Description: Commercial utilization of methane hydrate deposits in the seabed: The vast amount of natural gas bound in methane hydrates is considered as future energy resource by a growing number of states and companies in South-East Asia and North America. Successful field production tests showed that gas hydrates can be dissociated in the sub-surface by heat addition and pressure reduction while the released gas is produced via conventional drill wells. Laboratory studies demonstrate that CO2 from coal power plants can be applied to liberate methane from the hydrate structure and produce natural gas while the injected CO2 is safely stored as hydrate in the sub-surface. The commercial exploitation of sub-seabed gas hydrates may start in the next decade pending on the success of field production tests off Japan scheduled for 2012 and 2014. Specific environmental risks are associated with the future utilization of gas hydrates. These include the extinction of special benthic ecosystems relying on methane from hydrates as energy source, the triggering of slope failure, and leakage of greenhouse gases into the marine environment. Suitable measures have to be taken to avoid these risks. An appropriate legal framework should be established at the international level to meet the specific challenges and risks associated with the commercial use of gas hydrates in the marine environment.

Description: Within the German gas hydrate initiative SUGAR, we have developed a new tool for predicting the formation of sub-seafloor gas hydrate deposits. For this purpose, a new 2D/3D module simulating the biogenic generation of methane from organic material and the formation of gas hydrates has been added to the petroleum systems modeling software package PetroMod®. T ypically, PetroMod® simulates the thermogenic generation of multiple hydrocarbon components including oil and gas, their migration through geological strata, and finally predicts the oil and gas accumulation in suitable reservoir formations. We have extended PetroMod® to simulate gas hydrate accumulations in marine and permafrost environments by the implementation of algorithms describing (1) the physical, thermodynamic, and kinetic properties of gas hydrates; and (2) a kinetic continuum model for the microbially mediated, low temperature degradation of particulate organic carbon in sediments. Additionally, the temporal and spatial resolutions of PetroMod® were increased in order to simulate processes on time scales of hundreds of years and within decimeters of spatial extension. As a first test case for validating and improving the abilities of the new hydrate module, the petroleum systems model of the Alaska North Slope developed by IES (currently Shlumberger) and the USGS has been chosen. In this area, gas hydrates have been drilled in several wells, and a field test for hydrate production is planned for 2011/2012. The results of the simulation runs in PetroMod® predicting the thickness of the gas hydrate stability field, the generation and migration of biogenic and thermogenic methane gas, and its accumulation as gas hydrates will be shown during the conference. The predicted distribution of gas hydrates will be discussed in comparison to recent gas hydrate findings in the Alaska North Slope region.

Description: The accumulation of methane hydrate in marine sediments is basically controlled by the accumulation of particulate organic carbon at the seafloor, the kinetics of microbial organic matter degradation and methane generation in marine sediments, the thickness of the gas hydrate stability zone (GHSZ), the solubility of methane in pore fluids within the GHSZ and the ascent of deepseated pore fluids and methane gas into the GHSZ. Our present knowledge on these controlling factors is discussed and new estimates of global sediment and methane fluxes are presented. A new transport-reaction model is applied at a global grid defined by these up- dated parameter values. The model yields an improved and better constrained estimate of the global inventory of methane gas hydrates in marine sediments (3000 ± 2000 Gt of methane carbon).

Description: The production of natural gas via injection of fossil-fuel derived CO2 into submarine gas hydrate reservoirs can be an example of tapping a hydrocarbon energy source in a CO2-neutral manner. However, the industrial application of this method is technically challenging. Thus, prior to feasibility testing in the field, multi-scale laboratory experiments and adapted reaction-modeling are needed. To this end, high-pressure flow-through reactors of 15 and 2000 mL sample volume were constructed and tested. Process parameters (P, T, Q, fluid composition) are defined by a fluid supply and conditioning unit to enable simulation of natural fluid-flow scenarios for a broad range of sedimentary settings. Additional Raman- and NMR-spectroscopy aid in identifying the most efficient pathway for CH4 extraction from hydrates via CO2 injection on both microscopic and macroscopic level. In this study we present experimental set-up and design of the highpressure flow-through reactors as well as CH4 yields from H4-hydrate decomposition experiments using CO2-rich brines and pure liquefied CO2.

Description: Results from two recent field trials, onshore in the Alaska permafrost and in the Nankai Trough offshore Japan, suggest that natural gas could be produced from marine gas hydrate reservoirs at compatible yields and rates. However, both field trials were accompanied by different technical issues, the most striking problems resulting from un-predicted geomechanical behaviour, sediment destabilization and catastrophic sand production. So far, there is a lack of experimental data which could help to understand relevant mechanisms and triggers for potential soil failure in gas hydrate production, to guide model development for simulation of soil behaviour in large-scale production, and to identify processes which drive or, further, mitigate sand production. We use high-pressure flow-through systems in combination with different online and in situ monitoring tools (e.g. Raman microscopy, MRI) to simulate relevant gas hydrate production scenarios. Key components for soil mechanical studies are triaxial systems with ERT (Electric resistivity tomography) and high-resolution localstrain analysis. Sand production control and management is studied in a novel hollow-cylinder-type triaxial setup with a miniaturized borehole which allows fluid and particle transport at different fluid injection and flow conditions. We further apply a novel large-scale high-pressure flow-through triaxial test system equipped with μ-CT to evaluate soil failure modes and triggers relevant to gas hydrate production and slope stability. The presentation will emphasize an in-depth evaluation of our experimental approach, and it is our concern to discuss important issues of translating laboratory results to gas hydrate reservoirs in nature. We will present results from high-pressure flow-through experiments which are designed to systematically compare soil mechanical behaviour of gas hydrate-bearing sediments in relevant production scenarios focusing on depressurization and CO2 injection. Experimental datasets are analyzed based on numerical models which are able to simulate coupled process dynamics during gas hydrate formation and gas production.

Description: Gas production from gas hydrate-bearing sediments has been attracting global interests because of its potential to meet growing energy demand. Methane (CH4) gas can be extracted from CH4 hydrates by depressurization, thermal stimulation or chemical activation. However, it has never been produced on a commercial scale and the past field trials faced premature termination due to the technical difficulties such as excessive sand flow into the well, a phenomenon known as sand production. One exception is the trial at the Ignik Sikumi, Alaska in 2012, which was conducted by chemical activation followed by depressurization. During the trial, initial sand production ceased after two weeks while CH4 gas production continued for five weeks. The mitigation of sand production is deemed attributed to mechanical or hydraulic effects through formation of CO2-rich gas hydrates. This incident has highlighted the favorable effect of CO2 hydrate formation and needs to incorporate the chemo-processes into existing thermo-hydro-mechanical formulations. This paper presents an analytical formulation to capture the coupled thermo-hydro-chemo-mechanical behavior of gas hydrate-bearing sediments during gas production via CO2 injection. The key features of the formulation include hydrate formation and dissociation, gas dissolution and multiphase flow for both CH4 and CO2, facilitating CH4-CO2 hydrate conversion.

Description: This chapter talks about physicochemical properties of gas hydrate‐bearing sediments. Lab‐based experiments are the most cost‐effective and systematic approach to evaluate physicochemical properties and behavior of gas hydrate‐bearing sediments in a systematic way. Physicochemical property studies were largely focused on measurements with respect to homogeneous and reproducible gas hydrate distributions. The chapter includes overviews of thermodynamic and kinetic constraints of relevant processes of gas hydrate formation, dissociation and conversion, fluid transport in gas hydrate‐bearing sediments, thermal and electrical properties and distribution of gas hydrates. It reviews some flow‐through experimental systems and procedures for studying the behavior of gas hydrate‐bearing sediments with different research objectives. The chapter provides a brief overview on available systems for high‐resolution online fluid monitoring, as well as tools for a destruction‐free analysis of the multiphase sample with emphasis on tomographic techniques.