Publicou 12 edições por ano
ISSN Imprimir: 1091-028X
ISSN On-line: 1934-0508
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CHARACTERISTICS OF FRACTURES AND THE IMPACTS ON SHALE GAS IN THE WUFENG-LONGMAXI FORMATION
RESUMO
Key attributes pertaining to the natural fractures in shale are closely related to the generation and enrichment mechanism of shale gas and deeply affect shale gas producibility. Based on systematic observations of fracture systems in the Wufeng-Longmaxi formation in outcrop and drilling cores as well as using well logging data and argon ion-beam milling scanning electron microscopy analysis, this research reveals key insights into the effects of multiple types and configurations of fractures on shale gas at different scales. Studies documented that bedding-parallel fractures governed by deposition and diagenetic fractures are vitally important attributes of shales. These two types of fractures ranging from centimeter to micronanometer scale constitute the main parts of the bedding-parallel microfractures system in the shale. In the process of shale gas generation, microfractures are migration channels communicating organic matter and organic pores. The higher the organic matter content, where more shale gas accumulates, the more bedding-parallel fractures are found. Depositional bedding-parallel fractures and diagenetic fractures are generally prone to extend horizontally, and as a result there is markedly higher permeability in the horizontal direction than that in the vertical direction. Large-scale structural fractures are commonly at a high angle to bedding, which is unfavorable for shale gas preservation and enrichment since they provide a highway for the fast upward leak-off of the organic matter and shale gas from the reservoir. However, unlike the structural fractures, hydraulic fractures activated by staged fracturing of horizontal wells can successfully form a complex fracture network with the natural bedding-parallel fractures and diagenetic fractures. Thus, with fractures stepping deep into the shale formation, a pore-fracture system with a much higher connectivity is created and finally leads to a high and stable shale gas yield.