oa Deterministic inversion results in a difficult seismic acquisition environment: Example from a carbonate reservoir in United Arab Emirates

Transition zones between land and deep-marine environments are known to be difficult areas in which to acquire good quality seismic data. The objective of this study was to apply inversion techniques to better image a carbonate reservoir located in a difficult transition zone. The use of various sources and receivers during seismic acquisition resulted in a challenging dataset for reservoir characterization studies. An integrated seismic inversion approach, combined with special processing, was successfully applied to improve the reliability of the reservoir characterization results in the problem transition zone. A prior inversion study revealed a seismic data quality problem, which led the asset team to embark on an AVA (amplitude versus angle) study to improve the seismic image. A detailed evaluation of different anglestack cubes showed that better quality subsurface images with higher signal-to-noise (S/N) ratio occurred over the near- to mid-angle range. The high S/N ratio angle-stack was found to be the key to obtaining more<br>reliable inversion results for reservoir characterization. The integrated workflow used all available geological, petrophysical, producing and geophysical resources. The work emphasized obtaining detailed well ties to the seismic data for stable wavelet estimates, an improved structural definition and realistic geologic constraints for a more reliable inversion. Industry-leading, constrained sparse-spike inversion was employed to invert the seismic for an acoustic impedance model. An acoustic impedance-to-porosity relationship from well control was used to produce a porosity model. Upon completion, a qualitative map was produced, which showed the mismatch between the inversion and the input seismic. This map was used to identify low confidence problem areas,<br>which had a high correlation to the bathymetry over the field.