English to Russian Tech/Engineering Petroleum Eng/Sci Фрекинг

Что подразумевается под «head» в предложении «Thanks to the wide temperature operating range, LTC batteries are mainly used for horizontal drilling, also known as fracking that reaches head temperatures of 125°C (257°F).»
Статья: http://batteryuniversity.com/learn/article/bu_304c_battery_s...