Quantitative Analysis Of Clay Combined With Inorganic Organic Composite System

In the process of drilling, due to the hydration swelling, dispersion and exfoliation of the shale, it is easy to cause deterioration of borehole, the borehole wall instability and other complex situations. But the qualitative or quantitative evaluation of the shale hydration is not enough to solve the above problems at present. The chemical/mechanical coupling research provides the basis to solve the real and objective problem at the present stage and the key to solve chemical-mechanical coupling research is probably of the quantitative evaluation of the shale hydration.The quantitative analysis of clay bound water should purify clay samples first of all, test its purity through the X-ray diffraction, quantitatively distinguish the tight bound water, weak bound water and free water in the soil-water system through thermal analysis method, establish an analytical method to quantitatively evaluate the clay bound water.For the preparation of single ion clay and achieve maximum hydration status of clay hydration, organic matter, impurities, sandy, electrolyte should be removed in the process of sample preparation and the clay be fully saturated by single ion. Then the slurry which the particles diameter is less than0.5microns used in experimental study. The clay under the condition of p/ps=1.0and isothermal adsorption measured by thermo gravimetric analysis method. There are three inflection point on the DTG curves, which is a temperature range of75±5℃,140±5℃,210±5℃respectively. It is commonly believed that75±5℃corresponds to the free water limits, that140±5℃corresponds to weakly bound water limits, that210±5℃corresponds to the tightly bound water limits. But the temperature range of60～80℃corresponds to the transition points that the part of weakly bound water is converted into free water, so75±5℃regarded as the end of the free water is controversial. The bound water content of the dried clay ratio is231.3%, which is the sum of tightly bound water and weakly bound water, so the thermo gravimetric analysis method can’t distinguish between tightly bound water and weakly bound water. The clay tightly bound water ratio is51.4%that measured by Modulated differential scanning calorimetry (MDSC) in-50℃and the results is consistent with the single ion clay could absorb tightly bound water content according to the theoretical calculation. Therefore MDSC could quantitatively distinguish between free water, weakly bound water and tightly bound water. Then quantitatively analyze shale in two formation interval through MDSC, which the measured results have certain linear correlation with the results of the linear expansion rate. Using thermo gravimetric analyze the inhibition performance of NaCl, KCl, CaCl2, which the inhibiting performance order is CaCl2> KC1> NaCl. It shows that thermo gravimetric analysis could relatively evaluate the inhibition performance and explain the inhibition mechanism of inorganic salt, but the organic inhibitors also needs further research.