Rock Solid Images

Gas Hydrates

Gas hydrates are solids comprised of a hydrogen-bonded water lattice with entrapped molecules of gas. Gas hydrate reservoir characterization is, in principle, no different from traditional hydrocarbon reservoir characterization but, gas hydrates present a unique problem. While the overall thickness of the gas hydrate column may be hundreds of meters, the hydrates often occur in multiple thin layers of high porosity sand between alternating layers of lower porosity silt or as thicker more blocky sand formations. Determining the total volume of hydrates present in the stack of sands or varying thicknesses and properly characterizing these hydrates is a problem that Rock Solid Images has thoroughly researched for years and developed methods for the successful prediction, estimation and characterization of gas hydrates.

Rock Solid Images Experience

Rock Solid Images has been engaged in Research & Development into gas hydrate characterization using rock physics modeling and seismic attribute analysis since 2002. This experience has mainly been conducted in the McKenzie Delta, Northwest Territories, Canada and also offshore Japan in the Nankai Trough – specifically: Tokaioki, Kumamonda and Atsumi Areas

In both regions, data from multiple wells were used to establish and calibrate rock physics models that were subsequently applied to large volumes of seismic data to map the hydrate volume and rock physics transforms were developed to map gas saturation from seismic-derived attributes.

In addition to drawing upon its experience of characterizing gas hydrates via the use of elastic attributes, Rock Solid Images has developed two key technologies that can be adapted to gas hydrate characterization.

The first, developed during the Lithology and Fluid Prediction Project, is the ability to examine the inelastic behavior of reservoir properties, e.g. gas hydrate saturation, by modeling p-wave and s-wave attenuation (Qp, Qs) at the well-bore. This technology, which was recently awarded a US Patent (#7088639) and enables attenuation attributes derived from the seismic data to be calibrated to well data.

Secondly, Rock Solid Images has developed a new class of seismic attributes that have been specifically engineered for characterizing gas hydrates; they are termed “cumulative attributes”, or CATTs, and are obtained by a repeated integration of a seismic trace. This new approach opens an avenue for formally addressing the issue of “net-to-gross” in gas hydrate reservoirs as well as in conventional hydrocarbon deposits. This work is funded in part by the US Department of Energy as Seismic Gas Hydrate Quantification by Cumulative Attributes (CATTs) in the DOE/NETL Methane Hydrate Project.

Generalized Workflow

• Well Log Conditioning
• Geophysical Well Log Analysis
• Rock Physics Diagnostics
• Pre-Stack Seismic Data Conditioning
• Avatar
• Welltie
• Lithology and Fluid Prediction
• Simultaneous Inversion
• Seismic Attribute Calculation & Neural Network-Based Seismic Facies Classification
• Volume-Based Visualization and Interpretation

Data Requirements

• PSTM, NMO-corrected seismic gathers, angle stacks, full stacks
• PSTM velocity volume
• Interpreted surfaces
• LAS curves and supporting information for wells in each field
• VSP data, if available
• Any available information on expected lithologies, fluid properties, and pressure

Deliverables

• Conditioned log data for geophysical purposes
• Fluid Substitution Models and Synthetic Seismograms
• Effective Medium Models
• All individual seismic attribute volumes, e.g. Intercept, Gradient, Wideband Impedances, attenuation (intrinsic and extrinsic) attributes
• Classified seismic facies volume
• Volumetric estimates of gas hydrates and free gas.
• Predicted gas saturation volume

Relevant Publications

•  Rock physics of a gas hydrate reservoir
• 2003 - Jack Dvorkin, Amos Nur, Stanford University, Richard Uden and Turhan Taner
•  Seismic wave attenuation in a methane hydrate reservoir
• 2004 - Jack Dvorkin and Richard Uden
•  The challenge of scale in seismic mapping of hydrate and solutions
• 2006 - Jack Dvorkin and Richard Uden
•  Seismic reflections of gas hydrate from perturbational forward modeling
• 2006 - Ingrid Cordon, Stanford University, Jack Dvorkin, and Gary Mavko