Identifying Gas-bearing Carbonate Reservoir Using Extended Elastic Impedance

Document Type: Research Paper

Authors

1 Ph.D. Candidate, Institute of Geophysics, University of Tehran, Tehran, Iran

2 Professor, Institute of Geophysics, University of Tehran, Tehran, Iran

3 M.S. Student, Institute of Geophysics, University of Tehran, Tehran, Iran

4 Geophysics Expert, KPE Co., Tehran, Iran

Abstract

It is difficult to identify the carbonate reservoirs by using conventional seismic reflection data, especially in cases where the reflection coefficient of the gas-bearing zone is close to that of the carbonate background. In such cases, the extended elastic impedance (EEI) as a seismic reconnaissance attribute with the ability to predict fluids and lithology can be used. It allows for a better distinction between seismic anomaly caused by lithology and the one caused by the fluid content. The EEI attribute extends the available reflection angles and applies different weights to the intercept and gradient values so as to extract the petrophysical properties of the rock at a specific incident angle. Using the EEI attribute, we can estimate the elastic parameters such as shear impedance; the ratio of the compressional velocity to shear velocity; Poisson’s ratio; and bulk, Lame, and shear moduli, and petrophysical properties, including porosity, clay content, and water saturation. The known reservoirs in the study area are three oil-bearing formations namely, Surmeh (Arab), Gadvan (Buwaib), and Dariyan (Shuaiba), and three gas-bearing formations, including Kangan, Dalan, and Faraghan. The Dehram group is composed of Kangan (Triassic), Dalan, and Faraghan (Permian) formations. Permian carbonates of Kangan–Dalan and its equivalent Khuff have regionally been developed as a thick carbonate sequence in the southern Persian Gulf region. In this paper, parameters ๐œ†๐‘ and ๐œ‡๐œŒ extracted from the EEI method are used to characterize a carbonate reservoir. Our results show that the EEI can highlight the difference between the reservoir and non-reservoir formation to identify the gas-bearing areas.

Highlights

  • Extended elastic impedance (EEI) can be used as a seismic reconnaissance attribute with the ability to predict reservoir fluids and lithology.
  • EEI allows for a better distinction between seismic anomaly caused by lithology and the one caused by the fluid content.
  • Recognizing gas-bearing intervals by applying the EEI will ultimately reduce the drilling risk and cost in areas with carbonate reservoirs.
  • Application of EEI leads to the more reliable estimation of porosity and fluid saturation in carbonate reservoirs.
  • The proposed methodology illustrates the advantage of using ๐œ†๐œŒ and ๐œ‡๐œŒ for discriminating the reservoir rock properties, as compared to the conventional Vp and Vs analysis.

Keywords

Main Subjects


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