Microseismic Forward Base On Ray Tracing

Microseismic monitoring is a new seismic exploration technology in recent decades.-It’s widely used in many aspects such as the hydrocarbon reservoir exploration, coal mine monitoring, mine pressure monitoring, geologic disaster monitoring. It does this by observing small seismic events in production activities to monitor production activities and underground state. Microseismic monitoring technology is based on transmitting and Seismology. This technology can reduce costs and improve economic efficiency, widely recognized for its advanced. As the basis of micro-seismic inversion? micro-seismic forward modeling micro-seismic monitoring is one of the important research topics in microseismic monitoring, and it is an important tool for understanding seismic wave propagation. Therefore, the micro-seismic forward modeling has a great significance for hydrocarbon reservoir exploration.According to different principles, there are two methods for microseismic forwa-rd. One is ray tracing method and the other is wave equation method. This paper focuses on the ray tracing method. Ray tracing method determine the ray path in the actual formation by given the location of emission point and the receiving point. Shooting method and the bending method is the traditional method of ray tracing. With Kirchhoff s success in practice, ray tracing method obtain a rapid development and many new methods are emerging.Genetic algorithm is an optimization method based on natural selection and genetic mechanisms which can be used in almost all areas. This paper attempts to compare genetic algorithm and shooting method by ray tracing. By comparison, we can draw the conclusion that the interations base on shooting method is much fewer. In practical applications, the genetic algorithm prone to premature convergence problems. In the later stage of evolution, the genetic algorithm has a poor search capabilities. It is difficult to maintain a balance between maintaining the diversity of individuals and retaining outstanding individuals. The parameters of genetic algorithm(Such as population size, the biggest evolution of algebra, crossover rate, mutation rate, etc.) have a significant impact on operating results. It is very difficult to determine these parameters which obtained by experience. For a simple model, shooting method is simple and efficient, so that we use the shooting method for forward modeling results.The major steps of forward modeling are the following:First, establish layered model and the interface equation according to the geological data of work area. P-wave velocity near the two wells can be obtained by acoustic logging data. The velocity between the two wells can be striked by linear interpolation. S-wave velocity can be obtained through the empirical formula; The two wells intersect at two points with the formation. We can build the interface equation based on these two points. Second, we calculate the travel time of P-wave and S-wave after the ray tracing conducted between source and receiver. The model in this paper is a simple model so that we can calculate the travel time on segmentation. For complex models, we need to integrated along the ray path on t and calculate the travel time by the formula. Third, We produce synthetic seismograms with seismic wavelet and reflection coefficient. The seismic wave selected is Ricker wavelet and the sampling interval selected is0.25ms. Because of three-component geophones, we need to obtain the x, y, z components of Seismic waves.Through forward modeling we can draw the conclusion that the selected algorithm is accurate and efficient. The accuracy of model calculations can meet the demand of forward. Inversion can also be guided well.