Perm Journal of Petroleum and Mining Engineering (Dec 2019)
Well construction and drilling technology for thermal water production in challenging geological conditions
Abstract
The paper considers special aspects of well construction and drilling technology aiming to produce thermal water. The practice of exploration, prospecting and production of thermal water in challenging geological conditions of Central Mongolia and analysis of the results from earlier drilled wells suggest that the approved and implemented ground water well construction and drilling technology does not provide reliable protection of opened thermal springs from cooling in the course of water movement along the wellbore from its bottom to the wellhead. The reason for this is a significant heat loss due to high thermal conductivity of well construction elements (steel pipes). The developed and proposed promising well construction includes several sequentially run casing strings with mandatory cementing of outer annulus with cement slurry. This helps reduce total heat flow loss and increase wellhead temperature of thermal springs by 10–15 °С. It is also suggested to use double-wall casing (“pipe-in-pipe” system) with heat insulating material (polyurethane foam) filling the interstring annulus. Use of this technology will help reduce heat loss along wellbore by 20–30 %. For drilling in this region, it is advisable to use pneumatic and hydraulic hammers for drilling a pilot wellbore and further expand it using a roller-cone bit. URB-2A-2 drilling rig can be advised as a drilling machine. Successful thermal water exploration and prospecting operations in the territory of Mongolia is an important future-oriented goal. The technology of well casing with pipes using polyurethane foam will help reduce heat loss along wellbore by 20–30 %, thereby enabling production of water with wellhead temperature approximating formation temperature. The suggested groundwater well construction improves cost effectiveness of production.
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