A New Type of Hydraulic Hammer Compatible with Conventional Drilling Fluids

Abstract

This paper describes the tests and concept behind a new hydraulic hammer. The objectives of these tests were to evaluate penetration rate performance of this hammer when used in conventional drilling conditions. To date the usage of hydraulic hammers has been hindered due to limited compatibility with drilling fluids solids content. Therefore, this hammer was conceived to operate with all kinds of drilling fluid, including Lost Circulation Materials. Additionally, this hammer would be used with conventional tri-cone bits. This is significant because inter-bedded formations can be drilled without repeated changes to the bottom-hole assembly and drilling can continue in the event of hammer failure. The technology consists of a rotating valve system that alternately directs fluid to a piston that drives down a steel mass to strike the rear of the bit and then to a port that bypasses the piston. This action allows the mass to return to its original position ready for the next downward stroke. The valve operates at a known frequency that is directly proportional to flow rate. Due to these unique characteristics, the Hard Rock Drilling JIP decided to test the hammer, the results of which are discussed here. Introduction Compared to conventional techniques, percussion tools are capable of increasing penetration rates in hard rock. For example, while drilling granite, penetration rates of 30m/h have been achieved1. However, the usage of hydraulic hammers has been limited by solids content in drilling fluids and the requirement for specialized drilling bits2. Targeting this particular application, the development of a new hydraulic hammer was initiated by Andergauge in 1996. Key operational objectives were 1) Penetration rate increase (Figs 1 and 2) 2) compatibility with all kinds of drilling fluid, including lost circulation material 2) compatibility with conventional tri-cone bits. The technology consists of a rotating valve that alternately directs drilling fluid to a piston that drives down a steel mass to strike the rear of the bit (Figure 3). Drilling fluid then flows through a port by-passing the piston enabling the mass to return to its original position ready for the next downward stroke. The valve operates at a known frequency that is directly proportional to flow rate (Figure 4). The rotating valve continuously generates pressure pulses, driving the steel mass eight times a second, which delivers 80,000 - 100,000 lb impact force at the bit. The impact improves penetration rates, but is of a sufficiently low magnitude to avoid damaging bit journal bearings. The rotating valve concept is proven in another established drilling tool. It has been used to withstand harsh down-hole drilling conditions in over than 250 runs, some of which have exceeded 200 circulating hours. Three tests had already been conducted using the same type of bit, BHA configuration to drill identical formations with and without the hammer. The first occurred in Stavanger, Norway. In this test, the rate of penetration using the hydraulic hammer was recorded as 50% to 100% higher than without. The second test was performed in Indonesia and the rate of penetration with the hydraulic hammer was 84% higher than without. However, both tests presented durability problems. A third test, considered an endurance trial, was conducted in Oklahoma, USA. The longevity of the run determined the test to be a success, independent of the 22% rate of penetration increase achieved. This run was considered a breakthrough as the hammer proved that it was capable of:tri-cone bit compatibility;drilling fluid compatibility;life expectancy in excess of 60 hours; andincreasing rate of penetration. Consequently, the Hard Rock Drilling JIP decided to evaluate the performance and life expectancy of the hammer through a series of tests in Stavanger, Norway.

Vibro-impact model and validation of the axial dynamics of a vibration-assisted drilling tool

“…In a technological perspective, the development of a drilling system that combines the rotary motion (scratching) with a percussive action (indenting) is not a new concept in the oil well industry. Such concept can be seen in the Andergauge Hammer [17], the SDS Digger fluid hammer [12,23], the BBJ fluid hammer [22] and the NOV fluid hammer [5,8,9,18]. Preliminary field test results with these vibrationassisted drilling tools (VAD) have shown a significant improvement in the rate of penetration (ROP) when drilling hard-rock formations.…”

A bit–rock interaction model for rotary–percussive drilling

“…Several downhole hydraulic hammers have already been deployed and tested for RPD [2,4,7]. Such hammers convert a portion of the drilling fluid power into mechanical impacts directly upon the drill bit.…”

“…The major feature of the percussive action is to increase the zone of damaged rock directly beneath the area of impact, facilitating the rotary action. To date, laboratory and field tests with hydraulic hammers have shown improvements on the penetration rate by a factor of two or three in certain rock formations, even when combined with roller-cone bits [2,4,6,7]. Although these hammers have led a considerable increase of the penetration rate, they are not extensively used by the drilling industry because of two main reasons: inconsistent overall results and mechanical failure [5,8].…”