Prestack Ray Elastic Impedance Inversion Research And Application

AVO inversion has the earliest development, which use AVO attribute on oil and gas analysis, it’s one of the best significant methods. The process of solving geophysical parameters is a process of inversion, there are a lot of inversion methods, and nonlinear inversion method, which is more accurate, has a reliable inversion result. Nonlinear inversions includes the conjugate gradient method, gauss- Newton method, genetic algorithm and simulated annealing method, etc.Simulated annealing method is a global optimization algorithm, it can jump out of local minimum value through set up by accepting probability to achieve the global optimization result. But as a random algorithm, it’s calculation efficiency is low, which need to improve the method of decline temperature, and need to choose the right means of disturbance and acceptance probability to improve computational efficiency and stability of the algorithm. This paper use very fast simulated annealing(VFSA), by establishing a mathematical model for the trial, can get the range of the optimal solution, and establish the three parameter model experiment, the accurate three parameters is obtained through inverse solution.Elastic impedance inversion is a prestack elastic inversion, and it is an important method in prestack field. It need to assume the formation that p-wave velocity from top to bottom change is very small, but this is very different with actual layer situation. Elastic impedance got great development, ray elastic impedance, reflectivity impedance, generalized elastic impedance and Zoeppritz impedance and so on, which provides more methods for prestack inversion. The paper gives the derivation process of the elastic impedance, and use the Rutherford sandstone model for precision analysis, through which advantage in ray elastic impedance inversion parameters is found. Based on prior research, the nonlinear analytic method and Landweber- Fridman iteration method are used to inverse elastic three parameters, the two methods are able to get accurate inversion results, but the noise resisting ability remains to be improved. Last, the data of single well model is put in to test this method, and actual data is also put in to test.Elastic impedance inversion needs certain assumptions in angle domain, this do not conform to actual formation conditions. This paper puts forward the concept of p gather and the theoretical basis of p gather, and implements the extraction of p gather. Three parameters inversion method is studied on the basis of the theory of p gather, inversion effect is given on the basis of the same as the angle domain elastic impedance inversion data, from which we can see that the inversion result of using p gathers is better compared to the inversion of elastic parameters in angle domain, especially on the result of the shear wave velocity inversion. It has certain advantages. But the theory is insufficient, which is need to be improved.