Abstract:

Low permeability or ultralow permeability reservoirs are developed in the Yanchang Formation of northern Shanxi, in addition to the usual high impedance reservoir development, but also easy to form a low resistivity reservoir. Therefore, the discovery of low resistivity reservoirs has greatly widened the area of oil exploration and development fields. According to geologic characteristics of Chang 6-1 reservoir in the Yanchang formation of Fanchuan area, Zhidan oil field, combined with a large number of experimental and production data analysis and comparison, causes of low resistivity reservoirs in the area of macro-control mechanism and the factors were analyzed. We believe that the pore complex structure of Chang6-1 led to increased water saturation and high water salinity, high clay content and the presence of radioactive sandstone, which is the main reason for forming the low resistivity reservoir. Identification methods of low-resistivity reservoirs are presented by a large number of actual test comparison of oil and logging data. The results show that calculated spontaneous potential and spontaneous potential curve overlapping quickly and visually display oil layers, Crossplots of acoustic time-deep resistivity and gamma-deep resistivity can divide the oil and water layers. By the secondary log data interpretation of 85 exploration wells on the region, 45 low resistivity oil layers those are omission in the initial interpretation are found in the Chang 6 reservoirs, and oil layer number changes from 117 to 162 with a net increase of 27.8%.

Key words: low-lesistivity oil layer, cause character, control factor, identification methods, Fanchuan area, Zhidan oil field, reservoirs