Publication Date:
2020-05-26
Description:
Work at GZB (International Geothermal Centre) had been focused on several potential, novel micro type drilling technologies. These technologies have been investigated and discussed to determine possible future options. In this report the different technologies are being presented, starting with abrasive enhanced jetting, followed by pulsation and mechanically supported drilling, ending with percussion type mechanical rock destruction and drilling. Their influence on rock disintegration and drilling efficiency have been investigated in several laboratory experiments. These were carried out to manifest a better understanding of each potential technology. The results are being presented and discussed regarding the potential increase in drilling performance versus lessons learned within WP 5.1 as well as their applicability in the field. Water jets enhanced with abrasive particles have the ability to penetrate into virtually any rock type with rather low hydraulic power. However, the (downhole) applicability in the field is commonly a challenge due to extremely fast and high wear on the pertinent material and equipment other than the rock itself, including the jetting BHA (bottom hole assembly) and nozzles. In order to partly overcome this dilemma a dedicated nozzle for abrasive mixing has been designed and patented. It may be found under patent number DE 10 2016 125 916.0. Pulsating water jets are a different approach to enhance the efficiency of rock destruction via water jet. Both techniques are based on pure high pressure jets, one adding particles to a constant jet (abrasive jetting), the other one dividing and cutting a constant jet into small, short sections to generate not constant impulses (pulsation). Various tests were carried out under reservoir type conditions inside the autoclave system “iBOGS mini”. So far the effect of pulsation seems to be low compared to the suppressed cavitation erosion mechanism under elevated pressure conditions. A very different approach is the use of micro turbines powered by the high pressure water, combined with a mechanical drill bit. The hydraulic energy of the intensified water is not directly used to penetrate the rock, but rather to generate rotation even with substantial torque via a micro turbine system. Thus, the jetting action is neglectable, as the mechanical bit does the cutting into the rock mass with rather high rotation speeds. Testing showed rather high efficiency regarding drilling speed. The technology works also independently of the rock type. All tested rock types including granite were drilled successfully with rather low hydraulic power of 10 kW (e.g. turbine differential pressures of 150 bar and flow rates of about 40 l/min). Future testing at macro and meso scale levels are being planned to verify reliability, drilling direction and more. As of now, this technology seems to be the most promising for hard rock formations in the very near future. One challenge may be their slightly larger geometrical shape and size regarding the current downhole installation scheme. But this is underway to be solved in the near future. On the final end of the possible spectrum for high pressure jet drilling from pure jetting (e.g. SURE WP 5.1 to 5.3) to transforming the intensified, high pressure water to eventually generate and gain more mechanical support over jetting are percussion engines as being known and used in so called DTH (down-the-hole) hammers. Here, the intensified water does generate medium frequency mechanical blows (“pulses”, e.g. 50 – 70 Hz) by powering a piston and drill bit for rock disintegration with very high drilling speeds. The differential pressure across such a hammer with approx. 180 bar is at the same level as for the before mentioned micro turbines and thus, much lower than for direct high pressure water jetting. Compared to the turbine, the hammer works with a highly dynamic force and low rotation, whereas the turbine is based on a very constant load or weight on bit (WOB) with rather high rotation speed (RPM), generating more of a grinding effect. However, the hammer ́s geometrical shape, namely its length, makes it much more difficult to be deployed downhole for micro drilling, while also some rotation needs to be generated. Here is more work underway as well. To summarize high pressure jet drilling, the full scale of currently possible solutions from pure high pressure jetting to mechanically enhanced or supported jet type drilling including abrasives, pulsation, micro turbines and percussion motors were considered and being looked at regarding their possible application in hard rock formations and future potential.
Language:
English
Type:
info:eu-repo/semantics/report
Format:
application/pdf
Permalink