About the Course
SEG Honorary Lecturer Series. Time-lapse seismic reservoir surveillance is a proven technology for offshore environments. In the past two decades, we have seen this technology move from novel to necessary and enable us to monitor injection wells, water influx, compaction, undrained fault blocks, and bypassed reserves. Value is generated by influencing the management of our field operations and optimizing wells to reduce cost, accelerate production, and increase ultimate recovery.
Significant advances in technology are improving the quality of our data. Errors in acquisition repeats are nearly eliminated using permanently installed systems or dedicated ocean- bottom nodes. We now routinely obtain surveys with such a high signal-to-noise ratio that we can observe production-induced changes in the reservoir after months instead of years. This creates a demand for frequent seismic monitoring to better understand the dynamic behavior of our fields. Increasing the frequency of seismic monitoring will have a proportionate cost implication, and a challenge is how to design a monitoring program that maximizes the overall benefit to the field.
Reducing individual survey costs is important to enable frequent monitoring. Several techniques are considered for lowering these costs such as:
- Reducing the number of shots and/or receivers to minimize offshore vessel time. This includes shooting targeted (i4D-style) surveys on a frequent basis in between full-field surveys that are acquired infrequently.
- Use of smaller source arrays towed by less-expensive vessels.
- Semi-permanent ocean-bottom nodes that can be left on the seafloor for multiple on-demand surveys.
- Time-lapse VSPs that use permanent distributed acoustic sensors (DAS) in well bores.
- High-resolution 4D surveys that monitor shallow reservoirs cost effectively using low-cost vessels towing arrays of short-streamer cables (e.g., P-cable).
There is no single solution that works for every field, and we need to understand the pros/cons of the various technologies to select the best option for a specific field. Some results of applying these techniques to offshore fields will be discussed.