Understanding the hydraulic fracture (HF) re-orientation mechanism from artificial weaknesses is critical to screen-out prevention in the petroleum industry and caveability management in the mining industry. An improved discrete element method is proposed and incorporated in the Universal Distinct Element Code (UDEC) to simulate hydraulic fracturing in heterogeneous rocks, and its reliability is validated against previous laboratory experiments. The effects of rock heterogeneity and rock strength on HF re-orientation are unveiled to fill the research gaps in the existing knowledge. The results show that the proposed UDEC T-W (Trigon-Weibull distribution) model can well simulate HF propagation in rock samples of different homogeneity degrees and yields more realistic simulation results compared with the classic extended finite element method (XFEM). The HF re-orientation process depends on the combined effect of all the influencing factors. HFs tend to be directed by perforations if hydraulic fracturing is performed in relatively heterogeneous rocks, while the differential stress is more likely to dictate the HF propagation paths if rocks become relatively homogeneous. We also find that higher rock strength weakens the impact of the differential stress and favours the control of perforations over HF propagation. Finally, recommendations are provided for effective utilization of hydraulic fracturing at the mine site.
Abstract Ultra-low permeability, inertinite-rich, poorly cleated, dehydrated, overpressured coal seams deeper than 9000 ft (2740 m) in the Cooper Basin of central Australia represent a fundamentally different play type to shallow and “deep” coal seam gas reservoirs. Proof-of-concept gas flow was achieved in 2007. Four Patchawarra Formation coal seams were subjected to low-proppant concentration slick-water hydraulic fracture stimulation within a dedicated vertical wellbore at a depth of 9500 ft ...
Abstract The effects of rock inherent heterogeneity and grain size on hydraulic fracture initiation and propagation for different propagation regimes are investigated through two dimensional discrete element modeling. Random particle assembly is used to mimic rock inherent heterogeneity in the numerical model while regular particle assembly is used as the reference. The rock inherent heterogeneity mainly affects the hydraulic fracture net pressure in the viscosity dominated regime and the effect...
Last. Ming Cai(NU: Northeastern University)H-Index: 15
view all 2 authors...
Abstract Grain and contact are the two key components in 3DEC-GBMs (grain-based models) because they control the micro-mechanical behavior and consequently the macro-mechanical behavior of rock. Three types of grains – rigid, elastic, and breakable grains – are considered in this study to explore the influence of grain properties on the mechanical behavior of rock. Equivalent 2D plane strain problems are solved using 3DEC to reduce computation time. A non-uniform distribution of grain size is us...
#1Qingyuan He(UNSW: University of New South Wales)H-Index: 7
#2F. T. Suorineni(UNSW: University of New South Wales)H-Index: 12
Last. Joung Oh(UNSW: University of New South Wales)H-Index: 13
view all 4 authors...
Abstract Cave mining has become a popular underground mass mining method and extends its applications to more component orebodies at depths. To ensure continuous cave propagation, effective pre-conditioning of the orebody to improve its caveability and fragmentation sizes is essential. Hydraulic fracturing has been used as a pre-conditioning method in cave mining by creating artificial fractures in the orebody. In a previous study, the requirement for creating orientation-controllable hydraulic ...
Abstract Hydraulic fracturing plays an important role in the exploitation of oil, shale gas and coal seam gas resources – all of which contain natural fractures. We systematically explore the role of the pre-existing texture of such natural fractures on the form of the resulting stimulated reservoir volume (SRV). A blocky discrete element model (DEM) coupled with fluid flow is used to explore this response. Numerical predictions for the evolution of fluid pressure and fracture width at the well ...
Abstract In this study, a heterogeneous discrete element model of granite was built considering different mineral contacts, different mineral grains, and the percentages of minerals which were obtained from analysis of the gray-scale values of the rock picture. First, the contacts and grains parameters were fixed by simulating triaxial compression and fracture toughness tests. Then, the permeability of the numerical model was calibrated on constant head tests. Finally, a coupled hydro-mechanical...
Abstract A numerical study was performed to develop a framework for estimating the confined strength of rock blocks considering scale effects and in-situ heterogeneity (i.e. intensity of structural microdefects and degree of weathering). Grain boundary models using the Voronoi tessellation scheme within UDEC have been used to simulate the results of small (lab) and large (field) scale compression (unconfined and triaxial) and indirect tensile (Brazilian) tests on a series of progressively larger...
#1P.L.P. Wasantha(Freiberg University of Mining and Technology)H-Index: 13
#2Heinz Konietzky(Freiberg University of Mining and Technology)H-Index: 24
Abstract In-situ stress state in deep reservoirs is highly variable due to many factors and it markedly influence the propagation behavior of hydraulic fractures. The direction and extent of hydraulic fracture propagation are predominantly controlled by the in-situ stress state of reservoirs. We conducted distinct element method-based numerical simulations to explore the behavior of hydraulic fracture propagation and containment under varying in-situ stress conditions and fluid injection rates. ...
#1Qingyuan He(CUMT: China University of Mining and Technology)H-Index: 7
#2Zhibing Liu(CUMT: China University of Mining and Technology)
Last. Danqi Li(Colorado School of Mines)H-Index: 1
view all 4 authors...
The mechanical characteristics of brittle materials submitted to combined compression and shear loading (CCSL) have received considerable attention recently. Both dynamic and quasi-static CCSL tests have been experimented to simulate the realistic working conditions encountered by different materials. Nevertheless, how the external shear loading affects the microcrack fracturing of rock still excludes explanation. In this paper, a self-developed loading device, instrumented with acoustic emissio...