MINERALOGICAL RESTRICTIONS ON POROSITY IN THE TAYLOR SAND OF THE COTTON VALLEY GROUP, NORTHERN LOUISIANA SALT BASIN, CLAIBORNE PARISH, LOUISIANA
The Cotton Valley Group has been targeted for hydrocarbons since the 1940s. However, the reservoir was initially considered uneconomical to drill due to its low permeability and porosity. Since then, recent technological advances in hydraulic fracturing have allowed the Cotton Valley Sandstone members to become prolific, profitable plays, renewing interest in drilling and exploration across the northwest/northern Louisiana region. In this research, mineralogical restrictions on the porosity in the Lower Taylor Sand of the Cotton Valley Group were studied from core (10,035’ft/3,059m -10,150’ft/3,094m) from Blackburn Field, northwest Claiborne Parish. Twelve samples were taken at intervals throughout the Taylor Sand, starting at 10,150ft (3,059m) continuing to the top of the Taylor Sand 10,035ft (3,059m). Porosity and x-ray diffraction were previously measured at Von Goton Laboratories. Each of the samples was characterized using X-ray Fluorescence (XRF). Intervals containing greater than 3% total clay were analyzed using Scanning Electron Microscopy (SEM) imaging. Data from these methods were used to determine cement mineralogy and trace element geochemistry. Thin sections were created at twelve sampled intervals to analyze mineralogical diagenesis and its association with reservoir properties. Well log evaluation techniques were also used in this study to develop a calibration between physical core descriptions and the gamma ray log response. This relationship allowed specific recognition of lithology changes in the core and the reflected log response. Results show that the Lower Taylor Sand was deposited in a near-shore, lagoonal environment, where reworked quartz grains were deposited. Periods of transgression allowed mudstones to be deposited, while periods of low siliciclastic input allowed for limestones to be deposited. Fluids flowing through the units deposited calcite within the pore spaces, effectively destroying porosity. Clay minerals, however, were found to positively correlate with porosity and do not restrict porosity. Rather, clay minerals were found with increased porosity values, suggesting that the authigenic nature of the chlorite grains may have reduced the amount of calcite precipitated within the pore spaces. Overall, the Taylor Sand is highly heterogeneous throughout the core in the Blackburn Field.
Cotton Valley Group, Taylor Sand, porosity, calcite, quartz, X-ray Fluorescence, X-ray Diffraction, Geology
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