Research On The Geological Causes Of ShengLi Well Workover Platform Ⅲ Overturning Accident

Sep.7th,2010, the overturning accident of Shengli III well workoverplatform took place adjacent to well group platform of CB22C at Chengdaooilfield, which let two people fell in water and drowned. Against thisbackground, this paper intends to analyze and discuss the geological reasonsintegrated with regional geological elements behind the appearance.The basic data involve meteorological, hydrological, geological structureand shallow seismic profile of Chengdao area as well as results of theoreticalstudies. Utilizing acoustic image data of high-resolution multi-beam echosounder, side scan sonar and sub bottom profiler to determine theenvironmental features of accidental area. Generalize the evolution of YellowRiver Delta system, dynamic geomorphology development and classificationof Chengdao area. It also presumes types of geologic hazard that may occuraround this area. Combining with the character of Shengli III well workoverplatform itself and the situation of CB22C well group, the paper also analyzedthe geomorphology around the accidental platform; moreover it mainlydiscusses the geological reasons in three aspects: liquefaction of sea bedcausing landslide, soft strata deformation beneath the platform and pilefoundation scour of platform. In the end of this paper the author also givesseveral feasible reasons and analyzes those reasons comprehensively ingeological aspect. This paper considers that the accidental area belongs to thedisaster-prone zone under the influence of severe storm and relatively stronghydrodynamic conditions. Because of the relatively fixed work position againstthe CB22C well group, there some pile pit on the sea bed surface which isfluctuated. The sea bed scouring gradually leads to the undercutting of pilefeet meanwhile, strength of strata becomes decreasing, plus the affection of storm and strong wind caused by typhoon on platform forces on strata throughpiles causes liquefaction of the sediments below them, especially for those onthe slope to of the pile pits edge. As the further development of liquidation,sediments start to slide and the scale increasing or the soft strata begins todeformation. Eventually, many factors together result in this accident.This paper has theoretically enriched researches on sea bed instability,seabed scour and liquefied sediments landslide of study area as well as theregional environmental development regulation. Discussing causes of thisaccident and analyzing their internal relationships can provide references toprevention accidents alike and post a positive meaning to insure theproduction security of offshore platforms.