Multiple Approaches To Characterizing Pore Structure For A Range Of Sandstones Samples
Arawole, Samson Sunday
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Using various approaches, this work examines pore structure (geometry and connectivity) of a range of sandstone samples with their permeability varying by five orders of magnitude. The following four experimental approaches were used: Mercury Injection Capillary Pressure (MICP), Nuclear Magnetic Resonance (NMR), Fluid imbibition and Micro Ct Scan imaging. Fluid imbibition was also used to gauge pore connectivity of these sandstones. Furthermore, basic properties of air porosity and permeability were obtained on the samples before and after all four procedures and used as a basis for property comparison. “Specific” API brine permeability was also run on all samples for comparison as well as a verification of the sample’s reaction to fluid.While pore throats were extracted from mercury injection, pore bodies were drawn from nuclear magnetic resonance. Both of these results were compared with pore throats and pore bodies generated from the processed Ct Scan images. Average pore throat and pore body sizes were also enumerated from NMR, MICP and Ct Scan tests, and the results complement each other. The results of total porosity, permeability and pore size distribution were obtained and compare well among several approaches.Pore size distribution, pore throat distribution and coordination numbers from NMR, XCT and MICP were displayed by frequency distribution diagrams and analyzed. According to the results, the sample with the highest permeability (Idaho Gray sandstone) has the longest T2 time from NMR, highest throat size from MICP and Ct scan, and highest average pore size and coordination number from Ct Scan. This sample also has the least entry pressure from MICP test. Across all samples, the results show a direct correlation between permeability and T2 relaxation time from NMR, a high averaged coordination number from Ct scan and large throat from MICP, both confirming connectivity, and also providing inverse relationship to mercury intrusion entry pressure according to Washburn equation 3-1.The high-permeability Boise sandstone is frequently discussed throughout the thesis because it is one of the samples on which all of four experimental approaches have been used. From Ct scans tests, Boise has a single peak, or mono-modal, pore-size distribution curve, while two medium-permeability samples of Bandera Gray and Parker sandstones both have dual peaks.Fluid imbibition also shows a standard slope of 0.5 or more for high permeability samples (a typical Fickian behavior). All data collected indicate they could be correlated with connectivity and hence fluid flow in reservoir evaluation. Overall results of this integrated study demonstrate that the procedures highly complement each other despite the different principles and methodologies behind them.