ABSTRACT:

Frac&pack can serve the dual purposes of reservoir stimulation and sand control, which has been an important well completion technique in weakly consolidated sandstone reservoirs. At present, fracture initiation and propagation in weakly consolidated sandstone reservoirs hasn't been thoroughly investigated yet due to the low strength and high plasticity, resulti ng in lack of an effective evaluation method for fracturing parameters design. In this paper, a series of hydraulic fracturing physical simulation experiments were performed to investigate fracture propagation mechanism and the influences of fracturing parameters on the fracture morphology. In addition, a coupled hydro-mechanical numerical model based on rock mechanics and finite element method was employed to analyze the effects of formation permeability, fracturing fluid efficiency and injection rate on fracture initiation and propagation. The experimental and numerical results indicated that fracture fluid leakoff had significant influences on the fracture initiation and propagation in weakly consolidated sandstone. Single flat opening fracture tends to be generated under the condition of low permeability formation, high injection rate and high viscosity of fracturing fluid. Short and narrow fractures accompanied by shear dilation zones on both sides of the fracture would be generated if low efficiency fracturing fluid is used, which cannot accept proppants and thus are unable to prevent sand production. High efficiency fracturing fluid and high injection rate can induce longer and wider fractures as desired by the frac&pack operation. The results presented in this paper are expected to be beneficial for optimizing frac&pack designs in weakly consolidated sandstone reservoirs.

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