Objective Driven Solid Surface Roughness Characterization for Enhanced Formation Evaluation
- Shouxiang Mark Ma (Saudi Aramco) | Gabriela Leu (Halliburton) | Songhua Chen (Halliburton) | Mahmoud Eid (Halliburton)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 26-29 October, Virtual
- Publication Date
- Document Type
- Conference Paper
- 2020. Society of Petroleum Engineers
- 4.3.4 Scale, 1.2.3 Rock properties, 5.1 Reservoir Characterisation, 5.1 Reservoir Characterisation
- Contact angle measurement, Solid surface roughness, Rock pore structure, Formation evaluation, NMR logging
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Smooth solid surfaces of reservoir rocks are assumed in formation evaluation, such as NMR petrophysics and reservoir wettability characterization through contact angle measurements. Measuring the degree of surface roughness, or smoothness, and evaluating its effects on formation evaluation are topics of research. In this paper, we will primarily focus on details in characterizing solid surface roughness, though its applications will also be exemplified.
Surface roughness can be measured by methods of contacts and non-contacts techniques, such as stylus profilometer, atomic force microscopy, and different kinds of optical measurements. Each technique has different sensitivities, measurement artifacts, resolutions and sizes of field-of-view (FOV). Intuitively, while a finer resolution measurement provides the closest account of all surface details, the corresponding small FOV may compromise the representativeness of the measurement, which is particularly challenging for charactering heterogeneous samples such as carbonates. To balance the FOV and measurement representativeness, and to minimize artifacts, laser scanner confocal microscopy (LSCM) is selected in this study.
In developing a methodology for quantifying the surface roughness (R), more than 20 rock samples were selected to determine optimal resolutions for overall R quantification. Five symmetrical measurement areas were used per sample, as well as a range of magnifications to achieve resolutions from pore level of about 20 µm down to surface level of about 0.2 µm. The length scale of R is orders-of-magnitude smaller than the typical carbonate pore sizes; therefore, a pore size filter has been developed and applied to remove the solid surface pore size effect on R computation. Once the measurement is considered reliable, the R qualification, which is objective driven, is established.
Results for the more than 20 rock samples tested indicate that rocks with similar rock types have similar R values. Grainy limestones have relatively higher R values compared to dolostones, consistent to the latter's crystallization surface features. Muddy limestones have smoother surfaces, resulting in the lowest R values among the rocks studied. For sandstones, R varies with clay types and content. For rocks containing two distinct minerals, two R values are observed from the R profiles, which justifies the use of two surface relaxivity (p) values in NMR data processing of these rock types.
The second half of the paper is devoted to the use of R to improve the NMR based pore typing, i.e., the effect of solid roughness on the surface relaxivity, p, separated from mineralogy effects, thereby NMR based pore body size distribution. The importance of using R corrected p values is demonstrated with an excellent match between the enhanced NMR pore size distributions and that derived from independent measurement of micro-CT scanning.
|File Size||2 MB||Number of Pages||25|