岩船沖油ガス田にわける三次元地震探鉱データを用いた貯留岩分布予測

抄録

In many cases, predictions of turbidite reservoir distributions are not simple because their depositional patterns and property of reservoirs are liable to variation. In this case study of Iwafune Oki oil and gas field, integrated approaches for the prediction of the turbidite sand reservoir distributions are reported.
The rock facies and property at the well were correlated to the seismic data to clarify causes of the seismic amplitude. It is obvious that the gas sands showed low acoustic impedance (AI) and their AI contrasts generated high amplitude reflections. For the oil-producing interval, we found that the amplitude was caused by AI contrast between different rock facies.
The acoustic impedance data inverted from the 3D seismic traces were used for the reservoir interpretation. The gas sand reservoir could be predicted directly on as a low AI zone. For the oil reservoir, the net sand thickness distributions were estimated with a relationship between the net versus gross thickness in the lower AI intervals derived at well.
After those evaluations, we drilled two wells, the northern case expected as oil reserve and the southern one expected as a gas reserve. The recent drilling results reveals that, in northern one, for the extent of existing reservoir, our estimation was almost correct, but the main target expected as new reserve, was over pressured shale. For southern case, we drilled a high amplitude portion in existing reservoir expecting as thick gas zone, was thick and low impedance porous sandstone but an oil reserve.
These lessons show that the estimation of the target impedance was success, but the interpretation of impedance was non-unique. We should recognize such a risk whenever we use seismic attributes for E & P studies.