炭化水素の移動集積におけるＰｏｒｏｓｉｔｙ Ａｎｏｍａｌｙの重要性

Abstract

In order to initiate primary migration of the petroleum, the drainage areas relating to the traps are to be buried within the critical range in which the petroleum is generated. Petroleum expulsion from the source beds to the carrier beds can occur regardless of the formation of the traps. However, primary migration is only effective in forming commercial oil pools in cases where the reservoirs form traps and their caprocks have enough sealing capacities. In Japan, the carrying medium for petroleum in primary migration is pore water which is expelled from the source beds. Where the porosity anomaly of undercompacted argillaceous sediments is buried to the depth of the petroleum generating zone, the porosity anomaly zone plays two parts in forming petroleum deposits: In the first place, it's the potential source of the primary petroleum migration, and in the second place, it's the barrier to the upward migration of the liquid which is expelled from source beds. Where a permeable bed is sandwiched between two porosity anomalies, the permeable bed recieves the liquid expelled from the anomaly zones, and the liquid as forced to move laterally in the layer. This liquid movement in the permeable layer could form commercial petroleum deposits in the traps. We have been engaged in petroleum exploration mainly based on the structural control philosophy. However, the writer found that many commercial hydrocarbon deposits were confined within specific stratigraphic intervals relating to the porosity anomalies. For example, the porosity anomaly which lies immediately above the stratigraphic trap in the Minami-Aga field is important evidence in discovering the target zone of potential hydrocarbon deposits. Combining this porosity anomaly and other geological data, we will be able to point out the target stratigraphic zone for potential hydrocarbon deposits more precisely.