This paper proposes that nano-scale ultrasonic curable polymer and initiators can enter into the rock with drilling fluid in drilling process, in the presence of VDW force and electrostatic force, the polymer is absorbed and accumulates in fractures. Under the influence of ultrasonic transmitter set in the BHA, the initiator generates reactive free radicals to cure the polymer. In addition, the acoustic resistance in the fracture generates local high temperature, which can make the polymer crosslink and cure into a type of material of certain tenacity and strength, thus consolidate rocks near the wellbore as well as fill in fractures to strengthen the borehole wall. According to above theory, the study puts forward the design of ultrasonic curable drilling system and the design of downhole ultrasonic transmitter, and tests its properties. In addition, the study carries out the development of the ultrasonic curable system and the relevant downhole equipment and the application method, examines the application prospect of the technique from multiple aspects such as the impact of the fracture depth on the curing condition, the impact of the ultrasonic curable material on the permeability of the fractures, the impact on contact angle of shale surface and the impact on the strength of shale. The results show that the filter loss under HTHP is close to zero. This technique can effectively restrict the propagation of fractures, maintain the shale strength, and improve the strength of shale with faults. It is concluded from these tests that the ultrasonic strengthening technique can be applied to consolidate the caving section during shale gas drilling. The technology will be on trial in the shale gas drilling in West China, and is expected to be widely applied on unconsolidated sandstone and deepwater drilling to stretch the extension limits of the open hole.

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