A 4D seismic feasibility study has been performed on carbonate reservoirs of the Bu Hasa field onshore Abu Dhabi. It concludes to the feasibility of the method as a reservoir injection monitoring tool, an interesting result when several recent papers [1] have suggested that 4D seismic may not be applicable to Middle East carbonate reservoirs due to their rock physics characteristics.
2D full wave equation and 3D convolutional modelling approaches have been combined in this study in order to maximize the reliability of the predictions while optimizing the cost effectiveness of the study.
Because the assessment of repeatability noise indicated a realistically irreducible threshold for high resolution 4D surface seismic and a possible limitation for WAG monitoring, a 4D well seismic exercise was simulated which overcame those limitations.
The Bu Hasa Field, onshore Abu Dhabi, is a super giant carbonate oil field. The Lower Cretaceous Shu'aiba member of the Thamama formation is the main reservoir with porosity above 30%. This field has been producing since 1963 and production mechanism is involving peripheral water injection and crestal gas and water injection. (Figure 1)
The "monitoring" of this field is essential to optimize the production parameters and the value of using seismic information (4D) as an additional reservoir monitoring tool has been assessed [2]. Although seismic is not always considered as fit for purpose for limestone reservoir monitoring because of the stiffness of the rocks, Bu Hasa field is a favourable case because of the high porosities encountered. (up to 30%) Bu-Hasa oil is light and very compressive; therefore, the mechanical behaviour of the oil is closer to gas than water. This means injected water front movements should be more easily detected than injected gas front (in the oil).
