FORMING MECHANISM OF LOW RESISITANCE RESERVOIR IN JIAOWEI FORMATION OF WEIZHOU11-1 OILFEILD AND ITS LOGGING EVALUATION

Low resistivity oil reservoirs are common in some oil fields. Due to their complex forming mechanism, it is difficult to identify or separate them from water reservoirs in well logging curves. They are often ignored or misinterpreted. Therefore,it is of great significance to make in-depth study of the formation mechanism of low resistance oil reservoirs so as to select effective methods to identify them in later period for increase in oil reserve and production. Through a comprehensive analysis of research findings,it is found that tectonic and sedimentary characteristics control the formation and distribution of low resistance oil layers in the Weizhou 11-1 oil field from a macroscopic point of view. In terms of microscopic aspects, they are controlled by bound water, lithology, content of clay minerals and specific conductive minerals and other factors. Upon the basis of integrated study, we adopted a variety of methods to identify the low resistance reservoirs, such as, using the relationship between the improved relative gamma values and apparent formation water resistivity,the diagram of improved sp relative versus deep induction resistivity, and the cross plot of irreducible water saturation against apparent formation water resistivity and movable water analysis. The methods are proved effective in improvement of identification of low resistivity reservoirs.