Chengdao Sea Seabed Under Wave Action Erosion Prediction And Evaluation

ChengDao sea area is located in the north of the Yellow River Delta, in the neritic waters of south shore of Bohai Gulf. Engineering geology environment in this area is complex, mainly containing silt and clay silt in the sea bed, and seafloor erosion and other kinds of geo-hazards are developed here, producing huge threat to the oil-field safety.In this paper, in situ and laboratory erosion tests were run on fine-grained soil using the Cohesive Strength Meter in order to study the critical cohesive shear stressτc and erosion rate constantεM. A typical sea area in ChengDao sea area is taken as the study area. According to the tests results, one year erosion depth of the study area under the actions of tidal currents and wind waves was calculated using both Kandiah formula and Jepsen formula, and the right one was verified by comparing with the investigated data. The erosion depth in the strong wind wave was calculated using the verified formula, which provides consult material for preventing and reducing natural disasters of oil-field, and is of great significance for oil field construction. The main conclusions are as follows:(1) According to the in situ and laboratory erosion tests results, it has high relativity between the soil critical cohesive shear stress and its properties, containing median size, clay content, bulk density, water content and shear strength. The critical cohesive shear stress and erosion rate constant is exponential dependence.(2) The regression model between the soil properties and critical cohesive shear stress was built, which was used to calculatedτc of study area sediment according to the sediment properties, and the calculatedτc was 0.52Pa~1.74Pa.(3) The Kandiah formula and Jepsen formula were used to calculate one year erosion depth of the study area under the actions of tidal currents and wind waves. By comparing with investigated data, the Kandiah formula was verified to be suitable for the study area.(4) The erosion depth in the strong wind wave was calculated using the Kandiah formula. Erosion trend of study area is that area around 6~8m water depth is the most, reducing to around area. There are two erosion centers in the CB18 well filed and CB14 well filed. According to the erosion depth, the study area was divided to three regions: little erosion region, average erosion region and more erosion region.