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Application Answers

Setting Casing at Target Depthin Spite of Drilling Hazards

Drilling with Casing

 © 2009 Weatherford. All rights reserved.

Challenge

When performing inll drilling or sidetracks in thelater stages of eld life when depletion is a factor,

there is often a known drilling hazard condition

which can prevent reaching target depth. As

a result, the casing may need to be set higher 

A change to drilling-with-casing (DwC™) above the

hazard zone enables casing to be set at target depth.

than planned, with consequent diminution of thewell architecture and the probability of reduced

production rates. The challenge is to ensure that

the casing is set at the target depth to provide foroptimal well design.

The Answer

Drilling can continue conventionally until just

above the hazard zone, at which point the

bottomhole assembly (BHA) is pulled and replaced

with a DwC assembly, either casing or liner 

conguration as needed. The well is then drilled

ahead to target depth, eliminating the need to trip

out of the hole when the hazard is encountered,

avoiding wiper trips and mitigating the risk of setting casing high.

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Drilling with Casing

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Constraints

A well designer must balance a large number of 

considerations especially when planning a well in

which drilling hazards are known to exist. If DwC™ techniques are considered as a means of ensuring

that casing is set at the target depth through the

hazardous zone, then certain constraints clearly

apply:

• The design of the casing string to be used for 

drilling cannot be compromised when compared

to the completion requirements and connection

integrity must be maintained.• Similarly, burst, collapse, tensile, and torque

ratings must remain unaffected by the need to

use the casing for drilling.

• Conventional well-control practices must

be maintained.

• Rates of penetration should ideally be similar 

to those achievable with conventional drilling

methods to maximize time and cost savings.

• Conductor constrains surface hole size and

hence, casing program.

• No rig modications should be needed toperform DwC applications.

Features, Advantages and Benets

• Changing to DwC™ methods above the hazard

zone eliminates the need for an additional casing

string to be set with consequent optimization of 

the well architecture, maintenance of hole size

through the zone of interest, and realization of 

time and cost savings.

•DwC techniques eliminate the need for a

wiper trip to condition the well with consequent

cost savings.

• A change to DwC techniques allow drilling to

target depth through the hazard without mudweight change.

• Several models of Weatherford’s Defyer ™ 

assembly are available to suit various drilling

conditions and formation hardness. All have

features similar to conventional drilling bits

such as diamond cutting structure, jetting, and

tungsten-carbide gauge pads that will act as

a shoe for cementing purposes. They can be

readily drilled out like regular cement shoes after 

cementing operations.

• Because the annular space is small the

consequent annular velocity is greatly increasedand hydraulics optimized, thus allowing for 

better handling of the known drilling hazard

and improved hole cleaning when compared toconventional drilling techniques.

• Once on bottom, the casing can be cemented

in place with minimal delay under optimum hole

conditions, improving the cement job and long-

term well integrity.

• Gauge control is improved and thus the risk of 

washout and/or hole collapse is greatly reduced.

• The casing string is an integral part of thecementing process. When run with a oat collar 

it eliminates the risk of shallow gas inuxes while

drilling and making connections.

• The “smear” effect associated with rotating

pipe in close proximity to the wellbore results

in greatly improved hole conditions due to

the excellent mudcake characteristics that

are created.

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Drilling with Casing

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Frequently Asked Questions

DwC™ techniques are simple and require little or no deviation from conventional drilling practices;

however, there are a few questions posed regularly by operators considering the use of DwC technology.

What if the casing string gets stuck?

In some 800 jobs performed to date worldwide this

has not happened. Though clearly it is always a

possibility, it is thought that superior hole cleaning

provided by the increased annular velocity

combined with the positive features of the “smear”

effect make it extremely unlikely. If it does happen

the situation is no worse than getting stuck whilerunning casing conventionally and, though it may

not be possible to pull out, it may still be possible

to continue to drill ahead and reach bottom.

How do I log the well?

DwC technology is more applicable to

development drilling in known conditions where

formation data has already been gathered and

cased-hole logging will sufce.

Does it wear the casing?

Yes, but casing wear can be readily managed by

controlling the drilled section lengths during wellplanning.

What about centralization to improvethe cement job?

The string is typically run with solid-uted

centralizers in place for this purpose.

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Weatherford International Ltd.

515 Post Oak Blvd., Suite 600

Houston, Texas 77027 USA

Tel: 713-693-4000weatherford.com

Weatherford products and services are subject to the Company’s standard terms and conditions, available on request  or at weatherford.com. For more information contact an authorized Weatherford representative. Unless notedotherwise, trademarks and service marks herein are the property of Weatherford. Specications are subject to changewithout notice. Weatherford sells its products and services in accordance with the terms and conditions set fort h in theapplicable contract between Weatherford and the client.

Drilling with Casing

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Plan for drilling success and efciency. Learn

more about our DwC technology by contacting

an authorized Weatherford representative orvisiting weatherford.com.