Shale wellbore instability is a complex difficulty encountered during drilling all over the world. And the most important factor to determine shale wellbore stability is the distribution and expansion of micro-cracks in hard brittle shale. The usual ways to avoid collapse of shale wellbore mainly include increasing the inhibition of drilling fluid filtrate, improving the quality of drilling fluid cake and sealing the pores and micro-cracks near the wellbore surface. However, the shale wellbore collapsing difficulty was not solved effectively in field, which mainly because that the effective sealing is difficult to achieved in the case of crack width is unknown. Furthermore the drilling fluid cake is more difficult to be formed on shale sections because of the filtration rate is very low compared to sand sections under the same differential pressure.
A kind of nanomaterial has been applied to achieve a sealing film rapidly, improve the sealing strength of the cake and reduce the mud cake permeability, which have been verified through the use of sound wave propagation speed, the pressure transmission experiment and cake strength. The technology had also been used in Well Exp1, which exhibited a smooth borehole and the borehole enlargement rate was below the wells in the same block.