In 2019, Geothermal Scientific Investigations Limited (GSI) installed our deepest borehole seismic array to date. The GSI designed and manufactured instrument was installed at the Chinese Continental Scientific Drilling (CCSD) site in Donghai, China in August 2019. 

The requirements for the array: That it be New Zealand made; have a 10-year design-life; and allow full re-use of the 5.2 km deep borehole after the extraction of the tool on completion of the projected 10 year data collection mission. GSI was also charged with the design and supply of the physical installation. The installation was undertaken in conjunction with Chinese drilling crew (Sinopac) and CAGS staff in temperatures of 48 °C measured at ground level.

There are four levels, each containing triple axis 4.5 Hz and 15 Hz geophone componentry in addition to three temperature sensors. The sensor modules are installed at depths of 1.5, 2.5, 3.0 and 3.5 km. Instruments at each level are designed to withstand down-hole pressures of ~350 bar, continuous temperatures of 150 °C and hydrocarbons inside the borehole. The tool-holders were specially designed to provide coupling to the 171 mm inner-diameter borehole. A novel GSI design allowed the seismometer instrument modules to be placed centrally inside the drill string. This is a major advantage in allowing safe transit of the instrument string during installation and extraction procedures. GSI work in conjunction with Advanced Seismic Instrumentation and Research (ASIR). ASIR supply considerable depth and expertise in seismic software and research.

Earthquakes and micro-seismic activity at all four levels, in all three axial orientations have been clearly and continually recorded since the initial installation success on August the 26th, 2019.