Reservoir Structural Characterization at Multiple Scales Using Vertical Seismic Profiling, 3D Sonic Imaging from Dipole and Monopole Sources, and Wellbore Microresistivity Images: Case Study from Offshore Abu Dhabi, UAE
- J. Adam Donald (Schlumberger) | Nicholas Bennett (Schlumberger) | Peter Schlicht (Schlumberger) | Franciscus Van Kleef (ADNOC Offshore) | Ravi Verma (ADNOC Offshore) | Israa Suliman (Schlumberger) | Nobuyasu Hirabayashi (Schlumberger) | Saif Al-Kharusi (Schlumberger) | Yevgeniy Karpekin (Schlumberger)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- SPWLA 61st Annual Logging Symposium - Online, 24 June - 29 July, Virtual Online Webinar
- Publication Date
- Document Type
- Conference Paper
- 2020. held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors
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- 150 since 2007
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High-resolution wellbore measurements such as microresistivity images are routinely used to define structural information such as formation dip and azimuth to compare with low-resolution seismic migration. The scale differences between microresistivity images and seismic images range from millimeters to hundreds of meters, which is then compared with vertical seismic profile (VSP) data at tens of meters of scale and sonic velocities at less than 0.5 m scale. Sonic imaging techniques from both monopole and dipole sources can be further used to extend the volume of investigation around the wellbore and define true dip and azimuth of the formation extending 25–30 m into the reservoir.
When using the dipole source for sonic imaging and recording the single-receiver sensor data, we observe polarized shear reflections that present not just the linear and sinusoidal moveouts evident as a function of source-receiver offset and nominal receiver azimuth, but also a significant polarity signature that is a function of the reflected wave’s particle motion direction. A variation of 3D slowness time coherence (STC) is presented that correctly processes these polarized shear reflections to determine the dip and azimuth of the reflector. We then demonstrate how this new 3D STC processing is integrated into an automated processing that locates and characterizes the reflected arrivals in the filtered waveform measurements and then maps the corresponding reflectors in 3D along the well track. Of note is how the automated processing with the new 3D STC variation resolves the 180° ambiguity of the reflected dipole signal noted by previous authors. This is particularly important when imaging or mapping formation structure in a highly deviated wellbore, because the single-sensor data can image both above and below the wellbore, compared with conventional modal decomposed dipole waveforms, for which distinguishing top from bottom is ambiguous.
A case study is presented from offshore Abu Dhabi, in which an interbedded carbonate reservoir is examined with various acoustics measurements and microresistivity images. A detailed structural analysis is conducted using a walkabove VSP whereby the migrated image below the wellbore is used to compare with the sonic imaging results from azimuthal monopole and dipole sources. Migration images from the dipole shear clearly show subseismic-scale layers in comparison with the VSP migration. Structural dip and azimuth of these subseismic features provide detail 30 m into the reservoir.
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