Abstract

Turkey’s geothermal power has evolved significantly over the decade and sitting on rank 4 worldwide for the past few years with total of more than 1500 MWe installed capacity. It is known that reaching to heat source in earth’s crust and uncovering the energy consists of series of complex operations. Drilling a well is one major part of the series and contributes to the success of the project imperatively. Drilling a geothermal well has some distinct challenges, most of which are interrelated with drilling fluids. Therefore, design of drilling fluids and on-site execution play a substantial role for harnessing geothermal energy.

GEOS has a critical role as the lead service provider for drilling and completion fluids, solids control and waste management services in oil, gas and geothermal wells in Turkey; it contributes greatly to the geothermal industry with drilling of more than 270 deep geothermal wells with major operators in Turkey. As of the time this study was being prepared, GEOS has been the drilling fluids service provider for drilling of 91 geothermal wells with 3000 m+ depth in Turkey.

This study features the overview of drilling fluids system used in reservoir sections of 3000 m+ deep geothermal wells in Turkey; with up to ~2700 m open hole and up to 99 °C flowline temperature. High temperature resistant water-based drilling fluid, HOTDRILL ®, was used in the reservoir sections of the wells, with the depths of up to ~4800 m, and reservoir temperatures between 155-295 °C. HOT-DRILL® stands out due to its resistance to high temperature and keeping the hole stable in such long open hole reservoir intervals. Moreover, a special care was given to minimizing formation damage while designing and executing the fluid system.

In this study, we present a review of drilling the deepest geothermal wells in Turkey from fluids perspective. The paper not only delivers the drilling fluids related challenges faced during the drilling the deepest geothermal wells in Turkey; but also presents the design principles of drilling fluids used in the wells, supported with extensive laboratory work, actual field data and highlights of the projects.