Quantitative Characterization of Carbonate Pore Systems by Mercury- Injection Method and Image Analysis in a Homogeneous Reservoir

Abstract

Abstract The quantity of direct interest in the flow through porous media is not the properties of the matrix (e.g. grain size distribution) but rather the properties of the pore (e.g. pore size distribution). The determination of representative capillary pressures is of vital important for the mapping of the reservoir fluid distribution. Mercury porosimetry or mercury injection-capillary pressure curves are commonly used to measure the distribution of pores and pore throat sizes. Pore aperture size estimated from mercury injection tests has been used to categorize the rock by pore type, evaluate seals for traps and to explain the locations of stratigraphic hydrocarbon accumulations. In image analysis, the OM (Optical Microscopy) images provide macroporosity information, whereas the ESEM (Environmental Scanning Electronic Microscopy) images yield information on microporosity. Comparison of total porosity determined from plugs indicates that macroporosity and microporosity values based on image analysis match the plug data, confirming the validity of the method. The combination of macroporosity and microporosity data yields pore size distribution and pore shape information that can explain the distribution of physical properties, in particular permeability. Permeability can mainly controlled by the macropore shape in high-permeability samples, and by the amount of intrinsic microporosity in the low permeability samples. In this investigation three pore and port geometric systems have been recognized, 1) Type-1 system that belongs to mud dominated bioclastic peloidal packstone, at the top of reservoir, with good porosity and fair permeability shows large and smooth pores and ports as bimodal, 2) Type-2 system presented in mud dominated bioclastic peloidal packstone / grainstone with fair porosity and low permeability shows moderate to small pores and ports and 3) Type-3 system that has been seen in ploidal bioclastic grainstone and mud dominated planctonic foraminiferal packstone, packstone /wackestone and wackestone with low porosity and low permeability shows small pores and ports as matrix porosity.