The displacement efficiency and oil displacement profile are important parameters that determine the oil recovery efficiency. In accordance with the industry standard, these parameters are measured via flow experiments to displace oil with water or other injected agents (surfactants, polymers, micro-emulsions, etc.) from a porous medium model. During the experiment, flow products are sampled at predetermined time intervals, while the oil volume in the samples is measured visually. At the end of the flow experiment, the water saturation is measured in a Dean Stark / Soxhlet apparatus which allows to calculate the final displacement efficiency. Field experience shows that in the case of light oils displacement, the results of visual (volumetric) and estimated (according to the Dean Stark / Soxhlet apparatus) displacement efficiency determination methods demonstrate high match. However, in the study of heavy viscous oils capable of forming stable emulsions with water, the visual displacement efficiency determination may be accompanied by errors exceeding the measured value. Such significant errors in oil measurement in the samples lead to the impossibility of accurately determining the relative oil recovery profile during the experiment, especially in the case of sequential oil displacement by various injected agents. To eliminate this problem, a simple and accurate method for measuring oil in flow products is proposed. The method is based on the volumetric additivity rule for oil solutions density in chloroform. This method does not require any expensive equipment and can be performed in a conventional oil laboratory equipped with analytical scales and an electronic density meter. The authors describes in detail the experimental features of the method and its main metrological characteristics that meet the criteria of linearity, correctness, and intra-laboratory precision when measuring both heavy and light oil in the presence of reservoir water of a wide range of salinities. The described method has been successfully tested to determine the oil recovery profile in six flow experiments, showing high match of the results with the displacement efficiency estimated according to the Dean Stark / Soxhlet data.
References
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