Drilling apparatus and method

#Drilling for exploration and field preparation is a primary component of exploitation of natural resources, including oil, gas, water, minerals, and geothermal energy. Hammer drilling is often considered superior to other methods due to the best potential for the highest rate of penetration (ROP) and real-time seismic excitation for site properties and reservoir evaluation. However, the benefits can be mitigated at great drillhole depth, drilling mud pressure, density, and/or viscosity.

#The present disclosure addresses the problem of decreasing penetration rate with downhole percussion drilling caused by the increasing mud pressure with depth and mud density. Hammer drilling is an efficient technique regarding cost and speed in shallow depth. However, pressure, density, and viscous effects typically degrade its advantages with increasing depth. In a particular embodiment, the present disclosure provides an integrated drill bit, hammer engine, and hammering cycle actuation design that combines rock hammer action with water/mud pressure/velocity waves (PVW), in which mud expansion energy is synchronously converted into percussion energy. An integrated drill bit, hammer engine, and hammering cycle actuation design is provided that combines rock hammer action with a controlled, balanced volume to reduce pressure variation in the drillhole and reduce compression energy. In another embodiment, the present disclosure provides a method and apparatus using multiple drill bits, the motion of which are synchronized for efficient PVW excitation in the drillhole.

#According to one aspect of the disclosure, large-amplitude axial drill bit movement is allowed, which can increase the bit's impact energy for rock breaking by concentrating the overall, cycle-averaged energy to a shorter time period. Thus, this aspect of the disclosure can increase the “mechanical advantage” of the hammering action, that is, allowing for a long time period of hammer forward acceleration (at aF), followed by a short time period for impact deceleration (at aI), giving a high mechanical advantage of aI/aF. Axial drill bit motion is allowed at the face under extreme high drill string load, mud pressure, density, and viscosity. This free axial movement can be achieved by an arrangement of twin or triple drill bits and alternating, two- or three-phase bit motion control.

#FIG. 1(A) is a schematic diagram of a mud hammer engine with a moving piston being used in a drilling cavity for dynamic pressure wave creation in a method according to the present disclosure. FIG. 1(B) presents graphs of mechanical force (upper graph) and mud pressure (lower graph) versus time, showing the desired variation of mud pressure and mechanical force on the bit with time in the arrangement of FIG. 1(A).

#FIG. 2(A) is a schematic diagram of a mud hammer being used in a borehole, illustrating suction pressure creation with overall volume variation in the drill cavity using a borehole piston and a single drill bit. FIG. 2(B) presents graphs of, from top to bottom, drill cavity pressure, overall drill cavity volume change, borehole piston position, and drill bit position versus time for the arrangement of FIG. 2(A).

#FIG. 3(A) is a plan view of a mud hammer having twin, inner and outer, drill bits. FIG. 3(B) is a schematic diagram of a mud hammer being used in a borehole, illustrating suction pressure creation with overall volume variation in the drill cavity using a borehole piston and twin drill bits. FIG. 3(C) presents graphs of, from top to bottom, drill cavity pressure, overall drill cavity volume change, outer bit motion, and inner but motion versus time for the arrangement of FIG. 3(B).

#Unless otherwise explained, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. In case of conflict, the present specification, including explanations of terms, will control. The singular terms “a,” “an,” and “the” include plural referents unless context clearly indicates otherwise. Similarly, the word “or” is intended to include “and” unless the context clearly indicates otherwise. The term “comprising” means “including;” hence, “comprising A or B” means including A or B, as well as A and B together. All numerical ranges given herein include all values, including end points (unless specifically excluded) and any and all intermediate ranges between the endpoints.

#In one embodiment, the present disclosure uses multiple, such as at least two, reciprocating elements in the drillhole including at least one, or multiple, hammer drill bits; move the elements with alternation to each other in such a way that the net volume displacement by the moving parts in the drillhole, ΔV, is controlled to be minimum for reducing compression work and thus for loosing useful energy from the available amount from the drill engine for rock breaking; but if desired, keep a small component of ΔV for creating PVW for enhancing rock chipping by tensile stress; and synchronize the peak of the pressure depression wave with that of the impact moment of the drill bit's reciprocating motion to enhance, instead of hamper, rock breaking by the creation of PVW.

#Cyclic manipulation of downhole mud pressure around its mean in situ value is applied in high pressure systems. The disclosed method and apparatus can relieve downhole hammer drills from high mud pressure at critical instants, and work as if in a shallow well. Therefore, hammer drilling will made more practical for deep holes, allowing for its other advantages to be realized, such as increased bit life, improved trajectory alignment, low cost, and added benefits in seismic communications.