Numerical modeling of fracking fluid migration through fault zones and fractures in the North German Basin

Abstract

Gas production from shale formations by hydraulic fracturing has raised concerns about the effects on the quality of fresh groundwater. The migration of injected fracking fluids towards the surface was investigated in the North German Basin, based on the known standard lithology. This included cases with natural preferential pathways such as permeable fault zones and fracture networks. Conservative assumptions were applied in the simulation of flow and mass transport triggered by a high pressure boundary of up to 50 MPa excess pressure. The results show no significant fluid migration for a case with undisturbed cap rocks and a maximum of 41 m vertical transport within a permeable fault zone during the pressurization. Open fractures, if present, strongly control the flow field and migration; here vertical transport of fracking fluids reaches up to 200 m during hydraulic fracturing simulation. Long-term transport of the injected water was simulated for 300 years. The fracking fluid rises vertically within the fault zone up to 485 m due to buoyancy. Progressively, it is transported horizontally into sandstone layers, following the natural groundwater flow direction. In the long-term, the injected fluids are diluted to minor concentrations. Despite the presence of permeable pathways, the injected fracking fluids in the reported model did not reach near-surface aquifers, either during the hydraulic fracturing or in the long term. Therefore, the probability of impacts on shallow groundwater by the rise of fracking fluids from a deep shale-gas formation through the geological underground to the surface is small.

Shallow Aquifer Vulnerability From Subsurface Fluid Injection at a Proposed Shale Gas Hydraulic Fracturing Site

“…These results indicate that high hydraulic conductivity formations in the deep subsurface, but beyond the induced fracture extent, can be more effective barriers to upward fluid migration than low hydraulic conductivity formations. Numerical modeling of the North German Basin also showed horizontal fluid transport in more hydraulically conductive formations above the modeled fluid injection (Pfunt et al, ), suggesting that this protective mechanism is not unique to the proposed site.…”

“…Their worst‐case scenario, with fractures directly connecting the fracked shale to the shallow aquifer, resulted in aquifer contamination in 100 years. Further, Palat et al () and Pfunt et al () investigated the effects of faults on fracking fluid migration using models of the North Perth Basin (Australia) and the North German Basin (Germany), respectively. Neither study observed fracking fluids reaching the regional aquifers within the simulated timescales of 20 and 300 years, respectively.…”

Modeling the impact of a potential shale gas industry in Germany and the United Kingdom on ozone with WRF-Chem

“…Modeling the impact of a potential shale gas industry in Germany and the United Kingdom on ozone with WRF-Chem have been published on European shale gas and for the UK and Germany in particular, e.g., ACATECH (2016), AQEG (2018), BGR (2012), Broomfield et al (2014); Cotton et al (2014), DECC (2013), DECC (2014), Hays et al (2015), McGlade et al (2014), MULNV NRW (2012), Pfunt (2016), Sauter et al (2013), SGD (2013), Society (2012) SRU (2013), Stamford and Azapagic (2014), UBA (2013UBA ( , 2014.…”

Nonlinear Autoregressive Neural Networks to Predict Hydraulic Fracturing Fluid Leakage into Shallow Groundwater

“…The presence of low-permeability overburden rocks [4,18], production from the horizontal well [11,13,17], fracturing fluid imbibition into the shale reservoir [19,20], and mixing or other dilution processes during the transport [17,21] limit the vertical extent of fracturing fluid, thus reducing the contamination threat to shallow groundwater. Osborn et al [22] analyzed water samples from water wells in aquifers overlying northeastern Pennsylvania (active HF region) and New York (HF is currently not allowed).…”