The correlation of a multi-level porosity system with depositional cyclicity and log signatures: Deep Cretaceous reservoirs, Lake Maracaibo, Venezuela

Conference · Fri Mar 01 00:00:00 EST 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:7025045

Vahrenkamp, V C; Franssen, R C.M.W. ^[1]; Munoz, P J ^[2]

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1. Shell Research, Rijswijk (Netherlands)
2. Maraven S.A., Caracas (Venezuela)

The correlation of a multi-level porosity system with depositional cyclicity in cores from central Lake Maracaibo (SVS-225; SVS-229) allows indirect recognition of productive intervals on logs. Deep Cretaceous reservoirs of Lake Maracaibo include Barremanian to Turonian strata (Rio negro Sandstone, Cogollo Group, and La Luna Formation). In the shallow-water carbonates of the Cogollo Group, large-scale open-marine and restricted-marine cycles (thickness; 50-200 ft) are recognized in cores as well as on logs. Organic-rich and less organic-rich limestone layers (decimeter scale) of the deep-marine La Luna source rocks probably reflect Milankovitch cyclicity. Cogollo Group/La Luna reservoirs are characterized by a dual/triple porosity system related to depositional cyclicity. Open fractures act as highly productive fluid conduits while providing little storage capacity (upper level porosity system). Open fractures occur preferentially in open-marine depositional cycles of the Cogollo Group, and fractured intervals can therefore be recognized indirectly by their log signatures. In the La Luna Formation open fractures are concentrated in less organic rich layers. The lower porosity level provides mainly storage capacity but little permeability. It consists of stylolite and patchy intervals of matrix porosity. A network of closely spaced stylolites not only provides significant storage capacity (lower level system) but also serves as an intermediate permeability system connecting matrix porosity with open fractures. Comparison with cores and logs from other wells in the Lake Maracaibo region confirms the recognized cyclicity pattern and suggests regional validity of the reservoir model.

• OSTI ID: 7025045
• Report Number(s): CONF-910403-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 75:3; Conference: Annual meeting of the American Association of Petroleum Geologists (AAPG), Dallas, TX (United States), 7-10 Apr 1991; ISSN 0149-1423
• Country of Publication: United States
• Language: English

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