Uncertainty and Sensitivity Analysis of In-Situ Stress in Deep Inclined Strata

Abstract

In the development process of oil and gas field, the dip angles generally exist in deep strata, and the variability and dispersion in the mechanics parameters of the formation make the computation model of in situ stress for a gentle structure no longer applicable. In light of the fact that the dip angle was large and the geological structure was complex in Sichuan basin and Xinjiang basin, uncertainty of mechanical parameters and tectonic stress coefficients of the formation were analyzed by the Monte Carlo method based on acoustic logging data and stratigraphic dipmeter log data. Taking dip angle and dip direction into account, the uncertainty calculation method for in situ stress in deep inclined strata was proposed. Multi-factor analysis was used to analyze the sensitivity of various factors affecting the in situ stress in deep inclined strata. The results show that, the horizontal in situ stress calculation model adopted in this paper is more suitable for structurally intense areas. The horizontal stress confidence interval is more significant for oil and gas field engineering than single principal stress value. For PY gas field and TLM oil field with different geological conditions and rocks mechanical parameters of formation, the dip angle and effective stress coefficient are the most sensitive to the horizontal in situ stress.