Monday, 15 January 2018

CASING PIPES DESIGN, THEORY AND PRACTICE FROM A TO Z


Casing String Design

Introduction To Steel Casing Pipes Design CalculationsFrom 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 casing pipes technology has developed from rock to plaster to wood and then to steel. The functions of casing can be summarized as follows:

  • To keep the hole open and to provide a support for 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 basically 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 fresh water zones.
  • To provide a passage for oil and gas; most production operations are carried out through special tubing which is run inside the steel casing pipes.
  • To provide a suitable connection with the wellhead equipment (e.g. christmas tree). The steel casing pipes also serves to connect the blowout prevention equipment which is used to control the well while drilling.
  • To provide a hole of known diameter and depth to facilitate the running of testing and completion equipment.
By the year 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. Beginning about 1930 and continuing for the next several years, specifications were published in several issues of API standards 5-A to cover lengths, sizes, weights, threads, joints, and grades of the steel. In the following years many improvements have been made in thread and coupling design as well as higher pipe grades.

1) 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, and 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.

2) What Is Casing Material Properties Definition? 

In order to understand strengths of casing tubular materials, it is important to understand the basic terminology and process of manufacture of such materials.Casing Material Properties Definition chapter handles the definition of yield strength, hardness of steel and hardness of steel.

3) 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
  • Steel Casing Grade
  • Casing Coupling Types
You can find detailed explanation on Casing Pipes Specifications chapter.

4) How To Consider Corrosion Factors in Casing Design?

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

5) Casing Performance Properites

Casing must have certain properties in order 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.

How To Calculate Casing Burst Pressure?

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 Chapter, you will understand how the casing burst pressure rating is calculated.

Casing Collapse Pressure Calculations

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

Casing Tensile Strength Calculations

The tensile load of the pipe is the weight of the casing which acts to pull the pipe apart. The tension is always the greatest at the surface and decreases with depth due to the casing weight below the point of interest. In Casing Tensile Strength Calculations chapter, you will understand how to calculate the yield strength and casing joint strength

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 chapter, you will learn to calculate minimum collapse pressure under axial tension stress.

Safety Factors

Exact values of loading are difficult to predict through out 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 become deteriorated with time and will reduce this value to perhaps a saltwater value of 64 pcf. Due to this changes, we have to consider the safety factors.

6) Casing String Types Used In Drilling Wells

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

7) Casing Setting depths Design and Calculations

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

8) Casing Sizes Selection To Match Drilling And Completion Goal

The design of the casing sizes used in drilling onshore and offshore wells is performed from the bottom to the top, starting with the production tubing. In casing sizes selection chapter, you will understand 

9) 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.
The Casing Centralization Chapter of this article is to know how to position the casing centralizers while you are in the designing phase of the casing. The focus will be on is on the below items:
The objective of casing centralization.
  1.  Casing Centralizers different Types.
  2.  Casing Centralizers Spacing Formulas.
  3.  Casing Centralizers Installation Patterns.
  4.  Casing Centralizers Case Study


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