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Reef Reservoir Identification by Wavelet Decomposition and Reconstruction : A Case Study from Yuanba Gas Field in China

Cheng B., Xu T., Robbins B., Shen Z. M.

Acta Geophysica

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2015

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Vol. 63, no. 4

1025--1043

EN

The organic reef is a special type of carbonate reservoir which always dominates the spatial distribution, reserves and accumulations of natural gas. However, it is difficult to determine the organic reef’s internal structure and gas reservoirs due to numerous adverse factors such as the low resolution of seismic data, depth of burial, strong anisotropy, irregular spatial distribution and complex internal structure. A case study of wavelet decomposition and reconstruction technology applied to elucidate the features of organic reef reservoirs in the Changxing formation from Yuanba gas field shows that the seismic record reconstructed by high frequency signal can adequately describe the internal properties of organic reef reservoirs. Furthermore, the root mean square amplitude ratio of both low and high frequency data obtained from the reconstructed seismic data clearly show spatial distribution of gas and water in reef reservoirs.

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The Steinplatte complex (Late Triassic, Northern Calcareous Alps, Austria) - subsidence-controlled development of a carbonate-platform-to-intrashelfbasin-transition

Kaufmann B.

Acta Geologica Polonica

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2009

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Vol. 59, no. 3

341-357

EN

In Rhaetian (Late Triassic) times, the Hauptdolomit/Dachstein carbonate shelf situated at the passive continental margin of the northwestern Tethys was characterized by an extensional tectonic regime. Rifting and spreading movements fragmented this shelf into a loosely fitted mosaic of fault-bounded blocks characterized by a differential subsidence pattern. This is expressed in significant thickness variations of platform carbonates and in the formation of the intrashelf Kossen Basin. In this study, it can be demonstrated that tectonic subsidence triggered the development of a carbonate platform margin and that the influence of eustatic sea-level changes was negligible. The Steinplatte complex developed at the transition of the Kossen Basin to the Dachstein Carbonate Platform. Small-scale isolated carbonate mounds situated on a smoothly inclined homoclinal ramp characterized the initial phase and acted as nuclei of further carbonate buildup growth. However, only the ideal palaeogeographic position far enough away from the carbonate-suppressive terrigenous influence of the Kossen Beds, combined with vigorous carbonate production stimulated by rapid subsidence-caused sea-level rise, favoured continuous mound growth. Once established, the carbonate buildup was characterized by rapid aggradational growth, developing a palaeogeographic high with a steep slope and a depression with decreased sedimentation behind, several kilometres distant from the Dachstein Carbonate Platform. Contemporaneously, isostatic adjustment caused an accommodation minimum on the nearby margin of the Dachstein Carbonate Platform leading to its westward progradation. Fading out of subsidence caused filling of the former depression in the back of the buildup by prograding shallow-water Dachstein Limestones. Thus, a new platform margin was established in the Steinplatte area, elevated almost 200 m above the adjacent Kossen Basin. At the Triassic-Jurassic boundary, the Steinplatte complex was subjected to subaerial exposure by a sudden tectonic uplift followed by a rapid isostatic drop. Emergence is indicated by levels of karstified limestones directly underlying supposed exposure surfaces. Final drowning of the Steinplatte complex as well as of the whole Dachstein Carbonate Platform is indicated by the cover of Early Jurassic (Sinemurian) deeper water, ammonitebearing limestones (Adnet Formation).

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Dynamika rozwoju utworów koralowych środkowego oksfordu okolic Bałtowa

Gutowski P.

Volumina Jurassica

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2004

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Vol. 2, no. 1

17-28

EN

Coral facies developed on the Middle Oxfordian carbonate ramp were controlled in the region of Bałtów, NE margin of the Holy Cross Mts., Poland, by syndepositional activity of extensional fault blocks. Elevated parts of sea bottom were occupied since Early Oxfordian time by sponge bioherms successively colonized by coral reefs when grown up to the sea level. Micritic sedimentation prevailed in interbioherm denivelations. This micritic succession was replaced by soft-bottom coral buildups constructed by flat coral colonies, typical of a relatively quiet environment of the depths 20-70 m, and finally by coarse bioclastic grainstones and oncolites which are interpreted as talus of the coral reef constructed on tops of former sponge bioherms by branched and hemispherical coral colonies in very dynamic and extremely shallow water conditions.