A study of the effect of brittleness on hydraulic fracture complexity using a flow-coupled discrete element method

Hiroyuki Shimizu, Takatoshi Ito, Tetsuya Tamagawa, Kazuhiko Tezuka

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

In recent years, hydraulic fracturing has emerged as an important technique for the development of unconventional tight gas and oil reservoirs, particularly shale reservoirs. Production from a tight reservoir requires hydraulic creation of a highly fractured network for significantly improving the hydraulic conductivity of the reservoir. Field observations have empirically indicated that fracture complexity tends to be higher in the case of higher rock brittleness which is defined as the combination of the Young's modulus and Poisson's ratio of a rock. The brittleness is considered as one of the most important mechanical rock properties of unconventional tight reservoirs. However, the physical relationship between fracture complexity and the brittleness remains unclear. In this study, a series of hydraulic fracturing simulations were performed using a flow-coupled discrete element method to gain insights into the effect of the brittleness on fracture propagation. The brittleness was adjusted under different combinations of Young's modulus and Poisson's ratio for four rock models. Considering mechanical rock properties and pre-existing fractures, the effective stress in the case of lower brittleness reduced to the tension only around the tip of the hydraulic and pre-existing fractures. On the contrary, the tensile region was more widely distributed along the pre-existing fracture in the case of higher brittleness. The effective tensile stress in a wider region should induce more microcracks, thereby enhancing the possibility of the hydraulic fracture branching off from the pre-existing fracture. These considerations indicate a positive correlation between the brittleness and the complexity of a hydraulically induced fracture system.

Original languageEnglish
Pages (from-to)372-383
Number of pages12
JournalJournal of Petroleum Science and Engineering
Volume160
DOIs
Publication statusPublished - 2018 Jan 1

Keywords

  • Brittleness
  • Discrete element method
  • Hydraulic fracturing
  • Pre-existing fracture
  • Tight reservoir

ASJC Scopus subject areas

  • Fuel Technology
  • Geotechnical Engineering and Engineering Geology

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