What is the Difference between Pup Joint & X-Over / Crossover?
In oil and gas drilling processes, the drill string which is a long and heavy pipe comprising various parts plays a crucial role. Two such elements include pup joints and crossovers. They may seem quite similar at first glance, though they actually are not.
Pup Joints
A pup joint, also known as a pony rod, is a short piece of pipe that may be connected to the drill string to modify the length of the string depending on the drilling operation that is undergoing. Normal pup joints are usually small piping sizes and are available in sizes of 2, 5, or 10 feet.
Pup joints become necessary whenever there is a need to adhere to standard drill pipe lengths. Drill pipe or as it is commonly referred to as ‘tubular’ is normally available in certain standard lengths of approximately 30 ft. They are however utilized when an accurate drill string length is required since they can be added or removed to arrive at the required string length. For instance, if a 2500-foot drill is required, then 83 joints of 30-foot drill pipe will amount to 2490 feet. In addition to that, by adding a 10 feet pup joiner the exact length is attained without having to add more pipe length.
Wherever possible, the most common location for placing pup joints is at the upper end of the drill string underneath the kelly or the top drive. However, they can be positioned at any point within the string where fine-tuning of the variable is required. This means that drillers have short lengths of pup joints, which they can adjust to suit the foot of the well.
Only for controlling the length of the drill string, the pup joints are provided without any other function. They are regarded as primitive and in case of getting damaged, they are disposed of and not repaired.
X-Overs / Crossovers
On the other hand, crossovers commonly known as x-overs act as a connectors to help join the drill string parts or tools with dissimilar thread diameters, thread forms, or sizes. This enables different drill string sections and also tools to be joined.
Common types of crossovers include: Common types of crossovers include:
- Thread intersecting points – These are areas where it is possible to connect two threads that are of different sizes, pitches, shapes, and diameters, among other features.
- Weight passes through - Connect the drill pipe in different weights which vary from extra light, light, heavy, super heavy, and extra heavy wall thickness.
- Tool joint crosses – No more than 60 meters of cross-over connections between the drill pipe and heavy thick-walled drill collars or other bottom-hole assembly tools.
Crossovers enable the operator to achieve the best configuration of the drill string for the job that is needed in the drilling process. For example, extra heavy drill collars are required in order to beef up the weight near the drill bit in particular. But if they are used through the whole string length it increases cost and makes the process complicated. Using crossovers is effective since it ensures that collars and other specific gadgets are only placed in strategic positions.
Crossovers are generally short sections used exclusively for thread converting: however, there are cases when crossovers are a few feet, or more if transitioning from one type of drill sting component to another.
While buying disposable pup joints that are used only once before discarding, there are crossovers which if damaged, are reused after being refashioned. On a rig, one may come across hundreds of crosses to meet different connection needs of the structure.
Summary
- Pup joints are short, disposable columns employed in the makeup or trimming of the drill string to the correct length in feet.
- X-overs are adapters used to connect two different elements of drill string or tools with different thread sizes, weights, diameters, and other parameters for the best suitable configuration of the string.
While pup joints are designed to meet length demand exclusively, crossovers allow for joining incompatible drill string components as the necessity arises. All of them perform a very limited or minor but significant function in defining the make-up of a good drill string.
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