Residual oil saturation (Sor) is a particularly important parameter for depleted oilfields as it gives an indication to the potential effectiveness of an enhanced oil recovery program. The single-well chemical tracer test using reactive ester tracers such as ethyl acetate has been used extensively to accurately determine Sor. However, these tracers are typically highly volatile and have low flash points presenting a large impediment to their deployment in an offshore environment. We have investigated the behaviour of higher molecular weight diesters and triesters (ethylene glycol diacetate, propylene glycol diacetate and triacetin) as possible alternatives for this test as they are much less volatile and flammable. These compounds are particularly attractive chemical tracers as they are commonly used in the food and cosmetics industries and are generally recognized as have minimal health and safety concerns. The oil/water partition coefficient is a critical property of the tracer that dictates its behaviour and effectiveness for this test. For example, simple chromatography models based on the method of moments suggest that the optimal sensitivity range for the partition coefficient at Sor of 10 % is 4.5 to 13.5, at 20 % is 2 to 6 and at 30 % is 1.2 to 3.5. Through a series of laboratory experiments, we have determined the water/decane partition coefficients at a range of temperatures where decane is a mimic for crude oil. These experiments demonstrate that these diesters and triesters are suitable for a wide range of temperature and residual oil saturation conditions.

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