When the wellbore is collapsed and there are formations over the fish, you need to wash over the top of fish in order to clear any sands or debris. The washover pipe is used for this operation. It will slip over the stuck pipe and drilling mud will flush out any debris in the annulus between pipe and wellbore. The system normally consists of three elements: drive sub, washover pipes and rotary shoe.
Large-diameter pipe fitted with an internal grappling device and tungsten carbide cutting surfaces on the bottom. The washover pipe can be lowered over a fish in the wellbore and to latch onto and retrieve the fish.
Top sub threaded to connect with your working string at the top and with washover pipe at the bottom. Works as a cross-over between your washover string and your drill string.
The drive sub is manufactured with a pin down matching the washover string x a box up matching the drill string.
Washover Shoes are designed in various styles and sizes to service the many different conditions encountered in fishing and washover operations. Hard-faced dressing material is used to form the cutting or milling surfaces on the Rotary Shoes that are subjected to high abrasion and severe impact.
Shoes are dressed with a special hard-face compound made of crushed sintered tungsten carbide particles and a resilient matrix of nickel-silver alloy. Tungsten carbide particles have a hardness nearly equal to that of diamonds. They retain their hardness at high temperatures and are not affected by the heat generated from the cutting operation. The tough nickel-silver alloy matrix holds the tungsten carbide particles in place and cushions the particles against strong impact.