Browsing by Subject "San Marcos Arch"
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Item Depositional systems analysis of the Lower Miocene Interval in Refugio County, Western Gulf of Mexico Basin(2015-08) Eluwa, Angela Kelechi; Mohrig, David; Fisher, W. L.(William Lawrence), 1932-; Ogiesoba, Osareni C.Definition of the environments within a depositional system provides useful information about the possible depositional processes; and in turn helps predict the amount and caliber of sediments transported to the basin. This research analyzes variance attribute maps to identify the different environments of deposition within Refugio County, Texas; this analysis also addresses the possible influence by the San Marcos Arch on Lower Miocene deposition. The study area is subsurface, Lower Miocene strata of Refugio County situated in the western GOM basin. Numerous variance attribute maps were generated from a three dimensional (3D) seismic volume. These maps reveal that the stratigraphic section is predominantly an expanded regressive phase. The basal Miocene strata that immediately overlie the Anahuac Shale preserve the record of significant shoreline progradation as shown by a thick and laterally extensive complex of amalgamated beach-ridge deposits associated with longshore transport of sand. These beach deposits are overlain by a thick section dominated by incised valleys fills, and channel and channel-belt deposits. Subtle change in incised valley shape is interpreted to record change in distance or relative proximity to the shoreline. The logs from 17 wells are integrated with the 3D seismic data to quantify sandstone/shale variability and develop sand maps. The San Marcos Arch is a significant structural feature located towards the northeastern part of the study area. Contoured sand thickness maps of four intervals within the dataset indicate increase in sand thicknesses towards the northeast, indicating that the influence of the San Marcos Arch on sediment deposition had waned by the Lower Miocene.Item Mineral, fluid, and elastic property quantification from well logs and core data in the Eagle Ford shale play : a comparative study(2013-08) Kwabi, Essi; Torres-Verdín, CarlosOrganic shales have become one of the greatest sources of hydrocarbon thanks to novel production techniques such as hydraulic fracturing. A successful hydraulic fracturing job, however, is dependent on several rock properties such as mineralogy and elasticity. A reliable estimation of such properties is therefore necessary to determine ideal rocks for horizontal well placement. In this study, rock types within the Eagle Ford shale that would be suitable for hydraulic fracturing are identified through interpretations of available well logs and core data. A comparative study of petrophysical properties such as mineral content, kerogen type and maturity, porosity, and saturation in six wells is performed to characterize the Eagle Ford shale. Two of the wells studied are within the wet gas window of the shale while the remaining four are in the oil window. Based on the calculated petrophysical properties, rock typing was performed using k-means clustering. Two rock types (RT1 and RT2) were identified and their compositions compared in each well. Elastic properties for the various rock types identified were then estimated using the differential effective medium (DEM) theory and were validated through simulation of slowness logs. The final rock type assessment was then performed to identify ideal rocks for hydrofracturing. Results indicate that the Eagle Ford mineralogy varies greatly with depth and with geographic location relative to the San Marcos Arch, a geological arching prominence across the shale. Northeast of the arch, the Eagle Ford shale is clay-rich. Preferred rocks for hydrocarbon production, RT1, are characterized by volumetric concentrations of ~0.44 carbonate, ~0.09 kerogen, ~0.07 porosity, and ~0.42 clay; RT1 also exhibits high sonic velocities (> 3400 m/s and > 1500 m/s compressional and shear, respectively) and high apparent electrical resistivity (> 2 ohm-m). In the Southwest region, on the other hand, the Eagle Ford shale is mostly calcareous. Ideal rocks in the region, RT1, are rich in kerogen (~0.1) with carbonate content of ~0.56, ~0.1 porosity, ~0.19 clay content, and resistivity > 20 ohm-m. In both regions, porosity and pore aspect ratio displayed substantial effects on elastic properties. For example, over 80% decrease in Young’s modulus was quantified when pore aspect ratio approached zero; high pore aspect ratio is preferred for stiff rocks. Poisson’s ratio estimates were not always reliable therefore fracturability was assessed based on Young’s modulus estimates. The study shows that depth intervals exhibiting Young’s moduli above 18GPa and 21GPa in the Northeast and Southwest region, respectively, are suitable for hydrofracturing.