The goal of this two-year research project is to utilize a pressure/salinity responsive electrically active proppant (EAP) to characterize hydrogeological response of fracture network in simulated production conditions. The project seeks to develop an approach to remotely monitor changes in pressure and/or salinity within the fractured network in near real time. The methods developed and demonstrated during this study will lead to a better understanding of the extent of proppant-filled fracture networks, formation stress states, fluid leakoff and invasion, and characterizations of engineered fracture systems.

Bureau of Economic Geology (BEG) at the University of Texas at Austin - Austin, TX 78759

Sub Performers
Duke University – Durham, NC 27705
University of North Carolina – Raleigh, NC 27699

Hydraulic Fracturing (HF) has evolved to a sophisticated multistep process with varying flow rates, carrier fluids (e.g., gel or slick water), proppant loadings, and proppant grain sizes. Primary oil recovery from a hydraulically fractured reservoir is often a small fraction of the original oil in place ranging between 5 and 10% from tight unconventional reservoirs. As stated in the FOA1990: “Part of this problem is due to the inability of current well completion processes to effectively stimulate the entire reservoir volume in contact with the wellbore. Innovative technologies are needed that can help improve the effectiveness of reservoir completion methods, maximize stimulated reservoir volumes, and optimize recovery over the entire producing life span of a well”. To improve a well completion design, we first need to enhance the current fracture diagnostic techniques. However, detecting and delineating a subsurface hydraulic fracture is extremely difficult because the induced fracture network is only fractionally propped, and these propped fractures are generally very thin. Current diagnostic tools such as microseismic and tiltmeter monitoring can provide information on fracture extent but provide little or no information on the movement and final distribution of proppant or production fluids.

Previous works at the Bureau of Economic Geology (BEG), have resulted in a set of validated electromagnetic (EM) codes to interrogate HF extent remotely by EM geophysics. Based on these results, an updated multiscale, multimode forward and inversion approach will be developed. Lab studies will be carried out to characterize the impact of salinity and pressure changes and fluid flow on the electrical conductivity of an EAP pack. This information along with host rock properties will be used as input for solvers to discern feasibility of detection of salinity and pressure changes and will inform design of optimal EM survey configurations for successful demonstration of the concept. Once sensitivity of detection has been demonstrated in Year 1, field survey work will be conducted at the BEG’s Devine Field Pilot Site (DFPS) in Year 2.

This project has several significant impacts on energy production from hydraulic fracture networks and can be applied to the subsurface applications. By enabling the optimization of refracturing processes through monitoring fracture dynamics (e.g., flow, leakoff, pressure evolution, and salinity changes), this project results in more efficient production from hydraulically fractured reservoirs. The unique and comprehensive datasets collected in this study will be disseminated to the public and will lay the foundation for the advancement of additional geophysical mapping and modeling techniques. The highly instrumented and characterized EAP-filled fracture anomaly at the DFPS can be utilized as a unique asset to conduct and validate future studies related to this project.

• Planned and executed bottomhole and surface pressure monitoring, precise flowrate measurement, surface tiltmeter mapping, and passive wellbore distributed strain sensing (DSS) during the final EM survey at the DFPS.
• Conducted multiple injection cycles with variations in the injection rate and duration, and the injected fluid ion content
• Resolved the shortcomings of the previous survey by increasing the receiver spacing to 30 ft, centralizing the transmitter line with respect to the northwest-southeast symmetry axis of the receiver survey area, replacing the surface injection steel pipe with a heavy-duty polypropylene (poly) pipe.
• Conducted surface conductivity surveys to resolve topsoil conductivity uncertainty, which was assumed to be critical for the improvement of the EM inversion models.
• Developed discontinuous Galerkin frequency-domain (DGFD) model of a layered medium with an inhomogeneous surface layer and considered the January-2022 source and receiver experiment configurations.
• Imaged synthetic data from a time-lapse vertical seismic profiling (VSP) using distributed acoustic sensing (DAS) to determine the feasibility of detecting changes in elastic properties of the subsurface caused by fracture dilation at the DFPS
• Obtained permit for injection of saltwater into the DFPS from Texas Commission for Environmental Quality
• Conducted a pre-test to verify injectivity before the final test and validated hydraulic conductivity between the injection well and the new well
• Removed metal objects from the surface of the DFPS
• Drilled a new observation well at the southwest edge of the test site
• Conducted induction logging again in October 2021 and validated that the fracture signature was not affected by our first injection tests
• Developed a machine-learning model to perform EM inversion using the synthetic data
• Conducted active VSP to obtain the baseline velocity model and showed that the detection sensitivity using active VSP is significantly higher than surface seismic and passive VSP scenarios
• Developed more advanced laboratory fracture model that simulates the in-situ impedance response of the EAP-filled Devine fracture when high-pressure water or saline solution is injected into the fracture
• Developed hydrogeological and poroelastic models to simulate hydraulic fracture reopening using the injection rate and bottomhole pressure data that were collected during the September 2020 deployment
• Performed first injection cycle at the DFPS
• Completed quantitative assessment of the feasibility of EM measurements for detection of changes in fracture properties under different scenarios in the lab studies
• Obtained permit for injection of freshwater into the DFPS from Texas Commission for Environmental Quality

We attempt to demonstrate the applicability of an EAP pack in mapping hydraulic-fracture reopening or fluid diffusion through a hydraulic fracture. For this purpose, in the second field deployment in January 2022, we conducted multiple experiments at the DFPS consisting of freshwater and saltwater slug injections while running electrical surveys. Simultaneously, we collected bottomhole pressure and salinity, the injection rate and surface pressure using high-precision data loggers, DSS data in various monitoring wells, and tiltmeter data on the survey area. We are now focused on analyzing the collected EM data by reviewing changes in the surface electric field amplitude and phase in conjunction with the injection rate, and bottomhole pressure and salinity profiles. We are also developing EM inversion models and evaluating their performance in predicting the sensitivity of the electric field to water injection and fracture dilation at 175 ft depth.

$1,721,180.00

$430,288.00

NETL – Scott Beautz (Scott.Beautz@netl.doe.gov or 918-497-8766)
University of Texas at Austin – Mohsen Ahmadian (Mohsen.ahmadian@beg.utexas.edu or 512-471-2999)