A Method for Combined Jet and Mechanical Drilling

Abstract

Abstract A method has been developed for jet assisted mechanical drilling with fluid pressures of up to 34,000 PSI. This paper will present the most recent drilling results of an ultra-high pressure drilling system that integrates with existing drilling equipment, to provide two (2) fluid steams to the drill bit, one provide two (2) fluid steams to the drill bit, one of which is highly pressurized. High rates of penetration over conventional drilling rates have been observed from field drilling results. Based on the most current field drilling projects, this paper will present details concerning the method for combined jet and paper will present details concerning the method for combined jet and mechanical drilling as well as actual field drilling results. Introduction It has been shown by previous laboratory and field drilling in-vestigations that increases in hydraulic horsepower directed at the hole bottom results in significant penetration rate improvements over drilling rates employing conventional drilling fluid pressures. pressures. Early field drilling tests involving jet assisted mechanical drill bits with operating pressures of up to 15,000 psi resulted in increased penetration rates of 2 to 3 times conventional rates penetration rates of 2 to 3 times conventional rates when operated at 2,400 hydraulic horsepower. These tests involved pressurizing the entire fluid stream being circulated to the drill bit, and although higher penetration rates were observed, the system design did not achieve commercial realization due to the inability of the pumps, swivel, drill pipe, and bit nozzles to operate economically and reliably. Moreover, the elevated pressure of the circulating system made rig operations unacceptably hazardous. A newly developed drilling system takes advantage of the benefits of drilling fluid pumped at ultra-high pressures to enhance drilling performance while maintaining conventional rig operating procedures and safety. In this system, a small portion of the total downhole mud flow is pressurized to portion of the total downhole mud flow is pressurized to 34,000 psi and is conducted to the drill bit through a dual conduit drill string. This allows a highly concentrated stream of high velocity drilling fluid to be directed to the bottom of the hole through extended nozzle(s) in the drill bit. The impact of the high velocity fluid stream significantly assists the mechanical action of the roller cone rock bit allowing penetration rates of 2 to 5 times over conventional systems in comparable drilling conditions. The system has demonstrated that it can operate reliably and safely in the normal drilling environment while imposing no alterations to normal drilling operations. SYSTEM DESIGN AND OPERATION The ultra-high pressure drilling system is comprised of two basic equipment divisions: surface equipment and downhole tools. The surface equipment includes drilling fluid conditioning and the pressurization and delivery of clean drilling fluid to the drill string. The drill string and associated downhole tools include all the elements found in conventional rotary drilling: kelly, kelly valves, drill pipe, collars, stabilizers and subs, as well as the drill bit, but modified to allow the passage of two separate fluid streams to the hole bottom. The ultra-high pressure drilling system utilizes only a small fraction of the total circulating mud stream (30 to 40 gallons per minute), and thus a lower developed hydraulic horsepower per minute), and thus a lower developed hydraulic horsepower of 600 to 800 hhp versus the 2,400 hhp from earlier high pressure drilling attempts. The lower developed horsepower plus pressure drilling attempts. The lower developed horsepower plus the inherent safety of the ultra-high pressure system design reduces risk from the operation to a minimum, while maintaining greatly improved rates of penetration. This method continues to utilize the existing rig circulating system to prepare and deliver a high-volume, low pressure stream of drilling fluid in the conventional manner. P. 561