Abstract

This paper presents a review of the benefits and performance of downhole percussion hammers. The advancement of drilling technology and the extensive use of coiled tubing coupled with different downhole motors prompted another look at the percussion type of drills. Achieving very high extended reach wells also have nessitated a high axial driving mechanism. The potential benefits of the percussion type of drilling machine for future operations are given, supported by the performance of the tools. The use envelope and the benchmarks of the tools by different manufacturers down the years have been discussed. The hammers developed and operated have been supported by enough field runs to prove the sustainment of the tools. Different models of downhole hammers can be categorized as first generation tools which include the developments from early time to the development of Bassinger tools. The second generation tools from post-Bassinger to the recent developments are discussed broadly. The basic principle involved and the necessity to consider the correct stress waveform to simulate the performance of the downbole hammer energy transfer are reviewed.

Introduction

Millennia of time have transpired since the surface of the earth was first penetrated by human beings for their needs that could not be obtained on the suface of the earth. There are several milestones in the progress of cutting machines. Cable tool was an early form of making a hole by cutting rocks by impact through dropping a heavy hammer attached to a cable. The disadvantages of cable tool drilling were limited number of blows, slow rate of penetration (ROP) and weak cable link. Slowly, cable tool drilling was replaced by the rotary type of drilling methods. This resulted in continuous rock-bit interaction. Weight on the bit (WOB) was increased by increasing the number of drill collars above the bit. Continuous hole cleaning, using mud or air/gas as the circulating medium, contributed to better hole conditions as well as bit cooling and lubrication. The worldwide acceptance of the rotary method and tools made the introduction of new technology in drilling methods difficult. Recent increases in application of horizontal wells and in particular slim lateral holes, resulted in the development of coiled tubing drilling. Since, in coiled tubing drilling system the coiled tubing cannot be rotated, a downhole motor is essentially required for drilling. Despite the accelerating pace of improvements in downhole motors, efficient slimhole motors remain unavailable.

Percussion Drilling

Increasing cost per foot, using the conventional drilling methods and the flattening of the efficiency achieved by rotary drilling, have necessitated a re-look at other modes of cutting the rocks. This led to the idea of the percussive type of drilling. The word "percussion" means impact or collision or vibratory shock which is one of the most powerful forces. The principle of utilizing the energy generated by the impact load to cut the rocks, caught the eyes of the researchers early in the 1950s. The principle came down in the form of percussion drills and was called by several names, such as downhole hammer, percussion hammer, percussive drill, down-the-hole hammer, etc.

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