R.A. Mollison1, O.N. Fanini1, L. Yu1, B. Kriegshauser1, G. Ugueto2, J. van Popta3, T.V. Ragland4
(1) Baker Atlas, Houston, TX
(2) Shell Offshore, New Orleans, LA
(3) Shell EP Technology, The Hague
ABSTRACT: New 3DEX Induction Data And Tensor Resistivity Saturation Analysis Examples, Shell Ursa Field, Deepwater Gulf Of Mexico
Identification of productive deepwater reservoirs with conventional resistivity data is problematic. Formations containing highly conductive thin bedded shales and pay sands below the vertical resolution of the tool results in the 'low contrast, low resistivity pay' effect due to conductivity averaging (parallel circuit). Correct determination of net pay and true reservoir characterization is critical to deepwater field optimization. To overcome this problem, a new multi-component induction tool (3DEX(r)) was jointly developed by Baker Atlas and Shell EP Technology. The tool design has three mutually orthogonal transmitters and receivers to derive horizontal and vertical resistivity (Rh, Rv). The resulting Rv is a weighted average resistivity (series circuit) response that is more representative of the hydrocarbon bearing sand component. Rh and Rv are used in a tensor resistivity petrophysical model to determine laminar shale volume and laminar sand resistivity (Rsd).
A significant percentage of total oil-in-place in the Shell operated URSA Field, Deepwater Gulf of Mexico, is present in thinly bedded Bouma Tb-Td turbidite sands. 3DEX Rh & Rv were obtained in two development wells penetrating the "Above Magenta Reservoir". Petrophysical interpretation results using Thomas-Stieber and 3DEX laminar shale volumes indicate approximately one third of the oil-in-place is in the laminated sequences and oil saturations using Rsd are more consistent with core saturations when compared to traditional petrophysical models. Anisotropy ratio (Rh/Rv) can assist in distinguishing productive laminated sequences from non-productive slumps or deformed intervals. Anisotropy can aid in determination of well to well stratigraphic correlation, Bouma facies, and stratigraphic sequence boundaries.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado