Facies Architecture of the Bluejacket Sandstone in the Eufaula Lake Area, Oklahoma: Implications for Reservoir Characterization of the Subsurface Bartlesville Sandstone
Liangmiao “Scott” Ye, Dennis Kerr, Kexian Yang, 1999. "Facies Architecture of the Bluejacket Sandstone in the Eufaula Lake Area, Oklahoma: Implications for Reservoir Characterization of the Subsurface Bartlesville Sandstone", Reservoir Characterization—Recent Advances, Richard A. Schatzinger, John F. Jordan
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Outcrop studies of the Bluejacket Sandstone (Middle Pennsylvanian) provide useful insights to reservoir architecture of the subsurface equivalent Bartlesville sandstone in Glenn Pool field. Quarry walls and road cuts in the Lake Eufaula area offer excellent exposures for detailed facies architectural investigations using high-precision surveying and photomosaics. Subsurface studies include conventional logs, borehole image log, and core data.
Reservoir-scale facies architecture is reconstructed in four hierarchical lev-els: multistory discrete genetic intervals, individual discrete genetic interval, facies within a discrete genetic interval, and subfacies of the meandering channel-fill facies. From the Eufaula Lake to Glenn Pool field areas, the Bluejacket (Bartlesville) Sandstone, taken as a whole, represents an incised valley fill above a type-1 sequence boundary. It comprises two distinctive architectures: a lower braided channel-fill-dominated interval, regarded as representing the lowstand systems tract, and an upper meandering channel-fill-dominated interval, regarded as the transgressive systems tract.
Braided channel-fill facies are typically 30-80 ft (9-24 m) thick and are laterally persistent, filling an incised valley wider than the largest producing fields. The lower contact is irregular, with local relief of 50 ft (15 m). The braided-fluvial deposits consist of 100-400 ft (30-122 m) wide, 5-15 ft (1-4 m) thick channel-fill elements. Each channel-fill interval is limited laterally by an erosional contact or overbank deposits, and is separated vertically by discontinuous mudstones or highly concentrated mudstone interclast lag conglomerates. Low-angle parallel-stratified or trough cross-stratified medium to coarsegrained sandstones volumetrically dominate. This section has a blocky well log profile.
Meandering fluvial deposits are typically 100-150 ft (30-45 m) thick and comprise multiple discrete genetic intervals. Meandering channel-fill facies successions include basal trough cross-stratified medium-grained sandstones, medial low-angle-stratified fine-grained sandstones with numerous mudstone drapes, and an upper mudstone. Well log profile is typically a serrated bell shape. Splay facies is up to 20 ft (6 m) thick, and consists of ripple stratified and lesser trough cross-stratified, medium-grained sandstones separated by laterally persistent thin mudstones. Floodplain mudstones laterally and vertically segment, with the exception of very limited areas, channel-fill and splay sandstones into reservoir compartments.
Porosity and permeability values are mostly influenced by the discrete genetic interval (DGI) level. Lower DGIs, dominated by braided channel-fill facies, have the highest porosity and permeability, and show very weak permeability anisotropy. The upper DGIs, dominated by meandering channel-fill and splay facies, have progressively lower porosity and permeability vertically upward through the DGIs. Meandering channel-fill facies, particularly the middle channel-fill subfacies, have strongly developed permeability anisotropy.
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Reservoir Characterization—Recent Advances
Optimum reservoir recovery and profitability result from guidance by an effective reservoir management plan. Success in developing the most appropriate reservoir management plan requires knowledge and consideration of (1) the reservoir system, including rocks, fluids, and rock-fluid interactions, as well as wellbores and associated equipment and surface facilities; (2) the technologies available to describe, analyze, and exploit the reservoir; and (3) the business environment under which the plan will be developed and implemented. Reservoir management plans de-optimize with time as technology and the business environment change or as new reservoir information becomes available. Reservoir characterization is the process of creating an interdisciplinary high-resolution geoscience model that incorporates, integrates, and reconciles various types of geological and engineering information from pore to basin scale. The reservoir data are then conceptually and quantitatively modeled and compared to the historical production data and fluid flow distribution patterns within and beyond the limits of the reservoir to match well production histories and predict their behavior. The goals of reservoir characterization are to simultaneously (1) maintain high displacement efficiency, (2) optimize high sweep efficiency, (3) provide reliable reservoir performance predictions, and (4) reduce risk and maximize profits. Notice that in addition to the technical concepts that we normally associate with "characterization," maximizing profits is an essential element of this process. Papers from the Fourth International Reservoir Characterization Technical Conference (1997), sponsored by the U.S. Department of Energy, this publication is a unique compilation of 27 papers covering every aspect of reservoir characterization and has been a popular AAPG publication since that time. Using an interdisciplinary approach, the papers address qualitative information as well as integrated quantified data and culminate in a fully integrated study.