Shilin Chen

Field Investigation of the Effects of Stick-Slip, Lateral, and Whirl Vibrations on Roller-Cone Bit Performance

The effects of downhole vibrations on the performance of polycrystalline diamond compact (PDC) bits have been well discussed in recent years. However, most studies on the downhole dynamics of roller-cone bits have focusedon axial vibration and its effects. The questions that remain to be answered are what kinds of vibrations a roller-cone bit experiences and what the effects of these vibrations are on roller-cone bit performance. To investigate these questions, a series of laboratory and field tests was conducted. Downhole vibration data were recorded by an advanced instrumented sub. Soft- to medium-hard formations were drilled with four 8½-in, roller-cone bits (IADC 517). Three kinds of harmful vibrations were observed, and their effects on bit performance in terms of rate of penetration, insert breakage, and bearing/seal life are discussed.

A New Theory on Cutter Layout for Improving PDC Bit Performance in Hard and Transit Formation Drilling

This paper presents a theory on layout PDC cutters in force-balanced groups. A group of cutters consists of two or three single-set cutters, which is able to efficiently remove a ring of rock. By carefully selecting the order of layout cutter groups, a new feature of a PDC bit is obtained: any three or four consecutive cutters on a bit profile may form a force-balanced cutter group, which ensures the efficient removal of any ring of rock. The concepts are verified by a core PDC bit and by a fullscale PDC bit in laboratory tests. Two field applications are provided in the paper to further validate the theory.