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Sedimentology of the Reservoir Sandstones of the Middle Jurassic, Southeast Part of the Uvat Region


Royo, Gilberto Rafael1, A.A. Matigorov2, K. V. Zverev2, E.R. Chuhlanceva2, I.S. Didenko2 (1) JBC TNK-BP, Moscow, Russia (2) Tyumen Petroleum Centrer of BR-TNK, Tyumen, Russia


Uvat region has become increasingly important over the last ten-year period, with the discovery of significant reserves of oil within the Middle Jurassic seccessions. Main pay horizons of Sourth-East part of the Uvat region are the sandstone member Ju-4, Ju-3 and Ju-2 of the upper part of the Tyumen Formation. Analysis of the distribution of the reservoir rocks within the upper Tyumen Formation has been the focus of detailed sedimentological and 3-D seismic mapping. Sandstone members Ju-4 represent a phase of strong fluvial progradation during of a slow sea-level rise. Sandstone member is composed of fluvial channel fill and overbank/flood-plain strata that were deposited on a broad alluvial plain of low-sinuosity, sandy braided streams. The major architectural feature of the member is the superposition of the multilateral and multistory sheet sandstone complexes interbedded in finer flood-plain deposits. Fluvial sandstone members Ju-3 is formed within coastal plain during of a more fast sea-level rise. Sedimentological studies indicates that reservoir sand­stone bodies are developed mainly as elongate, laterally restricted sandstone bodies embed­ded in finer flood-plain deposits and mudstones of brackish transitional origin. Reservoir sandstones of the member Ju-2 are deposited along a terrigenous-clastics barrier island shoreline. Sandstone mamber are a composite sand-body consist of barrier bar and com­plex backbarrier deposites. Since no significant diagenetic change is imprinted on the sand­stones of the researched members, the most important factor controlling the porosity and permeability development in the reservoirs is the original depositional environments and resulting facies.