Print this pagePorosity Determination by 3D High-Resolution X-Ray Computed Microtomography and Its Correlation with Gas Adsorption Technique
In order to evaluate the productivity performance of the oil reservoir, it is necessary to investigate how easily the fluid can flow into the pore system. Several reservoir rock and fluid properties can be study through petrophysical parameters, such as, porosity which is the ratio of pore volume to the total bulk volume of the formation. This parameter can be presented as an absolute or as an effective value. The effective porosity is the fractional volume of pore space that permits fluid to flow in a rock and it is lower than the absolute porosity which is related to all connected void spaces, regardless of whether the pores are connected or dead-ended. The porosity can be determined in laboratories routines using cores from the formation, but all the techniques used in conventional petrophysical require sample preparation which leads, in most cases, to a destruction or modification of the used material. The unique technique that can determine some petrophysical parameters without sample preparation is the X-ray computed microtomography. This is a non-destructive test, resolution of microns and becomes a useful tool in study of inner characteristics of geological samples. In this work it was investigate cores from the reservoirs of Resende Formation which were collected in Porto Real, RJ/Brazil. This formation is characterized by sandstones and fine conglomerates with associated fine siliciclastic sediments and the paleoenviroment is interpreted as a braided fluvial system. The purpose of this study was to estimate the total cores porosity by microtomography and to correlate them with the gas adsorption porosimetry technique. The microtomography was acquired using a 3D high resolution microtomography system which have a microfocus X-ray and a CCD camera fiber-optically coupled to scintillator operated at 100 kV and 100 μA. Thirty-six samples at different depths of three oils wells were analyzed and a total of 961 2D slices were performed with a resolution of 14.9 µm. The porosity was estimated from the 3D analysis of binary images. The correlation between the conventional and microtomography techniques demonstrated that the porosity values were in the same range, but the last one has an advantage of being non destructive and more sensitivity to changes in 3D microstructures. It was also possible to perform a 3D visualization of the size and shape of pore volume presents in the rock performing tests without destroying the samples.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil