The Theories And Methods Of Inverting Formation Transverse Isotropy Using Acoustic Logging-while-drilling Data

Rocks in the earth's crust usually contains inhomogeneities,largely affecting the rock's property,especially for the acoustic aspect.The alignment of inhomogeneities can induce formation anisotropy.Evaluation of formation anisotropy is important for the reservoir properties interpretation,which has been developing from wireline logging to the logging-while-drilling measurement.By providing detailed research of the theory,numerical simulation and the field data processing of anisotropic formation evaluation in the LWD environment,we theoretically analyze the anisotropy induced by inhomogeneities alignment.In the following,we provide detailed theoretical formulations for calculating acoustic waveforms along a borehole with an anisotropic formation.Based on the theoretical analysis,we present an inversion method in LWD environment.The application of this method show good results in the field data processing.The major work of this paper consists of four parts as follows.In the first part,the theory of formation anisotropy induced by inhomogeneities is studied.We first provide theoretical foundation and numerical simulation method for the modeling of aligned inhomogeneities in homogeneous background medium.In the following,we theoretically analyze the characteristic of transversely isotropic compound material containing aligned ellipsoidal inhomogeneities.The effect of variational azimuth,form and type of inhomogeneities on medium effective modulus is modeled.In the second part,we provide detailed theoretical formulations for calculating acoustic waveforms along a borehole with an anisotropic formation.Firstly,the borehole response in transversely isotropic formation is studied.Meanwhile,A theory while drilling of cracked porous formation and cracks are derived.Aiming at solving the complexity of theory formulations caused by design of instrument measurement while drilling,a simple instrument equivalent theory is put forward.Detailed numerical simulation for borehole acoustic field is carried on the formation of cracks and along with drilling characteristics of drilling transversely isotropic formation.Equivalent theory was verified by analytic and numerical methods.The third part,we provide methods of anisotropy inversion by while drilling acoustic logging.Firstly,a method of frequency domain coherent is presented by extracting frequency dispersion characteristics from the time domain waveform.We then establish an objective function for the isotropic invertion.Eliminate the influence of frequency dispersion characteristics of LWD tool by calibrating tool parameters in isotropic formation,and the anisotropy will be gained.Aiming at the situation of lacking of shear information or seriousness of wave dispersion,a method of joint inversion is presented.A good agreement is showed between the processing result and the theoretical analysis.In the fourth part,field data is processed using the inversion method presented in this paper.The result of processing indicate a good adaptability in the measurement while drilling,and it also have a good application in tight unconventional formation data processing.