--> Architecture and Reservoir Qality of Low-Permeability Eocene Lacustrine Turbidite Sandstone From Dongying Depression, East China

AAPG ACE 2018

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Architecture and Reservoir Qality of Low-Permeability Eocene Lacustrine Turbidite Sandstone From Dongying Depression, East China

Abstract

Reservoir architecture and multiscale heterogeneity in turbidites represent serious challenges to production performance. In this paper, we report on the turbidites of the third member of the Eocene Shahejie Formation (Es3), which was deposited during extensive Middle to Late Eocene rifting in the Dongying Depression.

Deep-water, marine turbidite sandstones are known to form moderate to excellent petroleum reservoirs. The architecture and quality of lacustrine turbidites that act as petroleum reservoirs are less well documented. The Es3m interval is interpreted as a sequence set that is composed of four composite sequences: CS1, CS2, CS3 and CS4. A total of forty-five sequences were identified within these four composite sequences. Sand bodies were mainly deposited as channels, levees, overbank splays, lobes and lobe fringes. The combination of fining up and coarsening up patterns of lithofacies in architectural elements produces highly composite flow units. Large-scale heterogeneity is a function of third- and higher-order bounding surfaces. Microscopic heterogeneity is produced by diagenetic alteration processes (i.e., the dissolution of feldspar, the formation of authigenic clay and quartz cementation). The dominant kaolinization of feldspar and mobilization of materials enhanced the quality of the reservoir by producing secondary enlarged pores. In contrast, the formation of pore-filling authigenic illite and illite/smectite clays reduced their permeability. Recovery rates are higher in the axial areas and lower in the marginal areas of architectural elements. This study represents a significant insight into the reservoir architecture and heterogeneity of lacustrine turbidites; these understandings can be applied to exploit primary and secondary production from these fields.