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: The Black Sea has undergone several limnic and marine stages due to fluctuations in the global sea level. The exchange of saline water from the Mediterranean Sea to the Black Sea through the Bosporus Strait was interrupted when the sea level dropped below the Bosporus sill. This induced limnic conditions, while marine conditions were established after the reconnection to saline Mediterranean seawater. Extended river fan systems developed during sea level low-stands, providing large amounts of organic material being buried by rapid sedimentation on the slopes of the Black Sea margins. The biogenic degradation of this material produces most of the methane gas expelled into the anoxic water column today. This largely happens by ubiquitous cold vents at ~700 m water depth (i.e. at the stability boundary of methane hydrates) and by mud volcanoes in ~2000 m water depth. A significant amount of gas is expected to accumulate in the sediment within the methane hydrate stability zone. However, bottom-simulating reflectors, the seismic indicator for gas hydrates, are not found everywhere along the margin. Recent analyses of the Danube and Dniepr fans have revealed a discontinuous gas hydrate formation in an area with no active seeps, while areas of active seepage located in the vicinity of BSR reflections held no gas hydrates. In addition, the ongoing diffusion of salt into the uppermost Black Sea sediment pore space since the last glacial maximum further reduces the volume of the gas hydrate stability zone. Estimates of the total amount of gas stored in gas hydrates therefore require a detailed structural analysis prior to regional- or basin-scale modelling attempts.