Introducing the First LWD Crossed-Dipole Sonic Imaging Service

摘要

LWD Sonic logging has made great strides in the last decade, but measuring acoustic anisotropy has been largely out with the abilities of any of the industry tools. We introduce a new crossed-dipole, azimuthal imaging tool capable of measuring anisotropy in the same manner as wireline sonic tools do today, and even surpassing the resolution of wireline tools by taking advantage of the rotational behaviour of LWD tools. When we consider the real-time nature of LWD logging, new applications become possible , such as sonic geosteering, real-time sonic fracture characterisation (which measures deeper than current electrical fracture imaging methods), and azimuthal stress profiling for optimising wellbore stability. The tool has 4 azimuthal transmitters which can be operated as a monopole, dipole, crossed-dipole, or quadrupole as well as 4 azimuthal receiver arrays. An acoustic calliper is also integrated into each of the 4 receiver arrays for accurate measurement of hole size, shape, and tool position. The physics of LWD sonic logging is, in many ways, more complex than the wireline environment, due to the presence of a substantial drill collar, tool rotation, mud circulation, and drilling noise. We will review the effects of these factors on LWD Sonic data, including dispersion corrections that account for the drill collar and tool position as well as design considerations to minimise the effects of mud circulation and drilling noise. We then show modelling and field data to compare the accuracy of crossed-dipole anisotropy calculations and rotational anisotropy methods. Following that, we will consider the application of sonic imaging for geosteering by way of modelling and field examples.