Experimental and Numerical Investigations of Borehole Ballooning in Rough Fractures
- Mert Ozdemirtas (Total International) | Tayfun Babadagli (University of Alberta) | Ergun Kuru (University of Alberta)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 2009
- Document Type
- Journal Paper
- 256 - 265
- 2009. Society of Petroleum Engineers
- 4.3.4 Scale, 1.8 Formation Damage, 1.6.3 Drilling Optimisation, 1.6 Drilling Operations, 1.7.1 Underbalanced Drilling, 1.11 Drilling Fluids and Materials, 1.7.5 Well Control, 4.2 Pipelines, Flowlines and Risers, 1.6.9 Coring, Fishing
- fractal dimension, borehole ballooning, fracture roughness, fracture aperture, mud loss
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- 958 since 2007
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Borehole ballooning/breathing is a combined mud-loss/-gain event observed during drilling operations in naturally fractured formations. Factors controlling this phenomenon must be well understood to correctly interpret its symptoms observed during drilling to avoid mixing ballooning with other formation flow incidents that might lead to unwarranted well-control procedures.
A mathematical model defining the ballooning process was developed and solved numerically using finite-difference approximation. It was shown that fracture roughness and fracture deformation play a significant role in the flow of drilling fluid in and out of a single fracture. In this study, the focus was mainly on the effect of fracture roughness (characterized by the fractal dimension of the fracture surface) and fracture aperture.
The main goal of this work was to compare the numerical-model results with laboratory-scale experimental observations. Therefore, experiments were performed to study the mud-loss and -gain events in artificially fractured rock samples. Cylinders of Berea sandstone, Indiana limestone, and granite were used for the experiments (1-in. diameter, 3-in. length). Two different fracture types were used to analyze the effect of fracture-surface roughness on the flow of drilling fluid in and out of the fracture. To create smooth fracture surfaces, cores were cut precisely into two equal pieces using a blade. Alternatively, axial load was applied on the cylindrical rock samples until a longitudinal fracture with a rough surface was generated.
The results of experimental observations and numerical-model study on the importance of fracture roughness were provided. Situations where the degree of roughness becomes critical were identified.
|File Size||1 MB||Number of Pages||10|
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