For deep-water Gulf of Mexico, accurate salt geometry is criticaltosubsaltimaging.Thisrequiresthedefinitionofboth externalandinternal saltgeometries.Inrecentyears,external salt geometry (i.e., boundaries between allochthonous salt and background sediment) has improved a great deal due to advances in acquisition, velocity model building, and migration algorithms. But when it comes to defining internal salt geometry (i.e., intrasalt inclusions or dirty salt), no efficient method has yet been developed. In common industry practices, intrasalt inclusions (and thus their velocity anomalies) are generally ignored during the model building stages. However, as external salt geometries reach higher levels of accuracy, it becomes more important to consider the once-ignored effects of dirty salt. We have developed a reflectivity-based approach for dirty salt velocity inversion. This method takes true-amplitude reverse time migration stack volumes as input, then estimates the dirty salt velocity based on reflectivity under a 1D assumption. Results from a 2D synthetic data set and a real 3D Wide Azimuth data set demonstrated that the reflectivity inversion scheme significantly improves the subsalt image for certain areas. In general, we believe that this method produces a better salt model than the traditional clean salt velocity approach.
[1]
Yu Zhang,et al.
Practical issues of reverse time migration: true-amplitude gathers, noise removal and harmonic-source encoding
,
2008
.
[2]
G. H. F. Gardner,et al.
FORMATION VELOCITY AND DENSITY—THE DIAGNOSTIC BASICS FOR STRATIGRAPHIC TRAPS
,
1974
.
[3]
Børge Arntsen,et al.
Modeling of "dirty Salt"
,
2008
.
[4]
Shuo Ji,et al.
Mad Dog TTI RTM: Better than Expected
,
2009
.
[5]
J. Sun,et al.
Practical issues in reverse time migration: true amplitude gathers, noise removal and harmonic source encoding
,
2009
.
[6]
A. Tarantola.
Inversion of seismic reflection data in the acoustic approximation
,
1984
.
[7]
Yu Zhang,et al.
Traveltime information-based wave-equation inversion
,
2009
.