From: "James Clarke" Subject: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Unsent: 1 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3 Paleozoic Paleogeography of Timan-Pechora Province

Paleozoic Paleography of Timan-Pechora Oil-Gas Province
Internet Geology News Letter No. 172, December 2, 2002

Three main oil-gas plays are recognized in the Paleozoic section of Timan-Pechora province: Middle Devonian-lower Frasnian, lower-middle Visean, and Upper Permian.

The Middle Devonian-lower Frasnian clastic play. Thickness of these sediments increases toward the east; grain size decreases, and marine carbonates become more prominent in this same direction. The section consists largely of alternating sandstones and siltstones of quartz composition derived from the Timan high on the west.

In the Ukhta region in the south-southwest a paleo-delta is present where a river flowing from the northwest emptied into the sea. Thickness of this deltaic material is more than 600 m. This delta is about 100 km wide from east to west and 150 km long from north to south. On the west the sediments are continental fluvial, and on the east they are fore-delta marine.

Reservoir properties of the deltaic rocks are very good. Porosity commonly exceeds 17-20 percent, and permeability is several hundred to more than a thousand millidarcies. These rocks are favorable for oil and gas in non-structural traps.

In the north of the Timan-Pechora province there was a large marine embayment during the time of deposition of the Middle Devonian clastic complex. The main sources of detritus were on the northwest and southeast. Reservoir properties of these rocks are very good.

The regional seal for the Middle Devonian sediments is a member of the Kynov clays 15-60 m thick, which is present throughout the area of the Pechora-Kolva mega-arch.

Favorability of this play diminishes toward the north due to increase in compaction of the rocks.

Lower-middle Visean clastic play. This unit consists of quartz sandstone and siltstone. The configuration of the basin was essentially the same as during the Devonian. Paleo-river channels are present on the west, and these pass eastward into deltaic deposits and then into marine clays. These Visean clastics have good reservoir properties; however, there are no regional seals. Local seals are present in the play; otherwise, Permian clay-carbonate rock must serve as seals.

Upper Permian clastic play. Sediments of the Ufim, Kazan, and Tatar Stages are present here. The principal source area for these sediments was the rising Ural Mountains on the east; they are largely fluvial deposits. Thickness is as much as 3,000 m on the southeast.

The paleogeographic conditions of the Late Permian persisted on into Early Triassic time. Alluvial-deltaic deposits then extended on farther northwestward. Therefore, the sediments that are of interest for oil and gas will be successively younger toward the northwest.

Taken from Oknova, Rozhkov, and Lyubina, 1986; digested in Petroleum Geology, vol. 23, no. 11-12, two paleogeographic maps. Copyright 2002 James Clarke. You are encouraged to print out this News Letter and to forward it to others. Earlier News Letters are available at: http://geocities.com/internetgeology/
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