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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

The Role of Non-Seismic Methods in near-Surface Solutions: Applications of Seismic-Gravity Joint Inversion and Redatuming in South Rub Al-Khali, Saudi Arabia

Danielle Colombo1; Pieter van Mastrigt2; Abdulmohsin Al-Dulaijan2; Marco Mantovani3; Maurizio Sfolciaghi3; Tarek Nafi4

(1) Saudi Aramco EXPEC-Advanced Research Centre, Dhahran, Saudi Arabia.

(2) South Rub Al Khali Company Ltd, Al-Khobar, Saudi Arabia.

(3) WesternGeco, Milan, Italy.

(4) WesternGeco, Al-Khobar, Saudi Arabia.

Onshore seismic data from the Middle East are adversely affected by near surface and intermediate depth velocity anomalies. The correct estimate of the near-surface velocity field is fundamental to obtain reliable seismic images. Conventional velocity model building workflows based on refracted arrivals (i.e. First Breaks - FB) fail to appropriately reconstruct the shallow velocity complexities in the presence of large velocity inversions, sharp lateral velocity changes and noisy FB. In such cases, the integration of seismic with additional geophysical measurements (i.e. gravity-EM) can solve the shallow velocity modeling problem. Simultaneous Joint Inversion (JI) is an elegant and analytic method to address geophysical data integration. It is implemented in this paper for velocity model building in South Rub Al-Khali by taking advantage of the availability of high-resolution gravity data coincident with the seismic acquisition. The analyzed 2D seismic lines are sampling different near-surface geologic conditions such as dunes, sub-cropping carbonates and karsts. This corresponds to various degrees of complexity in the near surface velocity field and related distortions introduced in the seismic image when a conventional “statics” approach is used. An alternative approach to statics solutions is then explored by simultaneous JI of FB and gravity data residuals for the shallow velocity and density fields. Pre-stack wave-equation redatuming (WED) is then used to model and remove the effects of complex velocity patterns from the seismic data. Various degrees of improvement are obtained with the discussed workflow depending on the severity of the near-surface velocity complexities and shallow geologic conditions. The analysis of the results allows to identify specific roles for non-seismic methods for the solution of near surface problems in land seismic data processing.