The major reservoirs of Tahe oilfield consist of fractured-vuggy carbonates which underwent multiple stages of karstification and hydrocarbon charging.These reservoirs are of strong heterogeneity

complex oil-water contact and poor water shutoff effect.This study indicates that reservoir types and oil-water distribution patterns are the two key geological factors affecting water shutoff.The remaining oil distribution of the carbonate reservoirs of fractured-vuggy type is quite complicated due to the existence of big solution cavities

especially the high-angle fractures.The big solution cavities can make plugging water diffcult

while the high-angle fractures can easily result in complete shutoff

leading to poor shutoff effects.The fracture-vuggy reservoirs show quasi-homogeneity similar to sandstone reservoirs

thus their water shutoff effects are fair.Oil-water relationship pattern of quasi-homogeneous type corresponding to the reservoir types and wells with slowly-increasing or step-wise increasing water cuts have better water shutoff effects.Moreover

the existence of tight sections also can improve the water shutoff effects.