Showing papers by "George J. Moridis published in 2007"

Strategies for Gas Production From Oceanic Class 3 Hydrate Accumulations

Abstract: Gas hydrates are solid crystalline compounds in which gas molecules are lodged within the lattices of ice crystals. Vast amounts of CH4 are trapped in gas hydrates, and a significant effort has recently begun to evaluate hydrate deposits as a potential energy source. Class 3 hydrate deposits are characterized by an isolated Hydrate-Bearing Layer (HBL) that is not in contact with any hydrate-free zone of mobile fluids. The base of the HBL in Class 3 deposits may occur within or at the edge of the zone of thermodynamic hydrate stability.In this numerical study of long-term gas production from typical representatives of unfractured Class 3 deposits, we determine that simple thermal stimulation appears to be a slow and inefficient production method. Electrical heating and warm water injection result in very low production rates (4 and 12 MSCFD, respectively) that are orders of magnitude lower than generally acceptable standards of commercial viability of gas production from oceanic reservoirs. However, production from depressurization-based dissociation based on a constant well pressure appears to be a promising approach even in deposits characterized by high hydrate saturations. This approach allows the production of very large volumes of hydrate-originating gas at high rates (>15 MMSCFD, with a long-term average of about 8.1 MMSCFD for the reference case) for long times using conventional technology. Gas production from hydrates is accompanied by a significant production of water. However, unlike conventional gas reservoirs, the water production rate declines with time. The low salinity of the produced water may require care in its disposal. Because of the overwhelming advantage of depressurization-based methods, the sensitivity analysis was not extendedto thermal stimulation methods. The simulation results indicate that depressurization-induced gas production from oceanic Class 3 deposits increases (and the corresponding water to-gas ratio decreases) with increasing hydrate temperature (which defines the hydrate stability), increasing intrinsic permeability of the HBL, and decreasing hydrate saturation although depletion of the hydrate may complicate the picture in the latter case.

Strategies for gas production from oceanic Class 3 hydrate accumulations

Abstract: Gas hydrates are solid crystalline compounds in which gas molecules are lodged within the lattices of ice crystals. Vast amounts of CH4 are trapped in gas hydrates, and a significant effort has recently begun to evaluate hydrate deposits as a potential energy source. Class 3 hydrate deposits are characterized by an isolated Hydrate-Bearing Layer (HBL) that is not in contact with any hydrate-free zone of mobile fluids. The base of the HBL in Class 3 deposits may occur within or at the edge of the zone of thermodynamic hydrate stability.In this numerical study of long-term gas production from typical representatives of unfractured Class 3 deposits, we determine that simple thermal stimulation appears to be a slow and inefficient production method. Electrical heating and warm water injection result in very low production rates (4 and 12 MSCFD, respectively) that are orders of magnitude lower than generally acceptable standards of commercial viability of gas production from oceanic reservoirs. However, production from depressurization-based dissociation based on a constant well pressure appears to be a promising approach even in deposits characterized by high hydrate saturations. This approach allows the production of very large volumes of hydrate-originating gas at high rates (>15 MMSCFD, with a long-term average of about 8.1 MMSCFD for the reference case) for long times using conventional technology. Gas production from hydrates is accompanied by a significant production of water. However, unlike conventional gas reservoirs, the water production rate declines with time. The low salinity of the produced water may require care in its disposal. Because of the overwhelming advantage of depressurization-based methods, the sensitivity analysis was not extendedto thermal stimulation methods. The simulation results indicate that depressurization-induced gas production from oceanic Class 3 deposits increases (and the corresponding water to-gas ratio decreases) with increasing hydrate temperature (which defines the hydrate stability), increasing intrinsic permeability of the HBL, and decreasing hydrate saturation although depletion of the hydrate may complicate the picture in the latter case.

Gas Production From Oceanic Class 2 Hydrate Accumulations

Abstract: Gas hydrates are solid crystalline compounds in which gasmolecules are lodged within the lattices of ice crystals The vastamounts of hydrocarbon gases that are trapped in hydrate deposits in thepermafrost and in deep ocean sediments may constitute a promising energysource Class 2 hydrate deposits are characterized by a Hydrate-BearingLayer (HBL) that is underlain by a saturated zone of mobile water Inthis study we investigated three methods of gas production via verticalwell designs A long perforated interval (covering the hydrate layer andextending into the underlying water zone) yields the highest gasproduction rates (up to 20 MMSCFD), but is not recommended for long-termproduction because of severe flow blockage caused by secondary hydrateand ice A short perforated interval entirely within the water zoneallows long-term production, but only at rates of 45 7 MMSCFD A newwell design involving localized heating appears to be the most promising,alleviating possible blockage by secondary hydrate and/or ice near thewellbore) and delivering sustainably large, long-term rates (10-15MMSCFD)The production strategy involves a cyclical process During eachcycle, gas production continuously increases, while the correspondingwater production continuously decreases Each cycle is concluded by acavitation event (marked by a precipitous pressure drop at the well),brought about by the inability of thesystem to satisfymore » the constant massproduction rate QM imposed at the well This is caused by the increasinggas contribution to the production stream, and/or flow inhibition causedby secondary hydrate and/or ice In the latter case, short-term thermalstimulation removes the blockage The results show that gas productionincreases (and the corresponding water-to-gas ratio RWGC decreases) withan increasing(a) QM, (b) hydrate temperature (which defines its stabilityfor a given pressure), and (c) intrinsic permeability Lower initialhydrate saturations lead initially to higher gas production and a lowerRWGC, but the effect is later reversed as the hydrate is depleted Thedisposal of the large amounts of produced water does not appear to pose asignificant environmental problem Production from Class 2 hydrates ischaracterized by (a) the need for confining boundaries, (b) thecontinuously improving RWGC over time (opposite to conventional gasreservoirs), and (c) the development of a free gas zone at the top of thehydrate layer (necessitating the existence of a gas cap forproduction)« less

Oceanic gas hydrate instability and dissociation under climate change scenarios

Abstract: [1] Global oceanic deposits of methane gas hydrate (clathrate) have been implicated as the main culprit for a repeated, remarkably rapid sequence of global warming effects that occurred during the late Quaternary period. However, the behavior of contemporary oceanic methane hydrate deposits subjected to rapid temperature changes, like those predicted under future climate change scenarios, is poorly understood, and existing studies focus on deep hydrate deposits under equilibrium conditions. In this study, we simulate the dynamic response of several types of oceanic gas hydrate accumulations to temperature changes at the seafloor and assess the potential for methane release into the ecosystem. The results suggest that while many deep hydrate deposits are indeed stable under the influence of rapid seafloor temperature variations, shallow deposits, such as those found in arctic regions or in the Gulf of Mexico, can undergo rapid dissociation and produce significant carbon fluxes over a period of decades.

Evaluation of the Gas Production Potential of Marine HydrateDeposits in the Ulleung Basin of the Korean East Sea

Abstract: Although significant hydrate deposits are known to exist in the Ulleung Basin of the Korean East Sea, their survey and evaluation as a possible energy resource has not yet been completed. However, it is possible to develop preliminary estimates of their production potential based on the limited data that are currently available. These include the elevation and thickness of the Hydrate-Bearing Layer (HBL), the water depth, and the water temperature at the sea floor. Based on this information, we developed estimates of the local geothermal gradient that bracket its true value. Reasonable estimates of the initial pressure distribution in the HBL can be obtained because it follows closely the hydrostatic. Other critical information needs include the hydrate saturation, and the intrinsic permeabilities of the system formations. These are treated as variables, and sensitivity analysis provides an estimate of their effect on production. Based on the geology of similar deposits, it is unlikely that Ulleung Basin accumulations belong to Class 1 (involving a HBL underlain by a mobile gas zone). If Class 4 (disperse, low saturation accumulations) deposits are involved, they are not likely to have production potential. The most likely scenarios include Class 2 (HBL underlain by a zone of mobile water) or Class 3 (involving only an HBL) accumulations. Assuming nearly impermeable confining boundaries, this numerical study indicates that large production rates (several MMSCFD) are attainable from both Class 2 and Class 3 deposits using conventional technology. The sensitivity analysis demonstrates the dependence of production on the well design, the production rate, the intrinsic permeability of the HBL, the initial pressure, temperature and hydrate saturation, as well as on the thickness of the water zone (Class 2). The study also demonstrates that the presence of confining boundaries is indispensable for the commercially viable production of gas from these deposits.

Numerical Studies on the Geomechanical Stability of Hydrate-Bearing Sediments

Abstract: The thermal and mechanical loading of oceanicHydrate-Bearing Sediments (HBS) can result in hydrate dissociation and asignificant pressure increase, with potentially adverse consequences onthe integrity and stability of the wellbore assembly, the HBS, and thebounding formations. The perception of HBS instability, coupled withinsufficient knowledge of their geomechanical behavior and the absence ofpredictive capabilities, have resulted in a strategy of avoidance of HBSwhen locating offshore production platforms, and can impede thedevelopment of hydrate deposits as gas resources.In this study weinvestigate in three cases of coupled hydraulic, thermodynamic andgeomechanical behavior of oceanic hydrate-bearing sediments. The firstinvolves hydrate heating as warm fluids from deeper conventionalreservoirs ascend to the ocean floor through uninsulated pipesintersecting the HBS. The second case describes system response duringgas production from a hydrate deposit, and the third involves mechanicalloading caused by the weight of structures placed on the ocean flooroverlying hydrate-bearing sediments.For the analysis of the geomechanicalstability of HBS, we developed and used a numerical model that integratesa commercial geomechanical code and a simulator describing the coupledprocesses of fluid flow, heat transport and thermodynamic behavior in theHBS. Our simulation results indicate that the stability of HBS in thevicinity of warm pipes may be significantly affected, especially if thesediments are unconsolidated andmore » more compressible. Gas production fromoceanic deposits may also affect the geomechanical stability of HBS underthe conditions that are deemed desirablefor production. Conversely, theincreased pressure caused by the weight of structures on the ocean floorincreases the stability of underlying hydrates.« less

Response of oceanic hydrate-bearing sediments to thermalstresses

Abstract: In this study, we evaluate the response of oceanicsubsurface systems to thermal stresses caused by the flow of warm fluidsthrough noninsulated well systems crossing hydrate-bearing sediments.Heat transport from warm fluids, originating from deeper reservoirs underproduction, into the geologic media can cause dissociation of the gashydrates. The objective of this study is to determine whether gasevolution from hydrate dissociation can lead to excessive pressurebuildup, and possibly to fracturing of hydrate-bearing formations andtheir confining layers, with potentially adverse consequences on thestability of the suboceanic subsurface. This study also aims to determinewhether the loss of the hydrate--known to have a strong cementing effecton the porous media--in the vicinity of the well, coupled with thesignificant pressure increases, can undermine the structural stability ofthe well assembly.Scoping 1D simulations indicated that the formationintrinsic permeability, the pore compressibility, the temperature of theproduced fluids andthe initial hydrate saturation are the most importantfactors affecting the system response, while the thermal conductivity andporosity (above a certain level) appear to have a secondary effect.Large-scale simulations of realistic systems were also conducted,involving complex well designs and multilayered geologic media withnonuniform distribution of properties and initial hydrate saturationsthat are typical of those expected in natural oceanic systems. Theresults of the 2D study indicatemore » that although the dissociation radiusremains rather limited even after long-term production, low intrinsicpermeability and/or high hydrate saturation can lead to the evolution ofhigh pressures that can threaten the formation and its boundaries withfracturing. Although lower maximum pressures are observed in the absenceof bottom confining layers and in deeper (and thus warmer and morepressurized) systems, the reduction is limited. Wellbore designs withgravel packs that allow gas venting and pressure relief result insubstantially lower pressures.« less

A Hydrate Database: Vital to the Technical Community

Abstract: Natural gas hydrates may contain more energy than all the combined other fossil fuels, causing hydrates to be a potentially vital aspect of both energy and climate change. This article is an overview of the motivation, history, and future of hydrate data management using a CODATA vehicle to connect international hydrate databases. The basis is an introduction to the Gas Hydrate Markup Language (GHML) to connect various hydrate databases. The accompanying four articles on laboratory hydrate data by Smith et al., on field hydrate data by L?wner et al., on hydrate modeling by Wang et al., and on construction of a Chinese gas hydrate system by Xiao et al. provide details of GHML in their respective areas.

Modeling Hydrates and the Gas Hydrate Markup Language

Abstract: Natural gas hydrates, as an important potential fuels, flow assurance hazards, and possible factors initiating the submarine geo-hazard and global climate change, have attracted the interest of scientists all over the world. After two centuries of hydrate research, a great amount of scientific data on gas hydrates has been accumulated. Therefore the means to manage, share, and exchange these data have become an urgent task. At present, metadata (Markup Language) is recognized as one of the most efficient ways to facilitate data management, storage, integration, exchange, discovery and retrieval. Therefore the CODATA Gas Hydrate Data Task Group proposed and specified Gas Hydrate Markup Language (GHML) as an extensible conceptual metadata model to characterize the features of data on gas hydrate. This article introduces the details of modeling portion of GHML.

Evaluation of the Gas Production Potential of Marine Hydrate Deposits in the Ulleung Basin of the Korean East Sea

Abstract: Evaluation of the Gas Production Potential of Marine Hydrate Deposits in the Ulleung Basin of the Korean East Sea George J. Moridis, SPE, Matthew T. Reagan, SPE, Lawrence Berkeley National Laboratory, Se-Joon Kim, SPE, Korea Institute of Geoscience and Mineral Resources, Yongkoo Seol, and Keni Zhang, SPE, Lawrence Berkeley National Laboratory estimate of the resource is used as a basis of evaluation, its magnitude is sufficient large to command attention as a potential energy source 4,5 . This interest is further fueled by dwindling conventional hydrocarbon supplies, the rapidly expanding global demand for (and the corresponding rises in the cost of) energy, and the environmental desirability of CH 4 as a “clean” fuel. The emerging importance of hydrates as a potential gas resource was the impetus behind the proliferation of recent studies evaluating the technical and economic feasibility of gas production from hydrate deposits 5-11 , and provided the motivation for this study. The Ulleung Basin. This study focuses on the evaluation of the gas production potential from marine hydrate deposits in the Ulleung Basin of the Korean East Sea. The East Sea is a semi-closed marginal sea enclosed between the Eurasian continent and the Japanese Islands. The East Sea consists of three deep basins: the Ulleung, the Japan, and the Yamato (Figure 1). The Ulleung Basin, located at the southwestern corner of the East Sea, is a bowl-shaped pull-apart basin formed by extension of continental crust during the Late Oligocene to Early Miocene and by compression at the Middle Miocene 12 . The west side of the basin is bounded by a narrow and steep sloped continental shelf, and the north side by a plateau with numerous ridges and troughs. The south and east sides of the basin are broad and gently sloped (Figure 1). The basin has a water depth of 1500-2300 m, and gradually deepens toward the north and the northeast 13 . The sediment thickness at the center of the basin is about 5 km 14 , and increases to 10 km in its southern part 15 . Seismic stratigraphic analysis showed that the sediments in the Ulleung Basin consist of four distinctive subdivisions deposited in early Miocene to Quaternary 16 . Hydrates in the Ulleung Basin. Preliminary surveys conducted by the Korea Institute of Geoscience and Mineral Resources (KIGAM) between 2000 and 2004 suggest that there is a significant potential for gas hydrate occurrence in the Ulleung Basin 17 . The potential presence of gas hydrates in the basin has been suggested by several gas-related features identified by geophysical explorative analysis including (1) a shallow gas zone in the southwestern part of the basin, identified by high-resolution Chirp sub-bottom profiles and echo-sounding images, (2) gas-charged sediments and upward fluid migration, implied by acoustic turbidity and columnar structure of acoustic blanking in surveys of the area, (3) gas seepages on the continental slope, recognized by highly reflective, hyperbolic signals in the water column in echo- sounding images, (4) gas-related structures (pockmarks and domes) on the continental slope of the Ulleung Basin, detected by echo-sounding images 17 . Analysis of piston core samples recovered from the western Ulleung Basin 13 showed rapid sedimentation rates, Abstract Although significant hydrate deposits are known to exist in the Ulleung Basin of the Korean East Sea, their survey and evaluation as a possible energy resource has not yet been completed. However, it is possible to develop preliminary estimates of their production potential based on the limited data that are currently available. These include the elevation and thickness of the Hydrate-Bearing Layer (HBL), the water depth, and the water temperature at the sea floor. Based on this information, we developed estimates of the local geothermal gradient that bracket its true value. Reasonable estimates of the initial pressure distribution in the HBL can be obtained because it follows closely the hydrostatic. Other critical information needs include the hydrate saturation, and the intrinsic permeabilities of the system formations. These are treated as variables, and sensitivity analysis provides an estimate of their effect on production. Based on the geology of similar deposits, it is unlikely that Ulleung Basin accumulations belong to Class 1 (involving a HBL underlain by a mobile gas zone). If Class 4 (disperse, low saturation accumulations) deposits are involved, they are not likely to have production potential. The most likely scenarios include Class 2 (HBL underlain by a zone of mobile water) or Class 3 (involving only an HBL) accumulations. Assuming nearly impermeable confining boundaries, this numerical study indicates that large production rates (several MMSCFD) are attainable from both Class 2 and Class 3 deposits using conventional technology. The sensitivity analysis demonstrates the dependence of production on the well design, the production rate, the intrinsic permeability of the HBL, the initial pressure, temperature and hydrate saturation, as well as on the thickness of the water zone (Class 2). The study also demonstrates that the presence of confining boundaries is indispensable for the commercially viable production of gas from these deposits. Introduction Background. Gas hydrates are solid crystalline compounds in which gas molecules (referred to as guests) occupy the lattices of ice crystal structures (called hosts). The hydration reaction of methane, the main gas ingredient of natural hydrates in geological systems, is described by the equation CH 4 + N H H 2 O = CH 4 •N H H 2 O,…………………(1) where N H is the hydration number that varies between 5.75 (for complete hydration) and 7.2 1 , with an average value of N H = 6. Such hydrates occur at locations in the permafrost and in deep ocean sediments where the necessary conditions of low T and high P exist for their formation and stability. Current estimates of the size of the hydrocarbon resource trapped in hydrates vary widely 1,2,3 (ranging between 10 15 to 10 18 ST m 3 ), but the consensus is that it is vast, exceeding the total energy content of the known conventional fossil fuel resources. Even if only a fraction of the most conservative