Mitigation Strategies and Geologic Context of Lost Circulation at Steamboat Hills, Nevada

Abstract

Losing circulation of drilling fluids remains one of the most common and expensive problems facing geothermal energy development today, representing up to 20% of exploratory drilling costs and 10% of the costs of reservoir development. This is the third of four reviews of geothermal fields that experienced problems with lost circulation and will focus on the Steamboat Hills Geothermal Field in western Nevada. Steamboat Hills is on the eastern margin of the Sierra Nevada in an area where dextral shear and east-west extension predominate. The Steamboat Hills reservoir is within crystalline basement rocks (Cretaceous granodiorites and Paleozoic metasediments) at relatively shallow depths of 1000-2000’ and much of the heat is thought to be associated with Plio-Pleistocene rhyolitic volcanism. Permeability in this field is dictated by fractures in resistant formations that are related to extensional normal faulting. Depths of wells and lost circulation vary significantly, but losses are commonly associated with faults and fault intersections and preceded by secondary mineralization related to hydrothermal alteration of the host rock. Strategies to address lost circulation in Steamboat Hills include the use of large amounts of lost circulation materials, cement plugs in the cased interval, and drilling blind once in the production zone of the well. Common lost circulation materials and polymers used include proprietary blends, bentonite chips (in the cased interval), cottonseed hulls, and rice straw. In contrast to the previous fields examined, large amounts of lost circulation materials were observed to “cure” lost circulation on a semi-regular basis. Further experimental and modeling studies addressing lost circulation materials and strategies, informed by these case studies, are underway in order to develop a systematic understanding of contextually informed efficient and effective responses to lost circulation. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2022-0732 C.