SEISMIC DETECTION OF GAS HYDRATES IN THE NORTHERN GULF OF MEXICO USING INVERSION AND ROCK PHYSICS

Jianchun Dai, Robert Kleinberg, Haibin Xu and Nader Dutta
Schlumberger, Reservoir Services and Data Consulting Services
3600 Briarpark Drive, Houston, TX 77042 USA

Whether we treat gas hydrate as potential resource of energy or hazards, locating it subsurface requires the use of seismic technology. In this abstract, we discuss a five-step, integrated workflow that enables us to identify and quantify gas hydrates in the deepwater Gulf of Mexico (GOM). It includes: 1). Re-processing conventional 3-D seismic data at high resolution using an amplitude-preserving flow with pre-stack time migration, 2) a detailed stratigraphic evaluation to identify potential hydrate zones, 3) seismic attribute analysis to further delineate anomalous zones, 4) full waveform pre-stack inversion (FWPI) to characterize acoustic properties of gas hydrates in 1D (Mallick, 1995, Mallick 1999) and map in 3D using hybrid inversion (HI) technique (Dutta, 2002, Mallick & Dutta, 2002), and 5) quantitative estimation of gas hydrate saturation using rock property models. We illustrate the procedure using 3D seismic data, and estimate gas hydrate saturations in two study areas in the northern deepwater GOM.

A critical component of the current work deals with evaluation of rock models containing gas hydrates. Although we do not propose any new model, we do evaluate the numerical predictions of some of the key rock models with gas hydrates and validate those with well log data from Mallik and Blake Ridge wells. We find that a model in which the gas hydrate is a part of the rock framework produces consistent results as compared with well log data. This model is also found to be consistent with the recently available NMR data.