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.