Evaluation of the Release Mechanism of Sustained-Release Tracers and its Application in Horizontal Well Inflow Profile Monitoring

The inflow profile is an important parameter to evaluate horizontal well productivity; however, quantitative interpretation of the inflow profile of the horizontal wells both accurately and cost-effectively is a common challenge faced by horizontal well production technology. The sustained-release chemical tracer is a new low-cost, long-lasting, and simple technique for monitoring the inflow profile in horizontal wells. In this study, a new type of sustained-release tracer is developed using bisphenol A-type epoxy resin as the polymer matrix and 2,6-difluorobenzoic acid, 3,4-difluorobenzoic acid, and 2,3,4,5-tetrafluorobenzoic acid as tracers. Meanwhile, the release mechanism and the influencing factors (chemistry of the tracer, temperature, salinity, and flow rate) of the sustained-release tracer are studied experimentally. The experimental results show that the release mechanism of the sustained-release tracer can be divided into two stages. The first stage involved the erosion process, in which the fluid gradually contacts and wraps the tracer, and the release rate is very fast. The second stage included the diffusion process, which is the diffusion-dissolution process once the fluid is completely wrapped around the tracer, and the release rate of this process is slow. The temperature is directly proportional to the release rate of the tracer, whereas salinity is inversely proportional to the release rate, and the fluid velocity does not affect the release rate. Finally, three kinds of sustained-release tracers are applied in the field, and a method to interpret the inflow profile of the sustained-release tracer is proposed. The result of application indicates that the sustained-release tracer developed in this study can efficiently monitor the inflow profile of the horizontal well.