Study on impulse sound source reflector and while-drilling reservoir boundary ranging

In the process of logging while drilling, measuring the distance to the reservoir boundary can enhance the initiative of geosteering drilling, improve the target-hitting rate, and increase the oil and gas collection rate. In response to this requirement, this study focuses on the design of an impulse sound source reflector and its application in ranging reservoir boundaries while drilling, laying a foundation for further research on the application of impulse sound sources. In this study, a 3D model of a rotating parabolic reflector was developed using COMSOL software. Through numerical simulations, the energy focusing effects of reflectors with varying dimensions were analyzed to determine the optimal configuration. Subsequently, a model of the reservoir boundary near the wellbore during logging while drilling was established to simulate the propagation and reflection of acoustic waves in complex formations. The effectiveness of the reflector in reservoir boundary ranging was verified, and its calculation accuracy was determined. The research results indicate that: (1) The larger the depth H and opening radius R of the rotating parabolic reflector, the better the energy focusing effect in water, and the focusing effect is more sensitive to the depth H. Under the premise of meeting the size requirements of the 7-inch drill collar and achieving a favorable energy focusing effect, the optimal dimensions of the reflector are a depth of 0.045m and an opening radius of 0.012m. The optimized parabolic reflector significantly enhances the directivity and excitation energy of the sound source, achieving a 1.912-fold gain at 1 m along the axis of the reflector; (2) The numerical simulations verified the detection capabilities for boundary distances of 3m and 5m. Accurate calculations of the distance from the reservoir boundary to the drill collar were achieved without prior knowledge of formation velocity, with the relative error not exceeding 8%; (3) This method can balance the measurement requirements of longer distances and higher precision, and has certain application prospects.