The Role of Pre-existing Fractures in Constraining Stimulations in the Reservoir

We examine the discrete fracture network as identified through Seismic Moment Tensor Inversion (SMTI) of microseismicity associated with two stages of a multi-well treatment in an unconventional shale play in North America. By utilizing the identified fracture sets, their failure types, orientations and dimensions, we were able to consider the role pre-existing fractures have to constrain fracture growth within the reservoir, and identify the importance of well and stage spacing on the effectiveness of the completion design. Based on our observations, 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 subvertical fracture sets. Conversely, the stimulation of reservoir rock not influenced by previous stages (virgin rock) results in a significant increase in sub-horizontal fracturing associated with finely laminated bedding planes leading to increased containment within the reservoir. Additionally, growth upwards appears to be controlled by larger sub-vertical fractures. 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.