--> Predrill Prediction of Formation Pressure Using Seismic Data: A Case of Huaguang Depression, Northern South China Sea

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Predrill Prediction of Formation Pressure Using Seismic Data: A Case of Huaguang Depression, Northern South China Sea

Abstract

There were many researches on formation pressure prediction. However, the technologies of formation pressure prediction were not perfect, there remained many problems, such as: formation pressure prediction using well data, only predict the formation pressure surrounding wells, it can not forecast the distribution of formation pressure, and it can not reach the need of predrill prediction of formation pressure. Only using seismic data, predrill prediction of formation pressure can be achieved, and it is the key to extract high-precision velocity profile. Deepwater area of northern South China Sea is characterized by sparse well, shallow drilling depth and difficulty to get precise formation velocity. Considering the unique conditions in this area, this paper firstly builds a precise computation model of formation pressure prediction, and proposes a new method to extract high-precision velocity profile, finally forms a new method on predrill prediction of formation pressure using seismic data. A tendency prediction model for formation pressure has been improved through compressibility factor, a low frequency velocity model has been set up, and a relative velocity has been extracted by colored inversion. Then seismic absolute velocity is acquired by adding these two velocities together. Ultimately, with the new calculation model and high-quality seismic absolute velocity, predrill prediction of formation pressure has been conducted in Huaguang depression. Testified by measured pressure, the predicted results have a higher accuracy. Our study shows that hydrostatic pressure develops in Neogene, weak amplitude overpressure develops in Paleogene, and the pressure coefficient mainly ranges from 1.1 to 1.4 in Paleogene in Huaguang Depression. The magnitude and scope of overpressure in the Yacheng Formation were more than the Lingshui Formation. The body of overpressure is located on the deep depression in north of the depression, and there are two overpressure centers distributed in East sag and West sag respectively, and the maximum pressure coefficient is 1.5. The pressure gradually decreases from the center of the depression to the edges.