Summary
The present study focuses on the feasibility of a precise 3D numerical
modeling coupled with X-ray computed tomography (CT), which enables simple
analysis of heterogeneous fracture flows within reservoir core samples, as well
as the measurement of porosity and permeability. A numerical modeling was
developed and applied to two fractured granite core samples. One of the samples
had an artificial single fracture (sample dimensions: 100 mm in diameter, 150
mm in length), and the other had natural multiple fractures (sample dimensions:
100 mm in diameter, 120 mm in length). A linear relationship between the CT
value and the fracture aperture (fracture-aperture calibration curve) was
obtained by X-ray CT scanning for a fracture-aperture calibration standard
while varying the aperture from 0.1 to 0.5 mm. With the fracture-aperture
calibration curve, 3D distributions of the CT value for the samples (voxel
dimensions: 0.35x0.35x0.50 mm3) were converted into
fracture-aperture distributions in order to obtain fracture models for these
samples. The numerical porosities reproduced the experimental porosities within
factors of approximately 1.3 and 1.1 for the single fracture and the multiple
fractures, respectively. Using the fracture models, a single-phase flow
simulation was also performed with a local cubic law-based fracture-flow model
for steady-state laminar flow of a viscous and incompressible fluid. The
numerically obtained permeabilities were larger than the experimentally
obtained permeabilities by factors of approximately 2.2 and 2.7 for the single
fracture and the multiple fractures, respectively. However, these discrepancies
can be reduced to approximately 1.3--2.1 and 1.6--2.6, respectively, by simply
using the correction factor for the cubic-law equation proposed by Witherspoon
et al. (1980). Consequently, a precise numerical modeling coupled with X-ray CT
is essentially feasible. Furthermore, the development of preferential flow
paths (i.e., channeling flow) was clearly demonstrated for multiple fractures,
which is much more challenging to achieve by most other methods. Further
progress in modeling should enable the in-situ evaluation of heterogeneous
fracture flow within reservoir core samples, as well as the clarification of
the impacts of the heterogeneity on the productivity of wells and, for example,
the efficiency of recovery by water-/gasflooding.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
19 February 2010
- Meeting paper published:
8 December 2009
- Revised manuscript received:
8 December 2010
- Manuscript approved:
28 January 2011
- Published online:
9 June 2011
- Version of record:
15 September 2011
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