Adams DOE profiles MT profiles Lauren data collected adjacent to small intrusions have elevated vitrinite reflectance values ranging up to 2.21 percent. Coal-rank data (Walsh and Phillips, 1982) show predictable increases in maturation eastward across the region as the Cascades magmatic arc is approached. Preliminary petrographic analysis indicates that sandstones from the Morton antiform are largely plagioclase-rich, arkosic arenites, with variable porosity controlled by calcite cement and clay minerals. Unsubstantiated reports of secondary porosity in Puget Group units mapped in mines in the Morton area may be an indication of possible reservoir potential. However, extensive evidence for transpressive deformation, fracturing, and faulting of the Morton antiform must be considered negative factors for the occurrence of a suitable reservoir. Such considerations, along with the limited evidence for adequate source rocks, make the Morton antiform area a high risk exploration target, but possibly one of the few remaining to be tested in western Washington. 20 40 60 80 100 KM i___i EXPLANATION Quaternary volcanic rocks Tertiary subductkm complex Miocene Cohnnbia Ri»er Basalt Group Morton, Skate Mtn. and Carbon River aotifonns Tertiary rift sedimentary rocks Eocene Northcraft-Tukwfla volcanic rocks Eocene marine basalts of SOetzia Southern Washington Cascades conductor (SWCC) Jurassic-Cretaceous Rhnrock Inner Mesozoic and Paleozok rocks of the North Cascades Seismic profile MT profile X Volcano Figure 2 6a reflection data generally obtained. The system of late Tertiary sedimentary basins west of the Cascades (Fig. 2) has been interpreted as containing largely immature source rocks, but with some good reservoir rocks (Armentrout and Suek, 1985). These basins formed on basement consisting of oceanic basalts of the Coast Range province, and are filled with 3-5 km of marine sandstones, shales, and minor volcanic rocks. The only producing field with ongoing development in the Pacific Northwest is the Mist gas field, west of Portland, Oregon (Fig. 2). Eocene to Miocene sedimentary units in the Olympic Peninsula appear to contain good source rocks (Snavely, 1987) and some oil has been produced from the coastal zone of the Peninsula and in the Grays Harbor basin to the south (Braislin and others, 1971). Methane is venting from a fault zone on the north side of the Olympic Peninsula (Kvenvolden and others, 1987). Organic geochemical analyses by Kvenvolden and others (1987) suggest that the deep parts of the Olympic melange assemblage are mature for oil and gas, and Snavely (1987) suggests that the highest potential for oil and gas generation in the western Washington region occurs in the thick, accretionary melange-wedges of the Olympic Peninsula. Drilling in the Puget Lowland of Washington (Fig. 2) has not resulted in production, but many wells have produced shows of oil and/or gas. Gas seeps in the Black Diamond, WA area (Mullineaux, 1970) and elsewhere in the Puget Lowland are believed to derive from coal bed methane at sha...
Modeling the thermal history of the Illinois basin, Illinois, Indiana, and Kentucky (Figure 1) showed that the measured vitrinite reflectance (Ro) of the Upper Devonian-Lower Mississippian New Albany Shale, the main source rock unit used to calibrate the models, was suppressed. That is, measured Ro values (tables 1 and 3) are lower (less mature) than vitrinite reflectance equivalents based on other thermal maturity indicators. Observations indicated that the degree of thermal maturity in RQ profiles (constructed by extrapolating from the Middle Pennsylvanian (Desmoinesian) Herrin coal through the Upper Devonian-Lower Mississippian New Albany Shale) does not always increase with increasing depth of burial. In fact, the Ro of the Middle Pennsylvanian Herrin coal is similar, and in some instances greater than that of the Upper Devonian-Lower Mississippian New Albany Shale, yet the New Albany is up to several thousand feet deeper. The purpose of this report is to present new Ro (table 3) and Rock-Eval data (table 1), and illustrate the amount of suppression of selected New Albany Shale samples. Two Rock-Eval parameters, Tmax and hydrogen index, are compared with measured Ro data for several New Albany Shale samples from throughout the Illinois basin, and RO correction contours for the New Albany Shale are estimated (table 1 and Figure 1). Rock-Eval pyrolysis is used to evaluate rapidly, the petroleum generation potential of rocks, and it provides information on the quantity, type, and thermal maturity of the organic matter in a rock. Pyrolysis is the heating of organic matter in the absence of oxygen to yield organic compounds. Complete details of the Rock-Eval pyrolysis technique and associated problems are given in Espitalie and others (1977) and Peters (1986). The Rock-Eval pyrolysis technique yields several measurements that determine the thermal maturity and hydrocarbon generation potential of source rocks. Total organic carbon content (TOC) is a useful parameter for evaluating the quantity of organic matter in a potential source rock. Total organic carbon was determined using the Rock-Eval II instrument and is the sum of the carbon in the pyrolyzate plus the carbon from the residual oxidized organic matter. In general (depending on the type of organic matter, and lithology), fine-grained rocks having a total organic carbon content of greater than 0.50 percent are considered a potential hydrocarbon source rock. Rock-Eval pyrolysis also measures Tmax, tne temperature of maximum hydrocarbon yield. Tmax can be used as a thermal maturity indicator because the temperature for maximum hydrocarbon yield increases as kerogen matures. Hydrocarbons begin to be generated between Tmax values of 435°C and 440°C, and thermal cracking to gas and condensate occurs at about 460°C (Tissot and Welte, 1984). The hydrogen index (HI) is defined as the S2 yield (remaining hydrogen-generating capability of the organic matter) normalized by the total organic carbon content (TOC); in other words, the fraction of the total organic carbon ...
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