Core recovery criterion – a new optimization method of geological information quality in the geological conditions of the Grodziec Syncline Area

The increasing requirements for the quality and amount of geological information induce the development of new technological solutions. The authors present the optimization of the coring method for a newly defined criterion of maximum geological information quality. It enables the efficiency of works to be improved without investing in new specialist and expensive equipment. The statistical classification methods commonly used in medicine and the economy were used for analyzing the homogeneity of the drilled rocks. The quadratic discriminant analysis (QDA) and the Naive Bayes classifier method turned out to be most efficient, therefore they were selected from among other methods differing in the way the classification rules are built. The newly defined criterion of maximum geological information quality and the mathematical model of maximum core recovery allowed the amount and the quality of recovered rock material in the geologic conditions of the Grodziec Syncline to be incresed. The control of the process relied on detecting phenomena responsible for core damaging, i.e. erosiveness of drilling mud, mechanical damaging due to jamming in the core barrel and unstable operation of the core bit downhole. The analysis revealed that the main factor influencing the lower recovery of cores is mechanical damaging due to jamming in the core barrel. For the sake of controlling the core recovery, the authors defined and used the jamming index which defines the effect of weight on bit on momentary rate of penetration. The efficiency of this method was proved by a test performed in industrial conditions while drilling a successive wellbore in the Grodziec Syncline.