Mechanics of Fracture Propagation in Closely Spaced Clusters
- Ali Daneshy (Daneshy Consultants Int'l)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 26-29 October, Virtual
- Publication Date
- Document Type
- Conference Paper
- 2020. Society of Petroleum Engineers
- 2.1.3 Completion Equipment, 5 Reservoir Desciption & Dynamics, 2.2 Installation and Completion Operations, 3 Production and Well Operations, 2 Well completion, 2.5.2 Fracturing Materials (Fluids, Proppant), 2.4 Hydraulic Fracturing, 5.6.5 Tracers, 5.6 Formation Evaluation & Management
- cluster spacing, Fracture extension pattern, pseudo-open hole, merging axial fractures, random fracture location
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- 118 since 2007
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For more than a decade there has been a gradual reduction in perforation cluster spacing together with increased number of clusters and larger frac sizes. The main driver for this change has been increased production. In recent years the more common cluster spacing has been in the range of just a few tens of feet, even as low as only five feet.
This paper discusses the effect of reduced cluster spacing on propagation pattern of hydraulic fractures. It notes that fractures are more likely to initiate axially/longitudinally from perforations and reorient once they extend away from the wellbore to become perpendicular to the least principal stress. This process causes formation of a pseudo-open hole along the axial fracture near each perforation cluster and its existence has been verified by proppant tracer and fiber optic surveys. In cases of close cluster spacing these pseudo-open hole segments can merge and cover a much longer segment of the cemented liner. Merging of axial fractures will be further assisted by poor quality cement. This causes the fracture re-orientation to occur along a material weakness intersected by the merged axial fractures, somewhat like what would happen in an openhole completion. The net result is random location and number of fractures extending away from the wellbore. Presence and extent of the pseudo-open hole is demonstrated by proppant tracer surveys from actual field examples presented in the paper.
Paper concludes that there is a limit to usefulness of shorter spacing for increasing the number of created fractures. If too close, the randomness of fracture location and number can create results contrary to expectations. It recommends an alternate hybrid cluster arrangement consisting of bunching the closely spaced perforation clusters into multiple separate groups and using larger separation between the groups to avoid spread of the initiated axial fractures outside each group.
|File Size||828 KB||Number of Pages||9|
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