Changing wellhead height using equipment and technology for threading casing string at the wellhead

UDK: 622.
DOI: 10.24887/0028-2448-2019-12-150-152
Key words: change in wellhead height, injury hazard reduction, threading unit, high wellhead, low wellhead
Authors: D.V. Medvedev (RN-Uvatneftegas LLC, RF, Tyumen), M.M. Novikov (RN-Uvatneftegas LLC, RF, Tyumen)

While operating oil fields problems arise due to the change in the wellhead height. The main reasons for changing in the wellhead height that occur in field are an early arrival of the drilling rig on a just-constructed wellpad and swelling / subsidence of soil during operation. When working on a well with a high wellhead, the risk of injuries (falling from the rig floor) increases, as does the time for X-mas tree maintenance and servicing. In addition, difficulties arise when setting up workover rigs, which entail additional costs. When working on wells with a low wellhead, earthwork needs to be done since it is impossible to access the casing head for inspection and repair.

Having studied the practices used to date to change the wellhead height, the author of the article concluded that a threaded connection has to be used to change the wellhead height. It is important that the location of the couplings be selected for a particular well. So, it is necessary to develop a unit that allows to cut the surface casing directly at the wellhead, and then do threading to install the coupling. The article presents new equipment developed by RN-Uvatneftegas LLC together with GROM OJSC, a pipe threading unit of two standard sizes. The threading unit enables to bring the wellhead to the designed position in three stages. The first stage is cutting surface casing, which is done without using hot work. The second stage is shaping the nipple. After the nipple is shaped its size is checked using a caliber gauge. The third stage is threading. Depending on the type of thread, special equipment is selected, for example, a YE4 plate and a replaceable multi-faceted 4ERBUT075 plate manufactured by VARDEX are used to cut trapezoidal threads. Then a proper sized coupling and the zero nipple is installed in the casing head. The units have been put into operation in RN-Uvatneftegas’ wells. In 2018, 18 wellhead height change jobs were done.

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