•Kareem Hassan Ahmed Elfarash SEC 3•Hossam Hamdy Abd Eltwab SEC 2•Ahmed Gamal Ahmed Mohamed SEC 1•Mohamed Adel Elsemary SEC 3

SecondaryCementing

Plug-Back Cementing Squeeze Cementing

•It prevents damaging fluids from entering a producing formation. High-pressure from a squeeze job performed above the pay zone may force cement or wellbore fluids into a pay zone, causing damage and loss of production.

•It isolates an upper zone by forming a new bottom for the well from which formation tests can be run. The plug eliminates the chances of sticking your pipe below the testing assembly.

•It can be used to block off a problem area. For example, a permanent cement plug can be placed above a depleted zone without affecting the producing zones above the plug.

•Circulation loss generally occurs in porous or fractured formations, because drilling fluids or cement slurries flow into the fractures.

•A cement plug is sometimes set during drilling or cementing operations to stop lost circulation.

•A cement plug helps combat this problem since before the plug’s cement sets, it drifts into the cavities to block them off.

•At times, you do not or cannot perform vertical drilling. Perhaps an object is blocking the path downwards (for example, a broken string of pipe), the hole is deviated, or you want to drill toward a target which is off to the side of the hole.

•Before directional drilling can be performed, you need a seat or a bridge on which to set the tool. A cement plug can be used for this purpose.

MECHANISMMECHANISM

• Directional drilling or whipstocking is done by setting the plug, and then rotating the bit off the plug in another direction.

• The cement plug is called a whipstock when used in this way.

A whipstock plug provides a A whipstock plug provides a way to:way to:

• get around non-retrievable objects• correct excessive vertical deviations of the hole• drill a relief well

•When a dry or depleted well is abandoned, a portion of the casing that was left uncemented may be pulled from the hole.

•This leaves freshwater zones unprotected. In addition, highpressure zones may be uncovered.

•This allows fluid to migrate to the surface, and causes unfavorable surface conditions.

cement plugs are usually set:cement plugs are usually set:

• across and above potential oil and gas producing zones• above and below freshwater zones• above and below the bottom of any casing left in the hole• at ground level .

Squeeze cementing is the process of forcing a cement slurry through

perforations in the casing to a desired location to provide a seal across an

undesired gap.

A series of decisions must be made to determine :•If a problem exists•The magnitude of the problem•If squeeze cementing will correct it•The risk factors present•If economics will support it.

During placement water is driven from the slurry into a permeable formation to form a cement filter-cake which hardens to form a

seal.

• It is a common misconception that the cement actually penetrates the pores of the rock.

• As cement slurries have a mean particle size of 20-50 microns, it would require a formation

with a permeability of between 2-100 darcies for the cement grains to penetrate the

formation.

The need for squeeze cementing can arise for a variety of reasons during the drilling and production phases.

Some of the most common reasons are as Some of the most common reasons are as following:following:

• The repair of a faulty or inadequate primary cement job• To shut-off the flow of unwanted water or gas• The isolation of a zone prior to perforating for

production• To abandon a non-productive or depleted zone• To repair casing leaks.

The slurry is supjected to differential pressure that allows the slurry to cover the defective zone by the process of the liquid base filtering into the formation

Thus squeeze cementing is divided into:Thus squeeze cementing is divided into:

LOW PRESSURE SQUEEZE LOW PRESSURE SQUEEZE HIGH PRESSURE SQUEEZEHIGH PRESSURE SQUEEZE

1-LOW PRESSURE SQUEEZE

• Cement slurry is forced through the perforations at pressures below the formation fracture pressure.

• The aim of this operation is to fill perforation

cavities and interconnected voids with dehydrated cement.

• The volume of cement is small since no slurry is actually pumped into the formation. .

2-HIGH PRESSURE SQUEEZEIn some instances a low pressure squeeze will not accomplish the objective of the job due to:

• Channels behind the casing may not be directly connected with the perforations • Small cracks or microannuli may permit the flow of gas but not of a cement slurry• The impossibility of displacing plugging fluids

Mechanism

Placement of the cement slurry behind the casing is accomplished by breaking down formations at, or close to, the perforations. Fluids ahead of the slurry are displaced into the fractures, allowing cement to fill the desired spaces.

3-HESITATION SQUEEZESometimes pumping is continuous but more commonly it

is on a stop and start basis

A small volume of slurry is pumped in and A small volume of slurry is pumped in and the corresponding pressure increase is notedthe corresponding pressure increase is noted

Pumping is halted for a specific time and the Pumping is halted for a specific time and the pressure drop causedpressure drop caused by the slurry is notedby the slurry is noted

The cycle is repeatedThe cycle is repeatedIn this way pumping is easier and there is more time for

cement cake to develope

This process is done using:

• Drill pipes alone• Drill pipes with squeeze packer• Drill pipe with cement retainer• Retrievable or permanent bridge plug

DRILLABLE CEMENT RETAINER

Bridge plug

• The main objective of using a packer is to isolate the casing and wellhead while high pressure is applied downhole.

• The advantage of the retrievable packer is the fact that it can be set and released many times.

• Retrievable squeeze packers can be either compression set or tension set.

• Squeeze packers have a by-pass valve to allow circulation of fluids while running in and pulling out of the hole and also when the packer has been set

• Drillable or retrievable bridge plugs can be set to isolate the casing below the zone to be treated.

DRILLABLE CEMENT RETAINER

• Cement retainers are drillable packers provided with a two-way valve that prevents flow in either or both directions.

• Drillable cement retainers run on wireline are used instead of packers to prevent backflow when no dehydration of cement is expected, or when high negative differential pressures may disturb the cement cake.

When cementing multiple zones the cement retailer isolates the lower perforations and subsequent zone squeezing can be carried out without having to wait for the cement to set . These retainers are also used for well abandonment purposes .

BRADENHEAD PLACEMENT METHOD• This squeeze technique is the simplest of the squeeze

techniques and does not use a packer. • It is to be only practised with the Low Pressure

Squeeze Technique.• Open ended tubing is run to the desired depth, the

slurry is placed using the balanced plug method and the string raised above the plug. • The rams are closed and squeeze pressure applied

References

Well completion and servicing

Cementing 1