Wettability Quantification in Mixed-Wet Rocks Using a New NMR-Based Method: Experimental Model Verification
- Chelsea Newgord (The University of Texas at Austin) | Saurabh Tandon (The University of Texas at Austin) | Ameneh Rostami (The University of Texas at Austin) | Zoya Heidari (The University of Texas at Austin)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 24-26 September, Dallas, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2018. Society of Petroleum Engineers
- 2 Well completion, 2.4 Hydraulic Fracturing, 2.6 Acidizing, 1.6.9 Coring, Fishing, 1.6 Drilling Operations, 2.5.2 Fracturing Materials (Fluids, Proppant)
- Wettability Assessment, Experimental Verification, Complex Pore Structure, NMR Measurements, Mixed-Wet Rocks
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- 233 since 2007
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Nuclear Magnetic Resonance (NMR) measurements have been attractive options for fast wettability characterization of rocks in petroleum reservoirs. Several NMR-based wettability indices are documented in previous publications. These methods often require calibration at irreducible water and residual hydrocarbon saturations, which complicates their applicability in mixed-wet rocks at different fluid saturations. We recently analytically derived a new NMR-based wettability index and confirmed its reliability using pore-scale NMR simulations. This new model only requires calibration at fully water- and hydrocarbon-saturated states for different wettability states ranging from water-wet to hydrocarbon-wet. In this paper, we experimentally quantify the influence of wettability on NMR measurements and verify the reliability of the new NMR-based wettability model in the core-scale domain for partially-saturated rocks.
First, we measured the transverse relaxation (T2) distribution of the unmodified water-wet samples using a 2-MHz NMR spectrometer in selected core samples. Then, we modified the wettability of two samples by injecting anionic surfactants. For the third sample, we injected a naphthenic acid and decane solution into the core. We quantified the wettability of these samples using the Amott-Harvey method and sessile drop contact angle measurements. Next, we measured the T2 distribution of the water-, mixed-, and hydrocarbon-wet samples at partially water- and hydrocarbon-saturation states. Finally, we assessed the wettability of these samples using the new NMR-based method and compared the wettability estimates to those obtained from the Amott-Harvey wettability method.
We measured the wettability of the core samples to be in the range of −0.6 to 0.5 on the Amott-Harvey index. The calculated NMR-based wettability for the altered core samples were in the range of −0.66 to 0.51, which was in good agreement with the wettability estimates from the Amott-Harvey method. The experimental results demonstrated that our new NMR-based wettability model successfully estimates the wettability of mixed-wet rocks in a wide range of wettability and eliminates the need for calibration at irreducible water and residual hydrocarbon saturations. The outcomes can be used to improve the speed and reliability of NMR-based wettability characterization. The results from these core-scale measurements are promising for application of the introduced model to log- and field-scale wettability assessment in mixed-wet rocks with complex pore-structure and at different fluid saturations.
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