Inversion of Well Log Data with Apriori Information

In the hydrocarbon exploration the well is a complex source of information, beside the well logs the results of coring, mud logging and well test also can be used in the petrophysical interpretation. In the traditional procedure only the log values are used in the parameter estimation, which based on the maximum likelihood principle. The additional information is only used after the inversion, for confirming the results. The additional information also can be used in the inversion if they are regarded as an apriori information related to the rock parameters. In my work, the apriori information – core porosity data - was built in the inversion procedure by Bayes principle. The estimated probability distribution of core data involves the measurement error and also the effect of vertical inhomogenity of layers. In order to increase efficiency of Bayes type procedure, quality control has been built in. The log data and core data are compared statistically before the inversion, and in the case of significant differences the apriori data are not used. The efficiency of the modified inversion procedure is demonstrated by synthetic and field examples as well.. In both cases the modified inversion gives more accurate results than the traditional.