2012 Honorary LecturerSponsored by Shell

Middle East & Africa

Rocco Detomo, Jr.

Shell Nigeria Exploration & Production Company, Inc. Lagos, Nigeria

4D time-lapse seismic reservoir monitoring of African reservoirs

 
Abstract

Ian Jones

The world's growing attention to our industry's prudent operations has given rise to an increased demand for assessing the applicability of reservoir monitoring. The technical and visual demonstration of what is happening in a reservoir deep in the Earth, especially away from the immediate well bore, is of key importance for ensuring that fluids are moving as we have modeled them, and that the integrity of the reservoir is being maintained. 4D time-lapse seismic monitoring offers an effective method for detailing laterally extensive areas to monitor changes in both the geomechanical and elastic properties of the Earth.

The key to the 4D method is to insure that the 4D signals are detectable and identifiable from the noise and from other repeatable signals for which we cannot explicitly account. A 4D signal's detectability is dependent on the magnitude of the change in rock and fluid properties associated with the reservoir's production and on the level of random seismic noise. The ability to identify and interpret this 4D signal depends strongly on the repeatability of the seismic surveys, and the complexity of any other changes in the Earth, such as in the overburden. The greatest value in 4D is attained by assuring that the seismic experiment is repeated accurately and that the only changes seen are attributable to changes in the reservoir. There have been numerous reported examples where 4D measurements would have added key information to a field's operation, and a surprising number of examples where the most significant value derived from a 4D measurement was in seeing what was previously unexpected. We often make strong assumptions about what we know about our reservoirs between our points of well control.

Dr. Detomo will discuss how to assess the applicability of this technique to different geologic situations, examine key features of seismic acquisition, repeatability and seismic data-processing methods, and discuss repeat-survey interpretation strategies. Different acquisition strategies and systems will be highlighted, including marine and onshore cases. Industry examples of 4D time-lapse survey data from the Middle East and Africa will be shown with areas of typical value and business impact discussed. Fortunately, there are many African reservoirs where 4D time-lapse methodologies can be applied. Hopefully, at the end of this lecture, you will find yourself asking, "If I can detect the 4D signal, why would I not monitor my reservoir?"