Estimation of the water cycle related to shale gas production under high data uncertainties: Dutch perspective.

The potential water demand for fracturing fluids along with the possible flowback and produced water production is assessed for the Dutch Posidonia shale. Total water demand estimated for 25 years of the field development using historic data from the U.S. plays varies between 12.2 and 36.9 Mm3. The maximal annual water consumption of 0.95-2.88 Mm3 is expected in the peak years of shale gas production. These figures are much lower than the availability of any potential water sources, which include drinking water, fresh and brackish groundwater, river water, effluents of wastewater treatment plants (WWTP) and sea water. River water is considered the most promising water source for fracturing fluids in the Dutch Posidonia shale based on its availability (>6·104 Mm3/year) and quality (only bacterial composition needs to be controlled). Total wastewater production for the whole period of the field development is estimated between 6.6 and 48.0 Mm3. Wastewater recycling can cover significant part of the source water demand for fracturing fluid. However, high mineral content of the wastewater as well as temporal and spatial discrepancies between wastewater production and water demand will form obstacles for wastewater recycling. The assessment framework developed in this study may be applied for other shale gas fields with high uncertainties regarding subsurface properties, connate formation water characteristics and future legislative framework.

Transport of bacteriophage MS2 and PRD1 in saturated dune sand under suboxic conditions.

Soil passage of (pretreated) surface water to remove pathogenic microorganisms is a highly efficient process under oxic conditions, reducing microorganism concentrations about 8 log10 within tens of meters. However, under anoxic conditions, it has been shown that removal of microorganisms can be limited very much. Setback distances for adequate protection of natural groundwater may, therefore, be too short if anoxic conditions apply. Because removal of microorganisms under suboxic conditions is unknown, this research investigated removal of bacteriophage MS2 and PRD1 by soil passage under suboxic conditions at field scale. At the field location (dune area), one injection well and six monitoring wells were installed at different depths along three suboxic flow lines, where oxygen concentrations ranged from 0.4 to 1.7 mg/l and nitrate concentrations ranged from 13 to 16 mg/L. PRD1 and MS2 were injected directly at the corresponding depths and their removal in each flow line was determined. The highest bacteriophage removal was observed in the top layer, with about 9 log removal of MS2, and 7 log removal of PRD1 after 16 meters of aquifer transport. Less removal was observed at 12 m below surface, probably due to a higher groundwater velocity in this coarser grained layer. MS2 was removed more effectively than PRD1 under all conditions. Due to short travel times, inactivation of the phages was limited and the reported log removal was mainly associated with attachment of phages to the aquifer matrix. This study shows that attachment of MS2 and PRD1 is similar for oxic and suboxic sandy aquifers, and, therefore, setback distances used for sandy aquifers under oxic and suboxic conditions provide a similar level of safety. Sticking efficiency and the attachment rate coefficient, as measures for virus attachment, were evaluated as a function of the physico-chemical conditions.