Stratigraphy and source rock analyses of the Heath Formation in Fergus, Garfield, Golden Valley, Musselshell, Petroleum, and Rosebud counties, central Montana

<p> Three-dimensional fluid-flow simulation models provide attractive tools for understanding the potential behavior of the subsurface. Retention of high-resolution geologic heterogeneity in the characterization of large volumes presents significant challenges to this modeling. </p><p> A 2D dataset donated by Industry constrains a hierarchical stratigraphic framework based on 30,000 wells with log curves, 60 surfaces crossing the 70,000 cubic-kilometer Powder River Basin from Precambrian basement to top of the Cretaceous Lewis Shale. Five sedimentary systems subdivided into 25 stratigraphic intervals make up the 3D representation of 70 discrete modeling areas. These sedimentation regions group distinct sedimentary attributes (e.g., porosity, thickness, sedimentary architecture). These attributes relate to suites of rock properties, such as porosity, percentage of thickness with porosity and well log shape, which were compiled from 4000 wells with donated/purchased log ascii files, 15 cores, 300 wells with public core plug data, 115 published oil field reports, and basin rimming outcrops. </p><p> Sedimentary system analysis considered regional controls on the depositional setting from the craton-scale to the pore-scale and it employed techniques to group information and replicate the effect of fine-scale geologic heterogeneity in a static reservoir model. This process highlights the importance of understanding the role of tectonic anisotropy on the preservation of stratigraphic sequences when interpreting the depositional environment. Subdivision into the 70 sedimentation regions permitted calculation of the gross pore volume in each sedimentary system, using total porosity and a percentage of the vertical thickness for each modeling volume. The total volume calculated depended on the method; stratigraphic layering and sedimentation regions provided 600 cubic kilometers and equating to storage capability of over 250 gigatons of supercritical carbon dioxide, whereas using factors and no stratigraphy, the total volume was calculated at 460 cubic kilometers. </p><p> Pore volume distribution in the subsurface is more accurately characterized with high-resolution stratigraphic and sedimentation region analysis. Integrated tectonic analysis provides context that better constrains the application of outcrop analogs and depositional models, which guide sedimentation region analysis. This dissertation addresses the impact of geologic heterogeneity from crustal anisotropy to distributions of porosity and permeability and provides a tool to assess feasibility of gigaton-scale carbon dioxide sequestration. </p>

<p> Two industry acquired diatomite cores (Sisquoc Formation) from the Orcutt (Newlove 76-RD1) and Casmalia Hills (Stokes A-30804) oil fields were analyzed by core descriptions, laboratory analysis (XRD and SEM), and gamma ray logs. Based on these data, five distinct lithofacies, nine sedimentary features and compositional trends of both cores were established. Newlove 76-RD1 and Stokes A-30804 record an upward-shallowing succession at different depositional positions on the Pliocene paleo-slope of the Santa Maria basin. Stokes A-30804 reflects slope deposition on a lower flank of a paleo-bathymetric high receiving higher detrital influx from inter-ridge troughs. Slope deposition of Newlove 76-RD1 was closer to a paleo-bathymetric high where purer diatomaceous sediments accumulated. Within Stokes A-30804, purer opal-A dominant lithofacies contain the highest oil saturations. The diagenesis and precipitation of opal-CT and abundance of phyllosilicate significantly hinders oil saturation within lithofacies.</p>

<p> Though the Cotton Valley Group is productive in Mississippi, Louisiana, and Texas, little is known about production potential of the Bossier Formation (Lower Cotton Valley Shale) in southwest Mississippi. The Bossier Formation in Jefferson County, Mississippi is an organic-poor, carbonate-rich mudrock with siliciclastic intervals. Examination of cuttings by petrographic and scanning electron microscopy revealed fractures that have been filled by calcite and pore-filling pyrite. Porosity exists within and around pyrite framboids, in unfilled fractures, and within peloid grains. Organic matter is rare in Lower Cotton Valley samples suggesting it is not self-sourcing. Total Organic Carbon (TOC) values are low (0.86-1.1% TOC) compared to the productive Haynesville Shale Formation (2.8% TOC). Porosity of the Lower Cotton Valley Shale is low (2.5-4.2%) compared to productive Haynesville Shale Formations (8-12%). With current technology and gas prices, the Lower Cotton Valley Shale in Jefferson County, Mississippi does not have production potential.</p>

<p> The Middle Devonian Marcellus Shale is a natural gas producing formation that was deposited in the Appalachian foreland basin in what is now eastern North America. An unconformity truncates the Marcellus in southern West Virginia and progressively younger units onlap progressively older units. The zero isopach line that marks the edge of the Marcellus is mapped to reveal the southeastern boundary. A well production analysis is conducted to locate the region of maximum natural gas production. Four lithologic completions intervals in three different well fields are compared. This study shows that the most economically viable drilling is from the Marcellus Shale completion intervals that are less than 30 feet in Chapmanville gas field in western Logan County, West Virginia. Outside of the zero isopach are areas comprised of onlapping featheredges of younger formations that comprise a black shale unit mistakenly identified as &ldquo;Marcellus Shale&rdquo;. These areas produce significantly less gas than the &ldquo;true&rdquo; Marcellus Shale.</p>

<p> Integrated analysis of well and geophysical data can provide detailed geologic interpretation of the subsurface in Osage County, Oklahoma. Systems tracts and depositional system successions can be interpreted at marginal seismic resolution using well log motif with seismic reflector character within a depositional context. Shelf-prism and subaqueous, delta-scale clinoforms of Missourian age observed in 3D seismic were interpreted with greater sequence stratigraphic detail when coupled with wireline well logs. The Late Pennsylvanian Midcontinent Sea was thought to be approximately 150 feet average depth across the southern Midcontinent during the Missourian Stage, and deepen towards the Arkoma and Anadarko Basins to the south. Here we show that the Late Pennsylvanian Midcontinent Sea floor was in water depths greater than 600 feet and sloped to the southeast, toward major, southern basins, during the Missourian Stage in Osage County. Shelf-prism and delta scale clinoforms up to 600 and 300 feet of relief, respectively, were observed in paired seismic and well log cross sections, thickness maps, and structure maps dipping northwest at 052&deg; strike, upon a basin floor dipping southeast at 253&deg; strike. Lithologic and sequence stratigraphic interpretation revealed a mixed carbonate-siliciclastic system comprising of delta, offshore shelf, and carbonate buildup depositional systems of mesothem, 3rd order sequence magnitude. The observed succession included: 1) falling stage to lowstand, sand-prone, subaqueous delta, 2) transgressive to highstand offshore shelf and carbonate bank, and 3) falling stage delta. The depositional sucession demonstrates how carbonate banks related spatially to terrigenous sediment input in northeastern Oklahoma during the Late Pennsylvanian because of glacio-eustasy and possible tectonism.</p><p>

<p> The Tuscaloosa Marine Shale (TMS) in southwest Mississippi and south-central Louisiana has potential to become a prolific source of fossil fuels using hydraulic fracturing technology. The objective of this study is to better understand the sequence and regional stratigraphy, lithology, and character of the TMS. Studying the TMS&rsquo;s lithologic, depositional, and diagenetic properties is essential to maximize potential production. Characterization of the eastern TMS was performed with cuttings from two wells provided by the Mississippi Oil and Gas Board through MDEQ, and two provided by the USGS. Thirty-one petrophysical logs were correlated, to make cross sections and trace sequence stratigraphic intervals within the TMS. Results of the study showed lithologic variability and compaction across the study area, and a sequence stratigraphic correlation of the highstand systems track between the Tuscaloosa and Eagle Ford Groups. This research aims to work toward the greatest potential of the TMS as an unconventional reservoir.</p><p>

<p> Over the past 70 years the Mississippian strata of Northwest Arkansas have been studied in great detail. The study area is located on the escarpment between the Boston Mountains Plateau and the Springfield Plateau where a surface occurrence of Mississippian age rock allows for access to outcrops in close proximity to gas wells that encounter subsurface Mississippian strata. Many outcrops found in Northwest Arkansas expose Lower Mississippian (Kinderhookian-Osagean) strata that represent a full third order transgressive/regressive sequence that is unconformity bounded. These Mississippian outcrops are commonly treated as surface analogs to the Mississippi Lime Play in North Central Oklahoma. This thesis focuses on the analysis of Boone tripolitic chert in the subsurface utilizing wireline data available from selected gas wells within the study area. The primary goal of this project is to determine and quantify the subsurface stratigraphic position of tripolitic chert from wells that cut a complete section of the Boone Formation. 24 of the 27 (89%) wells within the study with bulk density logs penetrated a substantial section of the Boone Formation and confirmed the presence of tripolite through a density value less than 2.1 g/cc. </p><p> Analysis of wireline data from selected wells is used to characterize the Mississippian system with a specific focus on the distribution of tripolitic chert. Correlation of Mississippian gas production to tripolitic chert occurrence along with the correlation of subsurface data with outcrop data are secondary objectives.</p><p>

<p> The informally known &ldquo;Mississippian Limestone&rdquo; stratigraphic interval in north-central Oklahoma, U.S.A. bears no chronostratigraphic markers and has no formally established biostratigraphic framework to date. Conodonts collected from four &ldquo;Mississippian Limestone&rdquo; cores in Logan, Payne, and Lincoln Counties provide the means for better constraining the stratigraphic age of the interval over the area studied. Conodont extraction was conducted by acid digestion of whole-rock samples and heavy liquid density separation after which conodont genera and species types were identified from scanning electron microscopy. Biostratigraphically significant conodonts recovered in combination with chemostratigraphic work by Dupont (2016) and earlier studies by Thornton (1958), Curtis and Chaplin (1959), McDuffie (1959), Rowland (1964), Selk and Ciriacks (1968), and Harris (1975) indicate the &ldquo;Mississippian Limestone&rdquo; ranges from middle Osagean to late Chesterian in age. In general, conodont element recoveries were too low in quantity and too poor of quality for use as biostratigraphic markers. The relatively low recovery and poor preservation quality of the conodont elements are attributed primarily to the elements being reworked soon after deposition by frequent storms on a mid- to outer-ramp environment in a low-latitude carbonate ramp setting. The results of this investigation are most significant in that they help place Mississippian deposition over the area studied within the context of a global Carboniferous stratigraphy. The results also allow for the Mississippian interval in the study area to be more accurately related to time-correlative strata with similar or better age constraint for constructing more temporally meaningful depositional models of the Oklahoma basin.</p><p>

<p>Tidally-influenced sandwaves are common coastal features present in various settings, including shipping channels. The main shipping channel in Tampa Bay under the Bob Graham Sunshine Skyway Bridge (a.k.a. the Skyway Bridge) contains such sandwave bedforms. Between the years 2000 and 2017, these bedforms have been surveyed with multibeam echosounders (MBES) on 21 occasions with ranging coverage and quality of returns. Surveys between 2000 and 2009 used a 300 kHz Kongsberg EM3000; surveys between 2015 and 2017 used a 400 kHz Reson Seabat 7125. For comparable surveys, bathymetry, backscatter, slope, curvature, planform curvature, and profile curvature maps were created and analyzed. Spectral analyses were completed on the same cross-section for usable surveys, providing a period and amplitude for the bedforms. Sediment samples were taken in September 2015 using a Shipek grab. The sediment samples were analyzed for grain size and carbonate content. A bottom-mounted ADCP recorded velocity data semi-continuously over the same time period. These data were analyzed in an effort to investigate the forcing mechanisms that influence the bedform morphology. Mean grain sizes in the shipping channel under the Skyway Bridge range from 0.01 ? (0.99 mm, coarse sand) to 1.55 ? (0.34 mm, medium sand). Calcium carbonate content ranges from 25% to 87%. The sediment sample site most representative of the sandwave bedforms has a mean grain size of 0.01 ? and a calcium carbonate content of 87%. The calculated mean current velocity required to initiate transport of the D50 and D84 grain size percentile of the representative sediment sample site is 0.70 m/s and 1.05 m/s, respectively. Analysis of the ADCP-recorded velocity data shows that the calculated D50 critical velocity is frequently reached by peak flood and peak ebb currents except during neap tides, while the D84 critical velocity is reached only intermittently, mostly during spring tides. Analysis of MBES backscatter shows similar spatial patterns in two larger MBES surveys in 2004 and 2015. Bathymetric analysis of the sandwaves shows consistent characteristics through time. Wave crest analysis reveals that bedforms migrate in both the ebb and flood directions. Spectral analysis shows primary wave spatial frequencies range from 0.13 m-1 to 0.22 m-1, and primary wave periods range from 4.5 m to 6.0 m. The predominant wavelength of sandwaves within the study area is about 5 m, with an average wave height of 0.47 m. The maximum wave height along the axial cross-section analyzed is 0.8 m, observed in April 2017. The sediments comprising the sandwave bedforms are likely winnowed by tidal currents resulting in larger grain size and carbonate content than other areas of the shipping channel and surrounding bay. Consistent patterns in MBES backscatter over time indicate that the sediment distribution pattern in the study area have not significantly changed. The size and shape of the bedforms in the shipping channel beneath the Skyway Bridge are have been in a quasi-dynamic equilibrium over the past 13 years. The bedforms are shown to migrate in both the ebb and flood directions despite an average faster ebb current velocity than a flood current velocity. More frequent and consistent MBES surveys as well as more continuous ADCP data availability would allow for better understanding of sediment transport via bedform migration in tidally-influenced environments.