By Abdulrahman Tayar, Ahmad Khayyat, Mohammad Dawood
Saudi Aramco D&WO

Abstract

Drilling operations contain an often verlooked source of energy in the form of geothermally heated drilling fluids in drilling a well. The feasibility of utilizing geothermal energy from heated drilling fluids to generate power, thereby reducing carbon emissions and operational costs in drilling operations was studied. Through a proposed system involving an Organic Rankine Cycle (ORC), heat extracted from the circulating wellbore fluids is converted into useful electrical energy. The methodology involved a literature review, process engineering design, and simulation to optimize the system parameters. Promising results indicate significant potential for power generation and emission reduction, particularly when compared to industry-standard diesel engines.

Cultivating a Culture of Resilience and Continuous Improvement

Drilling operations worldwide generate substantial amounts of geothermally heated drilling fluid, which is currently underutilized if not completed untapped. The objective is to investigate the viability of harnessing this wasted heat to produce electricity, thereby mitigating carbon emissions and reducing operational costs. Currently, large volumes of drilling fluid are circulated during drilling operations, with the heat generated lost to the environment. Our proposed solution involves capturing this heat through an ORC system, then converting it into useful electrical energy. By doing so, we aim to reduce emissions, cut costs, and create a closed-loop system that enhances operational efficiency.

What would the system look like?

The proposed cycle involves redirecting wellbore fluids circulating out of the well during drilling operations. An ORC can be set up to extract thermal energy from the outflow fluids and then divert it back to the circulation system. The ORC system extracts heat from the fluids through an intermediate fluid, or refrigerant, in a heat exchanger. The intermediate fluid can then be used to power a turbine, converting its potential energy into mechanical work. The turbine, in turn, will power an electrical generator, converting kinetic energy into electrical potential energy, which can be utilized or stored in batteries. Figure 1 below demonstrates a step-wise procedure on how the heat extraction unit operates in drilling operations.

Heat extraction unit workflow showing power generation from mud circulated out of the hole

Figure 1

Fostering Collaboration: Partnering for Innovation and Resilience

A comprehensive literature review and process engineering design were conducted to determine design compatibility with drilling rig’s system and parameters, such as flow rate, mud properties, formation temperatures, and thermal gradients. Simulation studies were performed to verify the model and optimize the system on various parameters, to characterize the relationship between flow rate, temperature and energy recovery. The simulation model can then be used as a tool in the planning phase of a well, to provide insight into utilizing the system on a given well.

The Results

Simulation results demonstrate promising outcomes, with Figure 2 depicting net power generated against flow line temperatures and flow rates. The model has shown the economical inlet flowline temperatures to range from 153 to 276 degrees Fahrenheit. Flow rate was directly proportional to the net power generated, however at higher temperatures, that effect is diminished due to the rate of energy transferred between the fluids. From the wide variety of working fluids available commercially, R123 emerged as the most efficient working fluid due to its low boiling point and high thermal conductivity. Given an optimal turbine and generator design, the net power of the proposed system can yield up to 225 kilo-Watts per well. Benchmarked against the industry standard diesel engines, our design holds the potential to save up to 206 Metric Tons of CO2 by eliminating the need of 20,662 gallons of diesel that would have been used during drilling operations. Moreover, the system would result in a considerable decrease in fluid loss due to evaporation, as the drilling fluid is cooled down in a closed-loop. Imperatively, the system shows greater promise for application in producing wells, offering prolonged energy production compared to drilling activities, since produced fluids will naturally be at a thermal steady-state within the geothermal profile.

Simulation results showing net power generation (kW) corresponding to a range of flow line temperatures (°F) and flow rates (US Gallons/minute)

Figure 2

Conclusion

Harnessing geothermal energy from drilling operations presents a sustainable solution for reducing carbon emissions and operational costs. The proposed system demonstrates significant potential for power generation and environmental impact reduction, paving the way for greener and more efficient drilling practices. Further research and implementation efforts are warranted to fully realize the benefits of this approach.

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