The goal of this project is to develop and validate (through field tests) a new low-cost all-digital pressure sensing technology for in situ distributed downhole pressure monitoring in unconventional oil and natural gas (UOG) fields. The key innovation of the all-digital sensor concept is the built-in nonelectric analog-to-digital converter (ADC), which eliminates the need for downhole electronics for signal conditioning and telemetry.
Clemson University - Clemson, SC 29634
Despite the growing supply from alternative energy sources, we will still rely on fossil fuels for most of our energy needs in 2050. Over the past decade, UOG development has dramatically increased US production of oil and natural gas. Based on the EIA’s 2018 Annual Energy Outlook, these trends are expected to continue through 2050 when UOG resources are projected to contribute 70.1% of total U.S. oil production and 76.1% of total U.S. natural gas production. UOG development became possible and profitable due to technological advancements in extended-lateral horizontal drilling and multistage high-volume hydraulic fracturing. However, UOG developments are extremely cost sensitive and marginally economical in many instances. The recovery efficiency of UOG is despairingly low, perhaps 20% in gas-rich shale reservoirs and less than 10% in liquid-rich plays. The reasons for the lack of economics in many UOG resources are due to the heterogeneity of the reservoir rock, petroleum fluids characteristics, cost of well construction, and how hydraulic fracturing is performed. Due to the lack of knowledge, information, technological and economical limitations, the full potential of US UOG resources has yet to be realized. Technology advancements to recover UOG resources are critical in maintaining future US oil and gas production levels.
The all-digital sensors eliminate the needs for downhole electronics. As a result, the new sensors are more robust, cheaper and have less drift compared with existing sensors. Because the sensor outputs are digital in nature, the new sensors can be remotely logged over a long distance, and many sensors can be digitally multiplexed for distributed sensing using a single surface interrogation instrument to significantly save the cost. Through planned research and engineering work, these technical innovations will result in a new affordable tool to enhance the understanding of UOG reservoir behavior, control the stimulations and productions, improve recovery efficiency, and expand the development of emerging UOG plays. In addition to distributed pressure sensing, the all-digital sensing concept can be developed into a new multiparameter sensing platform in the future to include temperature and acoustics. Together with the pressure data, the permanently installed all-digital monitoring system will fill critical data gaps in big data analytics and machine learning applications to inform decision making and improve the ultimate recovery of UOG.
The all-digital downhole pressure sensor based on a nonelectric digitizer was designed, manufactured, and tested. Iterations of design, testing and modification have been conducted to optimize the sensor to meet the requirements in measurement accuracy, long-term drift, and reliability. The hermetic packaging of the sensor has also been gone through several design, simulation, prototyping and testing iterations to protect the sensors during its deployment and operation in the high-pressure downhole environment. The downhole sensor prototypes were then calibrated using a temperature and pressure-controlled testing chamber. The sensor interrogation instrument has also designed, prototyped, and tested to obtain high signal-noise-ratio and ensure long-distance data telemetry with a low error rate. A software package with a user graphic interface (UGI) has been developed to operate the instrument for automatic sensor logging and data recording/storage. The sensor multiplexing module has also been designed, manufactured, and tested. Five digitizers were successfully multiplexed and interrogated by using only five wires. The completed protype sensing system (including the packaged downhole sensors, instrument, and software) were installed and validated in a research wellbore. The sensors have successfully survived the installation process and successfully logged the downhole pressure data during and after the sensor deployment. The all-digital sensing system was able to measure the downhole pressure reliably over long time (15 days, limited by the availability of the research wellbore) and long distance (2550 ft, limited by the depth of the research wellbore), and the measurement results agreed well with that obtained by the reference sensor.
In the upcoming quarters, the team will be focused on further optimizing the sensors by reducing the hysteresis, decreasing the sensor size, and increasing the measurement resolution. The sensor multiplexing system will also be tested by interrogating multiple sensors in real time.
“Glass Additive and Subtractive Manufacturing of a Fiber Optic Rotary Encoder for Downhole Pressure Sensing,” X. Zhu, J. Tang, Y. Wu, X. Jiao, R. Nygaard, D. Cercone, H. Xiao, IEEE Sensors Journal, 2023.
Clemson University Project Review Presentation [PDF] [Video] October 2020
Project Landing Page
Kick-off Meeting Presentation [PDF] October, 2019