Optimization of Deep-Drilling Performance—Benchmark Testing Drives ROP Improvements for Bits and Drilling Fluids

Abstract

A critical cost in future deep-oil and -gas recovery is the cost to drill a well. This cost is dominated by the rate of penetration (ROP) that becomes increasingly important with increasing depth. Improving the technology of drilling and increasing the ROP was the object of full-scale laboratory testing conducted under a joint industry and Department of Energy (DOE) program titled "Improving Deep Drilling Performance" (Black and Judzis 2003). Simulations of deep-well drilling in the Arbuckle play and the Tuscaloosa trend were accomplished during 16 full-scale, high-pressure tests using four different 6-in. drill bits, three types of rock, and five different drilling fluids.This paper describes what is believed to be the first set of fullscale laboratory drilling tests yet performed at bottomhole pressures in excess of 10,000 psi. Accomplishments of the testing and analysis include the following:• Laboratory data was compared with field data to confirm that the simulated laboratory conditions provided similar results to what would be expected in the field.• ROP reductions were significant when "mudding up" at high bottomhole pressures.• Polycrystalline-diamond-compact (PDC) bits provided substantially higher ROP performance than impregnated or rollercone bits in the environment of this study.• The relationship between ROP and confined-rock strength is not a simple function of bottomhole pressure alone.• The mechanical specific energy (MSE) when drilling at high bottomhole pressure is often substantially higher than the rock's compressive strength, even when the bit is drilling efficiently.• Fluid invasion of intact rock and of rock broken up by the bit's cutting structure seems to play a major role in controlling ROP at these high bottomhole pressures.• Drilling-fluid compositions and properties that promote invasion without provoking formation damage, and bit-design features that facilitate the removal of rock debris from the hole bottom, hold promise for improving drilling efficiency in hard rock drilled at high bottomhole pressures.

Experimental Study of MSE of a Single PDC Cutter Interacting With Rock Under Simulated Pressurized Conditions

“…A few experiments were performed with water in the lower confining pressures, but the data scatter was too high. The cuttings recently have been shown to be made up of completely crushed and compacted rock particles, as opposed to the earlier perception of chips of elastic material bonded together (Judzis et al 2007). The reductions in cutting efficiency when cutting Indiana limestone are also more dramatic compared to cutting Carthage marble.…”

“…In their experiments, they found that the MSE for drilling rocks under atmospheric conditions is a number very close to the unconfined compressive strength (UCS) of the rock. While this phenomenon has been documented in several laboratory experiments (Cook et al 1991;Gray-Stephens et al 1994) and studied analytically by others (Kolle 1996;Detournay and Tan 2002), results of many full-scale experiments have shown that the strengthening of the rock because of shear dilatancy can only partly explain the reduced efficiencies and the high MSE required to cut rock under pressure (Judzis et al 2007;Black et al 2008). Pessier and Fear (1992) questioned whether the same comparison could be done under pressurized conditions using the confined compressive strength (CCS) of the rock instead of the UCS.…”

“…However, in all their experiments, even under ideal hydraulic conditions, the MSE that they measured during drilling a rock under pressure was much higher than the CCS of that rock under the same confining pressures. Judzis et al (2007) suggested that one possible reason for the high specific energies is the unproductive work that is being done on the crushed rock material held in place on the hole bottom by local differential pressures and that controlled invasion of the bottomhole by the drilling fluid can affect the drilling efficiency. While this phenomenon has been documented in several laboratory experiments (Cook et al 1991;Gray-Stephens et al 1994) and studied analytically by others (Kolle 1996;Detournay and Tan 2002), results of many full-scale experiments have shown that the strengthening of the rock because of shear dilatancy can only partly explain the reduced efficiencies and the high MSE required to cut rock under pressure (Judzis et al 2007;Black et al 2008).…”

Clay-Free High Performance Water-Based Drilling Fluid for Extreme High Temperature Wells

“…ROP is enhanced by HP WBM formulations that minimize bit balling and accretion. ROP can be further enhanced because of the low colloidal solid content of many HP WBMs (Judzis et al 2009;Beck et al 1995). These traits not only make HP WBMs an improvement compared to conventional water-based fluids (Rodriguez et al 2010), but HP WBMs can also deliver an IEF-level of performance in certain circumstances.…”

A methodology for the optimization of PCD compact core drilling in basalt rock

“…For example, optimization of rock cutting operations of both large diameter (e.g., [11,12]) and compact scale (e.g., [13,14]) operations have long been attempted with the aim of improving tool life, and consequently, penetration depth.…”