Oil/gas-bearing structures have been found underground at certain estuaries in China, and some are now being explorated. The main features of natural environments are introduced in this paper, in addition, the equipment of exploration and the means of delivery are considered. For future development, the plan of constructing projecting dyke and tidal island is proposed.
Most tidal zones are sandy and silty. Generally speaking, their slopes vary from 1/500 to 1/3000. Viewing in the mass, sea in some zones is retreating, such as the Liaohe River estuary in the Bay of Liaodongwan in Liaoning Province, sea in other zones is advancing, such as the abandoned Yellow River estuary in the Bay of Laizhouwan in Shandong Province The tidal ditches and ridges are developed but unstable For instance, the tidal ditch in Liaohe River estuary is 20-30m wide and 2-4m deep somewhere, while 2-3m wide and 0.5-1m deep in other places. The seabed topography of the abandoned Yellow River estuary is indicated in Fig.l There, ditches and ridges densely cover the unstable zone, the depth of ditch varies from tens centimeters to hundreds centimeters, the shape of eroded ridge is isolated, suboceanic layers are complex, and roughly composed of two-three layers. The surface of soil is very hard like a "crust", the equipments and tools are sure to subside if the "crust" breaks. The content of organic matter is very high and the corrosiveness is very intensive in all layers. The tidal change is very complex, there is tide in someplace, while no tide in other place the tidal range varies from 4m to 0.5m. In addition to regular astronomical tide, there is storm tide which is difficult to be predicted.
