When studying any processes, reference points are needed. In this case, it is necessary to conduct observations within the boundaries of the reservoir and beyond (preferably a stable background) in order to see the difference between these two objects.

If the goal is to monitor the movement of fluid in the reservoir, then you must understand the rock properties that the fluid is interacting with. Not just the acoustic impedance but also the chemical interaction between fluid and rock and the potential for compaction or fracturing of the rock as pressure changes. Core data would be essential to understanding the mineralogical and mechanical properties of the rock. The reservoir may undergo important changes that can influence the acoustic impedance as fluid properties change through time.

Rock physics modeling of reservoir changes is required before the firs 4D seismic acquisition using the available well log data. This will indicate if there is a 4D signature for the expected reservoir changes.

The methods startinf from the Gassman theory are mostly applicable to the sandstone reservoir. Care has to be taken when the carbonate reservoirs are considered. See, for example, Øystein et al. (2005 SEG, Adam, Batzle and Brevik (2006), Vanorio, Scotellaro and Mavko (2007) -SEG, Sain et al. (2008) SEG, and Jiang et al., (2013) SEG.

Thanks to colleague Zhanibek Katrenov, but I also like the answer to colleague Huseyn Ozdemir

Dear Volodymyr N. Bublias, Keith Winfree and Huseyin Ozdemir,

Thanks a lot for your answers and recommendations. This is helpful.

So, prior 4D seismic in carbonates we have to consider the geomechanical modeling, rock-fluid interaction and identifying reference points.

Just a few thoughts as you are clearly getting the right answers.

Some of the value of the project might be in the initial survey. If there is not already a good 3D survey, perhaps new drilling locations and better reservoir management may result and take some of the risk out of the 4D response.

The 4D requires a long term and probably large investment. You pretty much have to prove you will get a response that will create significant value for the production or reserves of the field. One way is the best petrophysical model possible. The details of this are probably what you are interested in; there are entire books on this (SEG). Probably the high carbonate velocities will be less of a problem than heterogeneity.

The next step better than just a model is an analog. Best would be a similar survey with similar geology, but also think about early and late seismic data of any kind from the field. Even better than an analog is a test. Choose a small area of the field that will demonstrate effectiveness, or if the initial 3D can be justified the subsequent survey(s) can be a smaller test until a useful response is demonstrated.

Good Luck!