In my last column, I wrote about the need to pull casing from the ground. Maybe you drilled a dry hole, or need to remove bent pipe or set a well screen by the telescoping method. I previously talked about two methods for casing not too tight in the ground: the slotted pulling head and pipe pulling jars. For casing driven down deep and really tight in the ground, we may want to use one of two other methods.
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Here, I focus on the first: a very popular tool called a casing spear (or, sometimes, trip spear). You can lower this tool to any position inside the casing and teeth expand to grip that inside. You need to use long-stroke jars just above the trip spear with a drill stem and rope socket above the jars. The stroke of these jars needs to be longer than the stroke on the machine, and the operator would generally set the stroke at its shortest length. Small water well rigs have a short stroke of about 18 inches, so we would need to select jars made for a stroke of at least 24 inches or, preferably, 30 inches. The reason for this is that the casing spear is adjusted at the surface to slide down inside the pipe.
When reaching the point where jarring will be used, the driller pulls up on the tool string and the pulling slips engage the pipe. After some light, almost tap-like strokes on the jars, you can apply full power to them and the teeth will dig into the pipe and grip it, moving it toward the surface. To release this tool, you stop jarring and apply a few downward blows. That causes a spring in the spear to retract the jaws, and you can then pull the tool and the string itself to the surface ' either because pullback finished or a section of casing needs removal. Avoid pulling from the same point in the casing every time you use the spear, as this might elongate the casing and ruin it.
Another reason for the long-stroke jars with a stroke of a fair amount longer than the stroke of the machine stems from downward force on the spear. Too much force can trip it, and then it has to be pulled from the casing and reset. This resetting is one of the disadvantages of this tool. I never owned a trip spear but I did borrow one on occasion, even rented one from a tool company. I found setting the jaws difficult ' in fact, almost tricky. This setting adjusts how large of diameter of pipe the trip spear will engage. If set too light, it will not engage the pipe and be ineffective. If set too heavy, the spear will not disengage, complicating the driller's problem. At least one manufacturer I know of advertises that their trip spear easily adjusts for different casing weights. I believe they have notches on the setting ring, a part of the spear. Other manufacturers use wood blocks to hold the jaws closed and they are quite tricky.
The big advantage of a trip spear comes from placement. You can lower it to the lowest part of the casing before engaging it. This is where the casing is tightest and the upward blow most effective. Casing has a springiness in it so that a blow at the top ' as I wrote about last time ' has affect than a blow near the bottom.
Another point about setting the machine to use the trip spear: If it has an adjustable stroke, set it in the fishing or pulling position with a fast rise and a slow drop. This is just the opposite of the drilling stroke. On a machine without this adjustment feature, the driller should select the shortest stroke possible. Under extreme conditions, he might go to medium stroke (with suitable fishing jars) but it is best to use the short stroke.
Most cable tools are pretty rough, tough and simple. They don't have moving parts and, with properly set up joints, work very well. Not so for the casing spear. I find these spears difficult to use. If you use one, follow the manufacturer's instructions to the letter. For example, one basic requirement is that the tapered 'ways' that the jaws slide on need to be very clean and nicely lubricated.
Manufacturers make trip-type casing spears to pull 3-inch ID pipe all the way up to 16-inch OD casing, which covers just about all the water wells drilled in the United States and abroad.
This wraps up my thoughts on casing spears. Next time, I'll get into yet another method to pull casing from the ground: the casing ring, a tool whose use and, indeed, selection is not simple.
As I write this very late July, we continue to have a rather nice summer in southern Michigan. We have had warm and slightly hot weather, but not terrible heat and high humidity. I know some of you in other parts of the country have had just terrible heat, and I feel for you. I also understand that drought is too prevalent in other areas. We have had enough rain to keep my infamous lawn green, although the buckhorn keeps coming back. Nearby corn and soybean fields look good and, if the weather holds, I think the farmers will have a good year. Until next time, work hard, work safe, enjoy life and remember pulling casing is just part of the job.
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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.
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
Disadvantages
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Near Casing Shoe Underreamer
Advantages
Disadvantages
Near Bit Underreamer
Advantages
Disadvantages
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
Disadvantages
Wireline retrievable Drilling with Liner (DwL)
Advantages
Disadvantages
Drillpipe retrievable Drilling with Liner (DwL)
Advantages
Disadvantages
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 ).
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