Drilling crews of Sinopec have encountered a series of troubles when drilling a formation called kazhdumi of Yadavaran oilfield, Iran in the last few years. The formation is buried in the depth from 3300 m to 3500 m, mainly including limestone, muddy limestone and some bituminous shale. Many microfissures exist in the formation and the equivalent density of formation pore pressure ranged from 1.19g/cm3 to 1.59g/cm3. Asphalt or heavy oil kicks occurred in drilling three wells in one and a half years, which contaminated the drilling fluid and made well killing difficult due to the kicks and lost circulation in open hole. Gas and hydrogen sulfide(the concentration is up to 40000ppm) were present in the wells, and finally two wells were completely abandoned and one partially lost, which frustrated the drilling engineering seriously. By analyzing the data of the drilled wells, the paper summarized the causes of the troubles, and put forward suggestions and conclusions that can serve as reference and guideline for drilling well in this area in the future. Drilling crews of Sinopec have encountered a series of troubles when drilling a formation called kazhdumi of Yadavaran oilfield, Iran in the last few years. The formation is buried in the depth from 3300 m to 3500 m, mostly including limestone, muddy limestone and some bituminous Many thinly layers exist in the formation and the equivalent density of formation pore pressure ranged from 1.19g / cm3 to 1.59g / cm3. Asphalt or heavy oil kicks occurred in drilling three wells in one and a half years, which contaminated the drilling fluid and made well killing difficult due to the kicks and lost circulation in open hole. gas and hydrogen sulfide (the concentration is up to 40000ppm) were present in the wells, and finally two wells were completely abandoned and one partially lost, which frustrated the drilling engineering seriously. By analyzing the data of the drilled wells, the paper summarized the causes of the troubles, and put forward suggestions and conclusions that can serve as refe rence and guideline for drilling well in this area in the future.