Natural fracture systems, hydraulic fracturing stimulations and fluid flow in shale gas reservoirs Dr Basim Faraj, V. P. International, Questerre Energy Corp. Quebec Oil and Gas Association (QOGA) Conference Hilton Montreal Bonaventure Hotel, Montreal October 23- 25, 2011 Outline • • • • • • Shale is different Fluids in natural fracture systems Fluid Loss during fracture stimulation Interaction of fluids flow with natural fractures Contamination of underground aquifers Conclusions Conventional Reservoirs: Scale Matters! (pore sizes and shape!) Sandstone reservoir pores ~50 µm Reef reservoir pores 50,000 to 100,000 µm 200 µm 10 cm (100,000 µm) Shale Gas Reservoirs: Scale Matters! (pore sizes and shape!) (Haynesville Shale) pores < 5 µm Barnett Shale pores ~ 5 µm 1 µm 10 µm Permeability Terminology Tighter than Tight Extremely Tight Very Tight 0.0001 0.001 100nD µD Granite Tight Conventional Low Tight 0.1 0.01 Moderate 1.0 High 10.0 Permeability (mD) 0 % porosity Limestone Montney shale Good Shale Barnett General oilfield rocks Sidewalk Cement US DOE Study (modified by B. Faraj, 2009) Microseismic Fracture Mapping Meyerhofer, 2008 5500 5600 5700 5800 5900 6000 6100 6200 6300 6400 6500 6600 6700 6800 6900 7000 7100 7200 7300 7400 7500 7600 7700 7800 7900 NW 8000 GR Scale 2:1 Fracture Height: 290-360 ft Depth: 6800 to 7100 ft After the initial flow, fluids will remain in the shale reservoir Fractures! Barnett Shale looking NE – perpendicular to well trajectory SE -4400 -4200 -4000 -3800 -3600 -3400 -3200 -3000 -2800 -2600 -2400 -2200 -2000 -1800 -1600 -1400 -1200 -1000 -800 -600 -400 -200 0 200 400 600 Depth (ft) L&S C3H Microseismic Mapping Side View Distance Along Wellbore (ft) Modified after Clawson, 2007 Barnett Shale Hydraulic fracturing height Is far away from aquifers 8,500 ft 4,500 ft Source: The American Oil & Gas Reporter, July 2010 Marcellus Shale Hydraulic fracturing height is far away from aquifers 8,500 ft 5,000 ft Source: The American Oil & Gas Reporter, July 2010 Stress Tensor and Deformation The presence and orientation of structural elements such as natural fractures and faults can be related directly to the stress tensor that gave rise to these features. Source: David Campagna, 2007 Darcy’s Flow Equation Q If Pb > Pa then there will be flow! If Pb = Pa then there will be no flow! Published 1856! Natural Hydraulic Fracturing (Doig Fm, Williston Lake, photo taken June, 09) Calcite veins Calcite fracture fill in conventional and shale: (evidence of paleofluid flow!) Calcite fill Bowen Basin Sandstone Calcite fill Barnett Shale Mineralized fractures of Montney Shale at Williston Lake, BC Calcite Faraj and Brown, 2010 Mineralization in Permian coals from the Bowen Basin, Australia Illite Ankerite Faraj, 1995 2 cm Conceptual Triassic water flow in the Bowen Basin, Australia Large hydraulic head is necessary For flow ~ 300 km scale Several km scale Faraj, 1995 Regional mineralization event in the Bowen Basin, Australia brought about by regional paelofluid flow over a period of 30 million years! Faraj, 1995 K/Ar ages of illite cleat-fills from the Bowen Basin, Australia 0 Depth (m) 200 ~14 Ma Year event ~20 Ma Year event 400 600 800 1000 250 240 230 220 210 K/Ar Age (Ma BP) Faraj, 1995 Conclusions • Slickwater fracking of shale is well-established technology. It is the only way that we are able to extract natural gas and liquids from these ultra tight rocks. • The bulk of the frac water remaining in the reservoir will stay there for millennia. As such, there is virtually no possibility of the frac water contaminating fresh water aquifers. Aquifers are also protected by casing and cement. • Natural water flow in porous rocks and fractures takes a very long time geologically (millions of years!) even with the presence of large hydraulic heads.