Abstract
The genesis of the overpressure carbonate reservoir is not controlled only by lithofacies, karstification and tectonic movement, but also by overpressure. The hydraulic fractures formed under overpressure and its connection and expansion to early solution vugs and structural fractures are the key factors to the high productive zones.
Kenkiyak Pre-salt Oilfield is the carbonate reservoir with a burial depth of more than 4300 meters. The matrix permeability is only 0.98md. It was considered as a very low permeability porous-type reservoir and was defined as the oilfield without economic benefit. According to this study, under the overpressure condition, that the pressure of the porous liquid is up to 80Mpa, the carbonate reservoir cracks to form natural hydraulic fractures. Reticulate hydraulic fractures combined with structural fractures and solution vugs make very good spatial configuration, and then form the pore-fractural dual- media reservoir. The high productive reservoirs form under the condition of the favorable sedimentary facies, karstification cells and structural locations.
Because of the overlying salt-dome with 120–3800 meters in thickness, the imaging of the seismic data is very poor and it is very difficult to predict reservoirs. The seismic processing techniques such as kirehhoff prestack time migration, diving wave tomo and CIP grid tomography are applied to improve the migration image and signal-noise ratio. Based on analysis of the control factors to the carbonate reservoir, using the data of the drilling, logging and dynamic test data, the lithofacies, palaeokarst and the fracture system are predicted and the distribution of the high productive zone is successfully predicted by applying the techniques of the seismic muti-attribute clustering analysis and seismic inversion. The average productivity of the new drilling wells in the predicted high productive zones is up to 300t/d, and the oil rate per day of the 2 wells is over 1000t.
