The oil and gas extraction process involves the drilling of wells that then traverse to processing plants. The casing pipe is an integral component of a well and is usually a tube made of hollow steel and used to make a borehole. It is pushed through the ground with the use of a pneumatic or hydraulic jack, after which the soil that has been displaced will be removed so that the carrier or product pipe can be inserted into the tube.
Casing Drift
The casing drift tests the roundness of the casing and checks for dents, bends, or anything that would block the passage of tools down the hole. Drifts can be customized so that they match the length and size of the tool. Commonly made of steel, some drifts are made of aluminum and non-metallic material such as urethane.
Casing Installation
Installing the casing can be done in two ways: by installing sections, which are then welded together, or by threading them together before installation. This enables the installation of wellhead equipment, blowout preventers, and both the production packers and tubing.
The Casing Size and Drift Chart includes measurements of a casing, with the diameter, length range, and weight per unit length included.
Casing Diameter
The diameter designations consist of three types.
The outer diameter is the measurement of diameter a casing is identified with, as its measure is from one outer wall to the other
The inner diameter is the measurement of the casing from one inner wall to another
The drift diameter guarantees the minimum casing diameter. This is important as it will show whether the casing is large enough or not for a specific bit to pass through.
Length Range
Using API (American Petroleum Institute) specifications, a casing has three length ranges, from 16 ft to over 34 ft and a maximum length variation of 5 and 6 ft.
Weight Per Unit Length
Casing weight is expressed in lb./linear ft and designated either as plain-end weight or nominal weight.
The plain-end weight/ft of the pipe is calculated as weight/ft without the threaded portion and coupling.
The average weight/ft is computed as the total weight of the threaded pipe’s average joint that has one coupling divided by the average joint’s total length.
The nominal weight/ft, as reflected in casing charts, approximates the average weight/ft of the pipe with API connections including couplings, threads, and upsets.
To calculate the weight is to determine the inner and outer diameter of the pipe using steel’s density (478 lb./cubic feet) and the following formula:
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