This paper is a summary of results of environmental analysis conducted by PGI-NRI, AGH-UST within the monitoring of natural gas prospecting in unconventional deposits. All elements of natural environment were analyzed and on this basis the qualitative and quantitative impact of drilling and hydraulic fracturing of shales could be assessed. Special attention was drawn to the analysis of the physicochemical condition of post-reaction fluids, soil gas in the well pad area and drilling fluids. The results of analysis reveal that prospecting works do not create a significant environmental hazard. Some indices connected, e.g. with the noise climate lightly exceeded permissible values. Nonetheless, if extensive prospecting and production of shale gas are involved, the environmental studies need to be broadened to supplement this report.

Shale formations have been recently treated only as source rocks and sealing packages mainly of conventional deposits. At present shales, which have a considerable concentration of highly mature organic matter appearing in complexes of over 30 m thick are used as unconventional sources for natural gas production with the use of advanced drilling technologies. Natural gas production in such rock formations necessitates performing a horizontal section in the borehole and a big number of hydraulic fracturing jobs. The unconventional shale gas deposits have been prospected also in Poland for a couple of years. Exploration works mainly concentrate on a vast area passing from Pomerania through Mazowsze to the Lublin region in Poland. The analysis of the geologic analyses reveals that the most perspective are shales in the Lower Paleozoic at a depth of 2500 m in the eastern part to about 4000 m in the western part of the area. The paper is focused on the quantitative and qualitative evaluation of environmental impact of natural gas exploration works from unconventional deposits. Special attention was paid to the hydraulic fracturing jobs in shales, which create particular hazard for water and soil environment. These hazards already appear at the stage of preliminary works, when big quantities of chemicals and water for frac jobs are stored in the rig area, and then, during realization of works, when the spent hydraulic fracturing fluid may penetrate the water-bearing horizons in the caprock. The composition of fracturing fluid used in Gapowo B-1A well are given along with the results of chemical analyses of a few parts of spent fracturing fluid samples pumped out from the borehole. The fluid turned out to be high in salt (high specific electrolyte conductance (SEC) and total dissolved substances (TDS) and a high toxicity for most of the living organisms). For this reason the spent fracturing fluid should not enter the environment without control.

The chemical characteristic of flowback fluid from hydraulic fracturing for shale gas exploration/production in various localizations is presented. The results of statistical analysis have shown that variability in the chemical composition of these fluids is statistically significant and depends on the time difference between fracturing process and flowback sampling as well as sampling spot within the installation for flowback collection. Parameters which depend on sampling schedule (time and spot of sampling) are as follows: electrical conductivity and concentration of ammonia, boron, barium, calcium, lithium, sodium, magnesium, manganese, sodium, strontium, silicate, bromide, and chloride. Independent parameters are pH, total organic carbon (TOC), concentration of potassium, and iron. The ranges of the values of the characteristic parameters were determined, taking into account the representativeness of the samples, supported by statistical tests. The methods for the reuse of flowback fluids in terms of chemical composition are presented.

Res er voir con fine ment by faults is im por tant for safe stor age of liq uid waste or hy dro car bons. Hav ing ac cess to 3D seis mic and bore hole data, we have in ter preted the tec tonic set ting of the Wysoka Kamieñska Graben (WKG) in the NW part of the Pol ish Ba sin and sub se quently made an in ter pre ta tion of the seal ing po ten tial of the graben-bound ing faults. The for ma tion and de vel op ment of the graben in the Late Tri as sic and Early Ju ras sic was con trolled by me chan i cal de coup ling in the salts of the Zechstein Group. The pri mary tec tonic fac tor trig ger ing the graben or i gin was dextral strike-slip move ment along the re gional fault zone in the Pa leo zoic base ment, transtensional ac com mo da tion of which in the Zechstein-Me so zoic cover led to de vel op ment of a horse-tail pat tern of grabens. Dur ing the Late Cre ta ceous, the graben un der went mi nor tec tonic in version. Seal ing po ten tial anal y sis of the graben-bound ing faults was per formed for the Triassic-Jurassic se quence in clud ing jux ta po si tion seal and fault gouge seal com po nents. Fi nally, we have fo cussed our in ter pre ta tion on the Ju ras sic se quence where the best res er voirs have been rec og nized. Our re sults in di cate good to mod er ate seal ing po ten tial of the Hettangian res er voir, poor to mod er ate seal ing of the Pliensbachian res er voir and lack of seal ing of the Bajocian res er voir. Hence, the Hettangian res er voir, char ac ter ized by large thick ness, low clay con tent and a large re gional ex tent, acts as a po ten tial storage for ma tion, be ing con fined by the graben-bound ing faults of the WKG. Key words: tectonic graben, salt de coup ling level, un der ground stor age, fault seal po ten tial, geo log i cal mod el ling.