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A Carbonate Reservoir Characterization Using AVO Analysis on 3D Seismic Data

Hassanzadeh Azar, Javid | 2008

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  1. Type of Document: Ph.D. Dissertation
  2. Language: English
  3. Document No: 39288 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Pishvaie, Mahmoud Reza; Javaherian, Abdolrahim; Nabi Bidhendi, Majid
  7. Abstract:
  8. In this project, some issues facing the application of AVO in carbonate reservoirs were studied,reviewed and discussed: physical relationships between elastic and reservoir rock properties to estimate compressional and shear wave velocities both on core measurements and well logging data, sensitivity analysis for Gassmann‐Biot and Kuster‐Toksoz rock physics models on the representative carbonate samples, lithology discrimination and reservoir characterization in carbonate intervals using AVO seismic attributes and specifically LambdaRho‐MuRho approach.The studied area (Azadegan Oil Field) is an area about 1174 km2 of 3D seismic data and was containing of six wells in the time of study. In this project, we used the existing well data and 3D PSTM seismic cube together for our AVO study. Whereas shear wave velocity is essential to provide the amplitude variation with offset approach, we extracted shear and compressional wave velocity logs at all existing wells and specifically whole Sarvak Formation (carbonate formation) using Gassmann model which predicts the velocities comparable with seismic wave frequencies. Considering Gassmann equations involves the known dry bulk and shear moduli, we used Kuster‐Toksoz model along with differential effective medium theory to contribute the effect of pore geometry on dry elastic rock moduli in addition to rock porosity. In this way we followed Xu and White method to calculate approximately pore volume fractions regarding to different pore aspect ratios. Therefore a good correlation between measured and predicted Pwave velocity logs was found all over Sarvak Formation. Also we could see a good correlation between measured and predicted S‐wave velocity logs at well A6 which has DSI log among all existing six wells (although few mismatches have been occurred in clay contaminated intervals).However the shaly intervals are usually less predictable and more troublesome. From the empirical point of view, we extracted linear and quadratic relations between P‐ and S‐wave velocities based on measured DSI log quantities at well A6. We obtained good correlations between measured P‐ and S‐wave velocities for both linear and quadratic regressions and that proposed quadratic form has effectively improved the prediction of S‐wave velocity in Sarvak carbonate Formation.Through using the AVO attribute sensitivity analysis on both core samples and well logging data,it was concluded that understanding rigidity, μ, and incompressibility, λ, offers the better attribute set into lithology and reservoir facies discrimination (porous, tight and shaly limestone)in the studied area. As an integrated seismic attributes study: coherency, P‐ and S‐impedance and Lambda‐Mu‐Rho seismic attributes, we would be able to characterize a carbonate reservoir interval in upper part of Sarvak Formation. Integrated map of horizon based coherency seismic attributes afforded the opportunity to reveal a widely distributed carbonate clastic channel deposits all over studied area. Based on generating windowed horizon based acoustic impedance, LambdaRho and MuRho maps we estimated reservoir properties of the interested horizon 30 ms below Top Sarvak horizon.
    A simultaneous cross‐plotting and cross‐section views in λρ‐μρ domain at the well A6 showed that distinction between tight and porous carbonate reservoir facies and the shaly facies is feasible for Sarvak Carbonate interval. Therefore we made attempts to discriminate shaly limestone, tight limestone and porous limestone on the studied seismic sections and confirmed that high shear modulus of carbonate reservoir can be helped to differentiate shaly intervals from reservoir zones
  9. Keywords:
  10. Fractured Carbonate Reservoir ; Amplitude Versus Affset ; Seismic Attribute ; Carbonate Resrevoirs ; Rock Physics ; Shear Waves Velocity Estimation ; Gassmann-Biot Model ; Lambdarho-Murho Attribute

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