Research On Anti-sloughing Drilling Fluid For Carbonaceous Shale In Tunnel Investigation Of Lan-Yu Railway

With the investment of railway and other national infrastructures increasing, the tasks of railway investigation are more and more year by year. In the investigation of railway, it's likely to encounter complicated technologic problems including loss circulation, wellbore blocking and collapsing when drilling in fractured formation, quick sand formation, shale formation, and formations with joint, fold and fault structures. The wellbore collapse has a serious effect to the investigation quality, and it will affect the schedule of construction. So it's necessary to have a research on the anti-sloughing drilling fluid.The non-invasive drilling fluid can form a thin and tough membrane with ultra low permeability on the rock surface, which can separate the drilling fluid and the formations. So it can prevent the hydration of the shale and the wellbore collapsing. The silicate drilling fluid can coagulate colloid when the pH value under 9, and the silicate can form sediment when it meet Mg2+ and so on. So this plugged zone can prevent the drilling fluid entering formations. In addition, the silicate also has inhibitive ability, which can prevent the hydration of the shale.Based on the carbonaceous shale collapsed easily in the tunnel investigation of Lan-Yu railway. Firstly, this paper analyzed the mechanism of wellbore collapsing in the shale. Secondly, on the mechanisms of the non-invasive drilling fluid and the silicate drilling fluid, this paper had researched them deeply. Lastly, based on the researches of dominant factors of the non-invasive drilling fluid and the silicate drilling fluid, this paper determined the adding amount of them separately through experiments, then it developed formulas of them with excellent performances.Through tests of general performances, the experimental data indicates that they have better rheological property and inhibitive ability, linear expansion rates of shale sample are about 0.6% to 0.8% and 0.1%. The filtration test of the non-invasive drilling fluid is also experimented by FA non-invasive filtration apparatus, in which the data of the test indicates that it has a perfect performance in the sand bed. And the blocking layer which is formed by the non-invasive drilling fluid has plugging ability to water. All of these experimental data indicates that they have perfect performances.Through the application on the carbonaceous shale in the tunnel investigation of Lan-Yu railway, they showed unique abilities in preventing loss circulation and wellbore collapsing.