This was a project in natural gas engineering (PGE 403).A short literature review on the developments of marine gas hydrates.

1. DEVELOPMENTS IN
MARINE GAS
HYDRATES

2. Prepared by
MODOU.L.JARJU
PGE 403
PROJECT
Near East University
Petroleum & Natural Gas
Engineering Department

3. INTRODUCTION
Natural gas hydrates are ice-like mixtures of natural gas and
water in which gas molecules are trapped within the crystalline
structures of frozen water. They exist in arctic regions of Soviet
Siberia, Canada, and the North Slope of Alaska where low
temperatures exist far beneath the earth's surface. Gas
hydrates are concentrated forms of natural gas and contain
about 160 to 180 times the natural gas by volume at standard
conditions. Because of the widespread existence of gas
hydrates, they are considered as an alternative source of
natural gas in the future.

4. Gas hydrates of interest to the hydrocarbon industry are
composed of water and the following eight molecules:
• Methane
• Carbon dioxide
• Ethane
• Nitrogen
• Propane
• Hydrogen sulphide
• iso-Butane & normal-Butane

5. A massive hydrate layer obtained from fine-grained sediment in a marine setting in
the Gulf of Mexico

6. The Mallik test site is located in the Canadian Arctic off
the Mackenzie Delta. In March, 2008, the Mallik 5L-38 test
produced the world’s first sustainable gas flare of methane
from a hydrate reservoir. The test lasted six days producing
13,000 m³ of gas. (not so unconventional)

7. GAS HYDRATE EXPLORATION
TARGET
• The extraction of methane from marine gas hydrate has currently been
assessed as having a vitality potential for alternative energy around the
world. There is high expectation on the increment of gas hydrate
exploration. Gas hydrate is notable to exist in an assortment of
structures that stance diverse openings and difficulties for vitality asset
investigation and generation process. Original Hydrate resources in-
place, as well as numerical simulations have indicated that only high
saturation o0f hydrate inn permeable reservoirs are considered
economically and technically recoverable.
• Expectantly in search for more hydrates resources, difficultly to recover
resources will be encountered especially in well-developed gas hydrates
“chimney” structures. it is likely that these structures will be produced as
technology advances

8. GAS HYDRATE EXPLORATION
TARGET
Gas hydrate pyramid in variety of forms.

9. TYPES OF PRIMARY RESOURCES OF GAS HYDRATES
1.Gas Hydrate as Pore fill in inherently(Naturally )
Permeable Sediments:
 Grain size
 Intrinsic permeability
 Case sample in japan Nankai trough
2.“Chimney” Structures:Most predominant world wide.
 Cylindrical accumulation
 roughly equal width and thickness (typically 100s of m).
 largest features often being much more wide than tall and
hence chimney.
 .amplitude reduction (“blanking”)
 vertical displacement of strata along the lateral margins are
major chimney characters .
3.Disseminated gas hydrates in muds:Low to moderate
Saturation

10. EXPLORATION PROCESS
The simplest and quickest method of identifying the zone of
possible gas hydrate occurrence is to examine the gas-hydrate-
stability zone.
The essential condition for gas hydrate stability at a given depth
is that the actual earth temperature at the depth is lower than
the equilibrium temperature of hydrates corresponding to the
pressure and gas composition conditions.

11. Recommended Exploration Processes
 There has been a huge evolution with regards to marine gas
hydrate evaluation and the following is one of most applied
technique applied in exploration phase of gas hydrate.
 BSR(Bottom simulation reflectors).


12. BSR(Bottom simulation reflectors)
The connection between the manifestation of “bottom simulating reflectors”
(BSRs) and gas hydrates were greatly elaborated in Bryan, Tucholke et al. and
Shipley et al in the late 1970s . Field confirmation of this connection was
provided through well logging and sampling across a prominent BSR on the
Blake Outer Ridge, offshore eastern North America.
The successful discovery of high concentration gas hydrates in sand-rich marine
reservoirs in the Nankai Trough in 1999 prepared for another setting for gas
hydrate investigation that recommended De-accentuation of BSRs and
development of more reliable indicators of sand-facilitated, high saturation
occurrences. This trend was accelerated as continued study of the nature and
generation of BSRs uncovered.
1) that their sign in seismic information is exceedingly touchy to the quality and
nature of the information
2)that the idea of BSRs is extremely sensitive to the event of free gas and
correspondingly, exceptionally unfeeling to the plenitude of gas hydrate. Inside
industry, profound water shallow danger evaluation yielded knowledge into
already unrecognized geophysical signs of the base of gas hydrate solidness.

13. Limitation of BSR(Bottom simulation reflectors)
 The limitations of BSR was confirmed after multi- well exploration drilling
and coring program prior to completion of an extensive seismic data
acquisition in 2004 in in the Nankai trough The limitation of BSRs in
exploration 1.high-concentration, sand-hosted hydrates , Saeki et al.
 The approach for gas hydrate exploration that integrates investigation of
BSRs was further extended by DOE-Chevron Gas Hydrates Joint Industry
Project and the Bureau of Ocean Energy Management’s in gulf of Mexico.
 the success of this resulted success of these efforts in delineating a number
of gas-hydrate-bearing deep water sands provided confirmation that viable
gas hydrate exploration can be conducted prior to drilling using existing
industry 3-D seismic data

14. APPROACHES TAKEN IN EXPLORATION
FIGURE 2:delineation of the GHSZ through reference to the
BSR

15. APPROACHES TAKEN IN EXPLORATION
1.Establishment of the extent of the gas hydrate stability zone (GHSZ):
 **seismic and well data beginning GHSZ 1.BSR 2.Bottom water temp
3.subsurface 4.Temp gradient 5.gas water geochemistry
2.Prospect for “direct” indicators of gas hydrate occurrence within the
GHSZ:
 Regional log data, Anomalies*** , Inpedence contrast
3.Mitigate geologic risk through evaluation of occurrence of reservoir
facies.
 Provides evidence of gas hydrate occurrence in sand-rich sediments.
 Cause of amplitude anomalies and impedance contrast can be for so many
reason.example faults.
 Broader evaluation of geological history for sand-rich sediments .
4.risk through evaluation of gas presence and migration
 Sea-floor evidence of active gas flux, gas chimneys,geochemical evidence of
gas presence,BSRs direct confirmation.

16. General overview of an approach to gas hydrate exploration

17. Status of BSRs in Gas Hydrate Exploration
The search for BSRs dominated the early stages of global gas
hydrate evaluation. As field evaluation of gas hydrate resource
potential has progressed, the relevance of BSRs became less
clear. The presense of a BSR, regardless of its nature, is certainly
not sufficient to indicate the occurrence of prospective
accumulations. In fact, a well-developed, regionally-pervasive BSR
is very likely a contra-indicator of prospectivity as it suggests a
diffuse (unfocused) gas flux within a homogeneously fine-grained
stratigraphic succesion.
Nonetheless, BSRs remain critical to gas hydrate exploration.
Primarily, the identification of a BSR (as defined broadly to include
associated seismic features that mark the base of the gas hydrate
stability zone) enables delineation of the BGHS and insight into
local temperature gradients. Further, where variable stratigraphy
includes a mix of muds and potentially-prospective reservoir-quality
units, the impact of traversing the BGHS (including phase reversals
and other events that are commonly considered to be a form of

18. Conclusion
Spurred by continuing favorable research and development results related to
gas hydrate occurrence and recoverability, the assessment of offshore areas for
the likely presense of potentially-recoverable gas hydrate accumulations is
expected to increase. It is recommended that effort initially focus on assessment
of potential occurrences in sand-hosted sediments, as field data and numerical
simulation indicate that. such deposits are amenable to recovery using known
drilling and production concepts.
An approach,which has proven to be effective in the past, is to 1) prospect
initially for potential direct indicators of gas hydrate occurrence within the defined
gas hydrate stability zone and then 2) mitigate the geologic risk inherent in such
prospects through evaluation of geological/geophysical/geochemical evidence
that associate those prospects with sand-rich reservoir facies and that may be
connected those facies with gas sources through recognized migration
pathways.

19. Reference
Boswell Ray,May 2014,Developments in Marine Gas Hydrate Exploration.
E. Dendy Sloan Jr,December 1991,Natural Gas Hydrates.
S.P. Godbole et al ,March 1988,Natural Gas Hydrates in the Alaskan Arctic.
