Abstract: It is important to make fine adjustments to the injection and production of oil fields based on detailed geological understanding of reservoirs for the development of high-water-cut wells in mature oil fields. This work has studied a detailed description of the middle and deep layers of the oil/oil-water/water reservoir in Bohai Bay and a data analysis of its actual oil production. It is assumed that some dry layers of water wells connected with oil wells demonstrate a certain degree of water absorption. Therefore, the effective use of a dry layer can further increase the injection-production ratio, improve the water drive degree, and ultimately enhance the water absorption ratio. The connection of a dry layer with an oil reservoir depends on many complex factors. This study has employed the principal component analysis and theory of fuzzy closeness to propose an identification method for the membership function of a fuzzy set using the integrated information of each discriminant variable. This method has reduced the dimension of initial variables while ensuring comprehensiveness and accuracy of the discriminant function.Research results show that the proposed method based on fuzzy closeness has achieved an accuracy of over 85% in terms of the effective identification of dry layers. A numerical simulation has been adopted for data analysis and comparison. The effective use of the dry layer has further enhanced the injection-production ratio and significantly improved the oil development. Considering the aforementioned factors, it is established that the comprehensive identification method is reliable and fairly practical for the future development of oilfields.

Key words: effective identification of dry layer, efficient use of dry layer, fuzzy closeness, principal component analysis, injection-production ratio