Study On T2 Spectrum Inversion And Fluid Identification And Evaluation Of Nmr

Conjugate gradient method and M-P generalized inverse method of NMR T2 spectrum inversion are proposed in this thesis. Conjugate gradient method builds up the inversion objective function at first, then searches the minimum of the objective function with the conjugate gradient algorithm that has quick convergence rate and quadratic termination,and puts Non-negativity constraint of T2 spectrum into practice by way of iteration and square at last. M-P generalized inverse method deduces the solution of M-P generalized inverse of the T2 spectrum inversion at first, then The stability and resolution of the solution are ensured by discarding some small singular values or adding damping term, finally, the non-negativity constraint of T2 spectrum is realized by iterative technique. Numerical simulation and practical application of core and log demonstrates:Both methods can be applied in T2 spectrum inversion of drilling core and well logging effectively; Conjugate gradient method can be used in the situation of the signal to noise ratio(SNR)≥5,but iteration non-negativity constraint is slow and square non-negativity constraint is easy to fall into local minimum of the function; M-P generalized inverse method can be applied in bimodal spectrum of SNR≥10 and trimodal spectrum of SNR≥20, its inversion velocity is larger than Conjugate gradient method in the inversion of log because it need singular value decomposition(SVD) once only as to continuous logging data.There are several influential factors of T2 spectrum inversion:Quality and parameters of echoes acquisition that include echo spacing,echo numbers, acquisition time and SNR, Presupposition parameters of inversion that include numbers and range of T2 value, shape of T2 spectrum that include single modal,bimodal and trimodal distribution. Quality evaluation and control indices of T2 spectrum inversion that include conditional number, echo data resolution matrix, T2 spectrum parameter resolution matrix, spread coefficient and variance are proposed. All kinds of influential factors above mentioned are studied applying numerical simulation and evaluation and control indices of quality.Approaches to improve quality of inversion are suggested so that they can direct prelog designing of core experiment and well logging.The method of NMR one-dimension T2 spectrum separation of reservoir fluid is proposed based on CPMG and DE(Difussion Editing) pulse sequence. It builds up multi-fluid relaxation model of Oil-Water and Gas-Water of reservoir firstly. Then non-difussion water T2 spectrum (surface relaxation spectrum), non-difussion oil T2 spectrum (bulk relaxation spectrum) and gas T2 spectrum (difussion relaxation spectrum) are inverted from several echo trains which come from CPMG and DE pulse sequence by robust inversion technique. By this method conincidence T2 spectrum of oil, gas and water can be separated from each one. It overcomes the defect of conventional fluid identification methods (TDA and DIFAN), which interpret and calculate apparent spectrum(composite spectrum of oil,gas and water). Forward and inverse numerical experiment from different water saturation in two phases of Oil-Water and Gas-Water shows that the inversion of non-difussion water T2 spectrum, non-difussion oil T2 spectrum and difussion gas T2 spectrum accord with those of artificial spectrum respectively well. So this method is feasible theoretically. Its practicability can be verified further by being used in identification and evaluation of reservoir fluid in laboratory and well logging.