Calculation Method of Three-Dimensional Fracture Pressure in Shallow Layers of Deepwater

摘要

Fracturing pressure is a key index to characterize the formation characteristics, and it is also a basic factorrnto determine well structure and safety. Furthermore, accurate calculation of formation fracture pressure isrnof great significance to determine the safe density window of drilling fluid precisely. Deepwater shallowrnnature is changeable due to shallow flow, shallow gas and other natural disasters. Despite the accuraterncalculation of the shale formation fracture pressure through computational model, the existing methodsrnstill exists some deficiency such as the lack of pertinence and intuitive of special layers.rnThis paper proposes a computational method of 3-D fracture pressure. Firstly, it calculates single pointrnof fracture pressure in deepwater shallow layers by lateral pressure coefficient method which is morernadaptable to the actual engineering. Then 3-D density data and 3-D velocity data can be worked outrnreasonably based on logging constrained seismic inversion technique by using the Jason inversionrnsoftware. Besides, it uses the Kriging interpolation method by combining inversion density data andrninversion velocity data to calculate pressure of each stratum. Finally, 3-D fracture pressure can be obtainedrnby applying interpolation technique again. After that, it designs the formation fracture pressure softwarernfor display,rnThis paper presents a case study of Yingqiong basin in South China Sea. First, it uses constrainedrninversion to get 3-D density data and 3-D velocity data, and then obtains the 3-D fracture pressure throughrnthe method based on the 3-D seismic data collected. It can conclude the spatial distribution characteristicsrnof the 3-D fracture pressure of the shallow region. And the value of the region has been compared withrnthe drilled wells fracture pressure gradient measured values sub regionally.rnThrough the comparison and analysis of the measured value, this method effectively improves therncalculation precision of 3D fracture pressure. It can be applied in the engineering design to improve thernengineering safety, thus it can be widely promoted.