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

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.

Optimum Fluid Injection Rate in Carbonate Acidizing Based on Acid Dissolution Morphology Analysis

“…There are many factors influencing the wormhole development, such as types of acid and rock, injection rate, surface/volume ratio, temperature, pressure, etc. , However, the main factor is the acid injection rate for a fixed acid and rock type. It has been generally acknowledged that surface dissolution is formed under a low injection rate, uniform dissolution is formed under a high velocity injection, and a wormhole is formed at a medium injection rate. − One of the purposes of this paper is to find the injection velocity boundaries between the three dissolution patterns.…”

Topological study of reservoir rocks and acidification processes using complex networks methods

“…This treatment consists of a reactive fluid flow injected in the inner rock of the reservoir, which creates a preferential path (wormhole) that optimizes the extraction of the hydrocarbon fluids. 40,41 Therefore, the characterization of the wormhole's structure is of vital importance to assess the efficiency of the stimulation procedure.…”