ABSTRACT:

Hydraulic fractures (HFs) are expected to communicate multiple natural fractures (NFs) to form a complex fracture network in multi-stage fracturing in a horizontal well. Thus, the interaction mechanism between multiple HFs and NFs should be revealed. In this study, a three-stage fracturing experiment was conducted to explore the effects of NF size, NF strike, and NF network on the HF-NF-interaction behaviors by sampling a core and using 3D-reconstruction technology. The results show that a HF is likely to be arrested by a large-size partially-opened NF when it encounters this NF. The strike of an inclined HF tends to keep the same as that of the NF, indicating that the HF strike is significantly affected by the NF strike in the near-wellbore region. Besides, given low-viscosity fluid and a low pumping rate, a NF network in the near-wellbore region may limit the length extension of HFs, resulting in a limited stimulated volume. For a HF, properly crossing a NF facilitates the increase of the stimulated volume.

1. Introducion

Natural fractures (NFs) typically widely distribute in unconventional reservoirs such as shales (Gu et al., 2020), tight sandstones (Liu et al., 2020), and metamorphic basement rocks (Wang et al., 2021). Using hydraulic fracturing technology, the hydraulic fractures (HFs) may communicate multiple NFs to form a complex fracture network (Maxwell et al., 2002), which maximizes the access to reservoirs. Previous studies (Lamont and Jessen, 1963; Blanton, 1982; Beugelsdijk et al., 2000; Olson et al., 2012) have discovered that when a HF encounters a NF, the HF can cross the NF directly, cross the NF with an offset, or be arrested and divert along the NF. Kolawole and Ispas (2019) even classified the interaction mode into nine categories for the case of a HF approaching a NF. Consequently, the interaction between HFs and NFs is a fairly complex process. To accurately predict the HF propagation path in naturally fractured reservoirs and optimize treatment parameters, it is necessary to clarify the interaction mechanism between HFs and NFs.

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