Based on small holes and caves developed in Lower Paleozoic carbonate reservoirs in Shaan-Gan-Ning Basin

two methods such as synthetic index method and acoustic time difference anomaly method were established using well log data so as to forecast oil and gas productivity.The synthetic index method is the product of resistivity and acoustical ways

which could be the synthetic reflection of oil volum in the reservoirs.According to the differences of synthetic indices

the productivity of the reservoirs in the basin could be divided into five productivity areas

and the coincidence rate is more than 75%.The acoustic time difference anomaly could be fine indicator of hydrocarbon abundance of underlying reservoirs.The more the acoustic wave curve deviates from compaction curve

the higher the productivity would be.The study area thus could be divided into four productivity zones

and the coincidence rate is greater than 70%.