Shear‐wave imaging using cross‐dipole acoustic logging tool

Abstract

The shear waves from a four-component cross-dipole acoustic tool were analyzed to provide an important method for the single-well acoustic imaging application. We analyzed the effects of wave radiation, reflection, and borehole acoustic response on the shear-wave reflection measurements. In particular, we studied shear-wave radiation from a dipole source and the wave's reflection from a formation reflector, showing that the shear waves generated by a dipole source in borehole have a wide radiation pattern. This allows for imaging reflectors at various dip angles crossing the borehole. More importantly, the azimuthal variation of the shear waves, in connection with the multi-component nature of a cross-dipole tool, can be used to determine the strike azimuth of the reflector. The analysis results establish a theoretical foundation for the borehole shear-wave imaging application. The theoretical results are utilized to formulate an inversion procedure for field data processing. The field data application not only validates the theoretical results but also demonstrates advantages of shear-wave imaging.

Unreliable determination of in situ stress orientation by cross multipole array acoustic logging in fractured shale reservoirs

“…In a homogeneous formation, the differences in horizontal principal stress are some of the most important factors causing shear wave anisotropy, which can be used to determine the orientations of S Hmax and S hmin . 36,45,46 Other nonstress factors in rocks, such as fractured formations or high-angle formations, also influence shear wave propagation. Therefore, in shale reservoirs with high-density fractures, it is not reliable to use XMAC logging to determine the direction of in situ stress.…”

“…During logging, middle-and high-angle fractures can cause changes in the radial wave impedance of the formation, thus causing the amplitude of the shear wave energy to attenuate and allowing the degree of attenuation to increase as the degree of fracture development increases. 36,46 Because of the development of secondary pores and fractures in sealed fractures (Figure 3C), when the effective stress increases, the contribution of fractures to the permeability is still great due to the filler supporting effect, and natural fractures still play a crucial role in reservoir seepage and propagation of FSWs. 57,58 The azimuth of shear waves is chiefly controlled by structural fractures and deviates from S Hmax .…”

“…When XMAC logging is used to determine the direction and magnitude of stress, it is necessary to differentiate between shear wave anisotropy caused by stress and that caused by other reasons, such as fractured or high-angle formations. 36,45,46 Some researchers 37 have proposed theoretical methods (e.g., strong changes in the position of shear wave velocity or the intensity of shear wave anisotropy) to identify such differences, but these methods do not apply to the study area. To obtain more realistic and accurate compressional wave, shear wave, and Stoneley wave time differences, correlation analysis is used to calculate the point with the highest correlation coefficient on the entire wave train by selecting appropriate filtering parameters, window length, step size, and other parameters to determine the maximum possible time difference for each corresponding wave train.…”

“…XMAC logging has been indicated to be a reliable method to determine the direction and magnitude of in situ stress. 36 The principle of using XMAC logs to determine the horizontal principal stress is shear wave splitting. 38,39 Shear waves mainly propagate in two directions; fast shear waves (FSWs) propagate along the fracture direction and spread faster, whereas slow shear waves (SSWs) propagate perpendicular to the fracture direction and spread slower.…”

Finite element simulation of bonding defects in cementing casing based on circumferential SH guided waves

“…Tang demonstrated the potential of utilizing SH waves for evaluating the cementing quality of cement rings in the casing (Tang et al, 2005). By arranging piezoelectric disctype sensors in a stacked manner along the axial direction of the casing, obliquely incident SH waves were effectively transmitted through both the casing and the cement, so as to evaluate the cementing quality of the casing (Tang et al, 2009;Tang et al, 2010). Doug Patterson and his research team used an electromagnetic acoustic transducer (EMAT) to excite circumferential SH waves in a casing (Patterson et al, 2015).…”