Application of an Engineered Drilling Fluid System for Drilling an Ultra HT Geothermal Well in Central Italy
Lucio BUSSAGLIA, Alessandro CASCONE, Davide PALLOTTA, Alessandro DEI
[Newpark Fluids Systems and Enel Green Power, Italy]
For study purpose, a joint venture composed by the Italian National Research Council and an Italian Geothermal Operator, decided to drill over an existing unproductive well in an extremely hot formation in Central Italy only for study purpose. Downhole environment while drilling the 8 ½” and 6” sections was unknown. Studies were performed and assumptions were taken to obtain predictions that leaded to hypothesize a final BHST at planned TD of 3,500 mTVD, up to 450 °C. Different kind of products were evaluated to design a drilling fluid weighted up at 1.50 SG, that after 24 hours of static aging, time needed to trip out of hole, can still provide Fluid Loss control, Viscosity, Carrying capacity and do not show any sign of flocculation, sagging nor gelation. Fluid design and validation processes performed in lab previewed to aged it 24 hours in static condition at 200 °C due to equipment limitation. Also an HPHT rheology on fresh and aged fluids were performed through the use of Grace rheometer at 200 °C and 8.000 psi. During the intensive testing campaign different kind of chemicals were tested, as suspending agent, weighting materials, synthetic polymers for viscosity and fluid loss as resins as well. The formulation was tuned to fit with both environment, extremely high temperature downhole and surface temperature. Operational advises on how to manage the fluid properly, how to provide quick treatments when in surface to re-establish fluid specs and an indication on the fluid dilution, were made on behavior seen during the test. The fluid design was completed providing solution also in case of losses and stuck pipe. For the first one in particular a one-sacs product, based on diatomite, perfectly seal the fracture occurred. The drilling fluid designed and adjusted while drilling with introduction of different synthetic polymers fit with requirements till a network of fracture were found and drilling of last meters were performed blind.
|        Topic: Drilling and Completion Technology||Paper Number: 21056|