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Research Papers: Petroleum Engineering

Evaluation of Fracture Asymmetry of Finite-Conductivity Fractured Wells

[+] Author and Article Information
Djebbar Tiab

 University of Oklahoma, Mewbourne School of Petroleum & Geological Engineering, 100 E. Boyd Street, Norman, OK 73019–1003

Jing Lu

 Petroleum Institute, P.O. Box 2533, Abu Dhabi, United Arab Emirates

Hung Nguyen

 Petro Vietnam, 18 Lang Ha Street, Ba Dinh, Hanoi, Vietnam

Jalal Owayed

 Kuwait University, P.O. Box 5969, Safat 13060, Kuwait

J. Energy Resour. Technol 132(1), 012901 (Jan 21, 2010) (7 pages) doi:10.1115/1.4000700 History: Received September 23, 2008; Revised October 06, 2009; Published January 21, 2010; Online January 21, 2010

Nearly all commercial hydraulic fracture design models are based on the assumption that a single fracture is initiated and propagated identically and symmetrically about the wellbore, i.e., the fracture growth and proppant transport occurs symmetrically with respect to the well. However, asymmetrical fractures have been observed in hundreds of hydraulic fracturing treatments and reported to be a more realistic outcome of hydraulic fracturing. The asymmetry ratio (length of short fracture wing divided by length of long wing) influenced the production rate adversely. In the worst case, the production rate could be reduced to that of an unfractured well. Several authors observed asymmetrically propagated hydraulic fractures in which one wing could be ten times longer than the other. Most pressure transient analysis techniques of hydraulically fractured wells assume the fracture is symmetric about the well axis for the sake of simplicity in developing mathematical solution. This study extends the work by Rodriguez to evaluate fracture asymmetry of finite-conductivity fracture wells producing at a constant-rate. The analysis presented by Rodriguez only involves the slopes of the straight lines that characterize the bilinear, linear and radial flow from the conventional Cartesian and semilog plots of pressure drop versus time. This study also uses the Tiab’s direct synthesis (TDS) technique to analyze the linear and bilinear flow regimes in order to find the asymmetry factor of the fractured well. With the fracture conductivity estimated from the bilinear flow region, dimensionless fracture conductivity and the asymmetry ratio are calculated. A technique for estimating the fracture asymmetry ratio from a graph is presented. An equation relating the asymmetry ratio and dimensionless fracture conductivity is also presented. This equation assumes that the linear and/or bilinear flow regime is observed. However, using the TDS technique, the asymmetry ratio can be estimated even in the absence of bilinear or linear flow period. It is concluded that the relative position of the well in the fracture, i.e., the asymmetry condition, is an important consideration for the fracture characterization. A log-log plot of pressure derivative can be used to estimate the fracture asymmetry in a well intersected with a finite-conductivity asymmetric fracture. The analysis using pressure derivative plot does not necessarily require the radial flow period data to calculate the asymmetric factor.

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Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 4

Δm(p) and t×Δm′(p) versus t for field case example

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Figure 5

ΔPw versus t0.5 in linear flow region for field case example

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Figure 1

Flow regimes for vertically fractured wells

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Figure 2

Asymmetrically fractured well

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Figure 3

Asymmetry factor versus βa for various fracture conductivities

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