DEVELOPMENTS IN MARINE GAS HYDRATES

DEVELOPMENTS IN MARINE GAS HYDRATES

• 1.
  DEVELOPMENTS IN MARINE GAS HYDRATES
• 2.
  Prepared by MODOU.L.JARJU PGE 403 PROJECT NearEast University Petroleum & Natural Gas Engineering Department
• 3.
  INTRODUCTION Natural gas hydratesare 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 ofinterest 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 hydratelayer obtained from fine-grained sediment in a marine setting in the Gulf of Mexico
• 6.
  The Mallik testsite 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 Gashydrate pyramid in variety of forms.
• 9.
  TYPES OF PRIMARYRESOURCES 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 simplestand 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) Theconnection 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(Bottomsimulation 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 INEXPLORATION FIGURE 2:delineation of the GHSZ through reference to the BSR
• 15.
  APPROACHES TAKEN INEXPLORATION 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 ofan approach to gas hydrate exploration
• 17.
  Status of BSRsin 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 continuingfavorable 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,Developmentsin 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. 