Petrophysics of Rotliegend sandstones for unconventional tight gas exploration case study of Polish Permian Basin

• Autorzy: Nosal J.
• Języki publikacji: EN

Abstrakty

EN

Tight gas is one of the unconventional gas accumulations. In tight reservoir, natural gas is trapped in impermeable sedimentary rock. Industry defines tight gas reservoir as a maximum 10% matrix porosity and maximum 0.1 mD permeability (excluding fracture permeability) sedimentary rock (Haines 2006). Gas is trapped by low permeability of the reservoir. Down-dip water contact and reservoir trap do not appear. Tight reservoir rock should be characterized by poor reservoir properties - low porosities, extremely low permeability and also small flow rates (Law 2002). Tight gas accumulations are expected to originate in deeper parts of Polish Permian Basin within Rotliegend sandstones (Kiersnowski et al. 2010). Depth of burial associated with time could allow occurrence of advanced diagenetic processes amending primary porosity. Area of research is located in the center of Polish Permian Basin - western Poland. It is a natural gas field Pxyz, where hydrocarbons are accumulated within aeolian Rotliegend sandstones characterized by low reservoir properties. Core samples from well Pxyz-2 from depth interval 3511.5-3626.0 m were selected for investigation. The porosimetric analysis (AutoPore 9220 mercury porosimeter) of 115 samples granulometric analysis of 20 samples (sieve measurements and SediGraph 5100 device) were performed in Polish Oil and Gas Company. Borehole survey revealed gas saturation in whole 172 m sandstone profile. Obtained results allowed quantitative characteristics of samples, both grain size and pore space. Average diameter of sand grain was in the range from 0.171 mm to 0.643 mm. Based on the above results, studied sandstones were classified as fine, medium and coarsegrained (Pettijohn et al. 1972). Porosimetric studies showed poor reservoir quality of sandstones. Weak filtration of samples was proved by low values of average capillary diameter and insufficient 45% percentage of pores with diameter greater than 1 jj.m. Average porosity samples is 7.575%, wherein samples from the upper part of sandstone complex have lower porosity values than those from the base. Total pore area ranged from 0.01 m /g to 2.73 m /g in whole profile. Research showed no total porosity and total pore area dependence on burial depth. It is connected with the domination of mechanical compaction in sandstones (Such et al. 2010). Changes in porosity and total pore volume showed the vertical variation in sandstones. Based on these results, zones predisposed to tight gas accumulations were distinguished. Granulometric and porosimetic studies performed on Rotliegend samples from the area of Pxyz deposit allowed better understanding of deep buried sandstones petrophysics. Parameters received from analysis confirmed possibility of tight gas accumulations in Rotliegend sandstones in the area of Pxyz gas field.

Słowa kluczowe

EN

gas reservoir; sedimentary rock

• Wydawca: Wydawnictwa AGH
• Czasopismo: Geology, Geophysics and Environment
• Rocznik: 2012
• Tom: Vol. 38, no. 4
• Strony: 511--512
• Opis fizyczny: Bibliogr. 5 poz.

Twórcy

autor

Nosal J.

• AGH University of Science and Technology, Faculty of Geology, Geophysics and Environment Protection, Department of Fossil Fuels; al. Mickiewicza 30, 30-059 Krakow, Poland

Bibliografia

• 1. Haines I., 2006. Tight Gas. Oil and Gas Investor, Hart Energy Publishing LP, Houston.
• 2. Kiersnowski H., Buniak A., Kuberska M. & Srokowska-Okońska A., 2010. Occurrence of natural tight gas in Polish Rotliegend sandstones. Polish Geological Review, 58, 4, 335-346.
• 3. Law B.E., 2002. Basin-centered gas systems. AAPG Bulletin, 86, 11, 1891-1919.
• 4. Pettijohn F.J., Potter P.E. & Siever R., 1972. Sand and Sandstone. Springer-Verlag, New York.
• 5. Such P., Leśniak G. & Słota M., 2010. Quantitative characteristic of porosity and permeability in Rotliegend sediments with potential tight gas accumulations. Polish Geological Review, 58, 4, 347-351.