Exploration for gas hydrates in the deepwater, northern Gulf of Mexico: Part II. Model validation by drilling

Abstract

This study examines the accuracy of the predictions of gas hydrate saturations made based on five-step analysis of 3D seismic data prior to 2005 drilling, logging, conventional coring, and pressure core sampling through the gas hydrate stability zone at two focus sites in the northern Gulf of Mexico. These predictions are detailed in Part I (2008). Here we conduct a detailed analysis of the gas hydrate saturation using both resistivity and P-wave velocity log data and analyze the pre-drilling predictions, which were made almost exclusively on the basis of seismic data, with no local logging control. Well log measurements, core data analysis, and pressure core-degas experiments all indicated general agreement with the pre-cruise analysis regarding the location and approximate concentration of gas hydrates in the sediments. We find that seismic predictions are generally consistent with log-based estimates after upscaling to seismic frequencies. We recalibrated the pre-drill model based on the new field data so that a refined version of the model could be used for future work.