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Thin-bedded strata and tuning effect as causes of seismic data anomalies in the top part of the Cenomanian sandstone in the Grobla–Rajsko–Rylowa area (Carpathian foreland, Poland)

Marzec P., Pietsch K. J.

Geological Quarterly

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2012

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Vol. 56, No. 4

691--710

EN

A high-amplitude anomaly in seismic signal, i.e. a bright-spot, which is the main direct hydrocarbon indicator, may also occur due to interference between the reflected signals from the top and base of a thin bed (the tuning effect). In such settings the main problem is to distinguish amplitude anomalies associated with lithological changes or changes in gas saturation from anomalies originating from the tuning effect. We provide a method of interpreting the composite seismic signal produced by the interference between reflections. Such reflections occur along the top of the Cenomanian sandstone in the area of the Grobla–Rajsko–Rylowa 3-D seismic dataset (southern Poland). The non-standard method presented here is based on interpretation of seismic data which was rotated by 270°. The results of seismic modelling were used to develop criteria for interpretation of such data. These criteria are based on the difference between information carried by the peak-to-trough amplitude and that by the total amplitude of rotated seismic data. The difference was used to define the transfer function and to remove the high-amplitude anomalies caused by the constructive interference between the reflected signals from the top and bottom of the thinning stratum. The final outcome of the study was a map showing the seismic amplitude response at the top Cenomanian reflector unaffected by the tuning effect. The map shows the extent of the area where high-amplitude anomalies do not correspond with changes in thickness and petrophysical parameters within the top part of the Cenomanian. These anomalies are caused by a lateral increase in thickness of the Turonian and/or an increase in the velocity within the bottom part of the Senonian (Coniacian) strata. The map can be used to determine precisely the boundaries of the Rajsko and Rylowa gas reservoirs as well as to locate the potential extension of the reservoir zone to the east of the Rylowa 6 borehole.

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Czy tłumienie fal sejsmicznych może być źródłem informacji o stopniu nasycenia skał zbiornikowych gazem? - studium modelowe

Pietsch K., Nawieśniak A., Kobylarski M., Tatarata A.

Przegląd Geologiczny

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2008

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Vol. 56, nr 7

545-551

EN

One of the main problems of hydrocarbon prospecting within the Carpathian Foredeep is identification of non-commercial objects that exhibit anomalous image on seismic sections.Within gas saturated layers, apart from acoustic impedance variations, seismic energy attenuation also changes which results in shadow zone under the reservoir. The lack of measurements which show variation of petrophysical parameters (velocity, density, attenuation) in relation to gas saturation as well as coexistent dependence of seismic image on a number of parameters resulted in development of non-commercial gas reservoir identification criteria on the basis of seismic modeling. The purpose of seismic modeling was evaluation of changes in seismic image caused by attenuation that is related to gas saturation degree. Theoretical wavefield was calculated for seismogeological model constructed for TO152005 profile within Łukowa gas reservoir. Wide range of performed modeling, with an assumption that attenuation is a function of gas saturation, emphasize low attenuation impact of fully gas saturated layers and high impact of partially saturated layers which changes both amplitude and frequency of theoretical wavefield within gas reservoirs. Above criterion could be a basis for identification of partially saturated reservoir layers, however, industrial application of the criterion requires more intensive research on dependence of seismic energy attenuation on gas saturation.

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Wykorzystanie atrybutów bazujących na danych sejsmicznych przed składaniem do oceny stopnia nasycenia gazem warstw złożowych, NE część zapadliska przedkarpackiego

Pietsch K., Tatarata A.

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

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2008

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T. 34, z. 2

301-320

PL

Dla poszukiwań naftowych w NE części zapadliska przedkarpackiego interesująca jest odpowiedź na pytanie, czy można na podstawie rejestrowanych przekrojów sejsmicznych opracować wskaźniki, które pozwoliłyby na ocenę stopnia nasycenia gazem przestrzeni porowej warstw zbiornikowych. Równoczesna zależność sejsmicznego obrazu złoża od wielu parametrów petrofizycznych powoduje, że ocena wpływu tych parametrów oparta została na wielowariantowych modelowaniach sejsmicznych. Modelowania (system Hampson-Russell (CGGVeritas)) wykonano dla modelu aproksymującego wielohoryzontowe złoże gazu "Łukowa" (profil sejsmiczny T0152005 zrealizowany przez Geofizykę Toruń Sp. z o.o, (Pomianowski et al. 2005) oraz dane geofizyki wiertniczej z otworu Ł-2). W niniejszym artykule przedstawiono wyniki testów procedur interpretacyjnych, które bazują na danych sejsmicznych przed składaniem (AVO Product, Fluid Factor, lambdap i microp, impedancja elastyczna). Potwierdzeniem poprawności opracowanych kryteriów jest zestawienie przypływów, wg próbnika złoża, ze zinterpretowanym przekrojem sejsmicznym.

EN

The question, whether it is possible to create such indicators that would allow to assess a saturation degree of reservoir pore space directly from seismic response, is interesting for hydrocarbon prospecting in the NE part of the Carpathian Foredeep. The dependence of seismic image of gas reservoir upon plenty of petrophysical parameters causes that the analysis of their influences on seismic response were based on seismic multi-variant modelling. Seismic model approximating "Łukowa" gas reservoir was constructed with Hampson-Russell System (CGGVeritas) accordingly with a geometry of profile no T0152005 acquired by Geofizyka Toruń Ltd. and additionally supported by log data from Ł-2 well. This paper presents results of the tests of interpretative procedures based on pre-stack seismic data such as AVO Product, Fluid Factor, lambdap and microp, elastic impedance. The correctness of established criteria was confirmed by a juxtaposition of an inflow rate obtained from a drill-stem tester and the interpreted seismic profile.