Enhancing Drilling Performance of Mud Hammers by Combining High Pressure Water Jets Slotting

Abstract

ABSTRACT Geothermal energy is a leading candidate in fulfilling our transition efforts to a clean, sustainable, non-intermittent and renewable energy source. However, high drilling costs act as a showstopper in geothermal exploration. One of the main factors contributing to this high price is the drop in drilling performance when drilling through hard crystalline granite rocks that are usually found at depths greater than 4 km. Studies show that increasing the drilling performance by a factor of 4 with respect to the current drilling rates of 1-2 m/h can reduce the drilling costs up to 65%. Percussion drilling using down the hole (DTH) hammer has proven to be efficient in drilling through hard rocks. In ORCHYD project, we combine high-pressure water jet (HPWJ) with a DTH hammer to increase the rate of penetration (ROP) by a factor of 3 to 4. The HPWJ creates a peripheral groove in the rock surface facing the drill bit. This peripherical groove of few millimeters is expected to release the rock surface from the surrounding confining stress regimes – requiring lower energy to break the rock using percussion drilling. It is also expected that the free surface created by the groove aids in reflecting the waves created during percussion. A DTH mud hammer is modified to allow the flow of HPWJ through the hammer body and redirect it to the periphery of the drill bit. The prototype developed in this work was tested on a laboratory scale drilling test rig under realistic downhole drilling conditions. At the current stage of the project, it is demonstrated that slotting peripheral grooves using the HPWJ improves the ROP of the hammer drilling system by a factor of 2 to 2.5. INTRODUCTION Deep geothermal energy is a promising and increasingly important source of energy production worldwide. Geothermal electricity production is particularly attractive for both rich and poor economies due to its ability to generate both heat and electricity, which are in high demand. Enhanced Geothermal Systems (EGS) are becoming more popular as they allow for combined electricity and heat production at geothermal power plants (Angelone (2014)). However, drilling operations are a major component of the total project cost, representing up to 40% of the total cost (Angelone (2014)). For a 3 km well, the cost can reach up to 15 M€ (Angelone (2014)), which makes it challenging to extract geothermal energy in an economically viable manner.