The Effect of Argillaceous Rock Fabric on the Primary Migration of Oil
Neal R. O’Brien, Marie D. Cremer, Dylan G. Canales, 2003. "The Effect of Argillaceous Rock Fabric on the Primary Migration of Oil", Siltstones, Mudstones and Shales: Depositional Processes and Characteristics, Erik D. Scott, Arnold H. Bouma, William R. Bryant
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The effect of shale fabric on the primary migration of oil is seen through scanning electron microscope analysis of oil morphology and microfracture network in two oil source rocks. SEM micrographs of oil produced by hydrous pyrolysis experiments from two well known source rocks (the Devonian-Missisipian Woodford Shale, Oklahoma and the Jurassic Kimmeridge Clay Formation, Dorset, England) show the following sequence of initial oil formation and movement: (1) within the shale matrix oil is initially generated in the Woodford Shale at 350°C for 1 day heating and in the Kimmeridge Clay Formation at 300°C for 3 days heating; (2) initial oil generation and microfracture formation occur at the same stage; (3) oil droplets continue to move along a pressure gradient out of the matrix into adjacent open microfractures; and (4) ribbons of oil fill the microfractures and move along the fracture network. The primary migration phase through the source rock appears to continue as oil is expelled. These observations highlight the importance of the argillaceous microfabric in influencing the primary migration of oil.
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Siltstones, mudstones and shales have been studied mainly with regard to clay mineralogy and general transport-deposition. Recent studies on deepwater deposits from cores and outcrops have shown that fluid flow properties of deepwater reservoirs are greatly affected by the presence of finer-grained deposits in the reservoir. Initial analysis indicates that the majority of these finer grained deposits have a large silt component and are closer to siltstones rather than mudstones, commonly called shales To date, little attention has been given to their characteristics resulting from different depositional processes.