Research And Application Of High Precision 3D Velocity Field In Complex Region

In previous seismic exploration course, in general, crash graph method was used for structural map, the purpose is to indicate the exploration and development.However, this method can be applied to the oil and gas exploration and development of the most early and the hydrocarbon reservoir of the simple reservoir cap combination, which is under the condition of simple and homogeneous formation and less fault. But with the development of the process of exploration and development, this kind of simple hydrocarbon reservoir is less and less, the underground condition is also more complex, If you continue to use constant velocity mapping, it will have greater deviation from the actual stratum, the error between the mapping result and the actual depth is large, the structural high point is not accurate, some small amplitude structural and subtle traps are not displayed in the figure. This method has not applied to the current situation.However, for seismic exploration, in the process of exploration and development speed is one of the most important factors, because of this factor, the seismic exploration can be conversed from the time domain into the depth domain. Speed is correct or not, has profound influence on the judgment of the subsurface depth and dip angle and so on, Therefore it will also directly affect the effect of structural map. For the current situation of exploration and development in china, the focus of exploration are concentrated in complex structure area, in which lithology and structures are varied and generally buried deeper, the fault type is diverse, generally the stratigraphic structure is broken, the vertical and horizontal seismic velocity change greatly so that easy to produce structural trap, if you do not understand these problems in the development process, it is easy to appear the defeat and causes huge economic loss. Only know the exact underground strata velocity, understand the speed of change, grasp the fault structure, in the deployment of development wells, can avoid the risk area and decline the risk to a minimum, so that they can obtain success. Application of variable velocity mapping technology to establish the high accurate three-dimensional velocity field can obtain the high accuracy tectonic map, which can be a good solution to the current problem.This paper studies on the establishment of the velocity field and the varying velocity mapping technique, analyzes the factors correlated with the speed, such as the basic concept of the speed, main factors affecting the formation velocity, the establishment method, process and application of velocity field, etc. For Saidone trough region as an example in the Erlian basin, it obtained the applicable methods and processes which fit to research velocity in the complex structure area, along the major faults of the eastern boundary and Jabu downthrown, Saidong trough developed a number oftimee, different source, different genetic types and thickness of glutenite. Because glutenite has large thickness, obviously seismic wave velocity is higher than the surrounding sand shale formation, the formation velocity change is very large, there are a lot of structural traps, so it is more difficult to grasp the accuracy of the structure and low amplitude trap. In the study area, it established a high precision velocity field, at the same time, based on the results of the establishment, it started the fine velocity analysis and reservoir prediction, and judged anomaly area and analysized the cause of abnormal velocity.Through the study of speed on Saidong trough the following are mainly realized: geological conditions of Saidong trough is complex, the local area formation is undulating, the effect of using the model chromatography to establish vebcity field is relatively the best, The effect also is good for problems of complicated structure, low amplitude structure and variable velocity mapping, The real structure in the underground has good reduction. By using the method of partition block, velocity spectrum was analysized, at the same time, establishment field work and correction work also were made by partition block to be consistent with the well speed and velocity field. Using the layer velocity profile can clarify the variation of velocity, using the residual interval velocity for reservoir prediction can provide reference materials; the method of studying speed should be diversified, and should be combined with a variety of technical means, research center should rely on the precise analysis of velocity, and the influence factors on the speed change were carefully researched and variously demonstrated to guarantee the match between the velocity field and the actual situation of the underground.