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S.B. Nielsen

Formation temperatures determined from stochastic inversion of borehole observations

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  • Department of Earth Sciences

Bottom Hole Temperature (BHT) observations are generally influenced by drilling‐induced thermal disturbances which must be corrected for. This paper presents a correction method based on a 1‐D conductive finite element model and an inverse procedure for parameter estimation. While the technique may be applied to any section of the borehole this paper focuses on the correction of bottom hole temperatures. Model parameters are mud temperature during drilling and circulation at the depth of BHT observations, borehole radius, thermal parameters of mud and formation, and the equilibrium formation temperature. Data are one or more successive BHTs and their standard deviations. Prior to inversion the model parameters are assigned reasonable values and standard deviations that reflect the confidence in those values. A high level of confidence implies small standard deviations and vice versa. The process of inversion extracts the most likely values of all free parameters including the equilibrium formation temperature. Furthermore, the initial uncertainties in all parameters and data are propagated into uncertainties in the final parameter estimates. The formation temperature estimate is an unbiased estimate of the true formation temperature when the a priori parameter estimates and their standard deviations are consistent with the actual physical conditions in the borehole and the formation. The method on average yields 5–10 per cent higher equilibrium temperature estimates than does the Horner plot method and displays a strong consistency with temperature obtained during production tests. This is of importance to the understanding of terrestrial heat flow density patterns, and thermal structure of sedimentary basins, and to the modelling of hydrocarbon generation. The theory and results from the processing of 41 BHT series from 27 industrial wells in the North Sea Central Graben are presented.

Original languageEnglish
JournalGeophysical Journal International
Pages (from-to)581-590
Number of pages10
Publication statusPublished - 1 Jan 1990

    Research areas

  • bottom hole temperature, equilibrium formation temperature, inverse estimation, thermal stabilization.

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