The Success Application of Weight Stack AVO Attribute for Channel Feature Imaging in Horst Trend Area, Arthit Field, Thailand
Platform “Alpha” is the first development platform in South Arthit field, locating in Horst Trend Area (HTA) of the North Malay Basin. Gas-bearing sands are in Formation 2 (FM2) Units 2E to 2A, in three prospects. The main prospect is a 4-way dipping structural closure in shallow targets and a nose trap in deeper target. The other two smaller prospects are in a different fault blocks. Results from two reference-wells reveal gas accumulations in the main prospect, and FM2 as the major reservoirs is fluvial sediment. Geophysical interpretation to confirm the presence of gas-bearing sands in FM2, is critical for South Arthit field developments; the interpretation, however, is challenging where seismic attributes extracted from the conventional seismic i.e., RMS amplitude and coherency cannot provide clear images for geo-bodies. Therefore, a technique using a Weight Stack AVO (WSAVO) attribute is selected to map sand bodies in shallow targets. This technique can reduce uncertainties in identifying the reservoir bodies and can guide for appropriate well planning for the platform. The WSAVO cube was generated to classify the interface of possible sand and non-sand features using the relationship of intercept and gradient, that was derived from geophysical logs modeling for all possible lithology interfaces. Then, the function was applied on intercept and gradient, which are calculated from angle stack seismic data. In the WSAVO attribute, positive values represent sand while negative values represent non-sand. The WSAVO attribute was generated to image channel-like features and possible sand bodies. Consequently, both sand bodies from WSAVO attribute maps and channel sand orientations from well correlations, were used as guides for well targeting. Sixteen wells were drilled in Alpha platform. Most of them encountered sands by indicating through positive amplitude in the WSAVO attribute; these wells show good results between 45 to 100 meters of pays. A few wells, as expected encountered only 15 to 25 meters of pay due to less sand development, and this corresponds to the figure from WSAVO attribute that shows less positive values. The result of this study shows that the WSAVO attribute is an effective tool that can image sand bodies and help guiding suitable locations for development well in the Horst Trend. Therefore, the WSAVO technique is recommended for future exploration and development activities to increase the success ratio of the project.
AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015