As low resistivity reservoirs have similar resistivity as water layers

it is difficult to differentiate water layers from low resistivity reservoirs

and to determine oilwater contacts by using conventional logging data. Experimental study on relationship between full waterbearing conductivity (Co) and solution conductivity (Cw) with samples from lowresistivity layers and nonlowresistivity layers shows that the additional conductivity contributed by clay minerals is the main factor leading to the low resistivity of the second unit of the Triassic in Jilake area. When this type of lowresistivity reservoirs is penetrated

anions on clay surface may absorb cations in the solution. The cations absorbed to clay surface in turn may further impede the migration of anions in the solution

resulting in ion retention in the low resistivity reservoirs and charge shielding. The negative difference of SP log of the lowresistivity layers decreases in comparison with the nonlowresistivity layers. A quasispontaneous curve (SPrt) of nonlowresistivity layers is then created and compared with the SP curve to identify lowresistivity layers. This method has been successfully applied to recognize the lowresistivity reservoirs in the study area.