The approach to the management of extractive wastes from shale gas exploration and appraisal is contingent on their physical and chemical characteristics, environmental and legislative framework (methods permitted by laws and regulations), as well as on technical (available waste recycling/disposal facilities) and logistic conditions (viability of waste haulage to these facilities). Whatever the kind of extractive wastes produced, they should be handled in accordance with the decision on the approval of waste management program, as made under Extractive Waste Act of 10 July 2008 (2008 Journal of Laws No. 138, Item 865, as amended).
A high content of water and, consequently, consistency of the wastes (colloidal/muddy for drilling wastes and liquid in the case of flowback fluid) is the key problem that makes it difficult to reuse extractive wastes. An additional problem is associated with a highly variable and hardly predictable chemical composition of the wastes (for example, high and variable contents of heavy metals and salts of alkaline elements in the form of chlorides, sulfates or carbohydrates).
According to the recommended sequence of extractive waste, management priorities, waste production should be first prevented, the volume of wastes produced minimized and negative effects of waste mitigated. To this end, various measures are applied, including drilling mud treatment facilities, such as shale shakers and centrifuges, formulations of drilling mud and stimulation fluids based on environment-friendly components, economical use of stimulation fluids and materials, the application of closed circuits, etc.
Proper waste management – i.e. waste recovery and disposal operations, made according to applicable laws and regulations in an environmentally safe way – is the second stage. Unprocessed 01 05 category wastes cannot be recovered or inactivated out of dedicated installations. To this end, several permitted methods are available, including:
- physical and chemical methods – solidification and stabilization of wastes using specific components and methods (e.g. with cement, bentonite, lime or fly ash), neutralization, heavy metal precipitation, leaching out of problem substances (e.g. chloride extraction),
- recycling – reuse of wastes, for example as construction material, e.g. in road building projects,
- incineration and thermal processing of wastes (hydrocarbon-containing wastes only),
- bioremediation – applicable exclusively to wastes that contain hydrocarbons,
- storage: in underground waste storage facilities, drilling waste inactivation facilities or other waste disposal grounds.
Currently, drilling waste reuse as a component of soil mixtures (with cement, bentonite, lime, etc.) for such applications as reclamation of municipal landfills, is the most commonly used waste management method in Poland. However, due to a number of concerns raised (mostly of a legal nature), continued use of that technique in the future is under a question mark.
Landfill rehabilitation with extractive wastes from shale gas exploration (source: Archives of NGI-PRI)
Flowback fluid is a difficult waste management target due to chemical composition and its unpredictable variability. Several flowback fluid recovery and neutralization techniques are available, including:
- use of treatment lines (also mobile ones) to treat the flowback fluids to a level enabling their reuse at subsequent fracturing procedures,
- flowback fluid pretreatment (e.g. for removal of particulates, degassing, removal of petroleum derivatives) to a level enabling its delivery to a municipal or industrial wastewater treatment plant or to other specialist facility for inactivation (treatment plant must hold a permit for recycling or inactivation of wastes attributed to the 01 05 subcategory),
- underground storage (the Borzęcin depleted gas reservoir is now available in Poland for underground tankless storage of wastes under a license).
In the case of extractive waste disposal at municipal or industrial landfills, it is prohibited to dispose of liquid wastes that contain more 95% of water in the total mass (except for sludge). Moreover, it is prohibited to dilute the wastes or mix them with other wastes, substances or objects in an attempt to meet the criteria of waste disposal at a given landfill.
Currently, there are approx. 30 installations in Poland that hold a permit for recovery or inactivation of 01 05 subcategory wastes and in theory may accept extractive wastes, including flowback fluid. These are:
- installations that use physical and chemical methods,
- installations for production of alternative fuels,
- cement mills,
- installations for production of construction materials,
- incinerating plants,
- wastewater treatment plants,
- extractive waste management plants,
- underground waste storage facilities,
- other waste storage facilities.
Based on permits held, the capacity of installations that are capable of extractive waste management is estimated at approx. 1.5 million Mg/year. It should be kept in mind, however, that in addition to extractive wastes most of these installations are intended for management of other wastes, too. In many cases the volume, kind and quality of the wastes that are accepted by an installation for processing depend on the demand for its final product (e.g. a construction material, alternative fuel, etc.). Therefore, the wastes are expected to meet specific criteria and parameters. In practice, extractive waste processing capacities are much lower than those declared by existing operators of the installations.
The logistical mismatch between existing waste management facilities (located mostly in south and west Poland) and shale gas exploration regions (north, central and east Poland) is another key problem. Transportation of wastes at very long distances (even as much 600 km) would generate huge costs and make that operation economically non-viable.
author: Anita Starzycka