Genesis and Evaluation of Low Resistivity Oil Formation in Tarim Basin

As petroleum exploration continues, a series of low-resistivity oil reservoirs have been found in the Tarim basin. The lowest resistivity of the oil reservoir is only 0.45 Ω·m, almost identical to the resistivity of water layer. Geological observations and experimental analyses on the Jurassic (J_Ⅳ) low-resistivity oil reservoir in Lunnan, Triassic (T_Ⅱ) low-resistivity oil reservoir in Jilake and Carboniferous (C_Ⅲ) low-resistivity oil reservoir in Hadexun indicate that the main causes of the low resistivity of the oil reservoirs are the local enrichment of pyrite and the additional electricity conducting effect of clay minerals and the low salinity bound water. Several evaluation methods using different data such as capillary pressure, oil saturation and rock electrical parameters under high temperature and high pressure conditions are presented. Using these methods, the calculated oil saturation increases by 8% to 25%, and the accuracy of well logging explanation increases by 5% to 8%.