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Transcript of Shale Gas
generally, high porosity
very low permeability fine-grained sedimentary rock (0.0625 mm) includes siltstone, mudstone, claystone specific type of mudstone
'laminated and fissile' mud-sized particles >50% terrigenous material w/ 50% <63microns, and are lithified and fissile dominantly 'clay' minerals ECRB definition: "a lithostratigraphic unit having <50% by weight organic matter, with <10% of the sedimentary clasts with a grain size >0.00625 mm and >10% of the sedimentary clasts with a grain size <0.0004 mm" Energy Resources Conservation Board shale mineralogy standard thin section petrography not effective grain size is too small X-Ray Diffraction (XRD) Scanning Electron Microscope (SEM) most common way to determine shale mineralogy BUT: cannot see texture sample must be powdered prior to analysis provides a QUANTITATIVE result only allows for increased magnification with good resolution relatively cheap
and quick expensive and slow can get semi-quantitative information, within the context of petrography (qualitative) may be able to get full quantitative results with an electron micropobe shale components relative to sandstones, shales have a greater amount of components fromed within the water mass from which they were deposited e.g. carbonate, silica, phosphate, organics significant vertical change
(mm-m scale) shales are susceptible to diagenetic changes e.g. Barnett shale: SiO2 from both detrital grains and recrystallized radiolaria important to distiguish the two,
effects the permeability shale fabric influences
fracability and matrix permeability shale properties it is essential to know something about shale, because there are some properties integral to the extraction of shale gas gas must be able to migrate to natural or induced fractures may be through interbedded sand- or siltstone, bioclast beds with high permeability effected by later biological and diagenetic processes depositional processes have a great influence on permeability e.g. bed thickness effects fracture spacing and ability to propagate vertically maturity 1. degree of sorting of grains 2. degree of thermal alteration of the rock (or organic matter) "immature shale" rock that has not generated liquid or gaseous hydrocarbons by thermal processes of interest is the dewatering if smectite clays and coversion of smectite to illite @ 100 C and (in part) coincides with hydrocarbon generation immature shale = smectite (swelling clays) mature shale = smectite illite Shale Rock Fabric probably more important than mineralogy when determining the mechanical and flow properties of a shale fracture patterns permeability Well Logs no clear protocol for shale gas interpretation in well logs most techniques are developed for conventional oil and gas shale is typically looked at as a cap or seal Nuclear Magnetic Resonance (NMR) can determine water and hydrocarbon saturation Fredonia, NY
Devinian, Dunkirk Shale
1.76 mcf/d Gamma Ray
Porosity generally high Original Gas in Place Total Recoverable Gas size of the shale deposit total organic content water saturation porosity permeability presence/absence of natural fractures reservoir pressure drainage area of each well formations reaction to fracturing other gases CO2, N2, C4H10 (butane), C5H12 (pentane), C6H14 (hexane) +/- H2S but.... can have a much longer period of production wide geographic extent 80 years Big Sandy Pool Devonian black shale in Kentucky up to 1000's square km Antrim shale in US is 75 000 sq km rarely, the intitial flow may be very high (1000-10 000 mcf/day), which declines to low flow rate in few months to years WCSB shale gas is often siltstone or multiple interlayered rock types e.g.
shale laminations serve 2 purposes 1. store free gas
2. transmit desorbed gas to the well bore Barnett Shale
Ft. Worth Basin Density low location and orientation of fractures Image Log Shale Gas Formation natural gas is generated in the shale and remains in the shale the shale is a seal, source rock and reservoir rock primary thermogenic degredation of organic matter secondary thermogenic cracking of oil biogenic degredation of organic matter adsorbed gas into kerogen material free gas trapped in non-organic interparticle (matrix) porosity free gas trapped in microporosity free gas trapped in a pore network developed with in organic matter free gas in natural or induced fractures (during stimulation) generally, methane content increases with increase in organic matter recovery rates tend to be low compared to conventional production. ~50-250 mcf/day avg: 330 mcf/day Production Horizontal and vertical Drilling ongoing
testing and vertical drilling ongoing
initial gas flow equiv. to Barnett shale pure shale gas reservoir
over 14 000 sq km
world class shale basin
GIP = ~300-800 Tcf