--> Abstract: Upper Paleozoic Mud Mounds Of The Bolchoi Karatau Mountains (Kazakhstan), Nature And Reservoir Impact For North Caspian Exploration, by P. A. Lapointe, H. E. Cook, N. Shirtliffe, and S. Dugravot; #90928 (1999).

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LAPOINTE, P. A.1, H. E. COOK2, N. SHIRTLIFFE3, and S. DUGRAVOT3
1Total, St Remy, France
2USGS, Menlo Park, CA
3Universite Journier, Grenoble, France

Abstract: Upper Paleozoic Mud Mounds of the Bolchoi Karatau Mountains (Kazakhstan), Nature and Reservoir Impact for North Caspian Exploration

The Upper Paleozoic carbonates of the Bolchoi Karatau Of southern Kazakhstan range from deep water to supratidal facies. They are geologically similar to the coeval carbonate platforms that contains the giant Tengiz oil field and other potential or discovered giant oil and gas fields of the North Caspian Basin.

The different sections studied show Mud Mounds ranging from Famennian to Bashkirian in age. The mapping of the mounds revealed complex bodies made of superimposed carbonate lenses. They appear located as cluster, commonly disposed on paleobathymetric lines.

They show significant facies change, both laterally and vertically. The carbonate build-ups mostly of microbial origin consist of mudstone to wackestone, with locally packstone limestones. They are not framework supported but mudsupported, frequently cemented (cementstone). A few are partly dolomitized. Their bioclastic content consists of crinoids, sponges, bryozoans and brachiopods. The deposition palaeoenvironments range from slope or deep slope to platform edge.

As a general statement, the reservoir characteristics of the mound facies are poor. In some cases, they are improved by:
1. dolomitization, leading to improved porosity and permeability;
2. karsting, providing double porosity systems in massive mud-rich skeletal mounds as karst process exploits the fracture system overprinting the mounds. Therefore there is a good potential drainage through karstic systems and storage within the 'matrix' rocks of low reservoir characteristics.

Mounds identification from borehole allows a better understanding of the sedimentological facies and furthermore prognosis of the reservoir zones.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas