| Popis: |
The determination of pore geometry and pore aperture size from mercury injection tests is a very helpful technique. Due to the amount of pressure data points that can be taken, a detailed characterization of the capillarity of the rocks can be accomplished. The size and geometry of the pores are related to variability in grain size, sorting and packing, as well as to factors such as the mineralogy and the diagenetic history of the formation. This paper presents the results of the integration of capillary pressure curves, conventional core analysis and petrographical Investigation, in a highly heterogeneous pore geometry, where a bimodal behavior of mercury-injection capillary pressure curves was identified, showing two main types of pore throat, one with a larger flow capacity than the other. This analysis was backed up by thin sections made in adjacent samples, where strong changes in sorting, grain size and increment in the percentage of clay matrix can be seen. The changes in pore geometry observed within such small distances, demonstrate the high heterogeneity of the reservoir rock. An attempt was made to classify the different rock types present in the reservoir, using the Winland (R35) relationship to calculate pore throat radius based on permeability and porosity. Despite the complexity of the pore system, it was found that R35 can appropriately represent the largest portion of the rock volume with the main pore throat radius that contributes to the flow. The fact that the mercury capillary pressure curves grouped by rock type always show the bimodal shape, was taken into account in order to understand the wells production in the reservoir, because the performance of the wells will depend on the volume of each main pore throat radius in the completed zones. |
