There are several other overshots available, but the Series 150 Bowen Overshot is the most popular and used throughout the world. Bowen also manufactures several other overshots that are very similar to the Series 150. We will discuss these later.
The Series 150 Bowen Overshot features positive engagement, and is a releasable overshot. It never requires left-hand rotation during it’s operation. It sets and releases using right-hand rotation and is releasable at any time during operation, should the need arise.
The Series 150 Bowen Overshot is available in many sizes and five different strengths. The five different strengths are designated by the following letters:
F.S. Full Strength
S.H. Slim Hole
E.F.S. Extra Full Strength
S.F.S. Semi Full Strength
E.S.H. Extra Slim Hole
These strengths are explained in the Bowen Manual #5/1150.
The Series 150 Bowen Overshot is used to engage, pack off, and retrieve twisted off or lost tubing, drill pipe, casing, tool joint, coupling, or other similar fish.
The Series 150 Bowen Overshot is considered a simple tool. It is, as far as the construction is concerned. It is made of three parts: the top sub, the bowl, and the guide. There are a multitude of accessories that can change the whole complexion of the overshot for many different circumstances.
The large spiral threads inside the overshot bowl are to accommodate the spiral threads on the outside of the grapple. They enable you to insert the grapple in the overshot. They also create a cone-like wedge that draws the grapple down when the overshot is picked up. The more you pickup, the
harder the grapple will grip the fish. This cone-like wedge is referred to as the draw and these threads should always be cleaned and well lubricated before putting a grapple in the overshot. This will reduce friction and enable the grapple to pull farther down into the draw. It works very much like slips in a rotary.
Grapples for all Bowen overshots have a minimum catch range above and below the designated catch size. Check Bowen manual #5/1150 for these catch ranges.
All grapples for a given size overshot have the same part number. For example: the spiral grapple and the basket grapple for a 5 ¾” O.D. overshot assembly #8975 is 6112. You should familiarize yourself with these numbers and use them when ordering grapples.
There are two types of grapples for the Series 150 overshot; a spiral grapple and a basket grapple. The spiral grapple catch size begins where the basket grapple catch size becomes too thin to have any strength. The spiral grapple’s maximum size is also the maximum catch size of the overshot. You cannot get spiral and basket grapples in the same catch size.
The Grapple is locked in place by a control, which goes in the overshot below the grapple. There are four kinds of controls: a spiral grapple control (all spiral grapple controls are the same size), a plain control (also all the same size), control packoff, and mill control packoffs. The latter two come in sizes to correspond with the grapple you run. Both have a rubber packoff in them. The mill control packoff has milling teeth on the bottom to help get over a burred fish.
There are five different packoffs for the Series 150 Bowen Overshot. They are as follows: Mill control packoff and plain control packoff, as mentioned above. The type “A” packoff is used with a spiral grapple. The type “A” packoff goes in the top of the overshot bowl above the grapple and packs off around the outside of the fish. They also come in sizes to correspond with the grapple size. The type “D” packoff goes in the top of the overshot bowl above the grapple. It packs off in the inside of the fish in a collar or integral joint box and is limited to the sizes you can get The packoffs mentioned above are not dependable. So do not ever assure the customer that they will hold a specific amount of pressure. The only one that is dependable is the High Pressure Packoff.
It has four elements that fit in a high-pressure packoff bowl. The high pressure bowl screws onto the overshot at the bottom where the guide normally goes, and the guide screws onto the bottom of it. The high-pressure packoff is available in nominal pipe sizes only, such as 2 3/8”, 2 7/8”, 3 ½”, etc. However, if you need to, and have a machine shop available, it is very easy to convert control packoffs to high-pressure packoff elements.
There are several different types of basket grapples for the Series 150 Bowen Overshot. The threads inside the grapple are called Wickers. The wickers are spiraled like threads. This helps to screw off of a fish when releasing the overshot. You can get basket grapples with different size wickers. If you are catching a fish that is soft, then a deep, wide wicker is best. If the fish is of a very hard substance, then a fine wicker is best. There is a left-hand wicker used when extreme right-hand torque is put in the pipe below the overshot. There is an N.I.T or Nitroloy grapple that is very hard steel and should be used when catching a fish of very hard steel, like P-105 tubing. It is available in nominal sizes only. There are basket grapples with stops built in. They prevent the grapple from getting below a collar, an upset, integral joint or a shoulder of any kind. It is almost impossible to release the overshot if you get below an upset or collar or a shoulder of any kind. These grapples with stops cannot be used to go over a nipple that is above a collar or upset. The I.D. of the stop is not large enough to allow the grapple to close enough to catch the collar or upset. There is another type of stop available, called a steel stop. It is a donut shaped steel ring that fits in the top of the overshot bowl, where you put the type “A” and type “D” packoffs. It is available in most any I.D. needed if there is a machine shop available.
Other accessories for the Series 150 Bowen Overshot are Mill guides, Oversize guides, Bowl or Top extensions, Bottom extensions, and Crossover Bushings.
The Mill guide is used to mill over a fish that is distorted in some way (such as flat, flared, or split) and to bring it back to the original size before engaging it with a grapple. A bottom extension should be run between the overshot bowl and the mill guide to insure enough room to get over the fish without rotating the grapple over the fish. Another use for the bottom extension is to help line up a crooked fish with the overshot before it reaches the grapple.
The Flush guide is sometimes referred to as a donut guide or smooth guide. It is usually used when stripping over a wireline to reduce the chances of cutting the line.
The oversize guide is used when an overshot is not compatible with the hole size. For example: If you run a 5 ¾” overshot in 7” casing, the casing is approximately 6 ¼” I.D. Therefore, you would not have room to
go by a fish or encounter trouble getting over the fish, but if you run a 5 ¾” overshot inside a 8 5/8” casing, (which is approximately 7 ½” I.D.), you would bypass a fish or have difficulty lining it up to go in the guide. So here you would run a 7” or 7 ¼” O.D. oversize guide. Another use for the oversize guide is where you are fishing for a small diameter fish in a large diameter hole, and cannot get a grapple with small enough catch for an overshot that is suitable for the hole size. You would run a smaller O.D. overshot that grapples were available for and an oversize guide that is compatible to the hole size.
The top extension is quite often misused by running it when it is not needed. It is a backup tool to be run when you need to get lower on the fish with a grapple. When you know a fish is split, undersized, or have already stripped a grapple off it, then you go back with the top extension and catch lower on good pipe.
The top extension should not be a larger I.D. than the maximum catch size of a basket grapple for the same size overshot. If it is, it has been modified and the yield strength is less than the book lists it. The crossover bushings are from the overshot threads to comparable sized washpipe on top of the overshot bowl as an extension when you need to cover a full joint of tubing and catch the collar. In a case like this, you would use a washpipe top bushing to eliminate one bushing. You would also use a steel stop in the overshot bowl. Another use for the crossover bushing is on the bottom of the overshot bowl to run a long extension, such as a long rotary shoe to line the fish up with the overshot before engaging the grapple.
Always check the I.D. of the top sub of the overshot to be sure it is not the same as the O.D. of the fish. If it is, you could get a friction bite when the fish goes in it and make it very difficult to release the overshot.
To release the overshot, you have to move the grapple up in the bowl so the grapple can open. You do this by jarring down on the work string. This is referred to as shucking the overshot. When you think you have done this, you pick up on the work string to a neutral weight and rotate the overshot to the right five or six rounds. Then pick up again and continue this way until the overshot is clear of the fish. If it will not rotate, then try again to shuck it. If you pick up too much weight after shucking it, it will not rotate.
When you have a fish in the rotary, it is sometimes hard to shuck the overshot. Here are some ways that work real well. If you still have your jar assembly on the overshot, close the bumper jars, then tie the cat line above the Mandrel. Pick up until the jars are opened, then drop them closed very rapidly. If you don’t have jars, latch a set of elevators around the same way.
You should never have to force an overshot over a fish. In fact, most of the time, you will not get any indication that the grapple is over the fish.
When it is necessary to put the torque in the pipe, you should hold 10,000 lbs. Or more strain up on the overshot to prevent it from releasing.
It is not necessary to put the rotary tongs on an overshot guide to tighten it. A 36-inch pipe wrench booked on the lip and hit two or three times with a sledgehammer is sufficient. Some overshots are pinned at the top. Top extensions are also pinned to insure against backing off when left-hand torque is applied to the overshot.
The connections above the bowl should be tightened with rotary tongs, and then the pins tightened. Always use caution when tightening these connections. They are fine threads; therefore, easy to pull the threads or mash the overshot bowl.
Always use caution when making up or breaking down tools to prevent damaging them. It is costly when tools are damaged.