Matthew W. Totten

Beyond whole-rock geochemistry of shales: The importance of assessing mineralogic controls for revealing tectonic discriminants of multiple sediment sources for the Ouachita Mountain flysch deposits

The origin of the Ouachita Mountains has been the focus of significant debate for decades. Considerable confusion also exists concerning the provenance of the Carboniferous flysch of the Ouachitas. Trace-element geochemistry of shales from the Stanley Group delineates the provenance of the sediments and provides clues to the plate tectonic evolution of the southern continental margin during Mississippian time. Th/Sc and Cr/Th ratios indicate a cratonic source for the majority of the Stanley Group sedimentary rocks. However, in several samples, low Th/Sc ratios and high Cr/Th ratios suggest a contribution from a mafic source. Using element ratio diagrams, all of the samples plot along a curve consistent with a two-component mixing model, consisting of a dominant felsic and a subordinate mafic source. The heavy-mineral fraction of these shales sequester many of the trace elements used in whole-rock studies. Monazite is ubiquitous in trace amounts and is the probable site for much of the rare earth elements in the whole rock. The occurrence of monazite almost exclusively in sialic igneous rocks implies that Sm/Nd isotopic signatures are not sensitive to sediment input from more mafic sources. In some Stanley shale samples, chromite and Mn oxides were identified and positively identify an oceanic crustal component as a source of Stanley Group sediment. The results of this study emphasize the importance of determining the mineralogic sites of trace elements, and realization of specific mineralogic contributions from mafic or sialic tectonic provenances.

Alterations in the Non-Clay-Mineral Fraction of Pelitic Rocks Across the Diagenetic to Low-Grade Metamorphic Transition, Ouachita Mountains, Oklahoma and Arkansas

ABSTRACT The transformation of smectite to illite has been cited by many authors as a source of silica during diagenesis of mudrocks. Illites themselves, however, undergo chemical changes as they recrystallize into micas during high-grade diagenesis/low-grade metamorphism. Average compositions of phyllosilicates from the literature suggest that an equivalent amount of silica is available from transformation of illite to muscovite as from illitization of smectites. The fate of silica released by this process has not been reported, but could be a major contributor to the silt-size quartz population. The quartz and feldspar fraction of pelites from the Stanley Shale (Mississippian) in the Ouachita Mountains of Oklahoma and Arkansas was separated using sodium bisulfate fusions. The mineralogy and the grainsize distribution of this fraction were determined using standard petrographic and X-ray diffraction (XRD) techniques. Bulk rock samples were analyzed using X-ray fluorescence (XRF) and instrumental neutron activation analysis (INAA) methods. The data obtained were related to illite crystallinity and vitrinite reflectance as reported by Guthrie et al. (1986) and Houseknecht and Matthews (1985). Both the percentage of quartz and the mean grain size of the quartz and feldspar fraction increase with greater illite crystallinity values. The growth in quartz is especially apparent in the finest size fractions. A corresponding decrease in the silica content of the clay-mineral fraction is also observed. Development of quartz polycrystallinity occurs across the same interval. Whole-rock chemical abundances show no statistical correlation with thermal maturity. Relative to titanium, both the major-element and the trace-element concentrations show little variation. Rare-earth element ratios do not correlate with thermal maturity and remain essentially constant. Our results are consistent with reported differences between quartz in schists and their shale precursors, and suggest that release of silica during diagenesis of phyllosilicates continues after the smectite-illite transformation. This silica precipitates as quartz within the pelite, consistent with the suggestion by Blatt (1987) that metapelites are the source of abundant silt-size quartz. The lack of whole-rock chemical variation with thermal maturity implies closed-system behavior across much of the pelite-to-metapelite transition.

Characteristics of mixed-layer smectite/illite density separates during burial diagenesis

Abstract We report a method to physically separate smectite from illite in natural shale samples. This method is based upon the large contrast in the density of mixed-layer clay minerals reported in the literature. Our objective was to investigate the behavior of separate density fractions of mixedlayer smectite and illite during burial diagenesis. Samples were obtained from shale cuttings hand-picked from a well drilled offshore Louisiana. Each sample was separated into 5 fractions: “pure” end-member smectite (EMS), smectiterich mixed-layer clays (SML), illite-rich mixed-layer clays (IML), “pure” end-member illite (EMI), and quartz (FGQ). The mineralogy of each clay-mineral separate as determined by XRD was reasonably consistent at all depths, although the abundance of the mixed-layer separates varied. The illite-rich mixed-layer fraction increased in abundance with depth at the expense of the smectiterich mixed-layer fraction. The fine-grained quartz fraction showed an increase in abundance, a decrease in average grain size, a loss of K-feldspar, and a heavier isotopic signature with depth. We did not, however, find a correlation with depth in the amount of the end-member clay fractions. The isotopic signature of the end-member smectite shows evidence of equilibration with depth, but the end-member illite does not. We conclude that the discrete illite fraction is detrital in origin and was not involved in the clay-mineral transformation at the depths sampled in our well. It reflects the sediment provenance. The results of this study illustrate the efficacy of the newly developed density separation technique for physically isolating clay mineral species from one another.

Detrital quartz as an indicator of distance from shore in marine mudrocks

ABSTRACT Eighty-nine surface samples and 17 subsurface samples of shale from the Blaine Formation (Permian) in western Oklahoma were examined to determine the variation in percentage of quartz and mean size of quartz with distance from a known shoreline. Samples were fused using sodium bisulfate to release the quartz from the mass of clay minerals. The surface samples gave areally and statistically meaningful trends; subsurface samples did not do so because of sampling difficulties. The mean percentage of quartz in surface samples decreases from 47 percent at a distance of 60 km from shore (more precisely, the sand-mud line) to 11 percent at 270 km from shore (r = .70), a loss of 10 percent quartz with each 60 km increase in distance. Mean grain size decreases from 5.2 at 60 km from shore to 6.9 at 270 km from shore (r = .71). Extrapolation of the data indicates that at the sand-mud boundary the percentage of quartz is 57 percent and the mean size of the quartz is between 4.75 and 5.1. The percentage of quartz in mudrocks can be a useful indicator of the position of the shoreline in ancient fine-grained epicontinental sea deposits.

Improved Regional Ties to Global Geochronology Using Pb-Isotope Signatures of Volcanic Glass Shards from Deep Water Gulf of Mexico Ash Beds

ABSTRACT Sedimentary beds rich in volcanic ash (ash beds) have been confirmed in several recent offshore Gulf of Mexico (GOM) exploratory wells. A petrographic/scanning electron microscope survey for volcanic glass shards on well cuttings and sidewall cores donated by the petroleum industry is currently ongoing at University of New Orleans (UNO). Fifteen separate ashes have been documented in our preliminary survey. We have also determined the paleontological ages of these GOM ashes with industry micro-paleo reports. The paleo-ages of these ash beds appear to be correlative with the ages of maximum flooding surfaces on industry sea-level curves. Due to their distinctive log and seismic response, thick ash beds are ideal candidates for use as precise time markers in the GOM subsurface if they can be tied to known eruptive events. Based on proximity in time, we believe that the most likely sources for these ashes are the Huckleberry, Lava Creek, Mesa Falls, Bishop, and other eruptive events that occurred in the Yellowstone Plateau from 0.6 to 12 mya. These eruptions had enormous ash volumes that covered much of the ancestral Mississippi drainage area. Isotopic analyses of glass shards from GOM ash beds indicate a lead isotope signature that matches volcanic tuffs in the Yellowstone Plateau and precludes other ash sources for the GOM ash beds.

Chapter 12 Heavy Minerals in Shales

Abstract Although shales dominate the sedimentary rock record, when compared to sandstones their heavy mineral fraction has received little attention. A principal reason for this disparity is the difficulty of density separations in rocks with high clay contents using organic liquids. These liquids work well for clean sandstones, but their effectiveness in clay-rich samples is limited by the adsorption of organic molecules onto clay minerals. Additionally, the small size of heavy mineral grains within shales demands advanced observational conditions, and considerable expertise that analysts must develop before undertaking these investigations. In this study heavy minerals were separated from the clay and light-mineral matrices of over 100 shale samples using lithium metatungstate (LMT), a non-organic heavy liquid. The sample sets include sites from Ordovician through Mississippian shales from the Ouachita Mountains of Oklahoma and Arkansas, USA, and Miocene through Pleistocene shales from the subsurface Gulf of Mexico (GOM). Heavy minerals include variable amounts of zircon, tourmaline, rutile, apatite, baryte, monazite, and xenotime. Opaque minerals are Fe, Ti, Fe-Mn, Ba-Mn, and Cr-Fe oxides, as well as Fe-rich micas. Comparisons with heavy-mineral contents of interbedded sandstones with the surrounding deep-water shales show that heavy minerals are equally plentiful and diverse in the finer-grained clastics. Tectonic and provenance interpretations based on trace-element geochemistry rely upon the assumption that signature elements are quantitatively transferred from the same source as the bulk of the sediments. Trace-element analyses of whole-rock and light-mineral separates indicate that heavy minerals are sometimes the dominant sites for some of the trace elements in shales. The potential control of signature trace elements by an accessory mineral phase, perhaps from a secondary, low-volume source terrain, needs to be addressed. We stress the importance of using the heavy-mineral fraction to complement the geochemical study of shales. Heavy minerals in shales can be as effective in determining sediment provenance as they have proven to be in sandstones. A source of some of the heavy minerals within shales could be from resistate mineral inclusions within both light and heavy host minerals. This is particularly important for zircon, rutile, and monazite, based upon their observed size in shales. This should be considered when using heavy minerals in shales for provenance studies.

3D Seismic Attributes Analysis to Outline Channel Facies And Reveal Heterogeneous Reservoir Stratigraphy: Weirman Field, Ness County, Kansas, USA

In this paper, we present a workflow integrating several post-stack seismic attributes to assist in understanding development history of our study area. We also aim to shape future drilling plans by outlining a channel fill zone of better reservoir quality, and to highlight reservoir boundaries of compartmentalization. Extracting and analyzing acoustic impedance and amplitude attenuation, guided by a time window focused on the bottom of the Mississippian formation, resulted in an understanding of the key seismic channel-facies framework and helped to explain some of the disappointing drilling results at Weirman Field. This study recommends integrating the revealed compartmentalization boundary and the seismic channel-facies framework in future drilling plans of Weirman Field.

Data-driven modeling of heavy oil viscosity in the reservoir from geophysical well logs

ABSTRACT Viscosity is the most crucial fluid property on recovery and productivity of hydrocarbon reservoirs, more particularly heavy oil reservoirs. In heavy and extra heavy oil reservoirs e.g. bitumen and tar sands more energy is required to be injected into the system in order to decrease the viscosity to make the flow easier. Therefore, attempt to develop a reliable and rapid method for accurate estimation of heavy oil viscosity is inevitable. In this study, a predictive model for estimating of heavy oil viscosity is proposed, utilizing geophysical well logs data including gamma ray, neutron porosity, density porosity, resistivity logs, spontaneous potential as well as P-wave velocity and S-wave velocity and their ratio (Vp/Vs). To this end, a supervised machine learning algorithm, namely least square support vector machine (LSSVM), has been employed for modeling, and a dataset was provided from well logs data in a Canadian heavy oil reservoir, the Athabasca North area. The results indicate that the predicted viscosity values are in agreement with the actual data with correlation coefficient (R2) of 0.84. Furthermore, the outlier detection analysis conducted shows that only one data point is out of the applicability of domain of the develop model.

3D Seismic Reflection Amplitude and Instantaneous Frequency Attributes in Mapping Thin Hydrocarbon Reservoir Lithofacies: Morrison NE Field and Morrison Field, Clark County, KS

Thin hydrocarbon reservoir facies pose resolution challenges and waveform-signature opportunities in seismic reservoir characterization and prospect identification. In this study, we present a case study, where instantaneous frequency variation in response to a thin hydrocarbon pay zone is analyzed and integrated with other independent information to explain drilling results and optimize future drilling decisions. In Morrison NE Field, some wells with poor economics have resulted from well-placement incognizant of reservoir heterogeneities. The study area in Clark County, Kanas, USA, has been covered by a surface 3D seismic reflection survey in 2010. The target horizon is the Viola limestone, which continues to produce from 7 of the 12 wells drilled within the survey area. Seismic attributes extraction and analyses were conducted with emphasis on instantaneous attributes and amplitude anomalies to better understand and predict reservoir heterogeneities and their control on hydrocarbon entrapment settings. We have identified a higher instantaneous frequency, lower amplitude seismic facies that is in good agreement with distinct lithofacies that exhibit better (higher porosity) reservoir properties, as inferred from well-log analysis and petrographic inspection of well cuttings. This study presents a pre-drilling, data-driven approach of identifying sub-resolution reservoir seismic facies in a carbonate formation. This workflow will assist in placing new development wells in other locations within the area. Our low amplitude high instantaneous frequency seismic reservoir facies have been corroborated by findings based on well logs, petrographic analysis data, and drilling results.

Rare Earth Elements (REE) as Transformation Indicators of Organic Matter; Case Study of the Woodford Shale, North Central Oklahoma

Summary The REE distribution patterns and total concentrations of the organic matter of the Woodford shale reveal a new potential avenue to investigate hydrocarbon maturation processes in a source rock. Ten samples of the organic matter fraction of the Woodford shale from north central Oklahoma were analyzed by methods developed at KSU. REE concentration levels in an average shale range from 170 ppm to 185 ppm, and concentration levels in modern day plants occur in the ppb levels. The REE concentrations in the organic matter of the Woodford Shale samples analyzed ranged from 300 to 800 ppm. The high concentrations of the REEs in the Woodford Shale, as compared to the modern-day plants, are reflections of the transformations of buried Woodford Shale organic materials in post-depositional environmental conditions with potential contributions of exchanges of REE coming from associated sediments. The distribution patterns of REEs in the organic materials normalized to PAAS (post-Archean Australian Shale) had the following significant features: (1) all but one out of the ten samples had a La-Lu trend with HREE enrichment in general, by an amount as much as 15%, (2) all had both Ho and Tm positive enrichments, (3) all but two out of ten had positive Eu anomalies, (4) most had Ce negative anomalies, although one was with a positive Ce anomaly, (5) all but three out of ten had MREE enrichment by varied degrees. We are of the opinion that the Ho and Tm positive anomalies in the organic materials of the Woodford Shale are reflections of enzymic influence related to the plant physiology. Similar arguments may be made for the Eu and the Ce anomalies in the Woodford Shale organic materials. The varied MREE enrichments are likely to have been related to some phosphate mineralization events, as the Woodford Shale is well known for having abundant presence of phosphate nodules. The trend of HREE enrichment in general for the Woodford Shale organic materials can be related to inheritance from sources with REE-complexes stabilized by interaction between the metals and carbonate ligands or carboxylate ligands or both. Therefore, a reasonable suggestion about the history of the REEs in the organic materials would be that both source and burial transformation effects of the deposited organic materials in association with the inorganic constituents had an influence on the general trend and the specific trends in the distribution patterns of the REEs. This study