Energy Geoscience (Jul 2020)
Geology and geomechanics of hydraulic fracturing in the Marcellus shale gas play and their potential applications to the Fuling shale gas development
Abstract
Geological characteristics, geomechanical behavior and hydraulic fracture propagation mechanism in the Marcellus shale gas play are analyzed and compared with China’s Fuling shale play. Successful experiences in hydraulic fracturing and shale gas development in the Marcellus shale gas play are summarized, which might be applicable in other shale plays. The main factors contributing to the successful development of the Marcellus shale gas play include adoption of advanced drilling and completion technologies, increases of hydraulic fracturing stages, proppant concentration and fluid injection volume. The geological and geomechanical mechanisms related to those technologies are analyzed, particularly the in-situ stress impacts on hydraulic fracturing. The minimum horizontal stress controls where the fractures are initiated, and the maximum horizontal stress dominates the direction of the hydraulic fracture propagation. Hydraulic fracturing performed in the shale reservoir normally has no stress barriers in most cases because the shale has a high minimum horizontal stress, inducing hydraulic fractures propagating beyond the reservoir zone, resulting in inefficient stimulation. This is a common problem in shale plays, and its mechanism is studied in the paper. It is also found that the on-azimuth well has a higher productivity than the off-azimuth well, because shear fractures are created in the off-azimuth well, causing main fractures to kink and increasing fracture tortuosity and friction. The Fuling shale gas play has a markedly higher minimum horizontal stress and much smaller horizontal stress difference. The high minimum horizontal stress causes a much higher formation breakdown pressure; therefore, hydraulic fracturing in the Fuling shale gas play needs a higher treatment pressure, which implies higher difficulty in fracture propagation. The small difference in the two horizontal stresses in the Fuling shale gas play generates shorter and more complex hydraulic fractures, because hydraulic fractures in this case are prone to curve to preexisting fractures. To overcome these difficulties, we recommend reducing well spacing and increasing proppant concentration to increase gas productivity for the Fuling shale gas development.
