Geomechanical Performance of Hydrate-bearing Sediments in Offshore Environments

" This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implies, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacture , or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. " 2 List of Figures Figure 1 – Diagram showing the effects of gas hydrate dissociation on oceanic hill slope failures and gas release. Figure 9 – Original (unbalanced) and balanced Oct-tree. In a balanced oct-tree, two adjacent cubes are always no more than one generation apart.. Executive Summary The objective of this multi-year, multi-institutional research project is to develop the knowledge base and quantitative predictive capability for the description of geomechanical performance of hydrate-bearing sediments (hereafter referred to as HBS) in oceanic environments. The focus is on the determination of the envelope of hydrate stability under conditions typical of those related to the construction and operation of offshore platforms. We have developed a robust numerical simulator of hydrate behavior in geologic media by coupling a reservoir model with a commercial geomechanical code. We are also investigating the geomechanical behavior of oceanic HBS using pore-scale models (conceptual and mathematical) of fluid flow, stress analysis, and damage propagation. We are using data from the literature and we are conducting laboratory studies to generate data to (i) evaluate the conceptual pore-scale models, (ii) calibrate the mathematical models, (iii) determine dominant relations and critical parameters defining the geomechanical behavior of HBS, and (iv) establish relationships between the geomechanical status of HBS and the corresponding geophysical signature. Four organizations, (SLB), who are involved in this project.. The objective of the UC Berkeley work is to develop a grain-scale model of hydrate-bearing sediments. Hydrate dissociation alters the strength of HBS. In particular, transformation of hy-drate clusters into gas and liquid water weakens the skeleton and, simultaneously, reduces the effective stress by increasing …