Date/Time
Date(s) - 04/10/2025
11:30 am - 1:15 pm
Location
Wynkoop Brewing Company
Categories
“Application of the Wave-Equation Based AVO Inversion on an unconventional field. A case study in a Vaca Muerta Fm., Neuquén Basin, Argentina.”
Hansel Gonzalez, Operations Team Manager and Pablo Benitez, QI Geoscientist, Delft Inversion.
Introduction:
Amplitude versus Offset (AVO) techniques have been key to obtaining important information from seismic data that have been used extensively these past few decades. The insights from these techniques can have a crucial business impact on projects concerned with the discovery and exploitation of resources, oil, gas, water, from the subsurface. This talk describes a fundamentally new approach towards inversion of seismic AVO information, which utilizes the full wave equation, applied to an unconventional reservoir. The technique, the Wave-Equation Based AVO Inversion, WEB-AVO, iteratively solves the full elastic wave equation while computing the subsurface properties but also the seismic wavefield at every point in the inversion domain. In this way not only primaries but also interbed multiples, mode conversions and transmission effect are properly handled. Additionally, by the implied de-tuning of the seismic amplitudes, an elastic property model can be obtained with a spatial bandwidth wider than what could be expected from the temporal bandwidth of the seismic data. The outputs are then the native wave-equation elastic properties, the Bulk and Shear moduli, or their inverses, the Compressibility and the Shear Compliance (plus density when possible), which often relate more closely to reservoir parameters of importance (Gisolf, 2017). This also implies that the technique is better suited to handle geological environments that might stress the linear wave propagation model assumptions, such as sections very high reflection coefficients (Gonzalez et al. 2020) , as well as possibly add additional sharpness to the geological boundaries by the subtle bandwidth extension (Haffinger 2020).
A Wave-Equation Based AVO Inversion (WEB-AVO) based reservoir characterization study has been successfully completed, targeting the Vaca Muerta Fm, in the Neuquén Basin, onshore Argentina. The high level objectives for this study were to better characterize the base of the sequence, a very strong reflection coefficient between the soft shale and a tight sand, for better lateral placement, as well as manage, with a true physical model, the non-linear energy (multiples and mode conversions) affecting the target zone. Additionally, any bandwidth extension would be welcome to sharpen the definition of the geological units as well as a more robust Young’s Modulus for geomechanical analysis. Lastly, optimizing time and cost by minimizing the seismic preconditioning was noted as a welcome objective.
Method & Results
A Wave-Equation Based Interbed Multiple Investigation workflow was applied on the well data in order to model the wavefields and see the interference from the overburden over the Vaca Muerta, as interbed multiples and mode conversions. Afterward, raw migrated seismic gathers were converted from offset to ray-parameter to be input into the inversion. Wells were then tied to the seismic with a fully elastic workflow. Subsequently, with an optimal starting model built and wavelet set selected, the WEB-AVO inversion was run over the field to produce the inverse of the Bulk and Shear Modulus, the Compressibility and Shear Compliance. From these volumes, a Young’s Modulus was created and a rock physics analysis was completed to supplement the interpretation of the native output parameters.
The inversion outputs, created using the raw migrated gathers as input, display clear internal detail within the target zone, a key objective in the study. The rock-physics cross-plots allow the identification of the different members of the Vaca Muerta unit which was a challenge for traditional methods. Quantitively, the cross-correlation values between the inversion and the well data is over 90% for the Compressibility, over 85% for both the Shear Compliance and the Young’s Modulus, and seismic residuals of less than 2%% at the wells and 3% over the whole 3D volume. This robust Young’s Modulus volume is expected to aid in geomechanical characterization. Additionally, the bandwidth of the resulting outputs displayed a notable extension on both below and above the seismic bandwidth.
Conclusions
This case study marks the first published example where the wave-equation based AVO inversion technology has been applied to an unconventional field, and it has shown the ability to provide uplift with often common challenges for unconventional reservoirs. These challenges include:
– Complex overburden that creates severe multiple and converted wave energy patterns.
– Need to see more detail within the stratigraphic units.
– Obtaining a robust Young’s Modulus, via Bulk and Shear Modulus, formula which doesn’t need the Density term.
– Requiring only raw migrated gathers allows for possibly significant time and cost savings invested in seismic data preconditioning.
Speaker Bio
Hansel Gonzalez has 24 years of experience working in reservoir geophysics. He joined the industry at Veritas DGC in 2001 after graduating from The University of Oklahoma with his M.S. in Geophysics, working under John P. Castagna. His career has focused on seismic reservoir characterization, dynamic and static, at all stages of field life, from both the service company and operator perspective. His experience ranges from conventional to unconventional exploration and development, Danish, Norwegian and UK North Sea, NWS of Australia, Offshore Angola, Paris Basin, Williston and Powder River basins, at all stages of field life. Hansel’s PhD work consisted of constraining the dynamic model via the use of 4D seismic on a deep-water West Africa field, while later obtaining an Executive Master of Management in Energy degree, jointly issued by the Institut Français du Pétrole and the BI Norwegian School of Management. Hansel joined Delft Inversion in 2019 and is currently Worldwide Operations Manager, based in the United States, where he manages the Company’s technical consulting services, leveraging his experience to apply the next generation AVO technology, WEB-AVO, to improve and increase the range of solutions provided by quantitative seismic methods to O&G, Geothermal and CCUS operators.
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