Determination of Fractured Zones by Well Logging in Low Transmissivity Geothermal Reservoirs in Kochani Valley, Macedonia, Yugoslavia

Abstract

Surface geophysical methods currently used have considerable limitations in localizing deeper fractures or fractured zones bearing thermal waters. When considering geothermal reservoirs with relatively low transmissivities, only a low number of hydraulically active fractures can be encountered. Their number depends statically on the borehole length in the reservoir penetrated. Using standard logging devices it is difficult to detect them during drilling operations. Recent researches in Kochani Valley geothermal area have given us some experience on detecting water bearing fractures. Production logs, such as gradient with differential temperature and flow meter log have revealed as very adequate in detecting them, especially when executed in developed wells. On the basis of this logs, wells were acid treated by injecting acid mixture into fracture depth and in this way specific yield was considerably increased, in some cases for several times.