Study On Forward Response Characteristics Of Fracture Scattered Waves By Dipole S-wave Remote Detection In Horizontal Wells

Unconventional reservoirs such as tight oil and gas reservoirs often have dense high-angle and small-sized fractures.These fractures play a positive role in increasing the permeability of the reservoir,but also play a negative role in causing horizontal casing deformation and inter-well frac-hit during oil and gas production,hydraulic fracturing,CO₂ injection,etc.They are the focus of geophysical exploration.In horizontal wells,dipole shear wave remote detection technology is often used to evaluate fractures near the well bore.However,due to the limited number of receivers and short offset of the logging tool,the log data collected in horizontal wells almost do not contain the reflected waves of small-size fractures,but mainly the scattered waves of fractures.In this thesis,we first numerically simulate the situation of fracture located outside the horizontal well in tight sandstone reservoir.The results show that when the fracture dip angle is greater than the critical value,the scattered S-wave will be generated when the shear wave propagates to the two endpoints of the fracture.Two scattered wave packets with different arrival times will be formed on the received waveform.When the polarization direction of the source is parallel to the fracture strike,the amplitudes of the excited scattered S-wave are strongest and no mode conversion occurs.In addition,it is found that the propagation of S-waves at finite fractures can induce the fracture to vibrate in dipole mode.Further,we investigate the situation that formation interface and fracture are both presented outside horizontal wells.When both the fracture and the formation interface are located at the upper part of the well bore,the fracture SH-scattered wave amplitude is on the same order of magnitude of the formation interface reflected wave amplitude.When they are kept at a certain distance,the presence of formation interface reflected waves does not affect us to pick up the fracture scattered wave.When the formation interface and the fracture are in the same orientation,the amplitude of the received fracture scattered wave is the strongest under the condition that the polarization direction of the source and receiver is parallel to the fracture plane,and the received waveform is mainly the generalized SH scattered wave corresponding to the fracture.We systematically study the generation mechanism and response characteristics of fracture scattered waves by dipole S-wave remote detection in horizontal wells,which provides theoretical support for evaluating small-size fractures near the well bore by using remote detection acoustic logging data of horizontal wells.