Browsing by Subject "Fayetteville Shale"
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Item Identifying and mapping clay-rich intervals in the Fayetteville Shale : influence of clay on natural gas production intervals(2013-12) Roberts, Forrest Daniel; Tinker, Scott W. (Scott Wheeler); Fisher, W. L. (William Lawrence), 1932-The Fayetteville Shale is composed dominantly of clay, carbonate, and siliciclastic minerals. A variety of facies have been described by other workers and in this study, defined by mineral content, biota, fabric, and texture. Because the Fayetteville Shale is one of the top shale-gas producing plays in the U.S., an inquiry into key drivers of good-quality production is worthwhile. In particular, a hypothesis that intervals of high clay content should be avoided as production targets is investigated in this study. A high level of separation between wire-line log neutron porosity (NPHI) and density porosity (DPHI) in the Fayetteville Shale is observed in contrast to the wire-line log responses from the Barnett and Haynesville Shales. Clay minerals have a significant effect on NPHI, which in turn affects separation between NPHI and DPHI (PHISEP). X-Ray Diffraction (XRD) clay data was available for three wells, and efforts to correlate XRD results to PHISEP led to establishing NPHI as a reasonable proxy for clay. Using NPHI as a proxy it was possible to pick clay-rich intervals, map them across the study area, and to determine net clay in the Fayetteville Shale. Maps of net clay-rich intervals were compared to a map of production, but revealed no obvious correlation. Stratigraphic cross-sections showing the clay-rich intervals revealed a clay-poor interval in the upper part of the lower Fayetteville. This interval is the primary target for horizontal well completion. It is bounded above and below by more clay-rich intervals. Establishing the clay-rich intervals via porosity log separation (PHISEP) is one tool to help determine possible stratigraphic zones of gas production and can lead to a better understanding of intervals in which to expect production.Item The Influence of Vertical Location on Hydraulic Fracture Conductivity in the Fayetteville Shale(2014-05-05) Briggs, KathrynHydraulic fracturing is the primary stimulation method within low permeability reservoirs, in particular shale reservoirs. Hydraulic fracturing provides a means for making shale reservoirs commercially viable by inducing and propping fracture networks allowing gas flow to the wellbore. Without a propping agent, the created fracture channels would close due to the in-situ stress and defeat the purpose of creating induced fractures. The fracture network conductivity is directly related to the well productivity; therefore, the oil and gas industry is currently trying to better understand what impacts fracture conductivity. Shale is a broad term for a fine-grained, detrital rock, composed of silts and clays, which often suggest laminar, fissile structure. This work investigates the difference between two vertical zones in the Fayetteville shale, the FL2 and FL3, by measuring laboratory fracture conductivity along an artificially induced, rough, aligned fracture. Unpropped and low concentration 30/70 mesh proppant experiments were run on samples from both zones. Parameters that were controllable, such as proppant size, concentration and type, were kept consistent between the two zones. In addition to comparing experimental fracture conductivity results, mineral composition, thin sections, and surface roughness scans were evaluated to distinguish differences between the two zones rock properties. To further identify differences between the two zones, 90-day production data was analyzed. The FL2 consistently recorded higher conductivity values than the FL3 at closure stress up to 3,000 psi. The mineral composition analysis of the FL2 and FL3 samples concluded that although the zones had similar clay content, the FL2 contained more quartz and the FL3 contained more carbonate. Additionally, the FL2 samples were less fissile and had larger surface fragments created along the fracture surface; whereas the FL3 samples had flaky, brittle surface fragments. The FL2 had higher conductivity values at closure stresses up to 3,000 psi due to the rearrangement of bulky surface fragments and larger void spaces created when fragments were removed from the fracture surface. The conductivity difference between the zones decreases by 25% when low concentration, 0.03 lb/ft^(2), 30/70 mesh proppant is placed evenly on the fracture surface. The conductivity difference decrease is less drastic, changing only 7%, when increase the proppant concentration to 0.1 lb/ft^(2) 30/70 mesh proppant. In conclusion, size and brittleness of surface fracture particles significantly impacts the unpropped and low concentration fracture conductivity.