Thermal state of the Taranaki Basin, New Zealand

Abstract

The Taranaki Basin is an active‐margin basin that has been significantly affected by Miocene subduction tectonics along the Pacific‐Australian plate boundary. We have analyzed its present‐day thermal state using 354 bottom‐hole temperatures (BHTs) from 115 wells distributed throughout the basin. The measured temperatures were corrected using an exact solution to Bullard's equation rather than the Horner approximation, thereby allowing for recovery dependence on well diameter and correction for some BHTs at early time after circulation had ceased. Thermal conductivity measurements were completed on 256 samples from eight wells, and matrix conductivities were determined for six end‐member lithologies by inversion. Formation conductivities are based on the conductivity and relative proportion of each end‐member component. Corrected BHTs, in situ thermal conductivity, and estimates of sediment heat production were combined to compute the present‐day, steady state heat flow. The average heat flow is 60 mW m−2, but important geographic variations are present: heat flow on the Western Platform is remarkably consistent at 53–60 mW m−2, attesting to its relative stability since the Late Cretaceous; heat flow in the southern part of the basin is 65–70 mW m−2 due to as much as 3 km of late Miocene erosion; on the southern onshore and to the south of the peninsula, heat flow is 50 ± 3 mW m−2, possibly due to the heat sink effects of crustal thickening; heat flow is highest at 74 mW m−2 on the northern peninsula adjacent to the Taranaki volcanic zone, suggesting a causal relationship between Quaternary volcanism and high heat flow.

The Awhitu volcanic complex, an offshore Pliocene volcano in the northern Taranaki Basin, New Zealand

“…The best-fit power law function to these data is: p = 968Z°1 13 where p is the density of sediments (kg/m 3 ) at depth Z (m). This density-depth relationship is consistent with the theoretical relationship determined by Funnell et al (1996) for mudstone in the Taranaki Basin (Fig. 4).…”

“…The solid line is the best-fit power law function p = 968 Z°" (where p = density and Z = depth) The dashed line is a theoretical density-depth relationship determined by Funnell et al ( 1996) for Taranaki Basin mudstone using grain density of 2650 kg/m 3 . Ttu difference between curves is probably due to sandstone in thi deeper parts of the sample wells Table 2 contains a summary of rock magnetisation data from the northern Taranaki Basin and adjacent area from the GNS Rock Catalogue (Whiteford & Lumb 1975;Mumme 1992).…”

Correção de dados de temperatura de fundo de poço (TFP)

“…(4) depende do quadrado do raio do poço, o que requer tempos de descanso mais longos para poços com maiores diâmetros. Tal exigênciaé contráriaà prática de perfuração comumente utilizada, pois nela,à medida que aumenta a profundidade do poço seu diâmetroé reduzido progressivamente; e são exatamente nos diâmetros maiores que se utilizam tempos menores de descanso (Funnell et al, 1996). Segundo Roux et al (1982), se t c /t d < 1/3 para todos os pontos, a técnica de Horner dá resultados aceitáveis.…”

Groundwater flow beneath Mt Taranaki, New Zealand, and implications for oil and gas migration

“…6 as wedging out on the northern side of the profile to provide 10'" 10 12 Fig. 7 Variation in permeability and hydraulic conductivity with depth in the region of the Kapuni field, calculated from the lithology of the sediments ("theoretical" trend, derived from Funnell et al 1996) and assumed in the vertical flow modelling (labelled "modelled"). The Moki Sand unit is assumed to be anisotropic, with k x being the horizontal permeability, and k y the vertical permeability.…”

“…These properties have been derived from theoretical estimates of bulk permeability based on the characteristic lithologies of each formation, and relationships between permeability, porosity, and lithology established by Funnell et al (1996). In a parallel study investigating the causes and timing of overpressures in the Taranaki Basin, Funnell et al have derived power relationships between permeability and porosity for sandstone, siltstone, mudstone, and limestone for the Taranaki Basin, which are consistent with petroleum industry measurements on cores, and with similar types of relationships used internationally in other basins.…”