case study of oil and gas

8/6/2019 Case Study of Oil and Gas

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Case study of oil and gas

Case 1:

Problem: Reaction between the pyrophoric iron reaction on the demister pad

According to Wikipedia, pyrophoric materials are reactive toward water as well as it

will ignite when contact with humid air. For example, iron sulphide and many reactive metalslike uranium

Above case happens when a vessel was previously purged with natural gas to remove

hydrogen sulphide content. The vessel was opened and a worker was washing the inside of

the vessel with water wand. However, the pyrophoric iron reaction on the demister pad

started to release sparks inside the vessel. The atmosphere inside the vessel exploded and the

worker was fatally injured.



The vessel containing hydrogen sulphide was purged with propane to a flare stack.

The workers opened the vessel for clean-out. When the manway was opened, an explosion

occurred resulting in four workers receiving burns to their faces and hands. Possible some of

ignition that caused the explosion was determined to be static discharge or metal-to-metal

contact.

Iron sulphide: a kind of pyrophoric material

which means it can spontaneously ignite

when exposed to air

Solution: Atmospheric testing

Atmospheric testing

Before performing work involving a vessel, tank or piping system that contained or may contain hydrocarbons or other hazardous materials, the interior may need to be

tested to determine if a flammable environment is present. Where testing is required,

it must be done before work begins and may be required at regular intervals or

continuously while conducting work. The most common unit of measuring the

explosiveness is the percentage of the flammable mixture¶s lower explosive limit

(LEL).

The LEL is the minimum concentrations of a substance that, when mixed with air,

may ignite. If there is too little fuel, the air/fuel mixture is considered too ³lean´ and

will not burn. The upper explosive limit (UEL) is the maximum amount of fuel that

when mixed with air, can burn. If there is too much fuel, the air/fuel mixture is

considered too ³rich´ and will not burn (see Figure 1). The wider the explosive range

for a particular substance, the more likely it is to burn or explode when mixed withair.



Case 2:

Problem: Purging and inerting



Figure 2 above shows an explosion that occurred in March 2000. It highlights the

practice of using air as a purging gas can be unsafe and impractical. There were three workers

killed in this incident when a compressed gas tank exploded as workers were preparing a

natural gas powered vehicle for crash tests. Air had been used to purge the tanks and lines

containing natural gas. An arc produced by the tank¶s electrically operated valve ignited themixture of natural gas and air.

In fact, using air as a purging gas significantly increases the risk of an explosion.

Typically, air forced through a system containing a flammable or combustible liquid residuecreates a mist cloud of airborne liquid droplets. Flammable liquid droplets evaporate quickly,

and can produce an explosive atmosphere. If there is enough liquid residues, the explosive

conditions may persist for a very long time ± longer than workers may be willing to wait

before beginning their work.

Solution: A non-combustible gas such as nitrogen or carbon dioxide should have been

used to purge the system. As well, the tank valve should have been de-energized and

locked out prior to work beginning.

How?



By diluting the hydrocarbons in the vessel or piping system with an inert (non-flammable andnon-reactive) gas such as nitrogen or carbon dioxide, or a compatible inert liquid such as

water. The atmosphere must remain non-explosive while workers perform their work. Duringthe work, all ignition sources must be controlled and monitored so that they cannot trigger a

fire or explosion.

Note that inerting/purging themselves may create hazards to workers by displacing the

oxygen in the environment. If a worker must enter a tank that has been inerted/purged, the

proper procedures and protective equipment must be used. Also, LEL meters will not read

properly when oxygen levels are less than 10 percent. Without enough oxygen, these meters

can give an incorrect low reading even if flammable vapours and gases still remain.

Here are some more cases of accidents during offshore oil and gas development~

1)Oil and gas accidents

Accidents inevitably accompany offshore development. They are the sources of

environmental pollution at all stages of oil and gas production. The causes, scale, and severity

of the accidents' consequences are extremely variable. They depend on a concretecombination of many natural, technical, and technological factors. To a certain extent, each

accidental situation develops in accordance with its unique scenario.

The most typical causes of accidents include equipment failure, personnel mistakes, and

extreme natural impacts (seismic activity, ice fields, hurricanes, and so on). Their mainhazard is connected with the spills and blowouts of oil, gas, and numerous other chemical

substances and compounds. The environmental consequences of accidental episodes are

especially severe, sometimes dramatic, when they happen near the shore, in shallow waters,

or in areas with slow water circulation.

Drilling accidents

Drilling accidents are usually associated with unexpected blowouts of liquid and gaseous

hydrocarbons from the well as a result of encountering zones with abnormally high pressure.

No other situations but tanker oil spills can compete with drilling accidents in frequency and

severity.

Broadly speaking, two major categories of drilling accidents should be distinguished. One of

them covers catastrophic situations involving intense and prolonged hydrocarbon gushing.These occur when the pressure in the drilling zone is so high that usual technological

methods of well muffling do not help. Lean holes have to be drilled to stop the blowout. Theabnormally high pressure is most often encountered during exploratory drilling in new fields.

The probability of such extreme situations is relatively low. Some oil experts estimate it at 1

incident for 10,000 wells [Sakhalin-1, 1994]. The need to drill lean holes emerges, on average,in 3% of accidental episodes.

The other group of accidental situations includes regular, routine episodes of hydrocarbon

spills and blowouts during drilling operations. These accidents can be controlled rather

effectively (in several hours or days) by shutting in the well with the help of the blowout

preventers and by changing the density of the drilling fluid. Accidents of this kind are not so

impressive as rare catastrophic blowouts. Usually, they do not attract any special attention. At



the same time, their ecological hazard and associated environmental risk can be rather considerable, primarily due to their regularity leading, ultimately, to chronic impacts on the

marine environment.

2) Two die on oil rig gas accident

12:01AM BST 12 Sep 2003

Two men have died following a gas "kickback" on a North Sea oil rig.

Sean McCue, 22, from Fife and Keith Moncrieff, 45, from Tayside, had been working on autility leg of the Brent Bravo rig near where the gas escaped, on Monday afternoon.

Authorities have refused to give details of how the men died although it is understood there

was no explosion. It is thought pumps to the seabed had carried a "kickback", or pocket of gas, within an oil well, to the surface.

The trapped gas may have been forced up the pipes and on to the platform, coastguards said.

Sixty non-essential workers were evacuated by coastguard helicopter after the gas wasdetected on the installation run by Shell Expro just before 4pm.

A statement from the company said: "Due to the build-up of gas in the utility leg, the

platform was downmanned of all non-essential personnel to the nearby Brent Alpha and

Brent Charlie platforms. The gas was quickly and safely evacuated."

Solution: Consider the following when preparing to work with a vessel, tank or pipingsystem that contains or may contain hydrocarbons:

(1) Identify hazards ± perform a thorough hazard assessment.

(2) Follow procedures ± procedures developed to control the identified hazards must befollowed. For example: Worker should wear proper attire which is personnel protective

equipment



Personnel protective equipment (PPE)

(3) Competent workers ± work must only be performed by qualified, trained and experienced

worker .

4) Material Safety Data Sheets (MSDSs) ± follow the manufacturer¶s handling

recommendations and precautions.

(5) Monitoring ± use properly calibrated gas monitors that are appropriate for the atmosphere

being monitored.

(6) Prepare the site ± the interior may need to be ventilated, purged, or inerted with a

compatible gas or liquid.

(7) Isolation ± a vessel, tank or piping system may need to be isolated to prevent the flow of

gases or vapours.

(8) Venting ± the contents of the vessel, tank or piping system may need to be safely ventedto a flare or safe area.

(9) Bonding and grounding ± when flammable substances are transferred from one system or

container to another, bonding and grounding of the components may be needed to eliminate

sparks due to the discharge of static electricity.

Results:

Hazard identification and assessment are essential parts of work planning.

Workers must be trained to understand the importance of identifying

potentially hazardous conditions. Only by understanding and applying

safety precautions, the risk can be reduced to minimum level

case study of oil and gas

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