This type of plug is used for snubbing job, like running tubing. It is a tubing plug mounted on the end of tubing string run in hole to make sure that the fluids in the hole will not flow into the tubing while running in hole. This can prevent blowout and function as a well control mean. While the tubing is run to the targeted depth, a slickline job is needed to pull out the prong.

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Note added at 401 days (2012-10-12 07:45:49 GMT) Post-grading
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这类堵头一般用在下油管作业（带压作业、不压井作业）中，是一种油管堵头，安装在油管串的底部，在下油管时能防止井内流体流入油管内，进而预防了井喷等事故，起到井控的作用。在油管下到设计深度后，井口油管挂安装完毕后，需要进行钢丝作业，将平衡杆拔出，进而允许油气井进行生产。