1 Cementing Techniques

TEACHING GUIDE

Primary Cementing Overview Module 231M001

Date: Sep 99 Module: CF01 Page: 1

TEACHING GUIDE

Date: Sep 99 Module: CF01 Page: 2

Primary Cementing The introduction of a cementacious material into the annulus between casing and open hole to : z Provide zonal isolation z Support axial load of casing strings and strings to be run later z Provide casing support and protection z Support the borehole

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• The definition of Primary Cementing is the introduction or placement of a cementitious material in the annulus between a casing and an open hole or previous casing. This means that we try to place some fluid that becomes hard with time, for example, cement into an annulus. (Try to get students to give the reasons) The reasons for this are: • The main reason to provide zonal isolation - to seal off certain zones from others (get examples of what we are talking about from students), • Another reason is to provide axial support for this casing and other casings that may be run later (liners, etc.). – Also to provide support and protection for this casing - against plastic formations (e.g. salt) and corrosive formation fluids (e.g. H2S, CO2, etc.). – Finally to provide support to the borehole - for plastic, water-sensitive or unconsolidated formations.

TEACHING GUIDE

Date: Sep 99 Module: CF01 Page: 3

Types of Casings z Conductor z Surface z Intermediate z Production z Liner

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•

These are the main types of casing strings that can be run in a well. We will go into detail of each one.

TEACHING GUIDE

Date: Sep 99 Module: CF01 Page: 4

Conductor z Purpose z

Prevents washing out under the rig

z

Provides elevation for flow nipple

z Common sizes and depths: z

30” - 20” Welded

z

20” - 16” Threaded

z

30’ - 200’ (< 100’ common)

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• Conductor • The conductor pipe does not need cementing most of the time since it is “driven” in. It is usually the very first casing to be run and may even be in the ground before the rig arrives on location. • The main reasons for running this type of casing are to prevent washing out of the weak formations just at surface (sands, gravels, etc.), and also to provide an elevation to connect a flow nipple to allow for flow back to the rig tanks. • The conductor pipe is usually a fairly large size pipe ranging fro 36” to 16” and they can be threaded or welded when they are driven, they are typically welded pipes. This type of pipe may not be standard API pipe - try to find 30” pipe in the handbook. If it is not, then special care must be taken when pumping to avoid collapsing or bursting the pipe.

TEACHING GUIDE

Date: Sep 99 Module: CF01 Page: 5

Conductor z Other Remarks: z Plugs not used z Careful pumping practices z Large excess required z Thru-drill pipe cementing common z BOP’s not unusually connected z Common Cements z

Accelerated Neat

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• Some special remarks about Conductor pipe: • Plugs are rarely used in these sizes of casings, which means that contamination can easily occur, starting inside the pipe and then continuing in the annulus. This is the reason why often cement is seen reaching surface long before it is expected. • Since the pipe may not be standard API and, in any case, burst and collapse pressures of large casings are very low, pumping has to be done carefully with the recording done completely. • Due to the formations at surface being very unconsolidated, there are usually very large washouts leading to excess volumes of 100 to 200% being pumped. • To avoid contamination inside the casing, through tubing or drill pipe cementing is usually performed. • The BOPs are not connected at this stage, so some care must be taken to avoid lost control of the well. In wells where formations could have extra pressure, the BOPs will be connected. • Accelerated cement slurries are used to cement these types of casings.

TEACHING GUIDE

Date: Sep 99 Module: CF01 Page: 6

Thru-Drill Pipe Cementing z Key Points: z Cement contamination z Channelling z Displacement z Pump until cement to surface

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• Thru-Drill Pipe Cementing • Cement contamination and channelling inside the casing is greatly reduced. • Displacement typical figures (get students to come up with values from the handbook): 400’ of 26” casing is 223 BBls; whereas, 400 feet of 5” DP only takes 7 bbls. With smaller displacment volumes, the job time can be dramatically reduced. • You can continue mixing and pumping until you have good cement to surface. This saves wasting money on cementing and ensures that good cement has arrived on surface before the end of the displacement. • This technique is used for most large casing sizes (OD > 13 3/8).

Date: Sep 99 Module: CF01 Page: 7

TEACHING GUIDE

Outside Cementing z Purpose z

Bring cement to surface

z Macaroni tubing used z Max. depth 250-300 ft

Tubing moved during job

z High friction pressures z Non-standard connections

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• Top Job or Outside Cementing: • Since the conductor casing is cemented in weak or unconsolidated formations, losses may occur or excess volumes may not have been enough. This causes the top of cement to be too low. In these cases, “top jobs” or outside cementing may be performed in order to bring the top of cement to surface. • Small OD or “macaroni” tubing is used. 2, 3 or 4 strings can be run in the annulus • Usual maximum depths range from 250 to 300 feet. • In some cases the pipes can be left cemented in place. If not, they may be lifted out as the cement is placed. However, this is a dangerous operation and quite difficult. Dowell employees should never get involved in this part of the operation. • Friction pressures are usually very high while pumping and care must be taken to avoid bursting the pipes. • The connections tend to be non standard, often made up by the rig welder just prior to the job. So extra care must be taken with surface pumping pressures. We should avoid proposing to make and supply these connections.

TEACHING GUIDE

Date: Sep 99 Module: CF01 Page: 8

Surface Purposes: z Protects surface fresh water formations z Cases off unconsolidated or lost circulation areas z Supports subsequent casing strings z Provides primary pressure control (BOP support) z Common sizes and depths: z

20” - 9 5/8” threaded

z

100’ - 3000’ (or more)

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• Surface Casing: • The main reasons for cementing Surface casings are the following: – To protect surface fresh water formations, – To case off unconsolidated or lost circulation zones near surface, – To support later casing strings, – To provide a means of connecting the BOP. • Typical casing sizes range from 20” to 9 5/8” or even less in the case of slim holes. They can be set at any depth, the restriction usually being the weight limits of the rig and the types of zones deeper in the well.

TEACHING GUIDE

Date: Sep 99 Module: CF01 Page: 9

Surface Cementing z Excess of 100% plus not uncommon z Recommend thru-drill pipe method to save z

Cement

z

Rig time

z Common cements: z

Lead light weight slurries with high yields

z

Neat tail slurries with good compressive strength

z

Reduce WOC to a minimum with accelerators

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• Surface Cementing: • Excesses are usually used to provide for unknown open hole diameters - these can range from 50 to 100%. (Explain how an excess is calculated). • As in conductor casings, the through tubing or drill pipe method of cement placement is preferred to reduce rig downtime (jobs performed quicker), save on wastage of cement (cement is mixed and pumped until it appears on surface, then the job is stopped), better quality jobs (less risk of channeling and contamination). • Typical cement formulations are: – Light weight, extended lead slurries that have a high yield which means lower cost and low density which means less chance of losses. – Neat tail slurries to provide casing support at the shoe. – The Waiting On Cement time should be reduced as much as possible with acclerators.

TEACHING GUIDE

Date: Sep 99 Module: CF01 Page: 10

Intermediate (Also called Protection) Purposes: z Separates hole into workable sections z

Lost Circulation

z

Salt Section

z

Overpressured Zones

z

Heaving Shales

z Common sizes and depths: z

13 3/8”, 10 3/4”, 9 5/8”

z

3000’ to 10,000’

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• Intermediate casings: • The main purpose for running and cementing intermediate casings is to separate the well into owrkable sections, isolating lost circulation zones, salt sections, overpressured zones, heaving shales and other downhole or surface conditions that would make further drilling difficult or dangerous. • Sizes and depths vary considerably from one operator to another and from field to another even within a field. Some typical sizes of casinga are 13 3/8”, 10 3/4” and 9 5/8” and the setting depths range from anywhere around 3000 feet down to 10000 feet.

TEACHING GUIDE

Date: Sep 99 Module: CF01 Page: 11

Intermediate Casings z Cemented to surface or to previous casing shoe z Two stage jobs common z Plugs, casing equipment, casing accessories usual z Good cementing practices are required z Large cement volumes z Common Cements: z

Typically filler slurries followed by high compressive tail

z

Specialised (light, heavy, salt - saturated, etc)

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• Intermediate casings can be cemented to surface or to somewhere within the previous casing shoe, depending on the clients requirements, formation fracture pressures, etc. Some latest developments have seen that some slients prefer to leave some open hole uncemented to allow for reinjection of cuttings and other drilling wastes. • If the inteval to be cemented is very long and low fracture pressure formations exist, the casing may be cemented in two stages (this will be covered in the next slide). • Usually casing accessories such as shoes, collars, centralizers, plugs, etc. are used as per good cementing practices. • As mentioned above, good cementing practices start to become important to ensure zonal isolation. To provide good zonal isolation, all the drilling fluid needs to be removed - this is typically the hardest part of cementing. The use of preflushes (washes and spacers), centralizers for good centralization, casing movement, controlled pumping (displacement) rates all are needed to perform this task of removing the mud efficiently. • Typically large cement volumes are used since depths are great together with large casing sizes. Often clients will have logged this part of the well and caliper logs are available to correctly calculate the volume of slurry required. This often makes costs an important issue. • The types of cement slurries used depends completely on the clients requirements for this section of hole and the conditions that exist downhole. Typically, extended lead and neat tail slurries are used with some retarders to control the thickening time as well as possible fluid loss agents, etc. In some cases specialized slurries may have to be used to control salt zones, gas migration, very lightweight for weak zones, etc.

TEACHING GUIDE

Date: Sep 99 Module: CF01 Page: 12

Two Stage Cementing Key Points: z Separation and

isolation of zones

2nd Stage

Stage Collar

z Reduces hydrostatic z Can leave zone in the

annulus uncemented (cement at TD and surface)

1st Stage

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• Two Stage Cementing: • Two stage cementing is a technique where a special type of collar is placed in a casing string - this collar allows ports or holes to be opened and circulation can be performed through them. • This is very useful in the following circumstances: – To isolate two problems zones within one open hole section, e.g. a high pressure zone and a low fracture pressure zone, – To reduce the hydrostatic pressure in the well when a weak formation exists - the first stage cement can be pumped and left to set and then the second stage can be cemented. – To reduce the wastage of cement in a well where only the bottom and an upper portion of the casing is to be cemented - with two stage cementing, some part of the hole can be left uncemented.

TEACHING GUIDE

Date: Sep 99 Module: CF01 Page: 13

Production Purposes: z Isolates the pay zone from other formations and the fluids in

them. z Protective housing for production equipment. z

Subsurface artificial lift

z

Multiple zone completion

z Screens for sand control z Covers worn or damaged intermediate string. z Common sizes: z

4 1/2”, 5”, 7”, & 9 5/8”

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• Production Casing: • The main reasons for running and cementing productioncasing strings are: – To isolate the pay zones and the fluids in them from other zones - the different zones may have different pressures; water and gas may stop or slow down oil production; and so on. – To provide a protective housing for subsurface production equipment (completions). – To act as initial screens for sand control. – To cover worn or damaged intermediate casings. • Depths and sizes varying considerably as in the case of intermediate casings but can be typically 4 1/2”, 5”, 7” upto 9 5/8”. CLients usually maintain casings sizes as a set from the beginning of a well to the end, e.g. conductor 30”, surface casing 20”, intermediate casins 13 3/8” and 9 5/8”, production casing 7”. • Production casings can be run as complete strings from TD to surface or only from TD to 100 to 200 feet inside the previous casing - these types of strings are called liners.