During hydraulic fracture propagation three regions may be identified from the pressure response, referred to as: 1) near-well, that extends tens of inches, 2) mid-field, that extends tens of feet and 3) far-field, which extends hundreds of feet from the wellbore. Each region can experience simple, tortuous, and complex fracture behavior, creating unique pressure signatures. In unconventional reservoirs geomechanical conditions may allow the creation of complex fracture networks (i.e., non-planar propagation) that can be initiated and propagated in multiple planes and generally having a dominant or primary fracture.
Specific to highly deviated and horizontal wellbores, complexity manifests itself as turning, twisting and longitudinal events as hydraulic fractures propagate in the near and mid-field regions, and then reorient in the direction of principal stress planes in the far-field. This creates an increased fracturing pressure that does not diminish instantly when the fracture treatment is shut-in and results in anomalously high apparent net pressures, as evidenced by amplified ISIP’s and rapidly declining pressures that dissipate minutes after shut-in. High apparent fracturing stress gradients are often seen that are much greater than the overburden stress gradients. Although suggestive, these high stress gradients are not indicative of horizontal fractures in the far-field, but rather related to fracture complexity in the mid-field. Understanding mid-field fracture complexity is critical in interpreting fracture treatment pressure responses and optimizing treatment designs in multi-stage/multi-cluster horizontal wells. This presentation discusses methods to properly identify and incorporate complex fracture pressure interpretation for fracture treatment design, post-job pressure matching and stage/cluster spacing designs related to fracture interference.