北海油田における油層マネージメントの例（ＷＡＧおよび４Ｄサイスミックサーベイ）

Abstract

Due to complicated nature of the fluvial sandstone reservoir, management of the Snorre Oil Field, located in Norwegian Northern North Sea, is quite challenging. The field has been mainly exploited under water injection scheme for several years, while WAG (water alternating gas) injection seems also promising in view of increased recovery as well as a gas disposal solution. However, the ongoing WAG pilot test indicates the difficulty in forecasting the movement of injected gas and evaluating WAG efficiency. The key uncertainty will be in the reservoir description and in some of the reservoir engineering parameters.A pilot test of 4D seismic survey has been initiated in Snorre Field, where the movement of gas front is to be monitored as time-lapse seismic response. Petroacoustic study and elastic modelling was performed to investigate the technical feasibility of monitoring the gas front under reservoir conditions in Snorre. The study indicated that gas in the reservoir could be monitored as significant response and also showed that low-noise survey and adequate procssing would be essential.A pilot survey started in 1996 and sea bottom cables have been employed as the receiver to secure accuracy and resolution of the time-lapse data. Only a base survey has been completed so far and further shooting will be done in 1997 after injecting sufficient gas to be monitored.The pilot survey is being performed to reduce the reservoir uncertainty and to establish a tool to monitor WAG process in the field. Aggressive reservoir management is required in Snorre Field to exploit the reservoir in an optimal way. The ongoing 4D seismic survey pilot test is expected to have an important contribution to the reservoir management in the field.