Hydraulic fracturing fluid migration in the subsurface: A review and expanded modeling results

Abstract

Understanding the transport of hydraulic fracturing (HF) fluid that is injected into the deep subsurface for shale gas extraction is important to ensure that shallow drinking water aquifers are not contaminated. Topographically driven flow, overpressured shale reservoirs, permeable pathways such as faults or leaky wellbores, the increased formation pressure due to HF fluid injection, and the density contrast of the HF fluid to the surrounding brine can encourage upward HF fluid migration. In contrast, the very low shale permeability and capillary imbibition of water into partially saturated shale may sequester much of the HF fluid, and well production will remove HF fluid from the subsurface. We review the literature on important aspects of HF fluid migration. Single-phase flow and transport simulations are performed to quantify how much HF fluid is removed via the wellbore with flowback and produced water, how much reaches overlying aquifers, and how much is permanently sequestered by capillary imbibition, which is treated as a sink term based on a semianalytical, one-dimensional solution for two-phase flow. These simulations include all of the important aspects of HF fluid migration identified in the literature review and are performed in five stages to faithfully represent the typical operation of a hydraulically fractured well. No fracturing fluid reaches the aquifer without a permeable pathway. In the presence of a permeable pathway, 10 times more fracturing fluid reaches the aquifer if well production and capillary imbibition are not included in the model.

Groundwater methane in relation to oil and gas development and shallow coal seams in the Denver-Julesburg Basin of Colorado

“…Although the total number of cases of thermogenic stray gas is relatively low, it is clear from COGCC complaint reports that individual cases pose significant safety, financial, emotional, and health risks to landowners (SI Appendix). Evaluation, mitigation, and prevention of these impacts should remain an ongoing high priority (32,39,40).…”

Mechanisms leading to potential impacts of shale gas development on groundwater quality

“…The magnitude of the impacts of unconventional O&G development on groundwater quality is difficult to assess as the requirement for monitoring groundwater near O&G well pads was just recently introduced in very few jurisdictions. Reports of incidents are mostly restricted to surface operations, and there are few reports of incidents leading to subsurface impacts . Long et al (2015) have concluded that direct impacts of fracking appear small but have not been investigated, and Jackson et al (2013) have advocated for field‐based research to fill the knowledge gap.…”

Effects of microstructure on water imbibition in sandstones using X‐ray computed tomography and neutron radiography

“…The study of multiphase flow in porous rocks is related to a broad field with important challenges [ Bruce and Klute , ; Richards , ; Sahimi , ; Singh , ; Washburn , ]. The investigation of water imbibition in porous rocks is important in a variety of contexts, including the recovery of hydrocarbons from ultralow permeability reservoirs [ Akin and Kovscek , ; Karpyn et al ., ; Li and Horne , , ], the disposal of nuclear waste [ Hunt and Tompson , ; Sahimi , ; Tompson et al ., ], the sequestration of CO 2 [ Doster et al ., ; Herring et al ., ], the environmental remediation [ Faybishenko et al ., ], and the protection of buildings and groundwater [ Birdsell et al ., ; Cheng et al ., ; Hall and Hoff , ]. Several nondestructive techniques [ Roels et al ., ], including nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI) [ Carpenter et al ., ; Leech et al ., ; Pohlmeier et al ., ] and γ ray attenuation [ Ferguson and Gardner , ; Nielsen , ; Nizovtsev et al ., ], have been applied to probe distributions of water saturation and to study the dynamics of liquid transport in porous materials.…”