IV. 2.1. Data interpretation: Conversion from raw data to information

The importance of interwell tracer testing in oil exploitation is indicated by the great number of tests conduced worldwide over the last 40 years. Normally,
water is injected into injector wells to ‘push’ the oil to the producer wells, from which it is extracted. The end of the secondary recovery process occurs when the water cut increases to the point where water injection becomes economically inefficient to continue further. At this stage, the fluid flow in the reservoir consists mainly of injection water. The oil remaining in the reservoir is largely stagnant (residual saturation) in the swept volume but can also comprise larger untouched oil volumes. This incomplete sweeping of the oil is a consequence of the natural heterogeneity of the reservoirs and the usually unfavourable mobility differences between water and oil. Hence, channelling of water between injector and producer wells is a very common problem that counteracts achieving acceptable sweep efficiencies.

The interwell tracer tests permit detection of this problem and also determination of some parameters of the watered zones, which are necessary for corrective action. Owing to the considerable uncertainty associated with fluid flow knowledge in the water flooding process, there is insufficient basis for assuming a very detailed reservoir model. Therefore, a ‘kit’ of simple methods can provide acceptable information, including moment analysis and Brigham based analysis.