Research On Velocity Calibration Method For Micro-seismic Monitoring Based On Ray Theory

In the structure of China’s oil and gas production, the proportion of low permeability oil and gas yield increased year by year. With the improvement of exploration level and the growing demand for oil and gas resources, low-permeability oil and gas will become the guarantee of future stable production for oil and gas in China. Hydraulic fracturing technology is not only an important technical measure to increase yield and injection wells, but also the most commonly used technique in the exploitation of low permeability reservoir. After years of application and development in the field of oil and gas exploration, Micro-seismic monitoring technology has become the most effective means of the current underground reservoir hydraulic fracturing monitoring. Due to the source parameters can not be directly controlled and the origin time is also unknown, therefore, accurate positioning for micro-seismic events is the most important task of the micro-seismic monitoring.Among the many factors affecting the micro-seismic location results, positional deviation caused by the velocity model error is particularly significant. In production, the initial layered velocity model created by the acoustic logging data often has a bad impact on the subsequent processing for microseisimic data because of the tough accuracy. In summary, to calibrate the velocity model before the microseismic event location is very necessary.This thesis based on the first arrivals data obtained from the ground microseisimic monitoring, the research object is to get a more precise velocity model of the target area. In this paper, the study of microseismic velocity model inversion calibration method is on the basis of the initial velocity model obtained from the acoustic logging data. Centered around the purpose and significance, the research status of the micro-seismic monitoring technology has been analyzed, characteristics and application status between the surface and downhole monitoring methods have been compared, and this paper also summarizes the study done by the experts and scholars currently in the micro-seismic velocity model inversion calibration.The research on this project mainly involves two issues: forward modeling and velocity model inversion calibration. To achieve the research objectives, this paper made an in-depth study of the numerical modeling methods based on ray theory and micro-seismic inversion algorithms. In terms of numerical modeling, the study is started from the principles of several major ray tracing methods, considering the features of the velocity structure in the micro-seismic target area and the requirements for computional speed and accuracy, we use the rapid and accurate two-point ray tracing method for horizontally layered media. To verify the feasibility and practicability of this algorithm, the comparison of its traveling time calculation result with the segmentlly iterative ray tracing method has been made in the modeling test, and we also compare it with the first arrivals data from the actual perforating. In the aspect of velocity model inversion calibration, this paper proceeds from the perspective of solving nonlinear least squares inversion problem, focuses on the numerical iterative solution, and according to the characteristics of actual micro-seismic monitoring, proposed the objective function based on moveouts of first arrivals of perforation. In the modeling computation, we analyzes the impact of first break picking errors and ground-based observations of the detector array layout range on velocity model inversion calibration. Finally, based on the perforating data from Shanxi Loufan hydraulic fracturing monitoring, the velocity model of this region were calibrated using the method in this paper, and the perforaton source has been relocated using the calibrated velocity model. From the location results, velocity model after calibration can locate the perforation position near the real position, velocity model inversion method herein is proved correction with feasibility and practicability. Key words:...