Applications of geochemistry and basin modeling in the diagenetic evaluation of Paleocene sandstones, Kupe Field, New Zealand

2021 ◽  
Vol 91 (9) ◽  
pp. 945-968
Author(s):  
Karen E. Higgs ◽  
Stuart Munday ◽  
Anne Forbes ◽  
Karsten F. Kroeger
Keyword(s):  
New Zealand ◽  
Element Abundance ◽  
Basin Modeling ◽  
Burial Diagenesis ◽  
Diagenetic Alteration ◽  
Partial Pressures ◽  
Diagenetic Reactions ◽  
Different Levels ◽  
Kupe Field ◽  
Thermal Decarboxylation

ABSTRACT Paleocene sandstones in the Kupe Field of Taranaki Basin, New Zealand, are subdivided into two diagenetic zones, an upper kaolinite–siderite (K-S) zone and a lower chlorite–smectite (Ch-Sm) zone. Petrographic observations show that the K-S zone has formed from diagenetic alteration of earlier-formed Ch-Sm sandstones, whereby biotite and chlorite–smectite have been altered to form kaolinite and siderite, and plagioclase has reacted to form kaolinite and quartz. These diagenetic zones can be difficult to discriminate from downhole bulk-rock geochemistry, which is largely due to a change in element-mineral affinities without a wholesale change in element abundance. However, some elements have proven useful for delimiting the diagenetic zones, particularly Ca and Na, where much lower abundances in the K-S zone are interpreted to represent removal of labile elements during diagenesis. Multivariate analysis has also proven an effective method of distinguishing the diagenetic zones by highlighting elemental affinities that are interpreted to represent the principal diagenetic phases. These include Fe-Mg-Mn (siderite) in the K-S zone, and Ca-Mn (calcite) and Fe-Mg-Ti-Y-Sc-V (biotite and chlorite–smectite) in the Ch-Sm zone. Results from this study demonstrate that the base of the K-S zone approximately corresponds to the base of the current hydrocarbon column. An assessment with 1D basin models and published stable-isotope data show that K-S diagenesis is likely to have occurred during deep-burial diagenesis in the last 4 Myr. Modeling predicts that CO2-rich fluids were generating from thermal decarboxylation of intraformational Paleocene coals at this time, and accumulation of high partial pressures of intraformational CO2 in the hydrocarbon column is considered a viable catalyst for the diagenetic reactions. Variable CO2 concentrations and residence times are interpreted to be the reason for different levels of K-S diagenesis, which is supported by a clear relationship between the presence or absence of a well-developed K-S zone and the present-day reservoir-corrected CO2 content.

scholarly journals Producing deflective online strategies: Lessons from New Zealand women’s management of social media engagement

2021 ◽  
pp. 1-16
Author(s):  
Sarah Hendrica Bickerton ◽  
Karl Löfgren
Keyword(s):  
Social Media ◽  
New Zealand ◽  
Public Engagement ◽  
Analytical Approach ◽  
Gender Effect ◽  
Social Location ◽  
Strategic Approach ◽  
Online Strategies ◽  
Twitter Users ◽  
Different Levels

Public engagement is a gendered experience, whether offline or online, something which is reflected in women’s experiences of social media. In this article, we seek to systematically explore the experiences from politically engaged women twitter users in New Zealand in order to draw some lessons, through a thematic and interpretative analytical approach, at four different strategic levels on how to deflect intimidating and aggressive behaviour. We conclude that understanding strategically how structural social locations like gender effect the ability to contribute to political participation and engagement, if addressed, can produce more inclusive and productive online political and policy spaces. Further, this strategic approach involves connecting together different levels of response to online negativity such as platform tools, space-curation, and monitoring, having these made coherent with each other, as well as with this strategic understanding of how structural social location plays into access and use of online political and policy spaces.

scholarly journals Simulating the impact of vaccination rates on the initial stages of a COVID-19 outbreak in New Zealand (Aotearoa) with a stochastic model

2021 ◽  
Author(s):  
Leighton M Watson
Keyword(s):  
New Zealand ◽  
Stochastic Model ◽  
Process Model ◽  
Branching Process ◽  
Total Population ◽  
Median Number ◽  
Vaccination Rate ◽  
Vaccination Rates ◽  
The Impact ◽  
Different Levels

Aim: The August 2021 COVID-19 outbreak in Auckland has caused the New Zealand government to transition from an elimination strategy to suppression, which relies heavily on high vaccination rates in the population. As restrictions are eased and as COVID-19 leaks through the Auckland boundary, there is a need to understand how different levels of vaccination will impact the initial stages of COVID-19 outbreaks that are seeded around the country. Method: A stochastic branching process model is used to simulate the initial spread of a COVID-19 outbreak for different vaccination rates. Results: High vaccination rates are effective at minimizing the number of infections and hospitalizations. Increasing vaccination rates from 20% (approximate value at the start of the August 2021 outbreak) to 80% (approximate proposed target) of the total population can reduce the median number of infections that occur within the first four weeks of an outbreak from 1011 to 14 (25th and 75th quantiles of 545-1602 and 2-32 for V=20% and V=80%, respectively). As the vaccination rate increases, the number of breakthrough infections (infections in fully vaccinated individuals) and hospitalizations of vaccinated individuals increases. Unvaccinated individuals, however, are 3.3x more likely to be infected with COVID-19 and 25x more likely to be hospitalized. Conclusion: This work demonstrates the importance of vaccination in protecting individuals from COVID-19, preventing high caseloads, and minimizing the number of hospitalizations and hence limiting the pressure on the healthcare system.

Clay mineral variation in Tertiary sediments from the eastern flank of the Niger Delta

Clay Minerals ◽  
1986 ◽  
Vol 21 (2) ◽  
pp. 211-224 ◽  
Author(s):  
S. P. Braide ◽  
W. D. Huff
Keyword(s):  
Clay Mineral ◽  
Niger Delta ◽  
Size Fraction ◽  
Clay Mineralogy ◽  
Burial Diagenesis ◽  
Carbonate Cement ◽  
Eastern Flank ◽  
Marine Facies ◽  
Diagenetic Reactions ◽  
The Relationship

AbstractDetailed clay mineralogical and chemical analyses of well cuttings of Tertiary sediments from two wells, Uruan-1 and Uda-1, on the eastern flank of the Niger delta, have been made in an attempt to investigate clay mineral burial diagenesis. The clay mineralogy indicates a transformation of smectite to an interstratified illite-smectite (I/S) phase. The relationship between ordered and random interlayering, however, is nonsystematic. The chemistry of the <0·1 µm size fraction shows some tendency towards a net gain in K2O and Al2O3 and a net loss in SiO2 with depth, but the relationship does not correlate well with the thermal gradient. The distribution of kaolinite and chlorite in both wells appears to be unrelated in any regular way to smectite transformation and these two minerals are considered to be either the products of other diagenetic reactions affecting various stratigraphic levels, or the result of primary sediment deposition. In well Uda-1, kaolinite decreases in relative abundance with depth. This trend has been interpreted elsewhere as indicative of a transition from nonmarine to marine facies. The results of this study indicate that lack of ion mobility, rather than availability, is a significant factor in retarding the formation of ordered I/S with depth, and that lithology, overpressuring, carbonate cement, and original smectite layer charge may be controlling factors in the smectite → illite transformation.

Deep burial diagenesis and reservoir quality along the eastern flank of the Viking Graben. Evidence for illitization and quartz cementation after hydrocarbon emplacement

Clay Minerals ◽  
2000 ◽  
Vol 35 (1) ◽  
pp. 227-237 ◽  
Author(s):  
R. E. A. Midtbø ◽  
J. M. Rykkje ◽  
M. Ramm
Keyword(s):  
Clay Content ◽  
Total Porosity ◽  
Reservoir Quality ◽  
Burial Diagenesis ◽  
Reservoir Temperature ◽  
Initial Composition ◽  
Eastern Flank ◽  
Diagenetic Alteration ◽  
Lower Permeability ◽  
Two Phases

AbstractThe Tarbert Formation on a north±south oriented structure along the eastern flank of the Viking Graben has been studied. The reservoir in the two wells studied is buried ~100 m deeper in the northern than in the southern well. The present reservoir temperature is ~130°C. The reservoir quality is good, but due to extensive illitization of kaolin, the northern well shows lower permeability values than the southern well, for similar porosity values. The initial composition of the analysed samples in the two wells is very similar. There are no significant differences in total clay content and both wells contain K-feldspars and kaolin. However, the diagenetic alteration is more advanced in the deeper well. Total porosity is about the same in both wells but, due to illitization, the ratio of micro- vs. macro-porosity is higher in the deeper well. Petroleum emplacement in the structure occurred in two phases: oil emplacement predates, whereas gas emplacement postdates, most of the quartz cementation. In the deeper well, illitization occurred after gas emplacement.

scholarly journals Probability of elimination for COVID-19 in Aotearoa New Zealand

2020 ◽  
Author(s):  
Rachelle N Binny ◽  
Shaun C Hendy ◽  
Alex James ◽  
Audrey Lustig ◽  
Michael J Plank ◽  
...  
Keyword(s):  
New Zealand ◽  
Model Parameters ◽  
Alert System ◽  
Control Effectiveness ◽  
Aotearoa New Zealand ◽  
High Detection ◽  
Community Transmission ◽  
Pessimistic Scenario ◽  
Different Levels ◽  
Clinical Cases

On 25th March 2020, New Zealand implemented stringent lockdown measures (Alert Level 4, in a four-level alert system) with the goal of eliminating community transmission of COVID-19. Once new cases are no longer detected over consecutive days, the probability of elimination is an important measure for informing decisions on when certain COVID-19 restrictions should be relaxed. Our model of COVID-19 spread in New Zealand estimates that after 2-3 weeks of no new reported cases, there is a 95% probability that COVID-19 has been eliminated. We assessed the sensitivity of this estimate to varying model parameters, in particular to different likelihoods of detection of clinical cases and different levels of control effectiveness. Under an optimistic scenario with high detection of clinical cases, a 95% probability of elimination is achieved after 10 consecutive days with no new reported cases, while under a more pessimistic scenario with low case detection it is achieved after 22 days.

Discovery of a 400 km2 honeycomb structure mimicking a regional unconformity on three-dimensional seismic data

Geology ◽  
2019 ◽  
Vol 47 (12) ◽  
pp. 1181-1184 ◽  
Author(s):  
Rosine Riera ◽  
Julien Bourget ◽  
Victorien Paumard ◽  
Moyra E.J. Wilson ◽  
Jeffrey Shragge ◽  
...  
Keyword(s):  
Seismic Data ◽  
Three Dimensional ◽  
Honeycomb Structure ◽  
Petroleum Exploration ◽  
Negative Consequences ◽  
Burial Diagenesis ◽  
Data Set ◽  
Seismic Reflection Data ◽  
Diagenetic Alteration ◽  
Basin Scale

Abstract Recognition of seismic unconformities is crucial for interpreting basin history from seismic reflection data sets in both siliciclastic and carbonate settings. While it is well established that non-erosional changes in sedimentary facies can create seismic reflections that mimic seismic unconformities (i.e., pseudo-unconformities), these features are generally considered to be localized and uncommon, and, therefore, are largely overlooked during interpretation. Diagenetic alteration of strata can also affect the morphology of seismic reflectors and mislead seismic interpreters. This study is based on a three-dimensional (3-D) seismic data set and documents a 400 km2 honeycomb structure (HS) masquerading as a regional erosional unconformity in the Oligocene–Miocene carbonate strata of Australia’s North West Shelf. This HS is located at the transition between the topsets and the foresets of clinoforms of carbonate to marly composition. The HS expression in 3-D seismic data cross sections is irregular, giving the HS the appearance of a truncated surface that could erroneously be interpreted as a regional seismic unconformity. Closer examination reveals that the HS crosscuts chronostratigraphic clinoform reflectors, and frequency extraction processing shows that the HS dominantly falls within a lower-frequency band than the clinoform reflectors. The morphology of the HS (i.e., continuous with densely packed cells) and its time-transgressive nature suggest that it has a burial diagenetic origin. This suggests that creation of pseudo-unconformities at basin scale by burial diagenesis may lead to surface misidentification, with negative consequences for paleoenvironmental studies and petroleum exploration activities.

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