Three Dimensional Forms of Closely-Spaced Hydraulic Fractures

Abstract

When creating arrays of hydraulic fractures in close proximity, stress field changes induced by previously placed hydraulic fractures can lead to deflection in subsequent fracture paths and coalescence between fractures. Any fracture coalescence can compromise the effectiveness of the treatment array and the fracture geometry will not be appropriately accounted for in reservoir or caving models. Here we present the results of an experimental study consisting of arrays of 4 closely spaced hydraulic fractures grown sequentially in 350x350x350 mm blocks of a South Australian Gabbro under different initial stress states and for notched and un-notched wellbores. In particular we focus on insights gained from 3-dimesional serial sectioning and digital reconstruction of the hydraulic fracture patterns that were formed. The results show that the curving hydraulic fractures typically do not exhibit a high degree of radial symmetry in their paths even though the fractures grew by radiating outward from a centrally located wellbore. The results also confirm model predictions that a subsequent fracture will curve towards a previous fracture when the minimum stress is zero and that this curving is suppressed when the minimum stress is sufficiently large. Finally, fracture initiation is shown to be critical to the symmetry of the fracture pattern and preponderance of branching and therefore effective notches that lead to initiation in the eventual plane of favored propagation have a profound impact on the hydraulic fracture geometry.

Interference Fracturing: Nonuniform Distributions of Perforation Clusters That Promote Simultaneous Growth of Multiple Hydraulic Fractures

“…Of course this assumption must be carefully evaluated because the same stress shadow that can suppress growth of some fractures will also cause the paths of most, if not all, fractures in the array (depending on symmetry) to be deflected. Here we justify the planar assumption, albeit tentatively, based on a previous numerical, laboratory, and minethrough study showing that arrays of sequentially-placed hydraulic fractures under realistic reservoir conditions can grow with small enough deflection that it can usually be neglected at the relevant scale of the problem (Bunger et al 2011, 2012, Kear et al 2013. That being said, simultaneous growth is expected to produce more complicated interactions because of the ability for the growing fracture tips to interact (Sesetty and Ghassemi 2013), and the assumption of planarity embedded in the present model must therefore be examined in detail in future work.…”

Numerical investigation of fracture spacing and sequencing effects on multiple hydraulic fracture interference and coalescence in brittle and ductile reservoir rocks

“…Fig. 20 shows the fracture fluid pressure and final geometry for four closely spaced hydraulic fractures that propagated sequentially inside a cubic block from experiment (Kear et al, 2013). It indicates that the fracturing pressure follows a KGD trend after breakdown and fractures tend to merge into each other at a distance away from the injection entries.…”

Numerical Investigation of Multistage Fractured Horizontal Wells considering Multiphase Flow and Geomechanical Effects

“…The following will consider the impact of fracture length on development results. The fracture length will directly determine the width of the SRV zone, which has a significant impact on seepage flow [29,30].…”