Preparation and Swelling Inhibition of Mixed Metal Hydroxide to Bentonite Clay

Use of Highly Dispersed Mixed Metal Hydroxide Gel Compared to Bentonite Based Gel for Application in Drilling Fluid under Ultra-High Temperatures

In order to solve the problem of poor dispersion and stability of mixed metal hydroxide (MMH), a kind of mixed metal hydroxide-like compound (MMHlc) gel was synthesized for use as the base mud in drilling fluid instead of bentonite gel. Na₂CO₃, Na₂SiO₃, and C₁₇H₃₃CO₂Na were used as precipitants to form MMHlc with larger interlayer spacing and smaller particle size. MMHlc was synthesized by the coprecipitation method at 25 °C with a metal molar ratio of Mg:Al:Fe = 3:1:1. The performance evaluation of the treated drilling fluid showed that MMHlc (S2) synthesized using Na₂SiO₃ as the precipitant had the characteristics of low viscosity, low filtration, and a high dynamic plastic ratio at 25 °C, which fully met the requirements of oil field application, and it maintained its excellent properties after being aged at 250 °C for 16 h. Linear expansion and rolling recovery experiments showed that the S2 sample had excellent rheological properties and good inhibition. X-ray diffraction and FT-IR experiments showed that S2 had the most complete crystal structure, its interlayer distance was large, and its ion exchange capacity was strong. The thermogravimetric experiment showed that the S2 crystal was stable and the temperature resistance of the crystal could reach 340 °C. Zeta potential, particle size analysis, SEM, and TEM results showed that S2 is a nanomaterial with a complete morphology and uniform distribution. The drilling fluid of this formula had the characteristics of low viscosity, low filtration loss, and a high dynamic plastic ratio, and it met the conditions for oil field application. Considering these results, the new MMH prepared by our research institute is a drilling fluid material that can be used at ultra-high temperatures and can provide important support for drilling ultra-deep wells.

Multi-Mixed Metal Hydroxide as a Strong Stratigraphic Nanoclay Inhibitor in Solid-Free Drilling Fluid

Solid-free drilling fluid has more advantages as a new type of drilling fluid compared with traditional drilling fluid, such as improving drilling efficiency, protecting oil and not having clay particles clog the oil and gas layer. In this study, Zn/Cu/Fe-doped magnesium-aluminum hydroxide (Mg-Al MMH) was prepared using the co-precipitation method and evaluated in solid-free drilling fluid. The inhibition mechanism of synthesized hydroxide was analyzed by X-ray diffraction, laser particle-size analysis and thermogravimetric analysis. The samples were directly used as drilling fluid base muds for performance evaluation. The results showed that the linear expansion rate of 4% M6-Fe was only 12.32% at room temperature within 2 h, that the linear expansion rate was 20.28% at 90 °C and that the anti-swelling rate was 81.16% at room temperature, indicating that it has a strong inhibition ability at both room temperature and at high temperatures. Meanwhile, the possibility of multi-mixed metal hydroxide as a drilling fluid base mud is discussed in this study. We found that 4% M6-Fe exhibited low viscosity, a high YP/PV ratio and high temperature resistance, and its apparent viscosity retention rate reached 100% rolled at 200 °C for 16 h, with a YP/PV ratio of 2.33.

Study on Preparation of Polymer-Modified Bentonite and Sand Mixtures Based on Osmotic Pressure Principle

Polymer-modified bentonite and sand mixtures (PMBS) are widely used in the engineering field due to their low cost and low permeability. In this study, different ionic types of polyacrylamides were used to modify bentonite to improve its swelling properties and impermeability. The physicochemical properties of polymer-modified bentonite were characterized by X-ray diffraction, particle size distribution, IR spectroscopy, SEM, and free swell index (FSI) to further demonstrate the successful organic modification of bentonite. To investigate the impermeability mechanism of PMBS from the perspective of osmotic pressure, the colloidal osmotic pressure of bentonite and hydraulic conductivity were compared. The results showed that anionic polyacrylamide (APAM) had the most obvious improvement on the swelling properties of bentonite, and 3% APAM increased the FSI of bentonite from 15 mL/2 g to 41 mL/2 g. With the increase in polymer dosage, the colloidal osmotic pressure of bentonite increased and the hydraulic conductivity of PMBS decreased significantly. The interior of PMBS is equivalent to a highly concentrated bentonite–sand–water system. When the colloidal osmotic pressure in the restricted space is higher than the external hydraulic pressure, it will prevent infiltration from occurring. When the external hydraulic pressure exceeds the high concentration of bentonite colloid osmotic pressure, the hydraulic conductivity may increase rapidly. Therefore, the impermeability of PMBS depends on the colloidal osmotic pressure of bentonite. Finally, it was confirmed that PMBS had a self-healing capacity by simulating damage to PMBS.