To study influence of diffusion coefficient, relaxation rates, pore component ratio and pore width on NMR T₂ distributions, a complex rock-pore system is simplified to an equivalent dual porosity medium in a mathematical physics model with Bloch's equation. ADI-FDTD and SIRT methods are used in numerical simulations of NMR transversal response and decomposition of NMR T₂ spectrum, respectively. It shows that transversal magnetization vector decay rate is proportional to diffusion coefficient and micro porosity, inversely proportional to pore width and nearly irrelevant to surface relaxation rate. NMR T₂ spectrum hardly reflects pore components and structure as diffusion coefficient is small and pore width is large. Special attentions should be paid to influence of diffusion coefficient and pore-size as evaluating pore structure by NMR.

A weighting approach for ray matrix in ART algorithm for ultrasonic computerized tomogrnphy of concrete is developed. Firstly。a low-resolution image is generated by BPT algorithm and which is used asinitial value of iteration.Then,information of lowresolution image is used as weighting coefficients for ray matrix of ART algorithm.Image information and numerical information are used fully.High speed and low speed abnormal units can be weighted.As data error is less than 0.5%.examples show that the accuracy and iteration speed of improved method are better than that of traditional ART algorithm.

We propose a method to invert two parameters(virgin zone resistivity,invaded zone) of dual lateral logging which is based on Newton-SVD of particle swarm.Reasonable initial values are selected by random particle swarm method.Newton-SVD is applied to invert dual lateral logging data.It improves stability and reliability of logging inversion greatly,and offers a radical way for setting initial values of inversion.Ideal model with noise and practical logging data are compared.It shows that the method eliminates effects of complex logging environments effectively and offer true formation parameters.