Investigation of the Effect of Overburden Pressure on Vuggy Carbonate Reservoir Core Properties

ABSTRACT

Overburden pressure in carbonate reservoirs is of great importance in understanding and improving productivity and recovery of hydrocarbons because it affects porosity, permeability, capillary pressure, particularly micro-inter-crystalline-framework and micro-fracture structures. As a result of this complexity, a Ruska Gas Permeameter was used at different pressures to measure the rock properties such as porosity and permeability of reservoir cores. The results were compared to CT-scan and NMR data.

In this research over 50 core samples were prepared from AB-Teymur carbonate oil reservoir (Iran). The samples were placed in the core holder and overburden pressures of 500, 1000, 1500, 2000 and 3000 psi were applied. Then Helium porosity and permeability were measured.

This paper describes a systematic experimental methodology to analyze the different permeability and porosity values for reservoir characterization. The new study has shown the role of particularly micro-inter crystalline pore structure in carbonate rocks through digenesis in providing various ranges of porosity and permeability. The different hydrostatic levels in the reservoir rocks achieve a range of micro-fracture scenarios. Hence carbonate formations generally have complex porosity and permeability based on variation of overburden pressure in comparison to siliciclastic sandstones and there are not enough works published in the literature.

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