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Reservoir parameters of deeply buried sandstones and their impact on fluid flow – a case study of the Rotliegend Sandstones from the Polish Permian Basin

Nosal J.

Geology, Geophysics and Environment

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2015

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Vol. 41, no. 1

116

EN

Reservoir parameters of rocks determine its ability to accumulate and transport reservoir fluids such as oil and gas. These parameters include, inter alia, porosity, permeability, and total pore area. Porosity is the capacity of a sandstone to store fluids. Permeability is the ability to transport them (Mc-Donald & Schmidt 1992) and is controlled mainly by pore – throat size (Pittman 1992). Finally, pore area is the total area of pore space. During burial rocks undergo diagenesis – physical and chemical changes, that affect their primary reservoir parameters (Boggs 2009). The aim of this work was to investigate reservoir parameters of the deeply buried Rotliegend Sandstones, their changes during diagenesis and impact on fluid flow. Research included petrographic examination of thin sections under transmitted light and petrophysical analysis of rock samples – mercury porosimetry and permeability analysis. For investigation were selected 58 core samples from 13 wells located within the Polish Permian Basin in the area of the Eastern Erg and the Central Basin, from a depth interval of 3415–4312 m. Samples were represented by Saxonian very fine-, fine- and medium-grained quartz and lithic arenites. The samples were divided into three groups, according to the location of wells within the Polish Permian Basin. The first group included samples from the central part of the Eastern Erg, the second – the westernmost part of the Eastern Erg, and the third – sandstones deposited within the Central Basin. Samples revealed variability in mineral composition, grain size and reservoir parameters between areas. The best reservoir properties were found within samples from the easternmost part of the Eastern Erg, whereas the weakest in central area of Eastern Erg. The effective porosity of rocks was in the range of 0.5% to 26%. In terms of pore space, the studied samples were classified as porous, in some cases with fractures, very heterogeneous and with small apertures. The increase of total pore area may correspond to the presence of authigenic clay minerals that grew during diagenesis. All those factors contributed to the reduction of potential fluid flow.

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

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

Acta of Bioengineering and Biomechanics

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2015

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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.

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

Nosal J.

Geology, Geophysics and Environment

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2014

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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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Basin-centered gas accumulations in Rotliegend Sandstones

Nosal J., Waliczek M.

Geology, Geophysics and Environment

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2014

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Vol. 40, no. 1

114--115

EN

Permian Rotliegend Sandstones are the most important gas reservoirs in north-west Europe (Gast et al. 2010). Those sandstones were deposited in playa, fluvial and aeolian depositional systems (Kiersnowski et al. 2010) and may host both conventional and unconventional deposits. The reservoirs are supplied in hydrocarbons by the Carboniferous sediments, lying directly beneath. Some of the unconventional accumulations may occur in conditions of Basin-Centered Gas System (BCGS). Basin-Centred Gas Accumulations (BCGAs), associated with BCGS, are gas-saturated, abnormally pressured, have a low-permeability reservoir and commonly lack of down-dip water contact (Law 2002). Two types BCGAs can be distinguished - direct and indirect, and they differ in the attributes of the system - the type of organic matter, thermal maturity, sealing and the distance of hydrocarbons migration. Direct Basin-Centered Gas Systems may occur in the area of the Polish part of the Permian Basin. The purpose of the present work was to indicate the Aeolian Permian Rotliegend sandstones as a reservoir rocks for direct Basin-Centered Gas Accumulations, according to the petrophysical properties and reflectance of vitrinite measurements. Analysis was performed on fifteen core samples located within the aeolian sediments of Eastern Erg (center of Polish part of Permian Basin) from the depth interval 3,559.3-4,275.9 m. Random reflectance of vitrinite was measured under oil immersion using Carl Zeiss Axioplan microscope in reflected monochromatic non-polarised light. Mean reflectance values were calculated for all measurement. Permeability measurements were done on plug-type samples (cylindrical with diameter 25.4 mm and length of between 20-40 mm. Plugs were drilled perpendicularto the cylinder axis. Values of average capillary diameter were obtained from porosimetric analysis on bulk samples with AutoPore 9220 mercury porosimeter. In each sample, the organic matter was dominated by vitrinite-like matter what could indicate humic organic matter typical for gas prone source rocks. The measured vitrinite reflectance values indicate that organic matter reached the maturation stages of hydrocarbon generation characteristic for the gas window phase (Ro > 2%). Values of average capillary diameter provedweak filtration. Permeability results shown typical values for tight sandstones from BCGS, lower then 0.1 mD. Analysis performed on aeolian Rotliegend sandstones from the area of Eastern Erg confirmed their potential as a reservoir rock for Basin-Centered Gas Accumulations. Humic type of organic matter and values vitrinite reflectance corresponding to gas window are specific for BSGAs. The analyzed samples of the aeolian Rotliegend sandstones are characterized by very low permeabillity, not exceeding 0.1 mD and slow flow rates, what determines capillary sealing of the accumulation. Short distance of hydrocarbons migration was confirmed by the location of Carboniferous source rocks. All those factors allow to classify the aeolian Rotliegend sandstones as a potential reservoir rock for Basin-Centered Gas Accumulations.

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Underground CO2 storage - case study of Jastrząbka Stara structure, SE Poland

Nosal J., Semyrka R.

Geology, Geophysics and Environment

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2012

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Vol. 38, no. 3

329--338

EN

Carbon dioxide injection into depleted oil fields is widely used. The injection enhances oil recovery and generates other advantages like: (1) decrease of carbon dioxide concentration in the atmosphere and (2) the possibility for CO2 emission trade. Geological and reservoir parameters of Jastrząbka Stara structure are discussed in this paper in the context of possible CO2 sequestration. Reservoir absorptivity and tightness, overburden thickness, storage capacity as well as social and economical aspects are taken into consideration. Based upon these factors, Jastrząbka Stara oil deposits may be classified as potential carbon dioxide storage site.Detailed data cannot be published due to Polish Oil and Gas Company (PGNiG SA) confidentiality requirements.

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

Nosal J.

Geology, Geophysics and Environment

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2012

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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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Basin-centered gas accumulations in Rotliegend Sandstones - case study of Polish Permian Basin, first results

Nosal J., Waliczek M.

Geology, Geophysics and Environment

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2012

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Vol. 38, no. 4

513--514

EN

Permian Basin covers one of the world's largest gas-bearing clastic formation - Permian Rotliegend Group. Reservoirs are supplied by Carboniferous sources, lying directly beneath. Permian Rotliegend sandstones belong to the most important gas bearing formations in Poland. They were deposited in playa, fluvial and aeolian depositional systems (Kiersnowski et al. 2010). Both conventional and unconventional accumulations occur in those sediments. Some of unconventional accumulations occur in conditions of Basin-Centered Gas System (BCGS). Basin-Centered Gas Systems are unconventionals with the greatest economical potential in the world. They are gas saturated, abnormally pressured, a low-permeability reservoirs commonly showing lack of a down - dip water contact. Two types BCGS can be distinguished - direct and indirect. Differentiation results from the attributes of the system - type of organic matter, thermal maturity, sealing and the distance of hydrocarbons migration (Law 2002). Direct Basin-Centered Gas Systems may occur in the area of the Polish part of Permian Basin. The purpose of present studies was indicating Permian Rotliegend sandstones as a reservoir rocks for direct Basin-Centered Gas Accumulations, which are associated with BCGS, according to reflectance of vitrinite measurement and permeability. Analysis were performed on eight core samples located within the aeolian sediments of Eastern Erg (center of Polish part of Permian Basin) from the depth interval 3702—4200 m. Vitrinite reflectance measurement (Ro) were performed on polished pellets, under oil immersion with Zeiss Axioplan microscope in reflected white light. Mean reflectance values were calculated for all measurement. Permeability measurements were done on plug-type samples (cylindrical with diameter 25.4 mm and length of between 20-40 mm. Plugs were drilled perpendicularly to the cylinder axis. In each sample organic matter was dominated by vitrinite. It could indicate humic organic matter typical for gas prone source rocks. The measured vitrinite reflectance values confirmed that organic matter reached the maturation stages of hydrocarbon generation, characteristic for the gas window phase (Ro > 2%). Permeability results shown typical values for tight sandstones from BCGS, lower than 0.1 mD. Performed studies on aeolian Rotliegend sandstones from Eastern Erg area confirmed the opportunity of Basin-Centered Gas Accumulations occurrence in those sediments. Humic type of organic matter and values of vitrinite reflectance corresponding to gas window phase are specific for BSGAs. Analyzed samples of aeolian Rotliegend sandstones are characterized by very low permeability, not exceeding 0.1 mD and therefore capillary sealing of the accumulation. Carboniferous source rock located directly beneath reservoir rock, confirmed short distance of hydrocarbons migration. All mentioned factors allow classifying aeolian Rotliegend sandstones as a reservoir rock within Basin-Centered Gas System.