Hydraulic fracturing of a naturally-fractured reservoir is a challenge for industry,
as fractures can have complex growth patterns when propagating in systems of natural
fractures in the reservoir. Fracture propagation near a natural fracture (NF) considering
interaction between a hydraulic fracture (HF) and a pre-existing NF, has been
investigated comprehensively using a two dimensional Displacement Discontinuity
Method (DDM) Model in this thesis.
The rock is first considered as an elastic impermeable medium (with no leakoff),
and then the effects of pore pressure change as a result of leakoff of fracturing fluid are
considered. A uniform pressure fluid model and a Newtonian fluid flow model are used
to calculate the fluid flow, fluid pressure and width distribution along the fracture. Joint
elements are implemented to describe different NF contact modes (stick, slip, and open
mode). The structural criterion is used for predicting the direction and mode of fracture
propagation.
The numerical model was used to first examine the mechanical response of the
NF to predict potential reactivation of the NF and the resultant probable location for fracture re-initiation. Results demonstrate that: 1) Before the HF reaches a NF, the
possibility of fracture re-initiation across the NF and with an offset is enhanced when the
NF has weaker interfaces; 2) During the stage of fluid infiltration along the NF, a
maximum tensile stress peak can be generated at the end of the opening zone along the
NF ahead of the fluid front; 3) Poroelastic effects, arising from fluid diffusion into the
rock deformation can induce closure and compressive stress at the center of the NF
ahead of the HF tip before HF arrival. Upon coalescence when fluid flows along the NF,
the poroelastic effects tend to reduce the value of the HF aperture and this decreases the
tension peak and the possibility of fracture re-initiation with time.
Next, HF trajectories near a NF were examined prior to coalesce with the NF
using different joint, rock and fluid properties. Our analysis shows that: 1) Hydraulic
fracture trajectories near a NF may bend and deviate from the direction of the maximum
horizontal stress when using a joint model that includes initial joint deformation; 2)
Hydraulic fractures propagating with higher injection rate or fracturing fluid of higher
viscosity propagate longer distance when turning to the direction of maximum horizontal
stress; 3) Fracture trajectories are less dependent on injection rate or fluid viscosity when
using a joint model that includes initial joint deformation; whereas, they are more
dominated by injection rate and fluid viscosity when using a joint model that excludes
initial joint deformation.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-12-8782 |
| Date | 2010 December 1900 |
| Creators | Xue, Wenxu |
| Contributors | Ghassemi, Ahmad |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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