DEDICATED SESSION RESERVES - 4D seismic data from the Ringhorne field in the North Sea are used to monitor water movement, improve existing reservoir models, and enable more cost-effective field operations. The 4D data and the results of elastic inversion also triggered an update to the volumetric assessment of the Paleocene Ty reservoir. Key uncertainties in resource estimation were effective reservoir thickness and area above the oil-water contact. Much of the sand is below seismic resolution, the reservoir is nearly transparent on stacked seismic data, and there is interference from the underlying strong top chalk reflection. The flat areas of the reservoir in the north and south of the field are sensitive to depth conversion, adding to volumetric uncertainty. The 4D survey showed water sweep where no sand had been previously interpreted. The down-dip limit of water sweep, as defined by the 4D image, indicates the position of the original oil-water contact. This provided the justification to lift the reservoir in places. The pinchout of the reservoir against the chalk was moved updip as a result of the inversion. As a result of the reassessment, the resource base for the Ty reservoir was increased by 40 percent.


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