ABSTRACT:

In situ stress disturbance due to initial fracture existing would make refracture propagation more complex. In this paper mechanics analysis and numerical simulation based on boundary element method have been done to caculate refracture morphology under the altered-stress condition and discusses related influencing factors. Then both of large scale experiment in lab and tiltmeter monitoring in field confirmed fracture reorientation. It showed there were three possible refrac results: (a) a new fracture would initiate at some angles even orthogonal to the azimuth of the initial fracture which is closed. (b) the initial fracture would reopen firstly and a new fracture would initiate at some angles subsequently. (c) instead of new fracture initiation, the initial fracture would reopen and reorient along the direction of maximum stress. The initial and reversal stresses, rock tensile strength, Young Modulus, fracture toughness and pumping parameters determine refrac results together. Field test also confirmed temporary plugging could make multiple fractures initiation to increase drainage area and enhance well production in refracturing. Although a part of the experimental settings is prepared for the special oilfield in China, the conclusions drawn in this study are rather general for refracturing design.

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