Abstract: The goal of this study is to solve the problem of frac interference in an area with many downhole complexities. After volumetric fracturing in Ma 18 well area of Mahu Oilfield, numerous downhole complexities were experienced in the third spud section drilling of middle-deep horizontal wells. In order to analyze the causes and solve the problems, the interferences of volumetric fracturing in drilling operation have been analyzed. From perspectives of complicated event, disposal cases, and phased prevention and control technical modification, combined with geological characteristics of different strata in the open-hole section of the middle-deep horizontal wells in this area, the main reasons leading to drilling complexities under the influence of volumetric fracturing were analyzed.Due to the influence of volumetric fracturing, leakage points were formed at the junction of the Jurassic and Triassic strata, which led to complex phenomena such as lost circulation and overflow The mudstone intervals in the deviated and horizontal sections were prone to wellbore instability and collapsing. Hence, the countermeasures for the dynamic leakage caused by volumetric fracturing, and the wellbore instability in the mudstone intervals of directional and horizontal sections were proposed. According to the research, during the third spud section drilling of middle-deep horizontal wells in the Ma 18 well area, the key elements for controlling the downhole complexities caused by volumetric fracturing were a consequences of plugging the leakage points in the open hole section, and supporting the wellbore in the mudstone intervals. These countermeasures could provide reference for drilling the same type of horizontal wells in Mahu Oilfield.