Atlantis ocean bottom nodes time-lapse observations

Abstract

Atlantis Field is a large field in the Gulf of Mexico that has significant imaging challenges due to a complicated overlying salt body. In 2005-2006 the world's first deepwater Ocean Bottom Nodes (OBN) survey was acquired over this field to improve imaging and to serve as a base line for future time lapse (4D) surveys. In 2009, which was two years after production started, the world's first OBN repeat survey was acquired. The results from this time lapse survey are presented in this abstract. Due to excellent repeatability of both sources and receivers, extremely low 4D noise has been achieved with an average Normalized Root Mean Square (NRMS) value as low as 5.3% after post stack processing. Unfortunately due to the imaging challenges the area with good data quality is limited. The most valuable time lapse observations are the time shift response in the part of the reservoir that has undergone the strongest pressure depletion. This time shift response can be related to reservoir compaction and confirms other observations seen in production data. The amplitude difference response occurs in a similar area as the time shift response, but is weaker than and opposite to predictions. Sensitivity to pressure response remains the main uncertainty as the observations in the amplitude data do not match observations from laboratory measurements on core data.