<p>The U.S. has experienced a natural gas “boom” due to development of unconventional shale plays and the intention to phase towards green energy sources but well development is an energy intensive process. There are multiple stages in unconventional well development that have high energy demands. Operations use electric drilling rigs powered by either three high-horsepower diesel engines (HHPDE) or three dedicated natural gas engines (DNGE) and associated generators depending on drilling company equipment and fuel availability. From a first law analysis, HHPDE are about 42% efficient at full load, while DNGE peak at about 33%. Most fuel energy is lost as heat rejected by the exhaust and radiators. Concurrently, during cold seasons rigs utilize diesel powered boilers to provide steam throughout the rig to prevent freezing and provide comfort. Our analysis focused on a combined heat power (CHP) approach as a means to improve the utilization factor (UF). 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 to represent four energy consumption scenarios based on different rig operations, including two one-hour drilling cycle, a one-hour tripping/casing cycle, and a 24-hour combined activity cycle. Exhaust and jacket water shale and tube heat exchangers (E-HEX, JW-HEX) were sized and designed in CHEMCAD software based on HHPDE full load operation and results were analyzed and compared in a 0-D MATLAB-SIMULINK software model for each of the four scenarios and each energy source. Commercially available E-HEX performance were also modeled, analyzed, and compared to designed E-HEX. HHPDE UFs improved on average from 35.6% to 54.71% if only E-HEX were used and improved to 57.92% if JW-HEX were also used. DNGE were less efficient than HHPDE; therefore, more waste heat was available and at a higher quality (temperature). DNGE average UF increased from 19.5% to 28.80% using E-HEX only. Heat recovery exceeded heat demand in all scenarios analyzed, limiting UF. Total UF could peak at 72.66% and 38.65% on average for HHPDE and DNGE respectively if additional heat were required in colder weather conditions. Due to the performance of DNGE E-HEX, a combination with JW-HEX was not necessary to be exanimated as heat recovered exceeded boiler’s heat demand throughout all cycles’ activity. CHP systems for HHP drilling rigs at unconventional well sites operating in cold conditions could save on average 83.8 liters of diesel fuel per hour of boiler activity; reducing CO<sub>2</sub> emissions on average by 224.7 kg per hour.</p>

Analysis on Combined Heat and Power Hybrid Systems for Unconventional Drilling Operations

Paper Proceedings: https://asmedigitalcollection.asme.org/ICEF/ICEF2021/volume/85512

ASME 2021 Internal Combustion Engine Division Fall Technical Conference (ICEF2021)

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