Optimization of Deep-Drilling Performance (December 2007)
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 105885, "Optimization of Deep-Drilling Performance:Benchmark Testing Drives ROP Improvements for Bits and Drilling Fluids," by Arnis Judzis, SPE, TerraTek; Ronald G. Bland, SPE, Baker Hughes; David A. Curry, SPE, Hughes Christensen; Alan D. Black, SPE, and Homer A. Robertson, SPE, TerraTek; Mathew J. Meiners, SPE, Hughes Christensen; and Timothy C. Grant, US DOE, prepared for the 2007 SPE/IADC Drilling Conference, Amsterdam, 20–22 February.
The drill bits selected for Phase-1 testing included a roller-cone bit to establish a baseline, two polycrystalline-diamond-compact (PDC) bits, and a diamond-impregnated bit. Sixteen tests were run during Phase 1. Test 1 used clean water to provide a baseline for idealized conditions. Tests 2 through 8 were run with 11-lbm/gal water-based drilling fluids with four different drill bits. These tests were designed to simulate conditions in the Arbuckle play. Test 9 provided a baseline test, but with the base oil. Tests 10 through 16 were designed to simulate drilling conditions in the Tuscaloosa trend with 12- and 16-lbm/gal oil-based drilling fluids and three drill-bit designs. Industry partners and the US Department of Energy (DOE) successfully completed benchmark testing of advanced diamond bits and high-pressure/high-temperature drilling fluids at high pressures. The full-length paper describes the results of this testing and identifies factors limiting rate-of-penetration (ROP) performance in deep wells and describes the development of drilling-fluid systems and bit-design philosophy to improve drilling performance significantly. Benchmark results match data from target field applications very well. This project is part of the DOE Deep Trek program. Sixteen full-scale tests of 6-in. bits were conducted at wellbore pressures greater than 10,000 psi.

Introduction
An important factor in future gas-reserves recovery is the cost to drill a well. This cost is dominated by the ROP, which becomes increasingly important with increasing depth. The object of this study was to improve the economics of deep exploration and development.
The original proposal was to test drill bits and advanced fluids under high-pressure conditions. Phase 1 of the proposal set out to establish a performance baseline and provide data upon which to make design improvements. Phase 2 sought to establish improvements in design, and Phase 3 aimed to take drill-bit and drilling-fluid improvements to the field for further testing and to commercialize the technology.
Earlier deep-drilling projects have reached a maximum circulating pressure of 7,500 psi. However, to simulate the deeper drilling environments desired for the Deep Trek program, it was necessary to circulate at more than 10,000 psi and generate confining and overburden pressures of 11,000 and 12,000 psi, respectively. To accomplish this, it was necessary to upgrade equipment and increase the pumping capacity of the drilling and completions laboratory.
There are a number of deep productive horizons in the US that present deep-drilling challenges. The test matrix developed for Deep Trek was based on two of these basins: the Tuscaloosa trend in southern Louisiana and the Arbuckle play in Oklahoma and north Texas.
The drill bits selected for Phase-1 testing included a roller-cone bit to establish a baseline, two polycrystalline-diamond-compact (PDC) bits, and a diamond-impregnated bit.