2013 年 78 巻 5 号 p. 360-365
An ICDP workshop proposal “Japan Beyond-Brittle Project (JBBP)” submitted by geothermal researchers mainly in Japanese and other countries was accepted by ICDP (International Continental Scientific Drilling Program) in 2012. The purpose of the scientific drilling project is to demonstrate the feasibility of a new concept of engineered geothermal system (EGS) in ductile formation zone. The target conditions of the JBBP well drilling are 3 to 5 km vertical depth, 350 to 500 °C estimated reservoir temperature, and 30 to 50 MPa estimated reservoir pressure. In this report, the author introduces the project outline, and discusses the technical problems relevant to drilling and completion such as extreme high temperature, hard and abrasive formation, low formation pressure and frequent risks of lost circulation, and HCl-H2S-CO2 coexisting low pH corrosive environment.