Gas Hydrate Deposits Research Articles

Numerical simulations of depressurization-induced gas production from gas hydrates using 3-D heterogeneous models of L-Pad, Prudhoe Bay Unit, North Slope Alaska

Gas production potential is estimated using a three-dimensional reservoir model based on gas hydrate deposits located in the Prudhoe Bay region of the Alaska's North Slope. The model incorporates two hydrate-bearing sand units using detailed reservoir geological and structural information obtained from past and recent drilling programs. Geostatistical porosity models, conditioned to log data from 78 wells drilled in the vicinity of the Prudhoe Bay “L-Pad,” were developed, providing 3D heterogeneity in porosity, porosity-dependent hydrate saturation, and intrinsic permeability. The simulations utilize both vertical and inclined wellbores to induce depressurization of the reservoir at a constant bottom-hole pressure. The results show the superior performance of the inclined well design. Average gas production rates during the first five years were ∼6.0 × 104 ST m3/day (∼2.1 MMSCF/day) and ∼2.7 × 104 ST m3/day (∼1.0 MMSCF/day) for incline and vertical wells, respectively. After 30 years 5.3 × 108 − 5.7 × 108 ST m3 (18.6–20.2 BSCF) and 6.2 × 108 − 6.4 × 108 ST m3 (22.0–22.7 BSCF) gas were produced using the vertical and inclined well configurations, respectively. The analysis reveals that 2D reservoir models with homogeneous representations for porosity and hydrate saturation significantly underestimate production potential. The heterogeneity implemented in this work provides complex porous network and preferential pathways for mobile phase flow to a producing well. Consequently, no secondary hydrate formation around a wellbore is predicted in contrast to models that utilize uniform porosity and hydrate saturation distributions.

Cenozoic lithogenesis in the Baikal rift zone

New data on the geological history and Cenozoic lithogenesis in depressions of the Baikal rift zone are considered with areas adjacent to Lake Baikal as example. In this region, rifting developed during the plain (Late Oligocene‒Early Pliocene) and orogenic (Late Pliocene‒Holocene) stages and was accompanied by the accumulation of plain coaliferous fan and orogenic molasses formations, respectively. The examination of Quaternary sequences in the Baikal region reveals that deposition and postsedimentary transformations of riftogenic sediments were intensely influenced by deep-seated water sources of the so far undivided stratal‒infiltration, elision, and exfiltration types, according to the classification in (Kislyakov and Shchetochkin, 2000). Deep processes in this region determined the elevated heat flow, volcanism, and extensive discharge of hydrothermal solutions and gas fluids. In our opinion, gaseous‒hydrothermal activity stimulated the formation of hydrothermal‒sedimentary rocks (dolomitic and calcitic travertines, geyserites, aluminosulfates), the accumulation of diatomaceous and carbonaceous oozes in Baikal, and the formation of a large methane gas hydrate deposit.

Manganese enrichments near a large gas‐hydrate and cold‐seep field: a record of past redox and sedimentation events

AbstractThe spatial distribution, mineralogy, and origin of manganese enrichments surrounding a large gas hydrate and cold seep field (Mississippi Canyon 118, Gulf of Mexico) are investigated in this study, to better constrain their biogeochemical context in deep‐sea sediments and to assess how gas hydrates may alter such records. Manganese depth profiles from 10 sediment cores, documented using centimetre‐scale X‐ray fluorescence core scanning, display highly‐enriched 1 to 10 cm thick layers. These manganese‐rich layers are more numerous, but of lower concentration, in close proximity to the field, and show no consistent relationship with sedimentology (clay vs. carbonate content) or the established chronostratigraphic framework at the site. X‐ray diffraction and sequential dissolution procedures indicate that the manganese enrichments are authigenic carbonates, which formed along a palaeo redox boundary during periods of prolonged steady‐state conditions. The hypothesis that spatial heterogeneity of this manganese record is linked to the nearby gas hydrate and cold seep field, by influencing redox conditions and/or sedimentation processes, is investigated here. Results are consistent with more frequent interruption of steady‐state sedimentation in closer proximity to the salt‐tectonic induced bathymetric mound, which contains the active cold seeps and gas hydrate deposits. Thus, spatial mapping of manganese enrichment horizons provides a tool to reconstruct sedimentation surrounding these volatile sea bed features, yielding a measure of past activity of gas hydrates and cold seeps.

Dynamic behavior of hydrate dissociation for gas production via depressurization and its influencing factors

Natural gas hydrate can be a potential energy resource to be developed in the near future. Gas production is feasible via depressurization, which has been applied for gas extraction from gas hydrate deposits in Messoyakha. Understanding the dynamic behavior of hydrate dissociation, i.e. the variations of pressure, temperature and gas production rate during the depressurization process, is important for process optimization and predications of geological hazards caused by hydrate dissociation. In this study, methane hydrate formation and dissociation experiments were conducted using a self-designed apparatus under different conditions in simulated porous media. Hydrate formation in sand packs with different hydrate saturations were simulated, and the dynamic behavior of hydrate dissociation process and its influencing factors were analyzed, illustrated by gas production rate, accumulated gas production, and the associated temperature and pressure changes in the gas production process. The experimental results show that hydrate dissociation can be inhibited in the early stage if the production pressure is low, which can cause a decrease of the local temperature in the dissociation zone and restabilize the hydrate, and the efficiency of gas production can be improved by reducing the production pressure gradually. High permeability of the sand packs is conductive to increase gas production rate, but it can also induce a fast decrease on temperature and pressure. The time for hydrate dissociation becomes longer in the case of a higher hydrate saturation, and depressurization along with other stimulation methods, such as thermal stimulation, may be required for efficient gas production.

Theoretical modeling of gas extraction from a partially gas-saturated porous gas-hydrate reservoir with respect to thermal interactions with surrounding rocks

A theoretical model has been constructed for the gas-hydrate reservoir that represents a unique natural chemical reactor, and the principal possibility of the full extraction of gas from a hydrate due to the thermal reserves of the reservoirs themselves and the surrounding rocks has been analyzed. The influence exerted on the evolution of a gas hydrate reservoir by the reservoir thicknesses and the parameters that determine its initial state (a temperature, pressure, hydrate saturation) has been studied. It has been established that the shortest time of exploitation required by the reservoirs with a thickness of a few meters for the total hydrate decomposition is recorded in the cyclic regime when gas extraction alternated with the subsequent conservation of the gas hydrate deposit.

A method developed to increase technological and ecological efficiency of gas production from hydrate deposits

Despite some international experience in gas production from gas hydrate deposits, mining companies are faced with a number of issues that have not been resolved so far. Among these issues, the particularly complex ones are technological problems and environmental efficiency. In the present article, there is a substantiation of the need to consider the particular structure of primary (marine) and secondary (land) gas hydrate deposits while choosing the method of extracting gas from them.The analysis of the practical experience of extracting gas from gas hydrate deposits has proved that one of the most effective methods of ecological production of methane from marine gas hydrate deposits might be the method of substitution. The method of decompression (reduced pressure) is the most effective one for development of secondary (land) deposits.The suggested method of technological planes has helped estimate the effectiveness of using hydrate substitutes such as hydrogen sulphide and carbon dioxide. This method has proved a certain advantage of hydrogen sulphide over carbon dioxide due to a larger conventional area of the technological plane and, therefore, a safer range of values of the technological parameters of gas extraction.The obtained results can be used in implementing the technology of gas extraction from hydrate deposits, especially in applying the substitution method to developing offshore deposits.

Gas hydrate accumulations related to focused fluid flow in the Pegasus Basin, southern Hikurangi Margin, New Zealand

The Hikurangi Margin, east of the North Island of New Zealand, is known to contain significant deposits of gas hydrates. This has been demonstrated by several multidisciplinary studies in the area since 2005. These studies indicate that hydrates in the region are primarily located beneath thrust ridges that enable focused fluid flow, and that the hydrates are associated with free gas. In 2009–2010, a seismic dataset consisting of 2766 km of 2D seismic data was collected in the undrilled Pegasus Basin, which has been accumulating sediments since the early Cretaceous. Bottom-simulating reflections (BSRs) are abundant in the data, and they are accompanied by other features that indicate the presence of free gas and concentrated accumulations of gas hydrate. We present results from a detailed qualitative analysis of the data that has made use of automated high-density velocity analysis to highlight features related to the hydrate system in the Pegasus Basin. Two scenarios are presented that constitute contrasting mechanisms for gas-charged fluids to breach the base of the gas hydrate stability zone. The first mechanism is the vertical migration of fluids across layers, where flow pathways do not appear to be influenced by stratigraphic layers or geological structures. The second mechanism is non-vertical fluid migration that follows specific strata that crosscut the BSR. One of the most intriguing features observed is a presumed gas chimney within the regional gas hydrate stability zone that is surrounded by a triangular (in 2D) region of low reflectivity, approximately 8 km wide, interpreted to be the result of acoustic blanking. This chimney structure is cored by a ∼200-m-wide low-velocity zone (interpreted to contain free gas) flanked by high-velocity bands that are 200–400 m wide (interpreted to contain concentrated hydrate deposits).

Controlled-source electromagnetic and seismic delineation of subseafloor fluid flow structures in a gas hydrate province, offshore Norway

Deep sea pockmarks underlain by chimney-like or pipe structures that contain methane hydrate are abundant along the Norwegian continental margin. In such hydrate provinces the interaction between hydrate formation and fluid flow has significance for benthic ecosystems and possibly climate change. The Nyegga region, situated on the western Norwegian continental slope, is characterized by an extensive pockmark field known to accommodate substantial methane gas hydrate deposits. The aim of this study is to detect and delineate both the gas hydrate and free gas reservoirs at one of Nyegga's pockmarks. In 2012, a marine controlled-source electromagnetic (CSEM) survey was performed at a pockmark in this region, where high-resolution three-dimensional seismic data were previously collected in 2006. Two-dimensional CSEM inversions were computed using the data acquired by ocean bottom electrical field receivers. Our results, derived from unconstrained and seismically constrained CSEM inversions, suggest the presence of two distinctive resistivity anomalies beneath the pockmark: a shallow vertical anomaly at the underlying pipe structure, likely due to gas hydrate accumulation, and a laterally extensive anomaly attributed to a free gas zone below the base of the gas hydrate stability zone. This work contributes to a robust characterization of gas hydrate deposits within sub-seafloor fluid flow pipe structures.

Experimental set-up design for gas production from the Black Sea gas hydrate reservoirs

Gas hydrate deposits which are found in deep ocean sediments and in permafrost regions are supposed to be a fossil fuel reserve for the future. The Black Sea is also considered rich in terms of gas hydrates. It abundantly contains gas hydrates as methane (CH4 ∼ 80–99.9%) source. In this study, by using the literature seismic and other data of the Black Sea such as salinity, porosity of the sediments, common gas type, temperature distribution and pressure gradient, the optimum gas production method for the Black Sea gas hydrates was selected as mainly depressurization method. It was proposed that CO2/N2 injection as a production method from the potential Black Sea gas hydrates might not be favorable. Experimental set-up (high pressure cell, gas flow meter, water-gas separator, mass balance, pressure transducers and thermocouples) for gas production from the Black gas hydrates by using depressurization method was designed according to the results of HydrateResSim numerical simulator. It was shown that cylindrical high pressure cell (METU Cell) with 30 cm inner length and 30 cm inner diameter with a volume 21.64 L in this study might reflect flow controlled conditions as in the real gas hydrate reservoirs. Moreover, 100 mesh portable separator in METU cell might be very useful to mimic Class 1 hydrate reservoirs and horizontal wells in gas hydrate reservoirs experimentally.

Перспективы нанотехнологий освоения газогидратных ресурсов арктического шельфа России

The paper contains the analysis of hydrocarbonic stocks of the Russian Arctic shelf. The expert quantitative assessment of methane volume in sea deposits of the region (both in absolute expression, and on separate objects) has been presented. Threats from climate change in relation to safety of mineral resources of sea gas-hydrates of the Arctic shelf of Russia have been considered. The economic assessment has been given to the existing technologies of developing sea deposits of gas-hydrates of the shelf; the innovative methods of their development on the basis of application of nanoparticles and nanomotors have been presented. Ключевые слова: Арктика, шельф, газогидраты, экономика, разработка, наночастицы и нанотехнологии.

High-resolution seismic velocity analysis as a tool for exploring gas hydrate systems: An example from New Zealand’s southern Hikurangi margin

The existence of free gas and gas hydrate in the pore spaces of marine sediments causes changes in acoustic velocities that overprint the background lithological velocities of the sediments themselves. Much previous work has determined that such velocity overprinting, if sufficiently pronounced, can be resolved with conventional velocity analysis from long-offset, multichannel seismic data. We used 2D seismic data from a gas hydrate province at the southern end of New Zealand’s Hikurangi subduction margin to describe a workflow for high-resolution velocity analysis that delivered detailed velocity models of shallow marine sediments and their coincident gas hydrate systems. The results showed examples of pronounced low-velocity zones caused by free gas ponding beneath the hydrate layer, as well as high-velocity zones related to gas hydrate deposits. For the seismic interpreter of a gas hydrate system, the velocity results represent an extra “layer” for interpretation that provides important information about the distribution of free gas and gas hydrate. By combining the velocity information from the seismic transect with geologic samples of the seafloor and an understanding of sedimentary processes, we have determined that high gas hydrate concentrations preferentially form within coarse-grained sediments at the proximal end of the Hikurangi Channel. Finer grained sediments expected elsewhere along the seismic transect might preclude the deposition of similarly high gas hydrate concentrations away from the channel.

Investigation of gas hydrate potential of the Black Sea and modelling of gas production from a hypothetical Class 1 methane hydrate reservoir in the Black Sea conditions

Gas hydrate deposits which are found in deep ocean sediments and in permafrost regions are supposed to be a fossil fuel reserve for the future. The Black Sea is also considered rich in terms of gas hydrates. It abundantly contains gas hydrates as methane (CH4∼80–99.9%) source. In this study, by using the literature seismic and other data of the Black Sea such as salinity, porosity of the sediments, common gas type, temperature distribution and pressure gradient, it was estimated that up to 71.8 (median) standard trillion cubic meters (tcm) of CH4 can be available in the Black Sea. Due to biogenic and thermogenic gas potential of the Black Sea, the composition of natural gas may also include ethane (C2H6), propane (C3H8) and other impurities. This is an indication of sI and sII types of hydrate potential in the Black Sea. Moreover, according to the seismic data, single and multiple bottom-simulating reflector (BSR) lines were observed in the literature. Therefore, there is a high potential of Class 1 hydrates (stable hydrate layer and an underlying free gas zone) in the Black Sea. In this study by using HydrateResSim numerical simulator, gas production potentials from a hypothetical Class 1 hydrate reservoir in the Black Sea conditions by depressurization (at different production pressures) and depressurization combined with wellbore heating were simulated. When the depressurization (production) pressure is lower, much more gas is produced but until certain value. If the depressurization pressure is very low, there is a risk of hydrate reformation and ice formation along the wellbore and/or inside the reservoir. Moreover, it was shown that wellbore heating might be necessary in order to avoid any hydrate reformation along the wellbore during the production. The effect of intrinsic permeability on gas production was also investigated. It was observed that until 400 mD, there is no important effect of intrinsic permeability on gas production but below 400 mD, the gas production is quite low because of very low effective permeability with 65% hydrate saturation.

Soaking Process for the Enhanced Methane Recovery of Gas Hydrates via CO2/N2 Gas Injection

Replacement technique is known as a promising method for potential energy extraction from gas hydrate deposits and greenhouse gas sequestration into deep ocean sediments. When it comes to the utilization of the replacement method in field applications, the soaking duration or the frequency of CO2/N2 gas injection becomes an important process variable. In this study, the influence of soaking duration and frequency on the CH4 replacement efficiency was quantitatively investigated for the first time by imitating the gas hydrate-bearing sediments. The CH4 replacement process with CO2/N2 was performed through two consecutive stages: dynamic replacement and soaking process. While any additional soaking process after the dynamic process enhanced the CH4 replacement efficiency from 35–36 to 52–60%, several replenishments of a fresh CO2/N2 gas mixture into the vapor phase were considered more effective than solely increasing the soaking time. The present study will help in establishing the basic process variables ...

Bayesian inversion of marine controlled source electromagnetic data offshore Vancouver Island, Canada

This paper applies nonlinear Bayesian inversion to marine controlled source electromagnetic (CSEM) data collected near two sites of the Integrated Ocean Drilling Program (IODP) Expedition 311 on the northern Cascadia Margin to investigate subseafloor resistivity structure related to gas hydrate deposits and cold vents. The Cascadia margin, off the west coast of Vancouver Island, Canada, has a large accretionary prism where sediments are under pressure due to convergent plate boundary tectonics. Gas hydrate deposits and cold vent structures have previously been investigated by various geophysical methods and seabed drilling. Here, we invert time-domain CSEM data collected at Sites U1328 and U1329 of IODP Expedition 311 using Bayesian methods to derive subsurface resistivity model parameters and uncertainties. The Bayesian information criterion is applied to determine the amount of structure (number of layers in a depth-dependent model) that can be resolved by the data. The parameter space is sampled with the Metropolis–Hastings algorithm in principal-component space, utilizing parallel tempering to ensure wider and efficient sampling and convergence. Nonlinear inversion allows analysis of uncertain acquisition parameters such as time delays between receiver and transmitter clocks as well as input electrical current amplitude. Marginalizing over these instrument parameters in the inversion accounts for their contribution to the geophysical model uncertainties. One-dimensional inversion of time-domain CSEM data collected at measurement sites along a survey line allows interpretation of the subsurface resistivity structure. The data sets can be generally explained by models with 1 to 3 layers. Inversion results at U1329, at the landward edge of the gas hydrate stability zone, indicate a sediment unconformity as well as potential cold vents which were previously unknown. The resistivities generally increase upslope due to sediment erosion along the slope. Inversion results at U1328 on the middle slope suggest several vent systems close to Bullseye vent in agreement with ongoing interdisciplinary observations.

Принцип выбора схемы разработки природных месторождений газовых гидратов на основе анализа процессов теплопереноса

Принцип выбора схемы разработки природных месторождений газовых гидратов на основе анализа процессов теплопереноса

Oil and gas pipelines with hydrophobic surfaces better equipped to deal with gas hydrate flow assurance issues

Gas hydrate deposition can cause plugging in oil and gas pipelines with resultant flow assurance challenges. Presently, the energy industry uses chemical additives in order to manage hydrate formation, however these chemicals are expensive and may be associated with safety and environmental concerns. Here we show the effect of a hydrophobically coated surface on hydrate formation in the presence of an antifreeze protein type I (AFP I) and a biodegradable synthetic polymer (LuvicapBio) in a high pressure crystallizer setup. The hydrophobic surface increased the hydrate induction time and reduced the hydrate growth significantly in pure deionized water (control). Furthermore, in the presence of 0.02 wt% of LuvicapBio or 0.014 wt% AFP I in the hydrophobic coated crystallizer; the hydrate growth was reduced to almost the same level as obtained with 0.20 wt% of LuvicapBio in a stainless steel crystallizer. This indicates that 10 to 14 times less KHI is needed in the presence of a hydrophobically coated surface. These experimental studies suggest that the use of hydrophobic surfaces or pipelines could serve as an alternative or additional flow assurance approach for gas hydration mitigation and management.

Difference schemes based on the support operator method for fluids dynamics problems in a collector containing gas hydrates

Difference schemes based on the support operator method are considered as applied to fluid dynamics in underground collectors containing gas hydrate deposits. A system of mass and energy balances describing fluid dynamics in a porous medium containing gas hydrate deposits is given. A dissipative hydrate equation is derived that determines the thermodynamic evolution of the parameters of the system. It is shown that the jumps in specific volumes and internal energy occurring in phase transitions play a crucial role in the stability of the evolution of the system in the dissipation thermodynamic module of the system. A family of rotation-invariant difference schemes of the support operator method on unstructured meshes is constructed for numerical computations. The schemes are tested on a series of model problems. Their numerical solutions are presented.

Evaluation of CH4 Gas Permeation Rates through Silicone Membranes and Its Possible Use as CH4-Extractor in Gas Hydrate Deposits

This preliminary study discusses the option of using silicone (PDMS) tubes for the extraction and monitoring of CH4 gas from hydrate deposits during decomposition. For this, the gas flow of gaseous and dissolved CH4 through hand-manufactured silicone tube membranes has been tested on a small lab scale. The permeability of pure CH4 gas at ambient pressure and 295K is in good agreement with literature reports. The permeability rate of CH4 derived from dissolved methane is expectedly lower and decreases by more than half. Theoretical assumptions and lab results are not in straightforward correlation. This leads to the conclusion that experimental constraints influence the permeability. These are mainly an increase of the gas stream resistivity due to the membrane-filling and membrane-sediment contact points as well as the effect of degassing dissolved CH4 on the tube surface due to pressure gradients. Therefore, the use as a monitoring tool needs to be individually tested before the respective application. Due to the robust nature of the membranes, their application as a tool for capturing gaseous CH4 during hydrate decomposition is a feasible goal.

Natural gas hydrates in the Rio Grande Cone (Brazil): A new province in the western South Atlantic

The Rio Grande Cone is a large-scale fanlike feature in the continental slope of the Pelotas Basin, Southern Brazil, where ubiquitous world-class bottom simulating reflectors (BSRs) are readily observed in seismic records. With the purpose of searching for natural gas hydrate deposits in the Cone area, four oceanographic cruises were carried out between May 2011 and July 2013, leading to the discovery of two pockmark fields, active faults and gas hydrates in shallow sediments. Multichannel seismic, multibeam echo sounder, side scan sonar and sub-bottom profiler records were used to map the shallow section and select sites for piston core sampling. Gas hydrates were recovered in several piston cores within muddy sediments collected inside pockmarks displaying high backscatter in the multibeam and side scan sonar data. We present two representative piston cores where numerous levels of gas hydrates occur, along with degassing features, authigenic carbonate and soupy sediments. Gas dissociated from gas hydrate samples is dominantly methane (>99.78%) with minor quantities of ethane. The chemical and isotopic compositions of the gas strongly suggest a biogenic origin for the analyzed samples. These new findings are regarded as strong enough evidence to consider the Rio Grande Cone as a new gas hydrate province.

When deep diagenesis in Arctic Ocean sediments compromises manganese-based geochronology

Abstract We used a diagenetic model to test the hypothesis that manganese-rich layers in gas hydrate-bearing Arctic Ocean sediments are reliable time markers for interglacial periods. In the model, diagenesis is fuelled by two sources of reactive carbon: particulate organic carbon settling to the sediment surface, and methane diffusing up from deep gas hydrate deposits. The model includes oxidation of organic carbon and soluble reduced manganese by oxygen supplied continuously from an invariant bottom-water oxygen reservoir; reduction of particulate manganese by hydrogen sulfide generated through anaerobic methane oxidation; transport of dissolved oxygen and manganese by diffusion; and advective transport of particulate components by burial. Particulate organic matter and particulate manganese are only supplied to the sediment during interglacials. Sulfate reduction is not modeled explicitly; instead, the effect of anaerobic methane oxidation on Mn reduction is simulated at the lower boundary of the model by prescribing that particulate manganese is reduced there to soluble Mn(II). The soluble reduced Mn then diffuses upward and is oxidatively precipitated to Mn(IV) by downward diffusing oxygen. The upward flux of soluble Mn(II) is thus a function of the rate at which particulate manganese is advected into the Mn-reduction layer at the bottom of the model; it is not synchronous with events at the sediment–water interface. Model runs reveal that, under idealized but realistic conditions for the Arctic Ocean, oxidation of upward-diffusing Mn(II) generates post-depositional manganese enrichments that cannot readily be distinguished from the manganese-rich sediment layers that accumulate during interglacials. This compromises the use of manganese-rich layers as proxies for interglacial periods. In contrast, manganese-rich layers may be used as first-order markers of interglacial periods in sediments where gas hydrates or other forms of reactive carbon are absent.