Preliminary study on borehole wall protection mechanism of ionic stabilizer ENI for shale gas reservoir in northwestern Hunan

A series of experiments were carried out to analyze the mechanism that a kind of ionic stabilizer named "ENI" improves wellbore stability of shale reservoirs in northwestern Hunan. Pulpification rate test of bentonite, shale hot rolling dispersion test and shale swelling rate test were employed to evaluate the inhibitive properties between ENI and other additives comparatively. Scanning electron microscope (SEM) was used to investigate the effect of ENI on the microstructure of carbonaceous shale. The test results show that ENI has excellent inhibitive properties; compared with the clear water, ENI solution decreased the pulpification rate of bentonite by 52.41%; the rolling recovery rate of the ENI solution was the highest under the action of clear water and three inhibitive solutions. Meanwhile, among the four drilling fluids formulations studied in this paper, shale swelling rate in the drilling fluid with ENI as the critical additive was the lowest, and the rolling recovery rate was higher than 80%, which was the highest. In addition, some material produced by ENI can fill tiny cracks or pores, and improve the integrity of rock. Compared with other additives studied in this paper, ENI was more effective to inhibit hydration expansion and dispersion of carbonaceous shale, and it is beneficial to maintain the wellbore stability.