Acta Geotechnica

, Volume 8, Issue 6, pp 597–618

A numerical investigation of the hydraulic fracturing behaviour of conglomerate in Glutenite formation

Authors

    • School of Civil EngineeringDalian University of Technology
  • Qingmin Meng
    • Oil Production Technology Research InstituteShengli Oilfield Branch Company
  • Shanyong Wang
    • Centre for Geotechnical and Materials Modelling, Civil, Surveying and Environmental EngineeringThe University of Newcastle
  • Gen Li
    • School of Civil EngineeringDalian University of Technology
  • Chunan Tang
    • School of Civil EngineeringDalian University of Technology
Research Paper

DOI: 10.1007/s11440-013-0209-8

Cite this article as:
Li, L., Meng, Q., Wang, S. et al. Acta Geotech. (2013) 8: 597. doi:10.1007/s11440-013-0209-8

Abstract

Rock formations in Glutenite reservoirs typically display highly variable lithology and permeability, low and complex porosity, and significant heterogeneity. It is difficult to predict the pathway of hydraulic fractures in such rock formations. To capture the complex hydraulic fractures in rock masses, a numerical code called Rock Failure Process Analysis (RFPA2D) is introduced. Based on the characteristics of a typical Glutenite reservoir in China, a series of 2D numerical simulations on the hydraulic fractures in a small-scale model are conducted. The initiation, propagation and associated stress evolution of the hydraulic fracture during the failure process, which cannot be observed in experimental tests, are numerically simulated. Based on the numerical results, the hydraulic fracturing path and features are illustrated and discussed in detail. The influence of the confining stress ratio, gravel sizes (indicated by the diameter variation), and gravel volume content (VC) on the hydraulic fracturing pattern in a conglomerate specimen are numerically investigated, and the breakdown pressure is quantified as a function of these variables. Five hydraulic fracturing modes are identified: termination, deflection, branching (bifurcation), penetration, and attraction. The propagation trajectory of the primary hydraulic fractures is determined by the maximum and minimum stress ratios, although the fracturing path on local scales is clearly influenced by the presence of gravels in the conglomerate, particularly when the gravels are relatively large. As the stress ratio increases, the fractures typically penetrate through the gravels completely rather than propagating around the gravels, and the breakdown pressure decreases with increasing stress ratio. Furthermore, the breakdown pressure is affected by the size and volume content of the gravel in the conglomerate: as the gravel size and volume content increase, the breakdown pressure increases.

Keywords

ConglomerateFracture propagationGlutenite reservoirHeterogeneityHydraulic fractureNumerical simulation

List of symbols

m

Shape parameter in Weibull’s distribution, defined as homogeneity index

σij

Total stress

\( \sigma_{ij}^{\prime } \)

Effective stress

εij

Strain

uij

Displacement

Fi

Components of the net body force

λ

Lame coefficient

G

Shear deformation modulus

α

Coefficient of the pore water pressure

p

Pore water pressure

k,k0

Permeability of element under stress and damage, initial permeability of intact element

Q

Biot’s constant

ξ

Permeability increase factor

β

Coupling parameter that reflects the influence of stress on the coefficient of permeability

D

Damage parameters, D = 0–1 depends on the loading history of the element

E0,E

Initial Young’s Modulus and Young’s modulus for damaged element

ft

Tensile strength of element

ft0

The peak tensile strength of element

ftr

Residual tensile strength of damaged element

\( \varepsilon_{t0} \)

Strain at the elastic limit, which is the so-called threshold strain for tensile damage

\( \varepsilon_{tu} \)

Ultimate tensile strain

ϕ

Internal friction angle

fc

Uniaxial compressive strength of element

fc0

The peak uniaxial compressive strength of element

fcr

Residual compressive strength of damaged element

\( \varepsilon_{c0} \)

Strain at the elastic limit, which is the so-called threshold strain for shear damage

Copyright information

© Springer-Verlag Berlin Heidelberg 2013