PETROPHYSICAL CHARACTERISTICS OF SOURCE AND RESERVOIR ROCKS IN THE HISTRIA BASIN, WESTERN BLACK SEA

C. Cranganu^1*, M. A. Villa^1,2, M. Saramet³ and N. Zakharova^1,4

¹ Brooklyn College of the City University of New York, Dept. of Geology, 2900 Bedford Avenue, Brooklyn, NY 11210, USA.

² Now at Occidental de Colombia, Inc. (OXY), Bogotá, Colombia.

³“Al. I. Cuza” University, Faculty of Geography and Geology, Iasi, Romania.

⁴ present address: Columbia University, New York, USA.

* corresponding author: Cranganu@brooklyn.cuny.edu

The petroleum system in the Histria Basin, Western Black Sea, includes Oligocene source rocks and Upper Cretaceous – Eocene reservoir rocks. Here we report on the petrophysical characteristics of these source and reservoir rocks using mercury intrusion porosimetry data from 14 core samples collected from five wells drilled on the East Lebada, West Lebada and Pescarus structures. Samples were in general dominated by carbonate lithologies with minor shales. Petrophysical parameters analyzed were:  median pore-throat radius, average pore-throat radius, apparent porosity, pore-throat size distribution, pore-throat type, pore-throat sorting, maximum threshold entry radius, pore-throat radius at 35% mercury saturation (R35), and air permeability. Reservoir rock quality was estimated using a permeability / porosity / pore-throat type plot.

The Oligocene samples showed little petrophysical variation. Samples were relatively homogenous and had the same pore-throat type (nano), were well sorted, had unimodal pore-throat distribution (suggesting the existence of a single fluid phase), had similar values for median and average pore-throat radius, and similar values for R35 and maximum threshold entry radius. Upper Cretaceous - Eocene samples were more heterogeneous in terms of petrophysical properties, and reservoir quality was in general higher than in the Oligocene interval. Average porosity and calculated air-permeability values were 18.4% and 0.37 mD, respectively for Upper Cretaceous samples; and 11.8% and 27.11 mD, respectively for Eocene samples. A case study of Oligocene and Cretaceous - Eocene samples from well West Lebada 817 is presented.

This paper represents the first petrophysical study of source and reservoir rocks in the Histria Basin, Western Black Sea. The results will help to establish the links between petrophysical characteristics, age and depositional environment for source and reservoir rocks in other basins bordering the Black Sea.

Key words: Black Sea, Histria Basin, Romania, petrophysical characteristics, mercury intrusion porosimetry, Oligocene source rocks.

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