Petrophysics Analysis of Shu'aiba Reservoir, onshore-oil field United Arab Emirates

Tanprasat, Surassawadee¹, Neil Hurley² (1) PTT Exploration and Production Thailand, Bangkok, Thailand (2) Colorado School of Mines, Golden, CO

Image analysis of thin sections and core-slab samples from the Shu'aiba reservoir can help to quantify their pore-size distribution and detailed porosity components. The results show the distribution of pore sizes range from 4.2 x 10 ^-5 mm² to 7.68 mm² in thin sections, and 0.023 mm² to 630.7 mm² in core slabs. The pore-size distribution can be classified into 3 groups,namely, micropore, mesopore and macropore, based on the minimum resolution of thin-section image analysis (6.5x10 ^-3 mm), and the average intersection-point value of pore-size distribution curves from thin sections and core slabs (0.858 mm). A linear relationship of a cross plot between mesoporosity plus macroporosity and core-plug permeability on a semi-log plot shows the influence of large pores on the formation's flow behavior. A comparison of pore-size distribution from core slabs to NMR-T₂ distribution shows a strong relationship between tails at the high end of T₂ distribution and the presence of macropores in the formation. Thus, the NMR log can be used qualitatively as a vug indicator. This detailed distribution of porosity components in the formation enables us to get a more precise petrophysics-based flow-unit determination that subdivides certain Reservoir Rock Types into smaller zones with specific characterization of flow capacity and storage capacity. The pitfalls from the 2D techniques used in this study are the derived porosity from image analyses, which, in fact, are less than the actual values. This is due to the excessively blue-colored shades of epoxy in the thin-section, and the pores that lie at the edges of the core-slab images, which were excluded from the pore-size quantification.