The Auto Picking Of First Break Time And The Research Of Near-surface Modeling Methods

The complex near-surface structure not only influences the exploding and receiving of seismic exploration, and it's difficult to obtain the high-SNR original data in field collection, but also influences the imaging and amplitude fidelity of the seismic data. So it's important to find out the near-surface velocity structure of complex area for solving the exploding problem, static correction problem in data processing, wave field extrapolation and amplitude fidelity.For the past many years, people have developed many kinds of methods for near-surface modeling. Among the 1-Dimensional investigative methods, there are shallow refraction and microseismogram log etc. And among 2-D and 3-D investigative methods, there are Interpolation, tomography, and first arrival refraction etc. Of these methods, first arrival refraction is widely used because it can build the general surface model quickly, and it's not complicated to realize it. The representational methods to build surface model by first arrival refraction are EGRM (Extended Generalized Reciprocal Method) and Delayed Time.On the basis of former research, in this paper we sum up the relative merits of EGRM and Delayed Time, and advance a new method for seeking the velocity of refraction, which is little affected by the surface and has a high velocity precision; And we raise a new method named Iteration Delayed Time (IDT), which has a high velocity of convergence and can seek a exact layer thickness. It is a good arithmetic to obtain the structure of surface velocity zone by computing the actual data. Refracting Layer Imaging (RLI) is an arithmetic which can form a image of refracting layer from the seismic data directly, and the image is similar to the CMP stacked profile by reflecting method, but the former is the structure of low velocity layer and can be accomplished simply; To sum up the advantages of GRM, IDT and RLI, we raise a more effectual method—Imaging Iteration Delayed Time, by which we sought the structure of low velocity layer in several areas and built surface model, and got perfect computing results.It's essential to pick up the first-arrival wave when building the surface model by first arrival refraction. There are many design procedures for picking up the first arrival wave automatically. Each method has a good effect for the data record which has a well first arrival quality. But with the reduction of the record quality, the reliability of first arrival wave by automatic pick is worse and worse. In the condition of complex surface, first arrival wave is interfered sometimes and changes too much, so the precision and speed of existing methods for picking up the first arrival wave automatically cannot adapt this condition. In most cases, the pick still to be done shot by shot with manpower. Base on this condition, in this paper a new method based on edge detection and boundary tracing is firstly introduced and based upon the idea of this method, the picking is accomplished firstly with the single track boundary detection and sample interpolation arithmetic. These methods have achieved well effects in the first arrival wave picking of actual data.Along with the increase of people's environmental consciousness and the advantage of vibrators itself, more and more vibrators are used to explode seismic signal. But because of the reason of vibrators itself, of its data the first arrival wave is less obvious than the first arrival wave from the explosive source, and "dual-wave arrival" and "multi-wave arrival" are often appeared. Owing to this phenomenon, it's hard to automatically pick up the first arrival of vibrators accurately. So it's an urgent problem to pick up the first arrival of vibrators. In this paper based on the first arrival characteristic of vibrators, a method for picking up the first arrival wave automatically is introduced for the first time.The primary contributions of this paper are as follows:1. For the first time this paper proposes a method for picking up the first arrival wave automatically based on the edge detection and boundary tracing:we consider recording traces an image and pick up the first arrival using marginal checking and boundary tracing of image processing.2. For the first time this paper proposes a method for picking up the first arrival wave automatically based on arithmetic of single track boundary detection and sample interpolation.3. For the first time a suit of pick up the first arrival wave automatically for the vibrators is introduced. From the research of first arrival wave characteristic of vibrators, Some of these methods are concerned with related correlation and energy methods, and based on them the tabu search and simulated annealing are firstly applied in the first arrival picking of controlled source.4. The paper proposes general smoothing: Improving the method of GRM to inquire the velocity of refraction.Hence,it can obtain the exact velocity of refraction when earth's surface is irregular.5. The paper proposes Iteration Delayed Time (IDT):By improving Delayed Time ,it can obtain more exact depth of near surface layer.6. The paper proposes Refracting Layer Imaging (RLI):Without any informations,it can handle recording traces and image the near surface layers.7. The paper proposes Imaging Iteration Delayed Time( IIDT): It synthesizes general smoothing and IDT and RLI,so it can increase the precision for seeking the velocity of refracting layer and thickness of surface layer.