Formation Pressure Prediction By Analysis On Bi-spectrum Velocity

Formation pressure is a basic data which is obtained in the process of oil fieldexploration and development. In the geological exploration process, in order toformulate and design reasonable scheme for exploration and improving the oil and gasproduction, we need to know the law of the distribution, migration, accumulation andother aspect of oil and gas in this area. Accurate prediction of formation pressure inoil field can provide important information for this; In the oil field drilling practice, inorder to reduce the occurrence of well leakage blowout accident,make drilling cycleshorten, increase drilling speed, we must design reasonable structure of well depth,use drilling fluid with accurate density. For this purpose, the accurate formationpressure prediction is of prime importance.There are a variety of abnormal pore pressure in the formation, generallyspeaking, high pore pressure formation have particular physical response, which isdifferent from normal formation. Formation with abnormal pressure have highporosity, low density, sound velocity and resistivity and so on. Geophysical methodwhich can reflect the characteristics of abnormal pressure could be used in the test ofpore pressure. Logging method can get detailed, accurate and intuitionisticinformation of physical parameters, but because it is the technology after event.So itcannot be used in the evaluation of the formation pressure. So using seismic data topredict pore pressure is particularly important. At present the method of using seismicdata to predict pore pressure mainly use interval velocity and the relation modelbetween the interval velocity and the formation pressure for predrilling pressureprediction. At the same time, using the method of the seismic exploration for pressurepredict can also provides a rich information of pressure distribution, which thelogging methods cannot done. According to the characteristics and principle of usingseismic data to predict pore pressure, we know that the accuracy of the predictiondepends on the interval velocity obtained by seismic data and the methods forprediction.In the underground medium, anisotropic properties widely exist. Seismicacquisition usually use large offset to accept for seismic waves. In the conventionalvelocity analysis, with the reflective layer increases, and the offset increases, the scan data will gradually increase the bias. So this paper combine principal componentanalysis (PCA) criterion with velocity analysis of bispectral scanning to pick upseismic velocity and two-way travel time.The traditional formation pressure prediction method most based on normalcompaction trend line. But setting up normal compaction trend line need morelithology parameters and geological information.the necessary development oftraditional method is researching methods which cannot rely on the normalcompaction trend line.Fillippone formula method is put forward in this kind ofsituation. A large number of practical experience proved it.This paper apply thevelocity parameter and time parameter to the Fillippone formula for improving theaccuracy of pressure prediction.