Abstract：Ground-borehole trielectrode gradient method based on DC resistivity detection principle was put forward after simulation experiments in water trough In this method,power supply electrode A is placed on the ground nearby a borehole ,power supply electrode B is planted at "infinitely far" point (the distance is about 5～10 times borehole depth)and two observation electrodes M and N,whose distance keeps constant,move point by point in the borehole to detect apparent resistivity.People can make gradient anomaly analysis from the high resistivity of reservoir to locate a hydrocarbon reservoir. Experimental results show that the new method avoids various noises from borehole and formations,and highlights small reservoir anomaly better than usual borehole-ground trielectrode gradient method The new method can be used to find even the high-resistivity hydrocarbon reservoir that is much smaller than lkmzand in the development phase of an oiI field,it can be adopted to locate the residual reservoir nearby the interval w here oil or gas has been exhausted already.
