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Title: Strategies for gas production from oceanic Class 3 hydrateaccumulations

Abstract

Gas hydrates are solid crystalline compounds in which gasmolecules are lodged within the lattices of ice crystals. Vast amounts ofCH4 are trapped in gas hydrates, and a significant effort has recentlybegun to evaluate hydrate deposits as a potential energy source. Class 3hydrate 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 edgeof the zone of thermodynamic hydrate stability.In this numerical study oflong-term gas production from typical representatives of unfracturedClass 3 deposits, we determine that simple thermal stimulation appears tobe a slow and inefficient production method. Electrical heating and warmwater injection result in very low production rates (4 and 12 MSCFD,respectively) that are orders of magnitude lower than generallyacceptable standards of commercial viability of gas production fromoceanic reservoirs. However, production from depressurization-baseddissociation based on a constant well pressure appears to be a promisingapproach even in deposits characterized by high hydrate saturations. Thisapproach allows the production of very large volumes ofhydrate-originating gas at high rates (>15 MMSCFD, with a long-termaverage of about 8.1 MMSCFD for the reference case) for long times usingconventional technology. Gas production from hydratesmore » is accompanied by asignificant production of water. However, unlike conventional gasreservoirs, the water production rate declines with time. The lowsalinity of the produced water may require care in its disposal. Becauseof the overwhelming advantage of depressurization-based methods, thesensitivity analysis was not extendedto thermal stimulation methods. Thesimulation results indicate that depressurization-induced gas productionfrom oceanic Class 3 deposits increases (and the corresponding waterto-gas ratio decreases) with increasing hydrate temperature (whichdefines the hydrate stability), increasing intrinsic permeability of theHBL, and decreasing hydrate saturation although depletion of the hydratemay complicate the picture in the latter case.« less

Authors:
;
Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE. Assistant Secretary for Fossil Energy.Gas
OSTI Identifier:
918823
Report Number(s):
LBNL-62758
R&D Project: G30801; BnR: AB0565000; TRN: US200819%%468
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Conference
Resource Relation:
Conference: 2007 Offshore Technology Conference, Houston,Texas, 29 April -2 May 2007
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; GAS HYDRATES; HYDRATES; POTENTIAL ENERGY; PRODUCTION; SENSITIVITY ANALYSIS; WATER; WELL PRESSURE; FE Fossil Energy

Citation Formats

Moridis, George J., and Reagan, Matthew T. Strategies for gas production from oceanic Class 3 hydrateaccumulations. United States: N. p., 2007. Web.
Moridis, George J., & Reagan, Matthew T. Strategies for gas production from oceanic Class 3 hydrateaccumulations. United States.
Moridis, George J., and Reagan, Matthew T. Tue . "Strategies for gas production from oceanic Class 3 hydrateaccumulations". United States. doi:. https://www.osti.gov/servlets/purl/918823.
@article{osti_918823,
title = {Strategies for gas production from oceanic Class 3 hydrateaccumulations},
author = {Moridis, George J. and Reagan, Matthew T.},
abstractNote = {Gas hydrates are solid crystalline compounds in which gasmolecules are lodged within the lattices of ice crystals. Vast amounts ofCH4 are trapped in gas hydrates, and a significant effort has recentlybegun to evaluate hydrate deposits as a potential energy source. Class 3hydrate 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 edgeof the zone of thermodynamic hydrate stability.In this numerical study oflong-term gas production from typical representatives of unfracturedClass 3 deposits, we determine that simple thermal stimulation appears tobe a slow and inefficient production method. Electrical heating and warmwater injection result in very low production rates (4 and 12 MSCFD,respectively) that are orders of magnitude lower than generallyacceptable standards of commercial viability of gas production fromoceanic reservoirs. However, production from depressurization-baseddissociation based on a constant well pressure appears to be a promisingapproach even in deposits characterized by high hydrate saturations. Thisapproach allows the production of very large volumes ofhydrate-originating gas at high rates (>15 MMSCFD, with a long-termaverage of about 8.1 MMSCFD for the reference case) for long times usingconventional technology. Gas production from hydrates is accompanied by asignificant production of water. However, unlike conventional gasreservoirs, the water production rate declines with time. The lowsalinity of the produced water may require care in its disposal. Becauseof the overwhelming advantage of depressurization-based methods, thesensitivity analysis was not extendedto thermal stimulation methods. Thesimulation results indicate that depressurization-induced gas productionfrom oceanic Class 3 deposits increases (and the corresponding waterto-gas ratio decreases) with increasing hydrate temperature (whichdefines the hydrate stability), increasing intrinsic permeability of theHBL, and decreasing hydrate saturation although depletion of the hydratemay complicate the picture in the latter case.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}

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  • 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 formore » 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 4.5 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 satisfy 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
  • Gas hydrates are solid crystalline compounds in which gas molecules are lodged within the lattices of an ice-like crystalline solid. The vast quantities of hydrocarbon gases trapped in hydrate formations in the permafrost and in deep ocean sediments may constitute a new and promising energy source. Class 2 hydrate deposits are characterized by a Hydrate-Bearing Layer (HBL) that is underlain by a saturated zone of mobile water. 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. Both classes of deposits have been shown to bemore » good candidates for exploitation in earlier studies of gas production via vertical well designs - in this study we extend the analysis to include systems with varying porosity, anisotropy, well spacing, and the presence of permeable boundaries. For Class 2 deposits, the results show that production rate and efficiency depend strongly on formation porosity, have a mild dependence on formation anisotropy, and that tighter well spacing produces gas at higher rates over shorter time periods. For Class 3 deposits, production rates and efficiency also depend significantly on formation porosity, are impacted negatively by anisotropy, and production rates may be larger, over longer times, for well configurations that use a greater well spacing. Finally, we performed preliminary calculations to assess a worst-case scenario for permeable system boundaries, and found that the efficiency of depressurization-based production strategies are compromised by migration of fluids from outside the system.« less
  • Class 1 hydrate deposits are characterized by a Hydrate-Bearing Layer (HBL) underlain by a two-phase zone involving mobile gas. Such deposits are further divided to Class 1W (involving water and hydrate in the HBL) and Class 1G (involving gas and hydrate in the HBL). In Class 2 deposits, a mobile water zone underlies the hydrate zone. Methane is the main hydrate-forming gas in natural accumulations. Using TOUGH-FX/HYDRATE to study the depressurization-induced gas production from such deposits, we determine that large volumes of gas could be readily produced at high rates for long times using conventional technology. Dissociation in Class 1Wmore » deposits proceeds in distinct stages, but is continuous in Class 1G deposits. Hydrates are shown to contribute significantly to the production rate (up to 65 percent and 75 percent in Class 1W and 1G, respectively) and to the cumulative volume of produced gas (up to 45 percent and 54 percent in Class 1W and 1G, respectively). Large volumes of hydrate-originating CH4 could be produced from Class 2 hydrates, but a relatively long lead time would be needed before gas production (which continuously increases over time) attains a substantial level. The permeability of the confining boundaries plays a significant role in gas production from Class 2 deposits. In general, long-term production is needed to realize the full potential of the very promising Class 1 and Class 2 hydrate deposits.« less
  • Class 1 hydrate deposits are characterized by aHy-drate-Bearing Layer (HBL) underlain by a two-phase zone involvingmobile gas. Such deposits are further divided to Class 1W (involvingwater and hydrate in the HBL) and Class 1G (involving gas and hydrate inthe HBL). In Class 2 deposits, a mobile water zone underlies the hydratezone. Methane is the main hydrate-forming gas in natural accumulations.Using TOUGH-FX/HYDRATE to study the depressurization-induced gasproduction from such deposits, we determine that large volumes of gascould be readily produced at high rates for long times using conventionaltechnology. Dissociation in Class 1W deposits proceeds in distinctstages, but is continuous in Classmore » 1G deposits. Hydrates are shown tocontribute significantly to the production rate (up to 65 percent and 75percent in Class 1W and 1G, respectively) and to the cumulative volume ofproduced gas (up to 45 percent and 54 percent in Class 1W and 1G,respectively). Large volumes of hydrate-originating CH4 could be producedfrom Class 2 hydrates, but a relatively long lead time would be neededbefore gas production (which continuously increases over time) attains asubstantial level. The permeability of the confining boundaries plays asignificant role in gas production from Class 2 deposits. In general,long-term production is needed to realize the full potential of the verypromising Class 1 and Class 2 hydrate deposits.« less
  • The estimate of technically recoverable gas from Devonian shale in Ohio ranges from 6.2 to 22.5 Tcf, depending on stimulation method and pattern size selected. This estimate is based on (1) a compilation of the latest geologic and reservoir data, (2) analysis of key productive mechanisms, and (3) examination of alternative stimulation and production strategies. The key findings of this study are: A substantial volume of gas is recoverable, although advanced technology will be required to reach economically attractive production rates in the state, well spacing can be reduced by half from the traditional 150 to 160 acres per wellmore » without severly impairing per-well recovery, and due to the high degree of permeability anisotropy in the shales, a rectangular, generally 3 by 1 well pattern leads to optimum recovery.« less