A Combined Thermal Spallation and Melting Technology by Plasma Jet for Deep and Hard Rock Reservoirs

Abstract

Summary With the increasing demand for oil, gas, and geothermal resources worldwide, the efficient and economical construction of wells in deep and hard rocks has become very important, but conventional mechanical drilling technology cannot achieve this. In this paper, a new noncontact combined thermal spallation and melting technology by plasma jet is proposed. This technology can excavate rock materials by disintegrating brittle rocks into small fragments and melting plastic rock. Especially for hard granite, this method exhibits high rock removal efficiency with low specific energy. Furthermore, the plasma bit is not in contact with the rock, thus avoiding bit wear. A thermal spallation and melting experiment system is established, and laboratory tests are conducted. The influence of plasma current, plasma gas flow rate, confining pressure, and the types of rock-on-rock removal efficiency and specific energy are also researched. Results show that this novel technology can efficiently remove hard rocks, and hard granite is more likely to be removed under confining pressure than under the absence of confining pressure, indicating the feasibility of accessing geothermal, oil, and gas resources from deep and hard rock formations.