Quantitative Description Method for Uncertainty of Formation Pore Pressure

摘要

Nowadays, the oil and gas exploration and development have been developed into the deep and complex formations. More and more abnormal pressure is encountered, which gives a great challenge to the safe and efficient drilling. Accurate description of pore pressure is of great significance to avoid drilling risk. The complexity of petroleum geology, the incompleteness of the logging or seismic data, the precision of the mathematical model and other issues can all lead to uncertainty in pore pressure prediction. The uncertainty of pore pressure is one of the fundamental causes for drilling risk. In order to address these challenges, a new quantitative description method for uncertainty of pore pressure was established. Firstly the sources of the pore pressure prediction uncertainty were analyzed. Then the uncertainties of Eaton index and normal compaction trend were, respectively, described. Finally the uncertainty interval of pore pressure was established based on Monte-Carlo simulation and normal information diffusion theory. The pore pressure prediction result obtained in this paper was not a single value, but an interval with probability distribution characteristic. The results of example showed that the measured values of pore pressure were all in pore pressure interval with confidence of 90%. Case study validated the feasibility and effectiveness of the proposed method.