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Single-well tracer test for Sor estimation

Apeiranthitis Nikolaos

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Year 2015
Type of Item Master Thesis
Bibliographic Citation Nikolaos Apeiranthitis, "Single-well tracer test for Sor estimation", Master Thesis, School of Mineral Resources Engineering, Technical University of Crete, Chania, Greece, 2015
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The Single-well Tracer Test is a test used extensively to measure the residual oil saturation- Sor in watered-out reservoir. Also, it is implemented in order to evaluate enhanced oil recovery (EOR) using chemicals, such as Alkaline/Surfactant/Polymer flooding. The tracer test, in particular, includes a water/oil partitioning tracer injection, along with water, to a radius of investigation of 30 feet around a test well. Then the well is shut in and the injected tracer, usually an ester, reacts with the formation water producing ethanol. The produced ethanol dissolves only in the water. When the well is again set on production, the produced water is measured regularly, in order to measure the concentration of the tracers; the remained unreacted ester, and the produced ethanol. Due to the fact that the ester is partitioning tracer and the ethanol is a passive tracer, a separation will be observed on the arrival of time that the peak concentration is measured. This separation gives the Sor estimation. A passive tracer is injected along with the ester, in order to monitor any losses of the injected volumes in the reservoir. During production the ester’s and the passive tracer’s peak concentration should arrive at the same time. The test is affected by several parameters, such as the reservoir temperature, the brine salinity and the temperature gradient that is created after the injection. The temperature affects the partitioning coefficient of the tracer in positive way, as also the reaction rate, with the same way. Brine salinity affects the partitioning coefficient in positive way, while the reaction rate of the tracer is affected negatively. In order to take into consideration initial temperature and brine effect, the part. Coefficient and the reaction rate are measured in the lab at reservoir conditions, using the formation water at the reservoir temperature. Furthermore, the injection is done with formation water in order to keep the salinity effect constant.The temperature effect, in terms of different reservoir and/or injection water temperature is examined, and also in terms of the different temperature gradient that is created using or not pre-flush water volume in order to cool down the reservoir. The reservoir temperature affects the results with the same way; more ethanol is produced, while the water temperature, affects the reaction only when pre-flush is used. Injection rate also affects the amount of the produced ethanol, with high injection rate to be optimal the test to be valid.Regarding the history matching conducted under the described scope and the temperature effects, better result were obtained when a pre-flush volume is injected. Also, more satisfying results were obtained with increasing the separate layers of the investigation interval. The final Sor estimation was not uniformly distributed though out the reservoir, varying from 10% to 26% at same cases. All simulations were done using the Chemical Simulator of the University of Texas (UTCHEM).

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