Effect Of Drilling Fluid Rheological Properties On The Hard Brittle Shale Stability

Currently hard brittle shale borehole wall stability problem is very outstanding in the drilling process,the influence of drilling fluid on the hard brittle shale stability is mainly aimed at the density,sealing and inhibition of some drilling fluid parameters,however,drilling fluid performance parameters include rheology,its influence on sidewall stability is also cannot be ignored,so the effect of rheology of drilling fluid on the hard brittle shale stability has a certain significance.Hard brittle shale borehole wall instability is mainly affected by the rock strength and circumferential stress state around borehole,at the same time,the micro cracks of hard and brittle shale are very developed,they are the main flow channel of fluid,and the flow in them is the main factor affecting the mechanical properties of hard brittle shale.So this paper mainly research on the influence of drilling fluid rheology on pore pressure in micro fractures and rock strength of hard brittle shale formation,get the following conclusion: with the increase of drilling fluid viscosity,the increase of pore pressure in micro fractures and the length of pressure transfer decrease,while the yield value of drilling fluid has little influence on pore pressure in micro fractures and pressure transfer length.For the strength of the hard brittle shale after soaking,the greater the viscosity of the drilling fluid,the lower the magnitude of the shale strength.It shows that improving the drilling fluid viscosity and other parameters is beneficial to improve the borehole stability of hard brittle shale under the condition of reasonable drilling fluid rheology.