Li, Wei (China University of Petroleum-Beijing) | Guo, Rui (China University of Petroleum-Beijing) | Tao, Guo (China University of Petroleum-Beijing) | Wang, Hua (China University of Petroleum-Beijing) | Torres-Verdín, Carlos (The University of Texas at Austin) | Ma, Jun (The University of Texas at Austin) | Xu, Chicheng (The University of Texas at Austin)
Diniz-Ferreira, Elton Luiz (Schlumberger) | Torres-Verdín, Carlos (PETROBRAS – Petróleo Brasileiro S.A. and The University of Texas at Austin)
Due to sea-level variations, cycles of sedimentation can often be recognized from well logs. It is possible to differentiate rock types based on such geological cyclicity; for petrophysical purposes we will refer to those rock types as fluid flow units. In the presence of thin layers, flow units can only be detected with core data. The cause of sea-level variation in this field is not well understood and remains a subject of study by geologists. Wells were drilled with both oil-base mud (OBM) and water-base mud (WBM). The oil bearing-zone of wells drilled with WBM gave rise to a conspicuous invasion profile on resistivity logs. It is possible to simulate this invasion profile in different layers and estimate their permeability. Conversely, wells drilled with OBM did not show a conclusive invasion profile in the oilbearing zone because of the lack of electrical resistivity contrast between oil and mud filtrate. Due to the complexity of the pore space and the spatial heterogeneity of the reservoir under consideration, conventional well-log evaluation seldom reproduces petrophysical properties consistent with core data. It is necessary to construct multi-layer petrophysical models based on geological information to improve the interpretation. A model that combined well logs and geological properties was key to select bed boundaries and to construct an earth model. The latter model was used to perform static and dynamic simulations - matching simulated resistivity, nuclear, and NMR logs with field measurements. Petrophysical properties estimated with those simulations were in agreement with core laboratory measurements. Interpretation was performed in the oil-bearing zone of three wells: two of them –Wells Η and Γ – were drilled with OBM, the remaining well –Well Χ – drilled with WBM (Table 1). It is not possible to perform a correlation between the evaluated wells using well-logs.