. Some of these have led to casing failures where no failure should have occurred. The important point here is that any casing purchased for use in oil or gas wells should meet the current standards as set for oil-field tubulars by the API or ISO.

Some casing is not covered by API or ISO standards. Some of this non-API casing is for typical applications, some for high-pressure applications, high-temperature applications, low-temperature applications, and some for applications in corrosive environments. Most of this type of casing meets API standards or even higher standards, but one must be aware that the standards and quality control for these types of casing are set by the manufacturer. It probably should not be mentioned in the same paragraph with the high-quality pipe just referred to, but it should also be remembered that there are some low-quality imitations of API products on the market as well.

1.3 Manufacture of Oil-Field Casing

There are two types of oil-field casing manufactured today: seamless and welded. Each has specific advantages and disadvantages.