Casing dan tali tiub adalah bahagian utama pembinaan telaga. Semua telaga digerudi untuk tujuan pengeluaran minyak atau gas (atau menyuntik bahan ke dalam formasi bawah tanah) mesti diikat dengan bahan dengan kekuatan dan fungsi yang mencukupi. Barang-barang tubular negara asal (OCTG) is a family of seamless rolled products consisting of drill pipe, casing and tubing subjected to loading conditions according to their specific application.
Dalam tiub minyak dan tiub, profil thread direka dan dibuat untuk menyediakan anjing laut hidraulik unggul antara peralatan dan paip. There are several types of Casing Threads used; they include:
Ⅰ.Buttress Thread– This type of thread profile is used in pipelines and wellbore tools. It is also used in liner tubular and well casings. The profile of the threading is usually in square cut shape. When the thread comes in contact with the mating thread, a hydraulic seal is created through interference fit which allows the buttress-threaded equipment to lock firmly.
Ⅱ.Round Thread – This thread profile is made for the tools and components used in slickline operations. It is also known as a knuckle thread. It is robust and can cause minimal wear and tear by dirt and other impurities inside the wellbore because of its round shape. The Round Thread profile is prepared as per API tubing grades. Round threads can be further divided into two types, iaitu, Profil Bulat Panjang Pusingan dan Profil Bulat Pusingan Pendek.