Porosity Prediction using 3D Seismic Inversion Kadanwari Gas Field, Pakistan

  • Nasir Ahmad
  • Giacomo Spadini
  • Arshad Palekar
  • M. Asim Subhani

Abstract

    In the western part of the Kadanwari field a gas bearing stratigraphic trap was identified in the G-sand of Lower Goru formation by drilling the X well. However, due to poor reservoir properties the well was not commercial. Thus, the challenge was to locate and quantitatively evaluate a drilling target in the sand body, which would have porosity values beyond the known producible threshold in the area.With this aim, 250 km of 3D seismic data was acquired in the area. The data was processed to pre-stack time migration, and acoustic impedance inversion was performed. This inverted data was used to generate a pseudo porosity volume to locate a “sweet spot” for porosity in the area. A linear relationship between Porosity and Acoustic Impedance was built based on the wire-line and CPI logs of the well X. The equation was obtained as a regression line for the clean G-sand porosity and acoustic impedance. The equation was applied to the available AIMP volume to obtain a pseudo-porosity volume. The inversion-derived pseudoporosity was compared with the CPI porosity at well X. As expected, the pseudo-porosity obtained from inversion provided a result with frequency content similar to the seismic data. For this reason the calculated porosity was not able to describe the details of internal variations of the G-Sand but capable to catch the bulk character of the target sand only. Using this pseudoporosity volume, a pseudo-porosity map was generated. On the basis of this work, the successful well Y was drilled. Due to the presence of complex mineralogy the effective porosity of well Y is still a question, however the sonic porosity was very close to the predicted porosity of 17-18%. On the basis of this success the Kadanwari Joint Venture has decided to acquire 3D seismic in the all field area, to apply the same technique in order to fully evaluate the remaining potential. According to authors knowledge this technique has not been used previously in the area for porosity prediction.

Published
2019-01-03
Section
Articles