title: Petrogenesis of the Tikorangi Formation fracture reservoir, Waihapa-Ngaere Field, Taranaki Basin

authors: Hood, Steven D.

subjects: Taranaki Basin

abstract: The subsurface mid-Tertiary Tikorangi Formation is the sole limestone and the only fracture-producing hydrocarbon reservoir within Taranaki Basin. This study, based on core material from seven wells in the onshore Waihapa/Ngaere Field, uses a range of petrographic (standard, CL, UV, SEM) and geochemical techniques (stable isotope, trace element data, XRD) to unravel a complex diagenetic history for the Tikorangi Formation. A series of eight major geological-diagenetic events for the host rock and fracture systems have been established, ranging from burial cementation through to hydrocarbon emplacement within mineralized fractures. For each diagenetic event a probable temperature field has been identified which, combined with a geohistory plot, has enabled the timing of events to be determined.
This study has shown that the Tikorangi Formation comprises a complex mixed siliciclastic-carbonate-rich sequence of rocks that exhibit generally tight, pressure-dissolved, and well cemented fabrics with negligible porosity and permeability other than in fractures. Burial cementation of the host rocks occurred at temperatures of 27-37°C from about 0.5-1.0 km burial depths. Partial replacement dolomitisation occurred during late burial diagenesis at temperatures of 36-50°C and at burial depths of about 1.0 km, without any secondary porosity development. Fracturing occurred after dolomitisation and was associated with compression and thrusting on the Taranaki Fault. The location of more carbonate/dolomite-rich units may have implications for the location of better-developed fracture network systems and for hydrocarbon prospectivity and production. Hydrocarbon productivity has been ultimately determined by original depositional facies, diagenesis, and deformation.
Within the fracture systems, a complex suite of vein calcite, dolomite, quartzine, and celestite minerals has been precipitated prior to hydrocarbon emplacement, which have substantially healed and reduced fracture porosities and permeabilities. The occurrence of multiple vein mineral phases, collectively forming a calcite/dolomite-celestite-quartzine mineral assemblage, points to fluid compositions varying both spatially and temporally. The fluids responsible for vein mineralisation in the Tikorangi Formation probably involved waters of diverse origins and compositions. Vein mineralisation records a history of changing pore fluid chemistry and heating during burial, punctuated by changes in the relative input and mixing of downward circulating meteoric and upwelling basinal fluids. A sequence of mineralisation events and their probable burial depth/temperature fields have been defined, ranging from temperatures of 50-80°C and burial depths of 1.0-2.3 km. Hydrocarbon emplacement has occurred over the last 6 m.y. following the vein mineralization events. The Tikorangi Formation must continue to be viewed as a potential fracture reservoir play within Taranaki Basin.

text: Petrogenesis of the Tikorangi Formation fracture reservoir, Waihapa-Ngaere Field, Taranaki Basin The subsurface mid-Tertiary Tikorangi Formation is the sole limestone and the only fracture-producing hydrocarbon reservoir within Taranaki Basin. This study, based on core material from seven wells in the onshore Waihapa/Ngaere Field, uses a range of petrographic (standard, CL, UV, SEM) and geochemical techniques (stable isotope, trace element data, XRD) to unravel a complex diagenetic history for the Tikorangi Formation. A series of eight major geological-diagenetic events for the host rock and fracture systems have been established, ranging from burial cementation through to hydrocarbon emplacement within mineralized fractures. For each diagenetic event a probable temperature field has been identified which, combined with a geohistory plot, has enabled the timing of events to be determined.
This study has shown that the Tikorangi Formation comprises a complex mixed siliciclastic-carbonate-rich sequence of rocks that exhibit generally tight, pressure-dissolved, and well cemented fabrics with negligible porosity and permeability other than in fractures. Burial cementation of the host rocks occurred at temperatures of 27-37°C from about 0.5-1.0 km burial depths. Partial replacement dolomitisation occurred during late burial diagenesis at temperatures of 36-50°C and at burial depths of about 1.0 km, without any secondary porosity development. Fracturing occurred after dolomitisation and was associated with compression and thrusting on the Taranaki Fault. The location of more carbonate/dolomite-rich units may have implications for the location of better-developed fracture network systems and for hydrocarbon prospectivity and production. Hydrocarbon productivity has been ultimately determined by original depositional facies, diagenesis, and deformation.
Within the fracture systems, a complex suite of vein calcite, dolomite, quartzine, and celestite minerals has been precipitated prior to hydrocarbon emplacement, which have substantially healed and reduced fracture porosities and permeabilities. The occurrence of multiple vein mineral phases, collectively forming a calcite/dolomite-celestite-quartzine mineral assemblage, points to fluid compositions varying both spatially and temporally. The fluids responsible for vein mineralisation in the Tikorangi Formation probably involved waters of diverse origins and compositions. Vein mineralisation records a history of changing pore fluid chemistry and heating during burial, punctuated by changes in the relative input and mixing of downward circulating meteoric and upwelling basinal fluids. A sequence of mineralisation events and their probable burial depth/temperature fields have been defined, ranging from temperatures of 50-80°C and burial depths of 1.0-2.3 km. Hydrocarbon emplacement has occurred over the last 6 m.y. following the vein mineralization events. The Tikorangi Formation must continue to be viewed as a potential fracture reservoir play within Taranaki Basin.

year: 2002

title: Neural multi-class classification approach to blood glucose level forecasting with prediction uncertainty visualisation

authors: Mayo, Michael

subjects: computer science

abstract: A machine learning-based method for blood glucose level prediction thirty and sixty minutes in advance based on highly multiclass classification (as opposed to the more traditional regression approach) is proposed. An advantage of this approach is the possibility of modelling and visualising the uncertainty of a prediction across the entire range of blood glucose levels without parametric assumptions such as normality. To demonstrate the approach, a long-short term memory-based neural network classifier is used in conjunction with a blood glucose-specific data preprocessing technique (risk domain transform) to train a set of models and generate predictions for the 2018 and 2020 Blood Glucose Level Prediction Competition datasets. Numeric accuracy results are reported along with examples of the uncertainty visualisation possible using this technique.

text: Neural multi-class classification approach to blood glucose level forecasting with prediction uncertainty visualisation A machine learning-based method for blood glucose level prediction thirty and sixty minutes in advance based on highly multiclass classification (as opposed to the more traditional regression approach) is proposed. An advantage of this approach is the possibility of modelling and visualising the uncertainty of a prediction across the entire range of blood glucose levels without parametric assumptions such as normality. To demonstrate the approach, a long-short term memory-based neural network classifier is used in conjunction with a blood glucose-specific data preprocessing technique (risk domain transform) to train a set of models and generate predictions for the 2018 and 2020 Blood Glucose Level Prediction Competition datasets. Numeric accuracy results are reported along with examples of the uncertainty visualisation possible using this technique.

year: 2020

title: William Grey Nicholls and Rihitoto Mataia

authors: Hart, Philip

abstract: The son of a Pakeha Maori, Nicholls had an illustrious ancestry on his mother’s side, and his wife Rihitoto Mataia also had a distinguished whakapapa. From the 1870s Nicholls farmed in Ohinemuri, and as a licensed interpreter played an important role in land transactions at the same time as he was becoming prominent in the Pakeha community. For over 30 years he invested in mining, starting at Te Aroha in 1880. He also invested in a variety of other enterprises, becoming prosperous through these investments, his farming, and in particular by acquiring and selling land. Over a 40-year period, Nicholls conducted many cases in the land court, and assisted Pakeha to acquire Maori land, and also acquired a considerable amount of land for himself and Rihitoto, who inherited many blocks from her father (but had to pay off his massive debts).
         Whereas Rihitoto was a prominent leader in the Maori community of Hauraki, Nicholls had the same role in Pakeha society. Active in a variety of initiatives to benefit the Ohinemuri community, he was a popular member and chairman of the Ohinemuri County Council, and late in life was elevated to the Legislative Council. Reputedly he assisted Maori in various ways, but clearly he identified rather more with his Pakeha ancestry. His career was a remarkably successful one, and his wife was also successful in maximizing the benefits that could be derived from her ancestry.

text: William Grey Nicholls and Rihitoto Mataia The son of a Pakeha Maori, Nicholls had an illustrious ancestry on his mother’s side, and his wife Rihitoto Mataia also had a distinguished whakapapa. From the 1870s Nicholls farmed in Ohinemuri, and as a licensed interpreter played an important role in land transactions at the same time as he was becoming prominent in the Pakeha community. For over 30 years he invested in mining, starting at Te Aroha in 1880. He also invested in a variety of other enterprises, becoming prosperous through these investments, his farming, and in particular by acquiring and selling land. Over a 40-year period, Nicholls conducted many cases in the land court, and assisted Pakeha to acquire Maori land, and also acquired a considerable amount of land for himself and Rihitoto, who inherited many blocks from her father (but had to pay off his massive debts).
         Whereas Rihitoto was a prominent leader in the Maori community of Hauraki, Nicholls had the same role in Pakeha society. Active in a variety of initiatives to benefit the Ohinemuri community, he was a popular member and chairman of the Ohinemuri County Council, and late in life was elevated to the Legislative Council. Reputedly he assisted Maori in various ways, but clearly he identified rather more with his Pakeha ancestry. His career was a remarkably successful one, and his wife was also successful in maximizing the benefits that could be derived from her ancestry.

year: 2016