True triaxial mechanical characteristics of tight sandstone with different oil and water staturation

Abstract

The occurrence of fluids such as water, oil or natural gas in tight sandstone reservoirs may affect the mechanical characteristics of tight sandstone. This paper selects tight sandstones of Yanchang Formation in Panlong area of Ordos Basin, and uses YSZS-2000 multifunctional electro-hydraulic servo rock true triaxial testing machine to study the mechanical characteristics of tight sandstones with different oil and water saturation degrees. Results show that: ①The oil contents have a weakening effect on the peak stress and elastic modulus of sandstones. Both the peak stress and elastic modulus decrease with the increase of oil saturation. The peak stress can be reduced by 5.35% and the elastic modulus can be reduced by 11.38% when it is "quasi-saturated". ②Sandstones containing water can be divided into the Pa-type and the Pb-type according to the water absorption characteristic curve. Water content weakens the peak stress of sandstones. When saturated, the peak stresses of a Pa-type and a Pb-type sandstone can be reduced by 11.58% and 15.95%, respectively. ③After observing the internal structure of the oil-soaked sandstone, it is found that the oil is concentrated in the fractures between the sandstone minerals, which lubricates the fractured surface and reduces the bearing capacity of the sandstone. The research outcomes of this article can provide a reliable basis for the exploitation of tight oil and gas.

Keywords

• true triaxial test
• tight sandstone
• mechanical characteristics
• peak stress
• elastic modulus