Abstract: Three gas fields have been discovered in the Chu-Sarysuy synclize: the Pridorozh, Ayraktin, and Zharkum. At the base of the section of the middle-upper Paleozoic complex of the Chu-Sarysuy synclize occur largely extrusive rocks of the Lower and Middle Devonian (thickness up to 1000 m). These occur in the Tesbulak depression, in the region of the Chuy block , and in the north part of the Muyunkom depression. Sediments of the Upper Devonian (Frasnian and Famennian) are known largely in zones of inherited downwarps within or near Caledonian synclines. The best known of these are in the region of the Nizhne-Chuy structural step in the Bestyubin area where sub-salt (500 m penetrated) and salt-bearing (800 m) sediments have bee n found. The Lower Carboniferous sediments consist of deposits of Tournaisian, Vizean, and Na murian age. In the central and southern parts of the Chu-Sarysuy synclize, the Tournaisian (200 m thick) consists predominantly of marine carbonates; toward the east t hey undergo facies change to clastic carbonates a nd clastic variegated rocks up to 500 m thick. Extensive transgression during Vizean time led to wider distribution of carbonate se diments. In the northeast, north, and southeast parts of the synclize. carbonate-clastic sediments up to 1500 m thick were deposited along with beds of anhydrite, carbonaceous shale, sandstones, and tuffs. With regression of the sea during Namurian time there was a reduction in the area of occurrence of marine carbonate deposits. The Namurian sediments in the north and east parts of th e synclize are largely elasti cs; these are 80‐170 m thick. Hercynian tectonic processes are relatively weakly expressed here ; consequently, granular reservoirs can be expected. Further, in the upper part of the Devonian section there are extensive sedi ments of shallow-water marine and lagoonal facies, which are favorable for oil-gas formation. Thick salt units of the Famenn ian and Lower Tournaisian can act as reliable seals for gas pool s. Commercial gas was found in sandstones of the Upper Devonian in the Pridorozh area in 1973‐74; well 3 here yielded 1.5 million m 3 per day. The gas consists of 71% methane and 1‐2% heavy hydrocarbons. Reserves here are estimated at 5 billion m 3 for the intra-salt sediments.
Publication Year: 1976
Publication Date: 1976-01-01
Language: en
Type: article
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