Customized Drilling Fluids Solutions for Challenging Geothermal Wells

Abstract

Abstract Geothermal wells are very challenging to be drilled due high temperature and the associated risks that involve this type of wells. In order to find the adequate solutions for the drilling fluid challenges on those type of wells, we did an extensive lab evaluation on multiple formulations, where we used our approved drilling fluids additives portfolio to customize the required water-based fluids (WBF) and invert emulsion fluids (IEF) formulations for high temperature wells. Wide lab testing on multiple WBF and IEF formulations were performed In-house, simulating the harshest conditions to properly customize the drilling fluids solutions for a Geothermal wells campaign. However, before start these geothermal wells campaign and after successfully lab testing verification, those formulation were implemented at the field in wells with Bottom Hole Static temperature (BHST) from 330°F (165°C) up to 450°F (232°C). Similarly, those drilling fluids were used to successfully drill, log and core across those challenging environments without any issue related to the thermal stability of the drilling fluids additives. In some of the wells, WBF was essential due logging requirements, for those wells, we relied on improved synthetic polymer thermal stable up to 475°F (246°C) to control the fluid loss, with the addition of temperature stabilizers and oxygen and H2S scavengers to optimize the polymers thermal stability. Also, we did utilize Causticized Lignite (CL) and chrome free methyl ester of sulfonated tannin (CFMEST) for better results as thinner and to help to control the fluid loss. Another fundamental additive in the formulation was the pre-hydrated bentonite used to enhance the suspension properties to avoid barite sag issues and to enhance the hole cleaning. Other wells were drilled with similar conditions for the Geothermal wells using IEF, for this type of fluid, efforts were established to formulate an innovative solution to the challenging high-temperature conditions in the studied area. The issues addressed included hole cleaning, hole instability for a narrow mud-weight window and reservoir damage. The strategy was based on the synergy of combinations between polymeric packages, emulsifiers, and filtration reducers of the engineered IEF formulations to build stable fluids and afford tight emulsion and fragile gel properties with minimal filtrations to the formations. As conclusion, we were able to customize Drilling Fluids Solutions for the multiple’s challenges expected during the Geothermal Wells operations. The excellent performance of those customized WBF and IEF formulations were delivered through use of novel emulsifiers chemistry, customized polymeric additives, innovative temperature stabilizers and a new multi-functional additive for narrow margin conditions, in preparation for this wells campaign.