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Horizontal detachments, planes of weaknesses and layer-parallel shortening in shale: recognition criteria and potential impact on hydrocarbon exploration and production
Schlumberger, Second Floor of the Palliser One Building, 125 9th Ave, Calgary T2G 0P6
Thursday Dec 14th 2017, 12:00 Noon
Shale units are commonly the place of predilection for horizontal detachments. Their occurrence during geological time or induced by human operations is reviewed. Their expression and our understanding of the mechanisms involved will be addressed using a series of examples from Canada, South America and South-East Asia.
Analogues include outcrops from the La Borracha Island (Venezuela), Miri anticline (Sarawak), Quito Road Cut, core observations from various locations and well data from the Western Canadian Sedimentary Basin.
Horizontal detachments can disrupt and misalign faults and fractures by displacing, the rock units or layers located above and below the detachment. These displacements may have effects on sealing capacity, migration paths, fracture density, fracture orientation and fraccability; they also play an important role of locking other faults. Each of these issues will be reviewed with examples.
In rocks units adjacent to horizontal detachments, diagenesis associated with pressure solution and slickensides commonly affect negatively the reservoirs with quartz-cement precipitation; such highly cemented zones can create seals and in other cases hydraulic frac barriers.
High-density tensile fractures are also commonly associated with layer-parallel shortening along shale-bed interface. Such mechanisms are best observed and illustrated in cores and with image logs; however, the extent of the enhanced porosity zones i clearly revealed and mapped by recognition of some abnormal pattern on porosity logs.
Some mega detachments have been identified in the Western Canadian Basin. After palinspastic reconstruction along horizontal planes, well-defined aeromag structures and hydrocarbon pools are getting perfectly aligned. Blow-outs and very high pressure gas kicks could be prevented as they are often associated with detachments and very low angle planes that can be “mapped” in 3-D.
Jean-Yves Chatellier graduated in geology from Lille, received an MSc in sedimentology from Calgary and MSc and PhD in structural geology from Paris. He worked around the world for Shell before taking a senior advisor position for the research lab of PDVSA in Venezuela. After seven rewarding years, and the discovery of two giant oil fields he left the country during the national strike to settle down in Calgary. There, at Talisman he worked on new play concepts and on unconventional plays of the Utica, Montney, Duvernay, Marcellus and Eagle Ford and has been recently involved in the Horn River and in the Permian Basin for various oil companies.