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Reducing Depth Uncertainties below Gas Cloud: Time-to-depth Conversion Methodology
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, EAGE Workshop on Velocities: Reducing Uncertainties in Depth, Apr 2016, Volume 2016, p.1 - 3
Abstract
Currently it is estimated that large percentage of PETRONAS’ reservoirs are affected by gas masking. Reserves estimation accuracy can be improved with enhancement in the structural interpretation through gas cloud. Significant velocity changes in the overburden can cause simple time-to-depth conversions to be in error. Gas cloud (PP) Time-to-Depth Conversion Methodology is carried out to develop and provide advanced standard procedure specifically for converting time structure map to depth in gas cloud affected areas. Synthetic and real data are tested to analyse the complexity and quantify the velocity variation in the area of shallow gas. It is important to establish proper velocity control and predict uncertainty in order to optimize time-to-depth conversion accuracy. Provided that there is no depth processing data, we have demonstrated that the proposed workflow provides high depth accuracy in the area under the gas cloud. We have shown that this method takes into consideration of both seismic velocity and wells provided that there is well or no well inside the gas cloud. With having well inside the gas cloud, there is only 1–4% depth error compared to without well inside gas cloud, 15–37% error.