Microseismic Monitoring Inversion Method Study

Micro-seismic technique is an important new technique in the field of low permeability oil reservoir reformation, which has been widely used to monitor oil-field production performance because of its high efficiency and low cost. However, in the actual process of oil reservoir exploitation, the information of micro-seismic generated is relatively weak, which brings great difficulty for locating the source accurately by inversion. To resolve this problem, a source inversion method in view of micro-seismic is studied in this paper.The basic approach of micro-seismic monitoring is receiving micro-seismic events which are produced or induced in everyday life by fixing up geophone layout in the radial source or land and by the inversion of these events to obtain micro-seismic source and other parameters, and then applying these parameters to monitor or guide the everyday production activities.Micro-seismic dates include generally two parts, perforation datas and the actual monitoring datas. Micro-seismic events are stimulated by perforation and recording micro-seismic time will help geophone positioning and to establish formation medium velocity model. But the actual monitoring data are mostly used for the inversion of fracture parameters. by conventional seismotectonic interpretation, log interpretation and interwell stratigraphic correlation, I have finished geologic model building, which takes layered homogeneous medium model based on shortest path ray tracing theory. The shortest path ray tracing method’s realization is based on Fermat’s principle about seismic wave transmission and Snell’s law. Fermat’s principle instructs that trajectory of seismic waves is along the path of least travel time, the purpose of seismic ray tracing is to find the path of least travel time about trajectory of seismic waves from seismic sources to every receiving point.First break picking is must be carried out in the micro-seismic datas processing, which refers to determine the time of origin direct P-wave in every seismic trace. Accurate first break picking is very important to calibrate horizon velocity, build medium model and inverse the micro-seismic hypocentral location. First break picking methods is studied and modified in this paper, making them to better meet the actual needs and enhancing the usefulness and reliability of the first break picking results.In this paper, I introduce several common inversion methods, P-S interval method, homoeotypic waves interval method and nonlinear method. The existing nonlinear methods include gradient method, newton algorithm, global search method, Bayesian algorithm, Monte Carlo method, simulated annealing algorithm and genetic algorithm. I mainly introduce gradient method, newton algorithm, Monte Carlo method, simulated annealing algorithm. Finally, according to the characteristics of this area, I choose the gradient descent method for inversion of orientation.Micro-seismic inversion of the basic steps include:(1)establishing forward modeling;(2)first break picking;(3)method of inversion:the gradient descent method for inversion of orientation.Based on a field of micro-seismic sourse inversion as an example, in this fracturing seismic surveillance, it produces four hundred micro-seismic events in which high signal-to-noise ratio, separately much clear p-s waves of micro-seismic events have two hundred sixty seven, through the artificial separation. I select these two hundred sixty seven micro-seismic events, and inverse successfully least one hundred ninety seven effective micro-seismic events. Making use of hydro-fracturing micro-seismic sourses3D display, we can observe fracture interspace shape from any direction. Micro-seismic monitoring technology may objectively provide the crack length, height, fracture orientation and so on.It is very useful to instruct fracture, calibrate software crack models, improve and enhance fracture transformation effect.we can use these information to optimize fracture design, well pattern or other oil-field development measure, thus enhance the recovery ratio.Reservoir engineers can determine the distribution of middle layers based on fracture Spatial locations, and then determine the development plan, design the location of new wells. Reservoir engineers can crack the spatial position to determine the distribution of middle layer, and then determine the development plan, design the location of new wells. Micro-seismic monitoring technology can also be used in reservoir fracturing and oil deposit driven monitoring. Through the analyse combined with fracture parameters and source points parameters,the main direction of maxinum flat ground stress and mininum flat ground stress in reservoir and the historic maximal value can be determined. The range of fracture, direction and size of fracture can be traced to locate. The objective evaluates to the effect of fracturing can guide the production and reduce the cost of exploit.