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<p>Shallow Water Flow (SWF) presence in the channel systems of the South Caspian Sea is confirmed by different researches and drilling evidences. SWF is a shallow drilling geo-hazard which associated with unconsolidated overpressure sands. When the drill bit reaches these zones, a large volume of overpressure water and sands flow into the wellbore, and causes drilling hazards and accidents. This introduce different challenges for logging operations in these zones, especially for acquiring S-wave velocity logs (Vs) which is necessary for predrilling investigation on the SWF zones. In this study, the cross-plots of Amplitude Versus Offset (AVO) were used to derive attributes such as intercept and gradient to predict the Vp/Vs ratio and S-wave velocity logs in the South Caspian Sea. Furthermore, we observed that the AVO-derived attributes such as fluid factor and gas indicator are more sensitive to SWF zones especially in the channel systems. The reason lies in the fact that rock properties of SWF zone is similar to the ones of gaseous sandy zone. Based on our analysis and the criteria of SWF, we observed that the low values of the S-wave velocity and high values of the Vp/Vs ratio logs are consistent with the low value of gamma-ray and low volume of the shales within the range of 825–925&#xa0;ms in our dataset. This interval which contain the buried channel system give us a high value for the fluid factor and gas indicator. Our results confirm that S-wave velocity log prediction using the AVO method is a reliable approach to identify unconsolidated sandy zones. This emphasis the usefulness of our proposed approach to reduce drilling risk by identifying SWF geohazard zones.</p>

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Identification of shallow water flows (SWF) geohazard in the deep-water southern Caspian basin, Iran: application of geophysical attributes and prediction of S-wave velocity log

  • 期刊论文

  • 发表日期：

    2026年6月2日

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  • Zohre Noorbakhsh Razmi,
  • Naser Hafezi Moghaddas,
  • Mohammad Reza Saberi,
  • Nasser Keshavarz Faraj Khah,
  • Farhad Nafisi,
  • Ali Pilevari,
  • Sayyed Reza Moussavi Harami

摘要

Shallow Water Flow (SWF) presence in the channel systems of the South Caspian Sea is confirmed by different researches and drilling evidences. SWF is a shallow drilling geo-hazard which associated with unconsolidated overpressure sands. When the drill bit reaches these zones, a large volume of overpressure water and sands flow into the wellbore, and causes drilling hazards and accidents. This introduce different challenges for logging operations in these zones, especially for acquiring S-wave velocity logs (Vs) which is necessary for predrilling investigation on the SWF zones. In this study, the cross-plots of Amplitude Versus Offset (AVO) were used to derive attributes such as intercept and gradient to predict the Vp/Vs ratio and S-wave velocity logs in the South Caspian Sea. Furthermore, we observed that the AVO-derived attributes such as fluid factor and gas indicator are more sensitive to SWF zones especially in the channel systems. The reason lies in the fact that rock properties of SWF zone is similar to the ones of gaseous sandy zone. Based on our analysis and the criteria of SWF, we observed that the low values of the S-wave velocity and high values of the Vp/Vs ratio logs are consistent with the low value of gamma-ray and low volume of the shales within the range of 825–925 ms in our dataset. This interval which contain the buried channel system give us a high value for the fluid factor and gas indicator. Our results confirm that S-wave velocity log prediction using the AVO method is a reliable approach to identify unconsolidated sandy zones. This emphasis the usefulness of our proposed approach to reduce drilling risk by identifying SWF geohazard zones.