Casing is a large diameter pipe that is lowered and cemented in place in order to line the borehole of an open well. Casing strings are strategically sized and placed into the well so that drilling operations can reach desired depths.

Each successive casing string that is lowered into the well and cemented in place is small enough to easily fit through the bore of the previous string. The first casing stings, known as the conductor casing, is fitted with a well headed after it has been cemented in place. The second type of casing is the surface casing which isolated the well from fresh water aquifers.

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Successive casing strings include intermediate casings and production casings. Intermediate casings are optional and are used to ensure that the well can withstand hydrostatic pressures without fracturing the surrounding rock formations. In some cases a liner can be used rather than cementing in intermediate casing strings. The last casing string is the production casing which runs into the producing reservoir.

Standards

ASTM D4428 - These test methods are limited to the determination of horizontally traveling compression (P) and shear (S) seismic waves at test sites consisting primarily of soil materials (as opposed to rock). A preferred test method intended for use on critical projects where the highest quality data must be obtained is included. Also included is an optional method intended for use on projects which do not require measurements of a high degree of precision.

Various applications of the data will be addressed and acceptable interpretation procedures and equipment, such as seismic sources, receivers, and recording systems will be discussed. Other items addressed include borehole spacing, drilling, casing, grouting, deviation surveys, and actual test conduct. Data reduction and interpretation is limited to the identification of various seismic wave types, apparent velocity relation to true velocity, example computations, effective borehole spacing, use of Snell's law of refraction, assumptions, and computer programs.

Resources

How Casing Protects Groundwater

How Does Casing Work?

Casing (borehole)