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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

Integration of Seismic and Well Data to Characterize Tar Mat in Carbonate Reservoirs

Tarek M. Matarid1; Christoph T. Lehmann1; Khalil I. Hosani1; David Cobb1; Adrian Smith2

(1) FDD-NF, ADMA-OPCO, Abu Dhabi, United Arab Emirates.

(2) CGGVeritas, Abu Dahbi, United Arab Emirates.

This paper presents an integrated approach using the 3D seismic and well data to enhance our understanding of the lateral and/or vertical distribution of the Tar Mat.

The study carried out utilizing a recent stat-of-the-art 3D ocean-bottom seismic technology (OBC) with high resolution and high quality offshore Abu Dhabi and several wells with excellent suit of logs, thousand feet’s of core data and geochemical studies.

A Model Based Acoustic Impedance Inversion was conducted following the 3D seismic reservoir mapping. A comprehensive porosity prediction analysis and validation were conducted for each well. The observation of the abrupt destruction of porosity in the well data associated with Tar Mat presence in the core did trigger the idea of computing the porosity derivative cube from the seismically predicted porosity cube. This significant and dramatic change in porosity associated with the Tar presence suggested that this porosity destruction might be visible in the seismically predicted porosity cube.

The derivative of the porosity volume after post-stack Impedance inversion was generated to visualize the rate of changes in porosities. The high negative porosity derivative in a highly porous section may represent the top of a tar mat. The high positive porosity derivative values also can be used to indicate Tar free developed porosity. Good match was found between the generated porosity derivative volume and the top tar from wells.
The cross-plots between the seismic acoustic impedance and porosity for all wells (including Tar wells) suggesting difficulty to distinguish between Tar and lithology change for porosities less than 10%.

The lateral Tar distribution was found to be predictable utilizing post stack 3D seismic acoustic impedance inversion followed by porosity prediction and its derivative volume.

The seismic Tar mat prediction on the porosity volume has provided new and important interpretation of the top of the Tar in the inter-well region and for the static model. Different Tar prediction schemes from seismic have been evaluated for further refinment. Differentiating in tight rocks and to recognize the remaining porosity plugged with tar remains ambiguous in the lower reservoir tight rocks. Therefore, a detailed sampling and geochemical analysis of the tar is being performed on the core to determine the base of the tar.