Abstract
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.
Highlights
Formation collapse pressure and formation fracture pressure are the upper and lower limits of safe drilling fluid density window to maintain wellbore stability
The rock mechanics parameters and in-situ stress input in the existing calculation model of formation collapse and fracture pressure are all treated according to the fixed value, and the prediction results of formation collapse and fracture pressure are all single value results
First of all, established and improved the existing calculation model of formation collapse and fracture pressure. On this basis, analyzed the sources of uncertainty in the calculation model of formation collapse and fracture pressure, mainly the in-situ stress and rock mechanics parameters, which are usually obtained through indirect mathematical model calculation based on seismic or logging data, so there are a lot of uncertainties
Summary
Formation collapse pressure and formation fracture pressure are the upper and lower limits of safe drilling fluid density window to maintain wellbore stability. In the actual drilling engineering, due to the particularity of the drilling engineering construction, as well as the uncertainty of geological conditions, the complexity of. First of all, established and improved the existing calculation model of formation collapse and fracture pressure On this basis, analyzed the sources of uncertainty in the calculation model of formation collapse and fracture pressure, mainly the in-situ stress and rock mechanics parameters, which are usually obtained through indirect mathematical model calculation based on seismic or logging data, so there are a lot of uncertainties. Based on Monte Carlo simulation, the quantitative characterization method of the uncertainty of formation collapse and fracture pressure is established. The prediction result of formation collapse and fracture pressure is not a single curve or value, but an interval range, which is more practical for drilling in complex geological environment
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