The Significance of Bedding Planes in Controlling Out-of-Zone Growth in Highly Fractured Shale Play

Abstract

Abstract

Hydraulic fracturing in shale hydrocarbon reservoirs with an abundance of natural fractures requires an understanding of the pre-existing natural fracture state and an assessment of whether at any point of the stimulation it is energetically favourable to move fluids along these pre-existing fractures in the reservoir. Depending on the injection, the failure of fracture sets could result in the activation of specific fractures, including bedding planes. By identifying which fractures are stimulated during injection it allows for operators the opportunity to potentially control fracture behaviour and improve designs.

Microseismicity offers a number of different avenues through which the fracture state can be evaluated. The energetics of an individual rupture can be imaged though an examination of the stress release parameters and the energy budget of the rupture process: events that are more efficient at radiating seismic energy are going to be investing less energy to the deformation processes and dissipating friction through heat. Further evaluation of the microseismicity through seismic moment tensor inversion, provided there are high signal-to-noise signals sufficiently distributed around the events, can resolve the orientations of the fractures and identify fracture type, fracture orientation and dimension.

Here, we examine the spatial-temporal fracture behaviour associated a zippered stimulation in an unconventional shale play in North America. Comparisons are made between two stages, near the toe and heal of the treatment well. Based on this comparison, we establish the importance of different fracture sets in effectively constraining the stimulation to the zone of interest.

Our observations suggest that nearby wells result in overlap of microseismic activity that pre-weakens the rock and generates opportunities for out of zone growth to occur along pre-existing sub-vertical fracture sets. Conversely, the stimulation of reservoir rock not influenced by previous stages (virgin rock) results in a significant increase in fracturing associated with finely laminated bedding planes leading to increased containment within the reservoir. Based on these observations, enhancements in productivity appears to be directly related to the activation of specific pre-existing fracture sets as controlled by the dynamic nature of the local stress regime that overprints the regional stresses.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016