At present, the method of formation pressure is mainly divided into pressure prediction before drilling, pressure monitoring while drilling, and post-drilling pressure detection. The drilling monitoring method and the post-drilling pressure detection method cannot predict the pressure value of the formation in front of the drill bit. The pre-drilling prediction method is used to predict pressure by seismic data, but the accuracy of the result is not high. How to infer the pressure information of complex and unknown drilling strata based on very limited known formation pressure information is the key technical problem to be solved in this paper. In order to solve this problem, a method based on grey theory is proposed to predict the formation pressure in front of the drill. The prediction results of formation pore pressure based on the method in this paper are compared with the monitoring results of formation pore pressure while drilling: the maximum error is 3.408%, and the average relative error is 3.038%, which indicates that the model has high accuracy. It can meet the requirements of field drilling construction. Through the research of this paper, it can provide more accurate pore pressure information of the formation to be drilled under the bit. Based on the pressure prediction results of the formation to be drilled, dynamic engineering risk assessment can be carried out, so as to assist the drilling operators to make quick and accurate decisions and prevent drilling risk caused by inaccurate understanding of pressure information.
The complex geological conditions of drilling, the difficulty of formation collapse and fracture pressure prediction in South Sichuan work area lead to the complex drilling and frequent failure, which seriously restricts the safe and efficient development of shale gas. In view of this problem, this paper has carried out relevant research. First of all, the existing calculation model of formation collapse and fracture pressure is established and improved; on this basis, the sources of uncertainty in the calculation model of collapse and fracture pressure are analyzed, mainly the in-situ stress and rock mechanics parameters, which have a lot of uncertainties; then, the uncertainty of rock mechanics parameters and in-situ stress is analyzed, and its probability is determined. Finally, based on Monte Carlo simulation, the quantitative characterization method of formation collapse and fracture pressure uncertainty is established. The prediction result of collapse and fracture pressure is no longer a single curve or value, but an interval, which is more practical for drilling in complex geological environment. The results of this study are helpful to better describe the collapse and fracture pressure of complex formation and can provide more valuable reference data for drilling design.
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