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Diagenetic impact on reservoir quality in deeply buried tight Rotliegend Sandstones - case study of Polish Permian Basin

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Nosal J.

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tom Vol. 40, no. 1

156--157

EN

During burial, sediments and rocks undergo physical and chemical changes due to temperature and pressure growth. All these processes are known as diagenesis (Boggs 2009). These changes play an important role in postedpositional modification of reservoir parameters, such as porosity, permeability and filtration. Primary porosity of rock may be reduced by cement precipitation, mechanical compaction, mineral reactions or pressure solutions, and moreover increased (secondary porosity) during burial, as a result of grain and cement dissolutions, mineral reactions or fracturing (Bjorlykke 1983). Permeability is controlled mainly by pore-throat size (Pittman 1992) and its loss corresponds to the decreasing volume of primary porosity (Pittman 1992, Dutton & Loucks 2010). The aim of presented work was investigation of diagenetic changes within deeply buried tight Rotliegend Sandstones from Polish part of Southern Permian Basin and their impact on reservoir properties of rocks. For the research were selected 26 core samples from 16 wells and depth interval 3439.8-4284.7 m. All wells are located within the aeolian sediments of Eastern Erg (central part of Polish part of Permian Basin). Samples are represented by medium - and fine - grained quartz arenites and wackes. Qualitative examination of samples included petrographic analysis of thin sections in polarizing microscope in transmitted light and scanning electron microscopy. Numerical characterization of pore space was obtained during petrophysical analysis on 11 samples, usingmercury porosimetry. Diagenetic processes strongly amended reservoir parameters of rocks. The greatest impact on the decrease of primary porosity had mechanical compaction. It resulted in the development of long grain contacts. As the main cement component were identified clays, with subordination of carbonate, ferruginous and anhydrite minerals. Porosity of analyzed samples does not exceeded 6%, permeability - 0.1 mD. Reservoir properties of Rotliegend Sandstones were affected by diagenesis, forced by temperature and pressure growth during burial. Primary porosity of sandstones was decreased by mechanical compaction and cement precipitation. Observed evidence of secondary porosity was created due to dissolution of less stable minerals - feldspars. Precipitation of authigenic clay minerals also highly reduced permeability and filtration of sandstones.

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

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Nosal J.

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tom Vol. 38, no. 4

511--512

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.

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Lower extremity power in female soccer athletes : a pre-season and in-season comparison

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Pietraszewski B. , Siemieński A. , Bober T. , Struzik A. , Rutkowska-Kucharska A. , Nosal J. , Rokita A.

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tom Vol. 17, no. 3

129--135

EN

Purpose: Lower extremity power is an important physical capacity of a soccer athlete. Power represents, and can be modified by, the training of strength and speed. Pre-season and in-season training differs in the relative emphasis on these two quantities. It is nevertheless desirable that the mechanical power remain the same or become higher during the in-season period. The purpose of this study was to identify changes in quantities related to “explosive strength” and to check whether, in collegiate female soccer players, pre- and inseason lower extremity power will remain unaltered. Methods: Twenty collegiate female soccer players, representing all field positions, participated. Lower extremity power was assessed by a series of drop jumps executed from four different heights (15, 30, 45, and 60 cm). Mechanical power was calculated using subject’s mass, jump height, and acceleration due to gravity. This value was further normalized by body mass of each athlete to obtain the relative (or normalized) mechanical power. Results: The normalized lower extremity mechanical power was highest when landing from the 30 cm height for both pre- and inseason periods. However, contrary to expectations, it turned out lower during the in-season than during the pre-season test, even though no significant differences were found between the corresponding jump heights. Conclusions: It is concluded that altered, perhaps inadequate, training strategies were employed during the in-season period. Besides, advantages of adding the relative mechanical power as a season readiness indicator are underlined compared with relying on the jump height alone.