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Jean-Yves Chatellier1, Renee Perez2
(1) PDVSA-INTEVEP, Caracas, Venezuela
(2) University of California, Santa Barbara, CA

Abstract: Timing of fluid flow and mass transfer revealed by numerical modeling of quartz and calcite cementation: examples from Maracaibo basin, Venezuela

Quartz overgrowth followed by late non ferroan-calcite, are the most important cements in the Eocene Misoa Formation, Maracaibo basin. The focus of this study is to quantitatively model the reservoir porosity evolution, based on compaction, timing of quartz cement and late calcite precipitation.

Quartz cementation can be modeled with a kinetic approach because the thermal history of the area is well constrained. The model assumes that the quartz cementation rate is dependent on surface area and time of exposure at high temperature.The time interval of calcite precipitation is inferred from matching and timing the available intergranular volume left by compaction and quartz cement with the amount of diagenetic calcite observed in standard petrography.

Results from modeling different samples from different wells in at least five oil fields over the Maracaibo basin gave the same age interval of calcite precipitation despite the difference in depth, maximun burial temperature, grain size and facies distribution. Our work shows that the calcite precipitation is related to one event of short duration related to one fluid flow and mass transfer event involving the whole Misoa Formation.The late calcite cement precipitated between 41 and 36 Ma from cooling ascending waters. The period of cementation is related to a change in the hydrodynamic system of the Maracaibo basin during gradual uplift and tilt due to the emplacement of the Lara Nappes.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana