Visualization of Acid Treatments With 3D Nuclear-Magnetic-Resonance Imaging

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 168198, “The First Visualization of Acid Treatments on Carbonates With 3D Nuclear-Magnetic-Resonance Imaging,” by M. Krebs, SPE, Clausthal University of Technology; B. Lungwitz, SPE, A. Souza, SPE, A. Pépin, SPE, S. Montoya, P. Schlicht, and A. Boyd, SPE, Schlumberger; and E. Vidoto, R. Polli, and T. Bonagamba, University of Sao Paulo, prepared for the 2014 SPE International Symposium and Exhibition on Formation Damage Control, Lafayette, Louisiana, USA, 26–28 February. The paper has been peer reviewed and is scheduled to appear in SPE Journal. Core-flow tests are usually conducted to test and model stimulation treatments at laboratory scale, to predict the performance of such treatments in carbonate reservoirs. The visualization of wormholes 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. This paper describes the use of nuclear-magnetic-resonance imaging (NMRI) as a nondestructive visualization method in correlation with 3D rock imaging. Introduction The experiments described in the complete paper were conducted with different core samples such as Indiana limestone, Silurian dolomite, Winterset limestone, and carbonate outcrops. The core samples were selected according to their properties, which greatly differ for each type with respect to their origin. The core-flow tests or acidizing tests performed in this study serve the purpose of simulating field treatments at laboratory scale. NMRI applies a gradient static magnetic field such that the strength of the field decreases with increasing distance away from the source. The Larmor frequency becomes dependent on the position of the nuclei, which will be associated with a single value of the gradient magnetic field. Hence, it is possible to locate the nuclei in a region radially around the source. More specifically, NMRI uses mostly pulsed gradient magnetic fields that belong to a group of linear gradient fields in order to link acquired signals to a specific volume element. Therefore, it is possible to locate the nuclei more exactly in the 3D space instead of only defining a region. The gradient fields are used for spatial encoding to acquire a location-dependent signal, and they are the slice-selection gradient, phase-encoding gradient, and frequency-encoding gradient.