Abstract:

The low resistivity oil layer has become one of the main reservoirs for increasing reserve and production for each oilfield. After the research of Putaohua low-resistivity oil layers in Puao oilfield, we find that the forming and distribution of low-resistivity oil layers are controlled by structure characteristics and sedimentary characteristics. In term of structure, low-resistivity oil layers mainly develop in the west ramp region and flat gradient region on two sides of nosing structure. In term of sedimentary system, low-resistivity oil layers main develop in the delta front sheet sand, and beach bar sandstones of shore-shallow lacustrine which formed in weak hydraulic condition. Under the control of macro-geologic factors, the micro-geological characteristics of low-resistivity oil layers are high bound water saturation, high salinity formation water and the added conductivity of shale. Base on core and logging data, aiming at the actual characteristics of low-resistivity oil layers, we choose quality factor instead of porosity of tradition experience formation to compute bound water saturation. According to the characteristics of cation exchange capacity and shale, we construct low-resistivity sensitive parameter and build high accuracy model of low-resistivity evaluation, then, determine the lower limit value of each parameters based on the test data. It makes the quality identifying turn to quantity identifying. The method has been applied in this area for evaluating 26 low resistivity formations of 17 wells, and it identified 25 of them. It obtains 96.15% rate of accuracy.

Key words: low-resistivity oil layer, macro-geologic factor, micro-geological characteristic, bound water saturation, clay minerals, mathematical model