Stress-sensitivity mechanisms and its controlling factors of saline-lacustrine fractured tight carbonate reservoir

Abstract

Although the stress sensitivity of carbonate reservoir has been investigated extensively, that of saline-lacustrine fractured tight carbonate reservoir still remains to be fully understood. In this work, permeability stress sensitivity behavior of saline-lacustrine fractured tight carbonate reservoir was investigated based on steady state test and pressure attenuation method. Several core analysis and time-dependent deformation experiments were adopted to reveal the factors and mechanisms of stress sensitivity. Experimental results showed that pressure attenuation method could be available for stress-sensitivity assessment of tight carbonate reservoirs. Rock permeability decreased with increasing in effective stress, which could be classified into three stages: rapid decline, moderate decline and stable-slight decline stage. Fractures had a strong stress sensitivity behavior and higher permeability recovery rate after stress unloading, showing the stronger elastic deformation, while tight matrix showed the opposite results with stronger plastic deformation. The increase in number of nano-intercrystal pores led to stronger stress sensitivity behavior. The relationship between the stress sensitivity and mineral type was qualitatively built, and stress sensitivity of carbonate reservoir was positively related to the content of dolomite, salt minerals and clays, and negatively related to the content of quartz and calcite. The time-dependent deformation of salt minerals strengthened the stress sensitivity of saline-lacustrine tight carbonate reservoir.