Sunday, July 18, 2010

Well control and completion

Drilling & Well Completion

Once the design well depth is reached, the formation must be tested and evaluated to determine whether the well will be completed for production, or plugged and abandoned.

To complete the well production, casing is installed and cemented and the drilling rig is dismantled and moved to the next site.
A service rig is brought in to perforate the production casing and run production tubing. If no further pre-production servicing is needed, the christmas tree is installed and production begins.

Well completion activities include:

Conducting Drill Stem Test
Setting Production Casing
Installing Production Tubing
Starting Production Flow

After production starts, the well may need further servicing.
If it's decided that the well will not be completed, then it will be plugged and abandoned.

Conducting drill stem test :
To determine the potential of a producing formation, the operator may order a drill stem test (DST). The DST crew makes up the test tool on the bottom of the drill stem, then lowers it to the bottom of the hole. Weight is applied to the tool to expand a hard rubber sealer called a packer. Opening the tool ports allows the formation pressure to be tested. This process enables workers to determine whether the well can be produced.
Potential Hazards:

Being pinched or struck by the drill stem test tools during floor operations.
Swabbing the hole on the way out with the test tool could cause a kick to occur, which could result in a blowout leading to injuries and deaths.

Being exposed to unexpected release of H2S or other gases or liquids.

A packer seat failure or fluid loss to an upper formation could cause a kick that might result in a blowout causing injuries and deaths.

Other hazards are similar to those encountered during trippingout/in.

Possible Solutions:

Wear appropriate PPE.

Instruct workers in handling and using the special tools required during drill stem testing.
Keep a method for filling the hole in place at all times. Before any test starts, the rig management must ensure that the blow-out prevention system includes a kill system that is capable of pumping fluid into the well below the annular preventer and at least on-set of pipe rams.
Run a pump-out-sub or downhole circulating device in the test string to to enable the system to be reversed.

Ensure all workers on the location understand the dangers before starting any drill stem test. They should be fully informed of and trained in appropriate safety procedures, including the use of safety equipment and breathing apparatus. If in an H2S area, post a sign indicating the test in full view for the general public to see. Post reliable people to stop them from coming to the location. Define a minimum of two muster points with all vehicles parked in an appointed area.

Setting Production Casing:
Production casing is the final casing in a well. It can be set from the bottom to the top. Sometimes a production liner is installed.

This casing is set the same as other casings, then cemented in place.

See Casing Operations and Cementing for more information on specific hazards and solutions.

Installing Production Tubing:
A well is usually produced through tubing inserted down the production casing. Oil and gas is produced more effectively through this smaller-diameter tubing than through the large-diameter production casing.

Joints of tubing are joined together with couplings to make up a tubing string. Tubing is run into the well much the same as casing, but tubing is smaller in diameter and is removable.

The steps for this activity are:

Tubing elevators are used to lift tubing from the rack to the rig floor.

The joint is stabbed into the string, which is suspended in the well, with air slips.
Power tongs are used to make-up tubing.
This process is repeated until tubing installation is complete.

The tubing hanger is installed at the wellhead.
New technology allows tubing to be manufactured in a continuous coil, without joints. Coiled tubing is inserted into the well down the production casing without the need for tongs, slips, or elevators, which takes considerably less time to run

More about subsea BOP controls :

What Should Happen during a blowout and steps to shut the well after you fail to "kill" it :

In a blowout, a rig worker presses an emergency button. A signal is sent from the rig down an electrical line to one of the control pods.  The BOP is a subsea blowout preventer which could be anything more than few thousands feet below sea level.

The control pod directs hydraulic fluid from the rig and from a bank of pressurized canisters, called accumulators … … through a valve, called a shuttle valve, and into the blind shear ram. Some blowout preventers have a separate emergency system with its own shuttle valve.

The blind shear ram under high hydraulic pressure cuts or shear through the drill pipe and seals the well, preventing oil from gushing out.

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