Thinking about the subtle reservoir exploration in Bohai sea: a case of 427 structure belt

For offshore hydrocarbon exploration with a high cost,reservoir size is of the key factors to constrain the exploration of subtle hydrocarbon pools.What needs to be discovered in Bohai sea is subtle pools with a certain size.The characteristics of sand body,as a core of research work are a key factor to control subtle reservoir size in a petroliferous depreesion, and it is required to investigate sand body characteristics by combining geological methods with geophysical techniques.During this combination,it is very important to build a geological model by an integrated analysis of 3 elements,i.e.stratigraphic sequence,sedimentary system and structure.All these have constituted a new research idea of one core,two disciplines' combination and three elements.There are also 3 techniques matched with the idea,including reservoir prediction technique,subtle trap identification technique and hydrocarbon accumulation analysis technique.Based on an analysis of 427 structure belt by using this idea and the 3 techniques,the small oil discoveries in the belt are considered lithologic pools with no commercial value because their reservoir rocks are deltaic fan sandbodies that are formed during lake flooding and are separated and lack of connectivity.To find sizable hydrocarbon pools in 427 structure belt,it is necessary to look for larger connective reservoirs of low system tracts in the lower slope,and large lithologic reservoirs of turbidite fans within high system tracts in the lower sag.