ESTUDOS PETROFÍSICOS DE ROCHAS CARBONÁTICAS DA AMÉRICA DO NORTE E AVALIAÇÃO DE MODELOS DE COMPRESSIBILIDADE DE VOLUME DE POROS

Abstract

In this work, we aimed to perform petrophysical studies on five groups of samples of carbonate rocks from three North American geological contexts, known for its association with hydrocarbon deposits - (i) Guelph Formation, Michigan Basin (Middle Silurian) samples GD; (ii) Edwards Formation, Central Texas Platform (Middle Cretaceous) samples DP, EW and EY; and (iii) Burlington-Keokuk Formation, Mississippian System (Lower Mississippian) samples BL. From these results, we evaluate two models of pore volume compressibility (Cpv), currently discussed in the literature (Horne (1990) and Jalalh (2006b)). Petrophysical studies of effective porosity/permeability vs. absolute variation of confining pressure revealed different structural reorganization behaviors due to the occurrence of different pore size populations. For three of the investigated lithologies (EW, BL and GD), the observed behavior under confining pressure was typically characteristic for the occurrence of a predominant microscale (diameter < 1 µm) range of pore volume, whereas for the remaining ones (EY and DP), a ruptile pattern was verified due to a possible predominance of pore volumes at mesopore (~ 1 3 µm) and macropores (diameter > 3 µm). Additionally, one of the lithologies (BL samples) showed typical behavior of sealants rocks. These patterns were confirmed by NMR and MICP combined tests. A wide range of effective porosities (~ 2 34%) obtained in this study indicated a reasonable evaluation of the selected pore volume compressibility models. It was concluded that the Cpv data estimated from our findings showed slightly higher compatibility to the model proposed by Jalalh (2006b), under the 95% confidence and 68% prediction intervals. New studies, based on larger sample space which also be representative of the larger lithological variability associated with carbonate rocks, are required to confirm such inferences.