What potential effects the shale gas exploration and production may have on the water management?
Shale gas exploration, appraisal and potential production is a huge undertaking that requires water supply at all stages of operations. Assessments of potential water sources, including available water resources, must be made already at an early project planning stage.
In shale gas exploration, appraisal and potential production water is used in the following stages:
- drill site (production site) construction – domestic water,
- well drilling – for drilling mud preparation (actual volume of water requirements will be contingent on the type of mud and borehole length),
- hydraulic fracturing – fracturing fluid is based on the water (that accounts for more than 90% of its composition),
- production site operation – domestic water for the staff.
Water management in shale gas exploration, appraisal and production is an important issue not only in terms of environmental aspects, but also for the local community (Fig. 1). Both quantitative (water requirements) and qualitative (potential water pollution in the area of operations) aspects are involved.
Process and domestic water consumption by production sites is common in Poland. According to available data, on average about 30 m3 of water are required daily for drilling a typical deep well. Normally, it takes a few weeks to drill the well. It is assumed that a drilling well of typical construction uses approx. 180 - 220 litres of mud per linear metre of the well being drilled, i.e. approx. 630 - 770 m3 of water for drilling the entire well. In the US, process water consumption (primarily for mud preparation) at well drilling stage ranges from200 to over 3000 m3 (Table 1).
Hydraulic fracturing operations, that require significant amounts of water over a short period of time, is the most controversial issue. On average, stimulation procedure performed in a 1 km-long leg (assuming that several well sections are fractured) requires more than ten cubic metres of water. Some of the water (approx. 12-30% on average) returns to the surface as flowback fluid. (www.ngsfacts.org).
For comparison, the volume of the water used (17 300 m3) for full fracturing made in the Łebień Well (the first shale gas exploration well with multi-stage fracturing in Europe) is equal to:
- the volume of 7 Olympic-size swimming pools,
- 17 seconds of water debit in Vistula River at Gdańsk,
- annual water requirements of 310 people,
- daily water consumption of 113,000 people,
- 5.5 % of daily water consumption in Warsaw.
Hydraulic fracturing operations in Poland are mostly based on the groundwater abstracted from:
- water wells made by investor on the drill site or in its proximity (under a water permit granted),
- water intakes (a set of water drilling wells) of municipal or rural water supply systems.
Locally, surface waters are used in hydraulic fracturing operations (e.g. water from disused mining pits).
Taking care of Poland's surface and ground water resources and their sustainable management is a major priority for Polish authorities and national legislation (the Water Law) which transposes the EU Directives (Framework Water Directive, the Groundwater Directive). A water permit is required for the abstraction of significant volumes of water over a short period of time.
Water permit for groundwater use is awarded based on information about water resources that are available for commercial use in a given area. On the other hand, water permits for surface water use are awarded upon considering information on the volume of abstracted water, water use conditions in the catchment area and the commercial water balance (information on available groundwater resources). This approach guarantees that national water management is conducted in a reasonable and safe way.
Groundwater is the main source of potable water supply to the population and accounts for 60% of all water used for domestic purposes. As of 31 December 2013, total commercial groundwater resources amounted to approx. 36.5 million m3/day, including almost 20 million m3/day available to areas that account of 58% of Poland's territory (source: PGI-NRI, PSH 2013). About 19% of all commercial groundwater resources are currently used in Poland.
Poland's available flowing water resources (considering environmentally protected minimum debit) are estimated at 10 billion m3/year (Diagnosis of existing water management status, KZGW 2010). Despite a significant geographic variability of these resources, there is no risk that abstraction of considerable surface water volumes may cause changes in hydrological regimes of the watersheds.
The groundwater and surface waters, should not be the only source of water used in drilling and hydraulic fracturing operations, even if their resources are considerable.
Water used in fracturing operations is not expected to meet high standards of quality. Therefore, reuse of flowback water after treatment seems to be the best solution. Moreover, the following should be considered:
- post-process water (cooling water, water from biogas plants),
- post-treatment municipal wastewater, or the so-called municipal water, i.e. water from storm sewers,
- post-mining water,
- brine water, e.g. from Jurassic aquifers,
- seawater in the coastal region.
The newest technology development enables the application of non-standard solutions that reduce water requirements and allow for reasonable water management in the upstream industry. The experience from North America, a region with a long shale gas production history, shows that continued efforts in that area are much needed. For example, in British Columbia (Canada) some operators of production fields successfully use treated municipal wastewater in hydraulic fracturing operations, instead of drinking water resources. Similar solutions are much commendable.
autorzy: Magdalena Nidental i Małgorzata Woźnicka
References:
1. Prowadzenie , aktualizacja i udostępnianie bazy danych GIS zasobów dyspozycyjnych i perspektywicznych wód podziemnych dla obszaru Polski (Maintenance, updating and accessibility of GIS database on available and prospective water resources in Poland) (PSH, 2013)
2. Diagnoza aktualnego stanu gospodarki wodnej (A diagnosis of existing water management status), KZGW 2010.
(http://kzgw.gov.pl/files/file/Programy/PPWP2030/Zalaczniki_do_projektu_P...)
3. Woźnicka M. Jaki wpływ na gospodarkę wodną może mieć wydobycie gazu ze złóż niekonwencjonalnych (Potential impact of shale gas production on water management), Przegląd Geologiczny vol.61, no. 6, 2013
