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1

Selected effects of VTI anisotropy on downhole microseismic data

Święch E., Pasternacki A., Maćkowski T.

Geology, Geophysics and Environment

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2016

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Vol. 42, no. 1

131--132

EN

Shale gas is one of the well-known unconventional resources of natural gas all over the world. This term refers to natural gas that is trapped within shale formations. Shales are fine – grained sedimentary rocks which can be reach resources of both petroleum and natural gas. This sedimentary rocks are heavily layered and in their nature exhibit VTI velocity anisotropy behavior (Van Dok et al. 2011). This statement indicates that the world among us is not isotropic and we should not neglect this fact in our geophysical research. Anisotropy, in general is the property of the material. It can be described as the attribute of a material’s property with respect to the direction in which it is measured (Pereira & Jones 2010). There are two essential types of anisotropy: VTI and HTI. Vertical velocity layering gives rise to VTI (vertical transverse isotropy) velocity in which seismic wave velocity is faster in the horizontal direction than in the vertical one. The second type of isotropy is horizontal transverse isotropy (HTI) which causes azimuthal traveltime variations. The common mechanism for this type of anisotropy is vertical aligned fractures in an isotropic background medium (Jenner 2011.) Authors of this study focused mostly on VTI as this type of anisotropy is present in shale formations, as a result of small scaled heterogeneities from fine layering (Thomsen 1986). The VTI anisotropy can be mathematically described by using three Thomsen parameters: epsilon, delta and gamma. Epsilon is a measure of the difference between the horizontal and vertical propagation velocities for compressional waves. Gamma parameter is a measure of the difference in the horizontal and vertical propagation velocities for horizontally polarized shear waves (SH waves). Delta parameter is not easily described either mathematically or qualitatively (Pereira & Jones 2010), but it influences the anisotropy velocities in medium incidence angles. These parameters can be mathematically expressed by equations proposed by Leon Thomsen (Thomsen 1986). In this study, authors present influence of VTI anisotropy on microseismic data recorded during hydraulic fracturing of shale intervals in one of the well located in Northern Poland. Authors points out how the anisotropy affects on microseismic events location, locating them in isotropic and anisotropic velocity models with usage of TGS algorithm. Furthermore, authors indicate possible solution to estimate VTI parameters based on microseismic data. VTI anisotropy parameters plays critical role not only in case of microseismic data analysis but also in processing of active seismic data. Authors proved that VTI anisotropy present in the investigated area has strong influence on microseismic events location especially in depth. Moreover estimation of VTI anisotropy parameters based on microseismic data with usage of Thomsen equations is possible.

2

Ludwigite-group minerals and szaibelyite: rare borate minerals from Vysoká – Zlatno skarn, Štiavnica stratovolcano, Slovakia

Bilohuscin V., Uher P.

Geology, Geophysics and Environment

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2016

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Vol. 42, no. 1

59--60

EN

Beside of sedimentary evaporitic rocks, borate minerals occur also in some high temperature contact-metamorphic rocks, especially in skarns, locally in association with Fe and Sn ore minerals (e.g., Anovitz & Grew 1996). The borate minerals are generally associated with the post-magmatic processes which occur in the contact aureoles of intrusive, acid to intermediary, calc-alkaline rocks (Pertsev 1991). Borate minerals of the ludwigite group and szaibelyite were identified from the Mg-skarn in the R-20 drilling core in depth of 1172 m during geological exploration for Cu- Au porphyry-skarn ores in the Vysoká – Zlatno area near Banská Štiavnica, in the Štiavnica Neogene stratovolcano, central Slovakia (Koděra et a l. 2010). Ludwigite-group minerals (LGM) form massive black aggregates (>5 cm large) of numerous acicular, euhedral to subhedral prismatic crystals (usually 0.2–3 mm long). Ludwigite associates with clinohumite, szaibelyite, clinochlore, serpentine-group mineral, magnesite, dolomite, hematite, rarely valeriite, chalcopyrite, and sphalerite. Under transmitted light, LGM crystals are mostly opaque; locally they are translucent with strong pleochroism in sections parallel to Z-axis (deep green – dark reddish brown). In BSE, LGM crystals show regular concentric, rarely oscillatory or irregular zoning caused by distinct element variations during their growth or partial alteration: the dark zones show enrichment in Mg, Al and Ti, in contrast to the pale zones which reveal larger amounts of Fe. The electron-microprobe analyses reveal growth evolution of LGM crystals from Al- rich azoproite with ≤ 79 mol.% of Mg 2 (Mg 0.5 Ti 0.5 ) (BO 3 )O 2 end-member] to Al ± Ti-rich ludwigite and Al-dominant LGM phase [“aluminoludwigite” with ≤ 53 mol.% of Mg 2 Al(BO 3 )O 2 end-member] in central zones, whereas rim zones of the crystals and secondary veinlets attain nearly pure ludwigite composition [87–99 mol.% of Mg 2 Fe 3+ (BO 3 )O 2 end-member]. Consequently, LGM from the Vysoká – Zlatno skarn show the largest composition al variations ever known from one occurrence and they reach the highest contents of Ti ( ≤ 17.4 wt.% TiO 2 , 0.39 apfu ) and Al ( ≤ 14.4 wt.% Al 2 O 3 , 0.53 apfu ) ever reported in LGM (Schaller & Vlisidis 1961, Marincea 2000, Pertsev et al. 2004, Aleksandrov & Troneva 2008, 2011). The compositional variations indicate the following substitution mechanisms in the studied LGM: Mg 2+ = Fe 2+ for the all compositions, Fe 3+ = Al 3+ for samples without higher amount of Ti, and 2Al = Mg 2+ + Ti 4+ or 2Fe 3+ = Mg 2+ + Ti 4+ for analyses including high Ti content. Szaibelyite MgBO 2 (OH) occurs as aggregates of fibrous crystals, up to 0.5 mm in size, replacing LGM. Zoning in szaibelyite was not observed. The amounts of Mg are uniform (0.98 to 0.99 apfu ), content of Fe 2+ oscillates from 0.2 to 1.2 wt.% FeO (0.002–0.014 apfu ) and indicates the Mg 2+ = Fe 2+ substitution. Szaibelyite also contains small ad mixtures of Mn (0.1–0.4 wt.% MnO), Al and Cr ( ≤ 0.3 wt.% Al 2 O 3 or Cr 2 O 3 ). The skarn mineralization originated as a result of contact thermal metamorphism of Miocene calc-alkaline granodiorite intrusion on host Middle to Upper Triassic limestones, dolomites, shales and evaporitic anhydrite beds (the Veľký Bok Group, Veporicum Unit). The evaporites were most likely the primary source of boron, where as Ti was probably derived from the granodiorite. Clinohumite and LGM (azoproite to Al ± Ti-rich ludwigite and “aluminoludwigite”) precipitated during the high-temperature contact metamorphic event at ~ 700°C and ≤ 100 MPa, whereas the youngest Al,Ti-poor ludwigite veinlets, szaibelyite, serpentine-group mineral, clinochlore, magnesite, dolomite, hematite and probably also sulfide minerals were formed during younger, lower-temperature hydrothermal-metasomatic event.

3

A comparative analysis of concrete strength using igneous, sedimentary and metamorphic rocks (crushed granite, limestone and marble stone) as coarse aggregate

Tsado T. Y.

Zeszyty Naukowe Politechniki Częstochowskiej. Budownictwo

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2013

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Z. 19 (169)

179--191

EN

This paper presents a comparative analysis of the effect of the physical properties of coarse aggregate (igneous rock - crushed granite stone; sedimentary rock - limestone and metamorphic rock - marble stone) on the compressive strength of Portland cement concrete and compare their characteristic strength. Tests such as sieve analysis, specific gravity, bulk density, void ratio, porosity, water absorption and aggregate impact value were carried out on aggregates to ascertain their physical properties as they affect the strength of concrete. The concrete strength comparison was confined to characteristic concrete strength of grade 20 and 30 N/mm² only. Two different mix proportions of 1:2:4 and 1:3:6, and water cement ratio of 0.5 and 0.6 for both mixes were used to cast concrete cubes which were hydrated for 7, 14, and 28-day periods respectively. The compressive strength tests conducted on the cast cubes was found to be within the stipulated value of concrete strength of 26.0 N/mm² for 28-day hydration period by British Standard specification. The 28-day concrete cubes cast with these aggregates shows that, at the low strength of 20 N/mm², igneous rock - crushed granite stone c concrete had the highest strength of 26.45 N/mm² followed by Sedimentary-limestone with 26.11 N/mm² and metamorphic rock - marble stone 26.03 N/mm² in that order, and also at the high strength of 30 N/mm², crushed granite concrete gave the highest strength to be 30.11 N/mm² followed by granite 29.78 N/mm² and limestone 29.53 N/mm² in that order.

PL

W artykule przedstawiono analizę porównawczą wpływu właściwości fizycznych kruszywa grubego (skały magmowej - łamany granit, skały osadowej - wapienie i skały metamorficznej - marmur) na ściskanie betonu poprzez porównanie charakterystycznej wytrzymałości. Kruszywo grube poddano badaniom: uziarnienia, gęstości nasypowej, gęstości, porowatości, wskaźnika porowatości, absorpcji wody i współczynnika wpływu kruszywa w celu ustalenia właściwości fizycznych, jakie mają wpływ na wytrzymałość betonu. Porównanie wytrzymałości betonu ograniczono do charakterystycznej wytrzymałości na ściskanie betonu o wartości 20 i 30 N/mm². Do wykonania sześciennych kostek betonowych zastosowano dwie różne proporcje mieszanki 1:2:4 i 1:3:6 i dwie wartości stosunku cementowo-wodnego 0,5 i 0,6, które dojrzewały odpowiednio przez 7, 14 i 28 dni. Testy wytrzymałości na ściskanie przeprowadzone na kostkach sześciennych wykazały, że przewidywana wytrzymałość betonu dla próbek 28-dniowych wynosi 26,0 N/mm², opierając się na normie brytyjskiej. Badania 28-dniowych betonowych kostek, w których zastosowano analizowane kruszywa grube wykazały, że dla wytrzymałości 20 N/mm²: beton z granitem miał największą wytrzymałość - 26,45 N/mm², beton z wapieniem 26,11 N/mm² i z marmurem - 26,03 N/mm². Dla wytrzymałości 30 N/mm² również beton z granitem miał największą wytrzymałość: 30,11 N/mm², następnie z granitem 29.78 N/mm² i wapieniem 29,53 N/mm².

4

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.

5

Badanie właściwości wytrzymałościowych betonów zwykłych i wysokowartościowych z kruszywami ze skał osadowych

Piasta W., Budzyński W., Góra J.

Inżynieria i Budownictwo

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2010

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R. 66, nr 8

445-448

PL

Przedstawiono wyniki badań i analizę statystyczną wpływu rodzaju kruszywa zarówno na wytrzymałość na ściskanie, jak i wytrzymałość na rozciąganie betonów o tym samym w/c. Na podstawie uzyskanych wyników stwierdzono przydatność kruszyw ze skał osadowych wysokiej jakości (dolomit i kwarcyt) do wykonywania betonów zwykłych i wysokowartościowych.

EN

On basis of own experimental results and analysis of variance, the significant effect of coarse aggregate on splitting tensile and compressive strength of high strength and normal concretes has been stated. The suitability of aggregates made from high quality sedimentary rocks - dolomite and the quartzite - for casting normal and high strength concretes is evidently confirmed.

6

Akustycznie stymulowane promieniowanie elektromagnetyczne obserwowane w ośrodkach porowatych nasyconych wodą lub ropą

Sobotka J.

Geologia / Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie

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2006

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T. 32, z. 4

479-497

PL

Przedstawiono wyniki badań zjawiska generacji wtórnego pola elektromagnetycznego w nasyconych skałach zbiornikowych znajdujących się pod wpływem drgań sprężystych. Ośrodek geologiczny, np. porowate, nasycone skały osadowe, składa się z szeregu energetycznie aktywnych elementów. Oznacza to możliwość wyprowadzenia ich ze stanu równowagi energetycznej przez doprowadzenie dodatkowej energii zewnętrznej (np. akustycznej), co w konsekwencji powoduje reakcję systemu w postaci, między innymi, wtórnego promieniowania elektromagnetycznego. Charakter promieniowania (amplituda, widmo częstotliwościowe, charakterystyki czasu) w dużej mierze uzależnione są od własności fizykochemicznych fazy stałej oraz nasycającego medium. W skałach nasyconych ropą generowane impulsy charakteryzują się podwyższonymi częstotliwościami i małymi amplitudami w porównaniu ze skałami nasyconymi wodą. Na podstawie badań teoretyczno-eksperymentalnych został udowodniony rezonansowy charakter tego zjawiska. Otrzymane wyniki wskazują na możliwość opracowania nowej diagnostycznej metody geofizyki poszukiwawczej.

EN

Physical properties of saturated porous media are unstable, which can be related to changes in their internal energy due to e.g. changes of acoustic pressure. Such processes usually are accompanied by electromagnetic radiation, parameters of which must be in strong relation to physical properties of rocks and the type of pore liquid. Results of experimental studies of electromagnetic radiation parameters of saturated sedimentary rock samples and borehole models in a powerful ultrasonic field are presented. It is shown that the amplitude of electromagnetic radiation induced in rock samples, saturated with electrolyte (NaCl solution) and subjected to a field of ultrasonic energy, increases dramatically compared to the amplitude of electromagnetic radiation induced in the same samples saturated with petroleum. The described results suggest that the field of ultrasonic energy alters the electromagnetic radiation of rock in various ways, depending on the type of pore liquid and on the relation between the liquid and the solid phases. A theoretical model explaining the obtained experimental results is proposed. Such behaviour of a multiphase system under the influence of an ultrasonic field enhances the informative possibilities of the methods of borehole logging and suggests possibilities of inventing new methods in geophysical prospecting.