Seismic 4D data has traditionally been acquired using repeat towed streamer surveys every 2–5 years. This is used to track fluid and pressure and has proved highly effective for influencing infill well locations and calibrating the reservoir simulator. Over the last 10 years the technology has evolved and is now relatively mature with several well documented case-studies demonstrating value of 3–5% reserves increase in post-plateau oil fields with a strong fluid response (1).
However, the long elapsed time between surveys limits its value in Reservoir Management where we would like to use time-lapse seismic to monitor the pressure field and the fluid flood fronts and therefore make decisions which maximise the sweep conformance and achieve ‘technical limits’ rate and reserves.
To do this, seismic data needs to be acquired at a frequency consistent with the timescale on which the decisions are made. Thus monitoring gas movement to minimise gas production in oil field may require seismic surveys every 3–6 months whilst providing data useful for optimising Base Well Management decisions on reperforations, restimulations, water shut-off and injection rates may benefit from seismic data every few months or even weeks.
As a first stage towards active management using "seismic surveillance", and specifically to aid in waterflood management, BP has installed a permanent seismic array over 70% of the Valhall field. The array cost $45million but the results have been technically spectacular (2, 3, 4). Learnings from this experience are still evolving but already cover aspects of reservoir management, infill drilling, Base Well Management, flow performance prediction and surveillance including the use of "Seismic PLTs" (2).
Following on from this success, BP is looking at the next wave of field applications as an integrated part of its FIELD OF THE FUTURE programme (5). Plans are now at an advanced stage to take forward two new projects in 2006 and several more are being discussed for application later this decade.