# Casing Design Calculations From A To Z

## Introduction To Steel Casing Design Calculations

From the earliest days of wells dug in the ground for various purposes, the need for some means of supporting the walls of the hole has been recognized. Many oil and gas wells of ancient times were lined or “cased” with rock. Over the years, the technology of casing pipes in drilling has developed from rock to plaster to wood and steel. And the need for casing design calculations was urgent.

## What are the functions of casing?

• To keep the hole open and support weak or fractured formations. If the hole is left without steel casing pipes, the hole may fall in, and the redrilling of the hole may become necessary.
• To isolate porous media with different fluid/pressure regimes from contaminating the pay zone. This is achieved through the combined presence of cement and steel casing pipes, so production from a specific zone can be made.
• To prevent contamination of near-surface freshwater zones.
• Most production operations are carried out through special tubing run inside the steel casing pipes to provide a passage for oil and gas.
• To provide a suitable connection with the wellhead equipment (e.g., Christmas tree). The steel casing pipes connect the blowout prevention equipment, which controls the well while drilling.
• Provide a hole of known diameter and depth to facilitate testing and running completion equipment.

By 1900, the regular oil field products had been reasonably well standardized. The earliest American Petroleum Institute (API) specifications on oil well steel casing pipes were issued in 1924. Then, beginning about 1930 and continuing for the next several years, specifications were published in several issues of API standards 5-A to cover the steel’s lengths, sizes, weights, threads, joints, and grades. In the following years, many improvements have been made in thread and coupling design and higher pipe grades.

## Casing Design Calculations Steps

### API Standards for Casing Pipes:

• API Bull 5C2, Performance Properties of Casing, Tubing, and Drill Pipe.
• API TR 5C3, Technical Report on Equations and Calculations for Casing, Tubing, Line Pipe Used as Casing or Tubing, and Performance Properties Tables for Casing and Tubing.
• API Spec 5CT, Specification for Casing and Tubing.
• ISO 11960, Petroleum and natural gas industries –Steel pipes for use as casing or tubing for wells.
• ISO 11961, Petroleum and natural gas industries –Steel drill pipe.
• ISO 13679, Petroleum and natural gas industries –Procedures for testing casing and tubing connections.

### What Is Casing Material Properties Definition?

To understand the strengths of casing tubular materials, it is important to understand the basic terminology and process of manufacturing such materials. The Casing Material Properties Definition article handles the definition of yield strength, steel’s hardness, and steel’s hardness.

### What Is the Parameters Which Specify Steel Casing Pipes

In the casing design, you have to understand the casing specification parameters, which are:

• Casing Size.
• Casing Length Range
• Casing Nominal Weight / Weight per unit length
• Casing Coupling Types

You can find a detailed explanation in the Casing Pipes Specifications article.

### How To Consider Corrosion Factors in Casing Design?

In Casing Corrosion, you will identify the casing corrosion mitigation if you have large volumes of H2S and CO2 and the Sulfide Stress Cracking in detail.

### Casing Performance Properties

Casing must have certain properties to achieve its functions in a well. The most important performance properties of casing include its rated values for axial tension, burst pressure, and collapse pressure.

#### Casing Design Calculations For Burst Pressure

Generally, the burst loads on the casing must be evaluated to ensure the internal yield resistance of the pipe is not exceeded. In Casing Burst Calculation, you will understand how the casing burst pressure rating is calculated.

#### Casing Design Calculations For Collapse Pressure

The primary collapse loads are supplied by the column of fluid on the outside of the casing, which acts to collapse the pipe. These fluids are usually the mud and possibly the cement slurry in which the casing was set. Therefore, the Casing Collapse Pressure Calculations article will help you understand how to calculate the collapse pressure rating for the casing.

#### Bi-axial Effects

The combination of stresses due to the weight of the casing and external pressures is referred to as ‘biaxial stresses’. In Casing Bi-axial Effects, you will learn to calculate minimum collapse pressure under axial tension stress.

#### Casing Design Calculations Safety Factors

Exact loading values are difficult to predict throughout the life of the well. For example, if mud of 75 pcf is on the outside of the casing during the running of the casing, this value cannot be expected to remain constant for the entire life of the well. The mud will deteriorate with time, reducing this value to perhaps a saltwater value of 64 PCF. Due to these changes, we have to consider the safety factors.

### Casing String Types Used In Drilling Wells

In Casing Types, you will find several types of casing strings and related topics, such as ( Casing Running and Cementing Preparation, Casing running – installation patterns, and Casing Running Procedures)

### Casing Setting depths Design and Calculations

The selection of the number of casing strings and their respective setting depths is generally based on considering the pore pressure and fracture pressure gradients of the formations to be penetrated. In casing setting depths, you will learn how to design the casing setting depths, the factors to be considered, and an example for such calculations.

### Casing Design Calculations For Sizes Selection To Match Drilling And Completion Goal

The casing sizes used in drilling onshore and offshore wells are designed from the bottom to the top, starting with the production tubing. In casing sizes selection, you will understand

### Casing Weights, Grades And Couplings Selection

To evaluate a given casing design, a set of loads is necessary. Casing loads result from running the casing, cementing the casing, subsequent drilling operations, production, and well workover operations. Mechanical loads are associated with casing hanging weight, shock loads during running, packer loads during production and workovers, and hanger loads.