Tubing grade guidelines

When selecting steel type for pipes and connections it is important to consider the corrosive environment that the steel will be subjected to. There are several parameters in the well that affect the corrosion, like temperature, chloride ion concentration, partial pressure of CO2 and H2S, pH and presence or absence of Sulphur [Craig et al. 2011].

When selecting a material there are certain aspects that have to be taken into consideration [NORSOK M-001 2004]:

  • Corrosivity;
  • Design life;
  • Availability;
  • Failure possibility and the consequences related to failure;
  • Resistance to brittle fracture;

API tubing steel grades are identified by letters and numbers which dictate various characteristics of the steel. For each grade, the number designates the minimum yield strength. Thus L-80 grade steel has a minimum yield strength of 80,000 psi. In other words, it can support a stress of 80,000 psi with an elongation of less than 0.5%. The letter in conjunction with the number designates parameters such as the maximum yield strength and the minimum ultimate strength which for L-80 pipe are 95,000 psi.

The following table shows the yield values for various API tubing grades:

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Tubing connection basics

Tubings are screwed together through connections, which could either be:

  • By means of integral joint (the most common type of connection on small diameter pipe),
  • Or by using a coupling (the most common connection); a collar with internal threads used to join two sections of threaded pipe.

Selection of tubing connections:

The type of tubing connections selected for a completion will depend mainly on the well characteristics. The connection must be able to contain the produced fluids safely and at the maximum pressures anticipated.

The basic requirements of a tubing string connection are:

  • Strength compatible with the operational requirements of the string during, and after running;
  • Sealing properties suitable for the fluid and pressures expected;
  • Ease of stabbing during make-up, and safe breakout when pulling the tubing;
  • Resistance to damage, corrosion, and erosion.

Types of thread connection:

There are two types of thread connection: API and Premium.

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Subsurface Safety Valve Basics

Safety valves are designed to automatically shut in the flow of a well in the event surface controls fail or surface equipment becomes damaged. They are classified according to the location from which they are controlled – surface or subsurface. In this article, subsurface safety valve types, operating systems, working principle, setting depth, and selection process are presented.

It is advisable, and in most cases mandatory, to have a secondary means of closure for all wells capable of natural flow to the surface. The installation on of a sub-surface safety valve (SSSV) will provide this emergency closure capability.

Courtesy Halliburton

Types:

To isolate the tubing, there are two basic types of safety valves:

  • Tubing conveyed: Tubing Retrievable Subsurface Safety Valve (TRSV),
  • Wireline conveyed: Wireline Retrievable Subsurface Safety Valve (WRSV)

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Slickline Service Tools – part 1

Slickline operations have been in use since the early days of the oil and gas industry. The development of equipment and technology for slickline operations has kept pace with the development of new methods and tools used in well completion, remedial and work-over operations. Slickline is used for depth determination, deviated hole surveys, temperature and pressure surveys, paraffin cutting, and cementing operations.  Slickline may also be used to set, retrieve, and manipulate chokes, circulating plugs, gage cutters, swaging tools, safety valves and gas-lift valves.

Various tools frequently used in slickline operations are described in this article.

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Christmas Tree & Wellhead

A Christmas Tree comprises a series of valves, spools, a choke, and connection. It used for production or injection wells such as oil wells, gas wells, water injection wells, water disposal wells, etc. It provides a means of controlling the effluents, ensuring the safety of the facilities and giving measurement tools access to the well.

The Difference Between a Wellhead & Christmas Tree?

Many times, the words Christmas Tree and Wellhead are used interchangeably; however, a wellhead and Christmas tree are entirely separate pieces of well equipment. A wellhead must be present in order to utilize a Christmas tree and is used without a Christmas tree during drilling operations. Producing wells that require pumps, such as Sucher Rod Pumping Systems, frequently do not utilize any tree due to no pressure containment requirement.

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