Simulation And Analysis Of The Remote Filed Eddy Current Testing Casing

Casing is a necessary cementing tool in the process of oil and gas drilling, its security and stability is very important. Nowadays, casing damage caused lower recovery, even oil damage , in some oil fields in our country. In order to discover defects of casing in time, NDT method should be used to defect detection, on this basis, the remote field eddy current(RFEC) , an kind of NDT method, is quickly developed. This method of casing damage detection shows a very good development prospect.Remote field eddy current has the advantage of detecting the whole casing wall, good adaptable to the environment and high sensitivity to crack. At present, most people believe that RFEC is based on the basis of diffusion energy flow and wave-like phenomena. In order to further understand the principles of REFC, the finite simulation software ANSYS was used to study its properties, and some inerratic defect in oil casing was stimulate, defect signal was got, then the signal is compared by the form and size of defects.According to Maxwell equations, the mathematical expression of the remote field signal was created, and detection signal was inductive voltage of detection coil. The forms of wall defect was observed by the change of induced voltage amplitude and phase angle, then the electromagnetic simulation unit, part of the finite element simulation software ANSYS , was introduced. Due to the axial symmetry of casing wall, two-dimension simulation model was established in order to observe characteristic of the RFEC, second through principle of REFC, the effect of remote field signals was observed, the two-dimensional axisymmetric defects was simulated in the form of harmonic excitation, the effect of the defect shape on the signal was obtained by analysis and comparison. Defect signals were further processed, and the defects signal surface was established by using response surface method, then three-dimensional model was established in order to simulate a more general form of defects, then the contrast of signal sensitivity with different trends of defects, and this can help to distinguish different type of defects in the future.Finally, in order to get more remote field signals, the remote field with pulse incentive was simulated, two signal parameters , the voltage amplitude and zero time were obtained, and this can provided more signal support in further distinguishing casing defects.