The Development and Application of Nitrogen-Containing Graphene for Oil-Based Drilling Fluids

The marine facies Leikoupo formation in the west of Sichuan Province is a broken formation, in the later stage of horizontal drilling, it is frequently unable to exert weight on the drill bit, and borehole wall instability is another problem that haunts the drilling engineers. Analyses of these problems show that the oil-based drilling fluids presently in use have plugging capacity and lubricity that are unable to satisfy the needs of operation. To improve the plugging capacity and lubricity of the oil-based drilling fluids, based on molecular structure design, a nitrogen-containing graphene is developed through a combination of nitrogen doping modification and molten salt method. Using experimental methods, such as thermal stability measurement, dispersibility stability measurement, XRD, IR spectrum and particle size analyzer etc., the thermal stability, dispersibility, structure, functional group and particle sizes of the nitrogen-containing graphene are studied. The nitrogen-containing graphene was tested for its compatibility, plugging capacity, lubricity and high temperature resistance in active oil-based drilling fluids, and its functional mechanisms in oil-based drilling fluids are analyzed. Experimental results show that when the concentration of the nitrogen-containing graphene in an oil-based drilling fluid is 0.5%, the high temperature high pressure filter loss of the drilling fluid can be reduced by 76.2%, and the coefficient of friction reduced by about 50%. The nitrogen-containing graphene works normally at temperatures up to 180 ℃. In field operation, the use of the nitrogen-containing graphene significantly mitigated downhole problems such as the inability to exert weight on bit, high friction and borehole wall instability etc. The use of nitrogen-containing graphene has provided a new clue and technical support for solving the aforementioned drilling problems.