The First Visualization of Acid Treatments on Carbonates With 3D Nuclear Magnetic Resonance Imaging (NMRI)

Abstract

Abstract Carbonate reservoirs with their high hydrocarbon potential show often a great heterogeneity in their inner rock structure, wherefore stimulation treatments are often necessary to maintain or establish fluid production. Therefore, core flow tests are usually conducted to test and model stimulation treatments within a laboratory scale in order to predict their performance. The visualization of wormholes that were created within core flow tests requires novel technologies for evaluation and pathway prediction purposes. Unfortunately, past visualization techniques were always associated with the destruction of the core sample and in that way, an increased demand raised in non-destructive methods. Nuclear Magnetic Resonance Imaging (NMRI) is such a method that fulfills the approach of being non-destructive. The technology is widely known by medical applications, but has never been used before in correlation with 3D rock imaging. Hence, this study developed a procedure on how to use the NMRI technology to visualize wormholes with NMRI in 3D. Therefore, a comprehensive study was started by initially choosing and obtaining various core samples that have different contents of calcite and dolomite. These core samples were imaged with the NMRI and μCT technology in their unchanged state as well as basic petrophysical experiments were conducted for initial experiments. The μCT technology was utilized as reference visualization technique, since it provides a very high resolution with a corresponding high level of detail. Afterwards, core flow tests were conducted on the core samples with various acid systems and wormholes generated. Finally, the core samples with wormholes were imaged again with the NMRI and μCT technology, whereby the NMRI acquisition technique was improved towards imaging of rock samples and the results were compared to the μCT results. The NMRI results showed moderate imaging achievements for the unchanged rock samples and high quality imaging achievements for the extracted wormholes.