Open hole fishing is one of the most critical operations in drilling. It involves a lot of expertise and experience of the personnel. This VDO by Weatherford Fishing Services demonstrates you about the open hole fishing. This is highly recommended for you to watch it. Additionally, the full VDO transcript is provided.
Full VDO Transcript – Open Hole Fishing VDO Training
Openhole fishing involves the removal of unwanted objects from the wheel bore. The objects can be tools, equipment and broken pieces of drill pipe, bits or tubulins. Openhole fishing begins following a Backoff in the drill string at or above the stock point of the fish in the wellbore leaving an accessible fish top.
The fish can be removed using special tools and techniques. A Scew-in sub is one of the most common fishing tools. Its modified pin can be used to catch an undamaged fish. The overshot tool because of its versatility is frequently used in fish recoveries. Its simple design includes a circulating and releasing action as well as a 360 degree catch of the fish. Normally the overshot or screw-in sub is connected to the bottom of the bumper sub and fishing jars on the fishing assembly. As the tool is lowered over the fish the top of the fish passes through the tool into the bowl. When the assembly is raised grapples engage the fish at a lower point and it is work free and pulled upward.
If the top of the fish is bent, twisted or broken it should be dressed off to provide a clean top so the grapple can secure it firmly. Dressing off is achieved with a Skirted or hollow fluted mill. Several types of mills are available for this purpose and other jobs.
In a washed out hole use of a hydraulic Knuckle joint located above the overshot kicks out under pump pressure to increase the sweep of the overshot to facilitate capture of an allusive fish. When the severe wash out, a Wall hook guide run on the bottom of the overshot further improves the search and capture of the fish.
When the fish cannot be dislodged by pulling with the overshot a jarring assembly run in the fishing string can be activated to strike heavy blows either up or down on a stuck fish to free it. The down action is achieved with a Bumper jar; essentially a slip joint with a sliding stroke. The impact enhanced by the weight of drill collars above the Bumper jar results in a sharp blow with the fishing string. Dropping the string quickly produces a sharp downward blow on the fish. This jarring action is especially effective in freeing PC Pipe or a string that is stuck as a result of an upward pull.
In many cases a stuck fish will require a powerful upward jar to free it. Hydraulic fishing jars permit an upward impact. The impact produced by a Hydraulic jar depends on the amount of pull taken on the tool before it trips. As indicated earlier the impact of a Hydraulic jar is enhanced by the weight of Drill collars placed above the tool. A jar accelerator further intensifies the effect of a jar at any depth. It is especially effective in shaft fishing operations where elasticity present in longer drill strings is not available. The use of an accelerator also keeps the energy of the jar impact form being lost a mole.
When a fish is stuck and cannot be jarred or worked free a widely used practice called Washover is employed. The Washover operation is the most successful way to free a fish and requires expert judgment in both pipe selection and in its proper running application. As mud and hole conditions are critical in many cases a bit drip may be necessarily to condition the hole prior to running the Washpipe.
Essentially Washover operation involve a pipe string that slips over the stuck fish allowing fluid to circulate in the annalist between the fish and the inner wall of the Washover pipe. Fluid under pressure flushes out debris cut lose by the rotary shoe run on the bottom of the Washover pipe. The washed over fish secured by an overshot or a screw-in sub and then be backed and removed to the surface.
The Washover pipe selected requires and inside diameter large enough to accommodate the fish and an outside diameter that can rotate without sticking in the open hole and still allow circulation.
Various types of Weatherford shoes are available. Each shoe is custom designed for a particular procedure. Tooth-type shoes for example are recommended when the formation to be cut is relatively soft. When metal such as tool joint or stabilizer blades must be cut the rotary shoe is dressed with Tungsten carbide or diamonds internally, externally or both; tailored specifically for the task. Proper rotary shoe selection requires expertise. An improper choice could severely damage the fish complicating the recovery operation. Occasionally the drill pipe maybe plugged, usually by mud. Cutting the freed drill pipe with a mechanical outside cutter run on the Washpipe would remove the obstruction and establish a clean workable top. Following Washover the Washpipe is pulled up and the shoe removed and replaced by a mechanical Outside cutter. Run into the well and over the freed fish the cutter is engaged. With a slight upward strain cutter knives are fed through the wall of the drill pipe fish and the fish is parted. Rotation is then stopped and the cut piece of fish is recovered and pulled to the surface.
When the fish is stuck off bottom a Washpipe spear may be run in conjunction with the Washpipe and screwed into the fish prior to the Washover procedure. This prevents a fish freed by the Washover operation from dropping to the well bottom and damaging the wellbore, drilling string or drilling bit.
Openhole fishing also involves the retrieval of Junk at the well bottom. Junk is defined as any unwanted material in the hole that hampers operations; such as, accidentally dropped tools, metal debris, parts of equipment including cones from drill bits. A commonly used retrieval tool is the Fishing magnet. Fishing magnets are especially cost effective for retrieving smaller fairish objects such as bit cones, slips and mill cuttings.
Permanent magnets have circulating ports around the outer edge so that fill and cuttings can be washed away exposing the Junk for proper magnetic contact. Magnets are furnished with flush guides, lift guides or mill guides which help in washing and securing the Junk. The magnet is lowered to the well bottom while circulating and then pulled to the surface. This activity may be repeated until the wellbore is cleared of all Junk.
Where Junk pieces cannot be caught by a magnet or consistent not fairish metals Weatherford employs specialized Junk baskets depending on the type of formation encountered. These retrieval tools consist of three basic types.
The simplest to use is called a Boot basket. It is run directly above a Junk mill or a rock bit that cuts the Junk into small pieces. Fluid circulation deposits these pieces into the basket which is raised to the surface.
In soft medium formations a coin tied basket commonly known as a Globe basket can be run to cut a short core in the bottom of the well. This core as well as any Junk contained in it is held in place by Retaining fingers and removed to the surface.
In hard formations a jet powered or Reverse circulating basket is a highly effective tool. Lowered to the bottom it rotates slowly with circulation to flushing settlings from the Junk. A ball is dropped into the drill pipe and pumped down until the ball seeps in the retriever. The flow of the fluid is diverted to the outside the tool which causes two things to occur. It establishes reverse circulation and a venturi effect which then creates a partial vacuum inside the Junk basket. These two forces propel the Junk into the basket. Captured Junk is secured by the hinged Retaining fingers. This action continues until all Junk is removed from the hole.