At present, most of the plugging agents for oil - based drilling fluids at home and abroad are composed of emulsified asphalt, oxidized asphalt, polymers, lignite resins, graphite spheres, etc. Most of these materials have no chemical activity and only have certain physical plugging effects. They are only effective for pores of a certain size. When there are heterogeneous pores and fractures, their effects are limited. In particular, these plugging agents are prone to aggregation in oil - based drilling fluids at high temperatures, thus failing to effectively plug.
Therefore, in order to improve the broad - spectrum plugging effect and high - temperature stability, a high - performance high - temperature - resistant plugging agent for oil - based drilling fluids must meet three conditions: First, the plugging agent has good high - temperature stability and does not aggregate in the oil - based drilling fluid. Second, the plugging agent should have adsorption groups and long carbon chains, a high oil - soluble substance content, and possess both chemical and physical plugging capabilities. Third, the particle size distribution of the plugging agent should be wide to improve the ability to plug fractures of various widths.
Based on the above three conditions, the company has successfully developed the high - temperature - resistant plugging agent for oil - based drilling fluids, ME - SHIELD. It is mainly a composite composed of sulfonated asphalt prepared using a unique chemical modifier and production process, oil - soluble inorganic nanomaterials, and oil - soluble polymers substituted with different alkane chain lengths. Its particle size distribution is wider. In the system, there are particles ranging from dissolved colloidal particles to relatively large solid particles equivalent to crushed asphalt particles. The wide particle size range improves the ability to plug fractures of various widths.
The main components of ME - SHIELD are specially modified sulfonated asphalt and substituted oil - soluble polymers. These two types of substances have long alkyl chains and are stably dispersed in the oil - based drilling fluid to form colloidal particles. Under the action of pressure difference, they deform and participate in the formation of the "inner filter cake", as shown in the figure. In addition, the sulfonated asphalt also contains a small amount of sulfonic acid groups, which can adsorb and coat the positively - charged shale fracture end faces to form a "separation membrane". Therefore, this type of plugging agents can enhance the plugging effect of the oil - based drilling fluid on micro - fractures in the formation and maintain wellbore stability.
