Abstract
The United States (U.S.) has experienced a natural gas “boom” due to the development of unconventional shale plays, but well development is energy intensive. Operations use electric drilling rigs typically powered by either three high-horsepower diesel engines (HHPDE) or three dedicated natural gas engines (DNGE) and associated generators. From a first law analysis, HHPDEs peak at about 42% efficient at full load, while DNGE peak at about 30%. Most fuel energy is lost as heat rejected by the exhaust and radiators. Concurrently, during cold seasonsor or in cold regions rigs utilize boilers to provide steam throughout the rig to prevent freezing and provide comfort.
Our analysis focused on a combined heat power (CHP) approach to improve the utilization factor (UF) of fossil energy consumed during unconventional drilling operations. Engine activity, boiler fuel consumption, and exhaust gas temperatures were recorded during winter drilling of an entire well in the Marcellus shale. Four characteristic activity cycles were extracted from recorded activity to represent four energy consumption scenarios. Exhaust and jacket water heat exchangers (E-HEX, JW-HEX) were designed and simulated, and results were analyzed in 0-D models for the four case scenarios. A 584-kWh hybrid energy management system (HEMS) was also designed and simulated into the model as another method to reduce fossil energy fuel consumption during well development.
HHPDE UF improved on average from 35.7% to 55.7% if only E-HEX were used and improved to 72.7% if JW-HEX were also used. DNGE average UF increased from 19.0% to 34.9% using E-HEX only. HEMS utilization improved UF up to an average of 76.9% and 39.1% for HHPDE CHP and DNGE CHP systems, respectively.
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