A First Look at 100% Thermally Stable Polycrystalline Diamond (PCD) for Oil & Gas Drilling
Authors: Zhan Guodong David , Lyons Nicholas , Al Otaibi Msalli , He Duanwei , Robertson Andrew 
Published: September 2022

Abstract
Since the late 1970's, research on the efficiency and cutting life of polycrystalline diamond compact (PDC) cutters identified elevated temperature due to frictional heating as one of the primary accelerants of wear to the diamond cutting edge. Temperatures as low as 700 °C activate the back-conversion process, whereby diamond transforms into graphite, due to the presence of catalytic metal in the diamond structure. The Oil and Gas industry responded by investing years developing technologies to reduce the temperatures that PDC's experience in application via improved hydraulics for cooling, higher quality surface finishes to reduce friction, and improved thermal stability via material structure and chemical treatments. PDC cutter technology has progressed substantially in the last 30+ years, but the challenge of synthesizing a perfectly thermally stable PDC still remains unmet until now. Recently, Zhan (2018, 2020, 2021a and 2021b) first developed a new strategy to synthesize ultrastrong and catalyst-free polycrystalline diamond (CFPCD) or binderless PDC cutters with a new world record as the hardest and tough diamond material and the highest thermal stability up to 1,400°C via his invented ultra-high pressure and ultra-high temperature (UHPHT) technology, which is three to seven times higher than conventional PDC cutters used in the industry. An initial laboratory study of a new catalyst-free extreme high pressure, high temperature CFPCD material provides the first instance of a catalyst metal free polycrystalline diamond structure that actually boosts rock cutting performance above and beyond that of the current state-of-the-art PDCs.
Proof of concept CFPCD specimens were evaluated against commercial, state-of-the-art non-leached (NL) and deep leached (DL) PDC cutters in the lab. Two CFPCD grades, A & B, were run through a series of tests to evaluate their potential for rock cutting and, ultimately, for use in oil & gas drilling applications. Laboratory testing was conducted on vertical borer wear tests, KIC fracture toughness tests, and thermal degradation monitoring tests.
Lab results reveal a threshold that must be exceeded in the synthesis of catalyst-free CFPCDs to achieve sufficient diamond intergrowth and structural integrity to surpass the current state-of-the-art DL PDCs. CFPCD grade A wore equivalently to a commercially available NL cutter and exhibited a toughness comparable to that of commercially available DL PDC material. Grade B, synthesized at a significantly higher pressure than grade A, cut 5.7 times the distance of a commercial NL PDC for an equivalent wearscar volume, and exhibited a 160 % reduction in wear volume comparing volume of diamond worn to volume of rock cut (or G ratios) to DL PDC after cutting the equivalent of roughly 50 miles of rock. The wearscar surface of Grade B also exhibited excellent integrity with no cracking or chipping damage compared to Grade A and commercial PDC grades. This is the first documented instance of a catalyst-free PDC achieving the best wear performance and integrity (fracture toughness) than the current PDC cutters offering on the market.
Thermal stability limits of PDC cutters has greatly improved in the past 20 years, but the best commercial PDC's still rely on extending leach depths with certain performance limits. For the first time in the industry, there is a PDC material than shifts this boundary without the use of catalysts and leaching technology, producing a truly differentiable PDC cutter.