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Macesanu C.,Wave Imaging Technology Inc.
SEG Technical Program Expanded Abstracts | Year: 2011

Reverse time migration in non-homogenous transverse isotropic media has recently become a standard procedure in imaging complex areas. The predominant computational framework used is that of the pseudo-acoustic approximation to the elastic equations, where the shear wave velocity is set to zero. There are several implementations described in literature. In this paper, we discuss the proper way to generalize the equations applicable to a homogenous TTI medium where the direction of the symmetry axis is constant to an inhomogenous medium, and we compare the numerical results we obtain with those obtained by alternate methods. © 2011 Society of Exploration Geophysicists.

A discussion covers the detection of excessive pressure in and under the pre-salt by imaging in the depths with base in the wave equation as a means to save time and expense in drilling wells. Topics include introduction; the method; normalization of the wave equation of the amplitude of the salt base; and analysis of velocity focusing of the wave equation method (WEM). The method of detection of excess pressure of two phases was tested with success in the BP reference model of velocity. The petroleum deposits in the pre-salt may represent the most significant base of remaining conventional petroleum resources in the US. However, as a function of geo-technological risks and engineering challenges, the recovery of this resource is nonconventional. Among the principal geophysical risks there are elevated pressures of pores directly under the salt, representing a risk to safety and to drilling, disabling the completion of a well at 30,000 ft (9,144 m) depth, relatively common in drilling in the pre-salt in the Gulf of Mexico. Because drilling costs in the Gulf of Mexico are normally over $(US) 100 million, there is great financial interest to reduce the added costs due to unforeseen appearance of excess pressure in the pre-salt. The system proposed before drilling to detect the excessive pressure under the base of the salt uses a seismic velocity of the pre-salt as substitute for the excess pressure. It normally costs less than $(US) 1 million and complements the detection of the excess pressure based on the vertical seismic profile (VSP) that is more costly.

Higginbotham J.H.,Wave Imaging Technology Inc. | Brown M.P.,Wave Imaging Technology Inc. | Ramirez O.,Wave Imaging Technology Inc.
SEG Technical Program Expanded Abstracts | Year: 2011

Evidence is provided in support of a single parameter hyperbolic "mudrock" line to relate S-wave velocity to P-wave velocity. This relation is shown to work for carbonate rocks and further evidence is given suggesting that the relation may work for general rock types. The evidence also shows that the hyperbolic mudrock line parameter changes slowly with rock type. Since the parameter changes slowly with rock type and can be related to the ratio of the AVA gradient and intercept, it is possible to predict a background value for the ratio of gradient to intercept that must be satisfied within a given tolerance. This allows the calibration of gradient to intercept for the seismic volume as a whole so that local anomalies are more accurately represented. © 2011 Society of Exploration Geophysicists.

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