Отправлено: 01.11.13 09:43. Заголовок: Inversion-based petrophysical interpretation of logging-while-drilling nuclear and resistivity measu

Inversion-based petrophysical interpretation of logging-while-drilling nuclear and resistivity measurements
Olabode Ijasan, Carlos Torres-Verdín, and William E. Preeg

GEOPHYSICS, VOL. 78, NO. 6 (NOVEMBER-DECEMBER 2013); P. D473–D489, 13 FIGS., 3 TABLES


ABSTRACT
Interpretation of borehole measurements acquired in
high-angle (HA) and horizontal (HZ) wells is challenging
due to the significant influence of well trajectory and bed
geometrical effects. Experience shows that accurate integrated interpretation of well logs acquired in HA/HZ wells
requires explicit consideration of 3D measurement physics.
The most reliable alternative for interpretation of well logs in
HA/HZ wells is with inversion techniques that correct
measurements for shoulder-bed, undulating well trajectory,
and bed geometrical effects while taking advantage of high
data resolution. We discovered an efficient layer-based inversion workflow for combined, quantitative petrophysical
and compositional interpretation of logging-while-drilling
sector-based nuclear (density, neutron porosity, photoelectric factor, gamma ray) and array propagation resistivity
measurements acquired in HA/HZ wells. A challenging synthetic benchmark example confirmed improved formation
evaluation with the layer-based inversion workflow across
hydrocarbon-bearing zones in HA/HZ wells, where estimated hydrocarbon pore volume and porosity increased
by 10% and 15%, respectively, with respect to conventional
interpretation methods. Furthermore, application of the inversion-based method to a field example of HZ well across
calcite-cemented siltstone layers confirmed its advantage
over conventional interpretation techniques.