What is the Advantage and Disadvantage of Casing Drilling System

Read more

Post Views:

3,246

Casing while drilling provides immediate benefits, saving both time and money by altering the steps needed for the drilling process. On top of this, the CwD system also provides a whole host of additional benefits. The benefits of casing while drilling can be summarized below;

Save Time and Cost

As mentioned in the introduction part, Basic Knowledge of Casing while Drilling (CwD), CwD is able to save operation time by cutting down flat time and reducing operational risk. When compared to conventional drilling, CwD can provide a time saving of between up to 37.5% of time spent on a well based on historical data from a field in Oman (-PA SPE Journal Paper &#; ).

Get Casing to Total Depth

Because of wellbore degradation, conventional drilling is usually unable to run casing all the way to the bottom of a hole. This degradation is caused by a number of factors, including wall damage, filter cake build up, and open hole time left for long time. However, a non-retrievable system allows casing string to drill all the way through ledges and other obstacles, fit through tight sections, and reach the TD successfully.

Reduce Formation Exposure Time

Introducing the casing during the drilling process also removes tripping times for BHA. This doesn&#;t just save on costs, but it also helps to reduce the formation exposure time that is usually an issue until cementing. This exposure time can cause mud degradation, salt creeping, and clay swelling, but these problems are eliminated by CwD. What&#;s more, since there is no need for an additional casing run after the initial drilling, there is less risk of the casing getting stuck.

Overcome Challenging Drilling Zones

CwD can also be used to deal with potentially challenging drilling zones, such as depleted formations, salt sections, and fractured zones. This is because CwD allows one to set and case off a zone instantly once it has been drilled. Conventional drilling, on the other hand, takes longer to deal with these areas, and can even complicate the problem, meaning a significant amount of both time and money is spent trying to recover the well, not taking into account the severe formation damage which can also be caused.

Improve Hole Cleaning

When CwD is used, it creates a small, uniform annulus between the casing and the borehore. This is beneficial because it means the drill is able to circulate and clear cuttings easily, without the need for a high slow rate. It is important to note, though, that drilling fluid properties and pipe movement need to be planned out carefully in advance to ensure that the hole remains clean.

Improve Hole Quality

By using casing while drilling, one can see that the hole quality is significantly higher than with conventional drilling. This is due to a process known as the plastering effect (Figure 2), in which cuttings and filter cake are crushed up and pressed into the formation by the rotation of the smooth pipe. This creates a low permeability wall cake. On the other hand, pipe rotation is not smooth in conventional drilling processes; a wall cake is produced, but it easily comes off the formation, and is therefore less effective.

Reduce Mud Loss

Thanks to the mud cake produced by cementing, drilling fluid is kept within the formation, thus sealing off the wellbore and preventing circulation problems. CwD therefore makes it possible to continue drilling in a more controllable fashion. CwD requires a lower flaw rate than a conventional drilling at the same annular velocity because the clearance between wellbore and casing is much smaller than wellbore and drill pipe. Therefore, hole cleaning can be improved. Conventional drilling requires that the drill be stopped to solve lost circulation problems, and often needs the setting of cement plugs, which can cause a great deal of hours non-productive time (NPT) which can soon add up to a great expense.

Wellbore Strengthening

Not only does this help to limit mud loss, but it also improves upon formation fracture resistance, a process known as wellbore strengthening. The cuttings and filter cake are crushed into the formation, sealing up tiny cracks and giving some additional integrity to the area around the wellbore, while also giving a wider mud weight window.

Improve Formation damage

Casing while drilling has a plastering effect, which is beneficial because it creates a mud cake layer that is impermeable, preventing the productive zone from being blocked up by both liquid and solid materials. Damaged zones are much smaller with CwD than conventional drilling, which is demonstrated in Figure 13. This means that the well is more productive, and damage is kept to a minimum. However, this point is still being contested by some, as the results of research may be seen to be inconclusive.

Reduce Operational Problems

Some operational issues such as stuck pipe and well control can be minimized by Casing while Drilling. The reasons are explained below;

• Stuck Pipe

A stuck pipe mechanism can be diagnosed into three major categories: differential, mechanical and solid induced stuck. In theory, a larger casing area should be more likely to suffer from a differential stick, but in practice, it is actually less likely. This is due to the effects of plastering, which creates a fine, impermeable layer that acts as a barrier, and keeps differential pressure to a minimum.

Mechanical sticking usually comes about due to micro-dogleg, undergauge holes, or mobile formation. CwD eliminates the first two causes by starting and ending the drill process with the casing. In terms of mobile formation, CwD reduces exposure times to limit the risk of this happening.

As CwD results in superior hole cleaning, the pack-off which is caused by cutting accumulation is drastically lowered. In addition, the plastering effect provides additional structural support. This means that CwD helps to eliminate the problem of stuck pipes, and is therefore useful for wells with a stuck pipe problem.

• Well Control

Conventional drilling often causes well control situations which need to be dealt with accordingly. This is due to tripping; therefore, since CwD eliminates tripping BHA, this risk is reduced. With retrievable BHA systems, the large by-pass between the BHA and the casing eliminates swabbing, and keeps the casing string firmly on the bottom, further reducing the risk of well control.

References

Australian Drilling Industry Training Co (ed.) () The drilling manual: The manual of methods, applications, and management. 2nd edn. Boca Raton, FL: CRC Press.

Bourgoyne, A.T. () Applied drilling engineering. Richardson, TX: Society of Petroleum Engineers.

Cantu, C. () Technology adoption: No risk means no gain. Available at: http://www.drillingcontractor.org/technology-adoption-no-risk-means-no-gain- (Accessed: 11 December ).

Karimi, M., Moellendick, T. E., & Holt, C. (, January 1). Plastering Effect of Casing Drilling; a Qualitative Analysis of Pipe Size Contribution. Society of Petroleum Engineers. doi:10./-MS

Schlumberger Limited . () TDDirect Casing-Drilling and liner-drilling technology. Available at: http://www.slb.com/services/drilling/drilling_services_systems/casing_drilling.aspx (Accessed: 11 December ).

Mitchell, R.F., Miska, S.Z. and Aadnoy, B.S. () Fundamentals of drilling engineering. Richardson, TX: Society of Petroleum Engineers.

PennWell Corporation () Casing drilling marks a century of progress. Available at: http://www.offshore-mag.com/articles/print/volume-72/issue-10/drilling-and-completion/casing-drilling-marks-a-century-of-progress.html (Accessed: 11 December ).

Sánchez, F. J., Said, H., Turki, M., & Cruz, M. (, June 1). Casing While Drilling (CwD): A New Approach To Drilling Fiqa Formation in he Sultanate of Oman&#;A Success Story. Society of Petroleum Engineers. doi:10./-PA

Tesco Ltd () Tesco Drill-Lock-Assembly. Available at: http://www.drillingcontractor.org/dcpi//dc-julaug04/July4-Tesco.pdf (Accessed: 11 December ).

Weatherford Ltd () Drilling with Casing services. Available at: http://www.weatherford.com/en/products-services/well-construction/tubular-running-services/total-depth-services/drilling-with-casing-services (Accessed: 11 December ).

Post Views:

8,299

Casing while drilling (CwD) has been around for many years and it is one of proven technologies that can save both time and money. CwD is a process where a well is simultaneously drilled and cased; the casing is used for the drill string, and is rotated to the drill and cemented into the well at TD. One of the main benefits of this process is that it greatly cuts down on the tripping time needed to pull out the bottom hole assembly (BHA) and run the case- if not removing this need entirely. Therefore, the flat time is reduced, and the process is made more economically viable.

As shown in Figure 2 below, which is an example of Casing while Drilling utilized in one of oilfields in Oman for drilling surface section; this process can save up to 37.5% of time spent on a well based on historical data.

Link to KSQ Technology

Types of Casing while Drilling Systems

Three main types of CwD, which is determined by the configuration and operation of the drill, are as follows;

• Non-Retrievable Casing While Drilling System

• Retrievable BHA Casing While Drilling System

• Drilling with Liner Systems

Non-Retrievable Casing While Drilling System

The non-retrievable system is the simplest type of CwD. In this case, the system is made up of a drillable bit or drill shoe, a casing string, and a casing drive system. The drill shoe is fitted securely to the bottom of the casing string; the latter is rotated by a power swivel which is hooked up to the drive system. This system only offers a limited number of options- it can only drill in a straight hole, and to a pre-determined depth.

Multiple drill shoes are available, which vary according to hardness and strength. Figure 4 is an example of a drill shoe manufactured by Weatherford.

In order to provide proper rotational movement, and to pump through casing, water brushing is normally used in the drilling process. However, this is not a viable option when drilling using CwD, since the make up and breakout of water brushing means that the drilling threads are more likely to become damaged. The casing drive system used for CwD is specifically built based on the casing spear principle integrated with a cup-type packer seal. This then internally slots into the new joint of the casing. It is then able to connect to, pump, and rotate the casing properly. Once the casing joint is drilled down, the casing drive system rapidly disengages by releasing the casing spear. However, this spear requires a large gripping surface to properly distribute the load and prevent pipe deformation. The internal catch is suitable for large casing up to 13-3/8&#;, whereas an external catch is necessary for casing which is smaller than this.

Retrievable BHA Casing While Drilling System

The retrievable casing while drilling BHA system strikes a balance between conventional drilling tools and CwD. The main advantage of this system is that it can be steered, and used with both conventional measured while drilling (MWD) and logging while drilling (LWD) tools.

Most BHA systems are connected to the bottom of the casing string, and drill a pilot hole. This hole can then be enlarged using one of three methods: 1) a reaming casing shoe, 2) a near casing shoe underreamer, or 3) a near bit underreamer.

Advantages and disadvantages of all three hole enlargement methods are shown below;

Reaming Casing Shoe

Advantages

• Maintain good directional control and LWD reading
• No risk of reamer not collapse when retrieving

Disadvantages

• Rat hole equal to BHA length. This will leave the longest rat hole among three methods.
• Limited reamer RPM equals to casing RPM

Near Casing Shoe Underreamer

Advantages

• Shorter rat hole
• Enable to improve reamer performance with PDM

Disadvantages

• Risk of underreamer stuck

Near Bit Underreamer

Advantages

• Shortest rat hole
• Enable to improve reamer performance with PDM

Disadvantages

• Risk of underreamer stuck
• Effect on LWD reading and directional control performance

The pilot BHA connects with the main casing, using Drill-Lock-Assembly (DLA) to set in the casing profile nipple (CPN). Once it has reached the TD, the BHA can then be retrieved using a drill pipe or a wireline; which method is used will depend on the weight and angle of the BHA.

The BHA system can cause a rathole of the same length as the BHA itself; for that reason, there are two techniques used to minimize the rat hole. Firstly, the DLA may be released at the TD, and reamed down with a casing reamer shoe up to the full bit length- this method can damage the BHA, though. An alternative to this method is to place the underreamer behind the bit; when the BHA reaches the TD, the DLA is then released, and the casing is able to be run all the way to the bottom. However, by positioning the underreamer behind the bit effects when using an LWD reading can impact upon directional control performance, particularly when using a rotary steering system (RSS). RSS is a popular choice when using CwD, given that it performs better than mud motors or positive displacement motors (PDMs). Drilling with mud motor is particularly difficult to use in conjunction with CwD, because it requires a larger contact area with the wellbore in order to effectively control the tool face.

With this system, cementing is usually done after BHA retrieval. Using a pump down float, which is dropped into the casing and pumped to lock in at the CPN, the cementing can be quickly and easily performed normally.

Drilling with Liner Systems

Drilling with Liner (DwL) works in much the same way as the previous two systems, except it does not involve the use of a casing drive system. The liner hanger setting tool is connected to the drill pipe, and then attaches to the power swivel at surface. There are three sub-types of this system: non-retrievable, wireline retrievable and drill pipe retrievable.

Once the drill has reached the TD, the non-retrievable DWL is able to set the liner hanger, and then complete the cementing job. With a retrievable DWL, the BHA needs to be retrieved once the liner hanger has been set, before a liner wiper plug latching system or cement retainers are run with the liner top packer and seal assembly to set in the polished bore receptacle (PBR) atop of liner. When the seal assembly is attached to the liner, the cementing can then be carried out normally.

The advantages and disadvantages of each system are listed below

Non retrievable Drilling with Liner (DwL)

Advantages 

• Minimal rat hole
• No downhole tools to retrieve
• No rig modifications
• Not as expensive as others
• Quick cementing upon reaching section TD
• Relatively simple operations

Disadvantages 

• Limitations in drilling shoe size used
• No directional and MWD capabilities
• Only cased hole logs can be acquired
• Possible lack of availability of technology
• Torque limitations

Wireline retrievable Drilling with Liner (DwL)

Advantages 

• Directional and LWD capabilities
• Higher torque applications than non-retrievable DWL
• No rig modifications

Disadvantages

• Higher operating cost
• Multiple trips are required to retrieve BHA
• Possible lack of availability of technology
• Rathole length equals to BHA length
• Risk of BHA being irretrievable
• Unable to cement immediately upon reaching TD

Drillpipe retrievable Drilling with Liner (DwL)

Advantages 

• Directional and LWD capabilities
• Downhole tools can be retrieved in one trip after setting liner
• Highest torque applications
• No rig modifications
• Stable drilling system with low vibrations

Disadvantages 

• Higher operating cost
• Possible lack of availability of technology
• Rathole length equals to BHA length
• Risk of BHA being irretrievable
• Unable to cement immediately upon reaching TD

References

Australian Drilling Industry Training Co (ed.) () The drilling manual: The manual of methods, applications, and management. 2nd edn. Boca Raton, FL: CRC Press.

Bourgoyne, A.T. () Applied drilling engineering. Richardson, TX: Society of Petroleum Engineers.

Cantu, C. () Technology adoption: No risk means no gain. Available at: http://www.drillingcontractor.org/technology-adoption-no-risk-means-no-gain- (Accessed: 11 December ).

Schlumberger Limited . () TDDirect Casing-Drilling and liner-drilling technology. Available at: http://www.slb.com/services/drilling/drilling_services_systems/casing_drilling.aspx (Accessed: 11 December ).

Mitchell, R.F., Miska, S.Z. and Aadnoy, B.S. () Fundamentals of drilling engineering. Richardson, TX: Society of Petroleum Engineers.

PennWell Corporation () Casing drilling marks a century of progress. Available at: http://www.offshore-mag.com/articles/print/volume-72/issue-10/drilling-and-completion/casing-drilling-marks-a-century-of-progress.html (Accessed: 11 December ).

Sánchez, F. J., Said, H., Turki, M., & Cruz, M. (, June 1). Casing While Drilling (CwD): A New Approach To Drilling Fiqa Formation in he Sultanate of Oman&#;A Success Story. Society of Petroleum Engineers. doi:10./-PA

Tesco Ltd () Tesco Drill-Lock-Assembly. Available at: http://www.drillingcontractor.org/dcpi//dc-julaug04/July4-Tesco.pdf (Accessed: 11 December ).

Weatherford Ltd () Drilling with Casing services. Available at: http://www.weatherford.com/en/products-services/well-construction/tubular-running-services/total-depth-services/drilling-with-casing-services (Accessed: 11 December ).

If you are looking for more details, kindly visit Casing Drilling System.