Low-permeability reservoirs are usually developed through natural depletion and the loss of formation pressure is not restored

causing stress sensitivity of reservoirs.We chose the lower 8

th

member of the Lower Shihezi Formation in Sulige-Jier area

the Ordos Basin as a case study.Through downhole geological survey

core observation

systematic sampling and testing

and lab correlation and analysis

we studied the coupling relation between the petrologic characteristics and stress-sensitivity and found out that the rock types of the layers of interest are mainly lithic quartz sandstone

followed by siliceous quartz sandstone and small amount of lithic sandstone.The samples were tested with model CMS-400 high-pressure porosity and permeability analyzer.The initial permeability was low and stress-sensitivity was medium to strong and the two presented an obvious positive correlation.Among the rock components

the soft debris and matrix that have low hardness and stability are easily deformed

crushed and displaced under exogenic action.Their contents have positive correlations with the stress-sensitivity.Detrital quartz

rigid debris and cements such asquartz and daphnite have higher hardness and stability and remain stable under exogenic action.And their contents have negative correlations with stress-sensitivity.Different rocks have various stress-sensitivities because of their different petrologic characteristics.During the development of oilfields

we suggest to optimize deliverability by using production pressure differentials at different levels.