CHARACTERISTICS OF WEATHERED METAMORPHIC ROCKS CRUST IN BOHAI SEA AND ITS QUANTITATIVE PREDICTION

With the discoveries of the oil and gas fields of weathered crust type, such as the Jinzhou 25-1 south, Jinzhou 20-2 and Bozhong 26-2 oilfields, and the breakthrough of the Bozhong 19-6 Gas Field of billions cubic meters in reserve in the past two years, the weathered Proterozoic-Archaean metamorphic rocks have become one of the key exploration targets in the Bohai Sea. In order to reveal the structure of the weathered crust for effective use of the reservoir prediction method to the buried hills consisting of metamorphic rocks, based on coring, thin slices, logging, major elements and physical property data, the vertical structure of the weathered crust of metamorphic buried hill and the controlling factors of weathered crust are studied in this paper. By using the Q-type clustering method and the grey correlation coefficient, the weathered crust of metamorphic rocks can be divided into five vertical sequences, and their development status is obviously affected by lithology, structure and preservation conditions. Among them, the sedimentary environment of the cover, which is often ignored by previous researches, are of great significance as far as the preservation conditions for the weathered crust type of oil and gas fields are considered. According to the variable factor classification for the 11 drilled weathered crusts, four reservoirs fall in classes I-IV from top to bottom. The method has been successfully applied in the prediction of the Bozhong 19-6 weathered crust gas field and should be referred in the future.