Abstract
Triaxial tests are performed on sandstone of an ultradeep well in Tarim Basin at high temperature 160°C and room temperature using GCTS RTR-1500 triaxial rock testing system. Sandstone’s full stress-strain curves under different experimental conditions are plotted, and a modified Duncan model is proposed based on experiment and theory. A simple analytic treatment of compressible gas flows in porous media is used to forecast the gas flowing pressure distribution. The compressive strength under room temperature is given via the logging data. The Hoek-Brown criterion is used for sandstone failure. It is shown that the temperature has a significant impact on elastic modulus of sandstone, but doesn’t affect Poisson ratio of sandstone. The modified Duncan model can predict the peak of the stress-strain curve of the sandstone. It is given that the variation of the compressive strength with the temperature. A field case verified that the proposed wellbore stability model could predict the safety pressure drawdown for an ultra-deep gas well during well test
1. INTRODUCTION
With the increasing demand for oil and gas worldwide due to emerging economies, oil and gas explorations are moving to more harsh environments, with more wells being drilled under high pressure and high temperature conditions. The initial reservoir equilibrium pressure in an ultradeep gas well can reach 100MPa or higher. As the high pressure gas in an ultradeep gas well moves toward the wellbore, it experiences increasing expansion and this expansion reaches a maximum at the exit to the wellbore. Expansion-induced gas acceleration can significantly impact the pressure distribution near the wellbore [1-4]. The properties of rock mechanics is summarized for different kinds of rock under high temperature [5-8]. Heuze et al [5] summarized the properties of the granite mechanics at high temperature. The effects of confining pressure and temperature on the granite mechanics was given by Lau et al [6]. Bayer and Welte [7] gave the effect of temperature on rock mechanical properties in source rocks via triaxial compression test. Using the computer simulation methods, Teich-McGoldrick et al [8] gave the effect of temperature on rock mechanical properties in mirrorstone rocks.
