Study On Plugging Agent For Oil - Based Drilling Fluids And Its Action Mechanism

When lost circulation happens in the water-based or oil-based drilling fluid, the bridge plugging agents are needed to end the leakage. As the conventional plugging materials, such as the calcium carbonate, walnut shell are hydrophilic, they do not work well in the oil-based drilling fluid. This paper researches on the plugging effect and mechanism of one kind of resina granulated plugging material, which works along with the fiber plugging material in the oil-based drilling fluid.Useing fractured bridge plugging as the research object, this paper researches plugging effect of bridge material in simulated fracture. At first, this paper studies the current plugging evaluation equipment, analyzes their advantages and defects and proposes a new idea that uses wedge fracture to evaluate bridge material. This paper develops a new type of fractured plugging simulation equipment to evaluate the effects of single and combined ions of some representative plugging materials. This article presents the concepts of fractured bridge plugging such as "throat plugging","front plugging","middle plugging" and "tail plugging". In order to achieve the destination of "throat plugging" and "middle plugging", this paper carries a series of experimental researches.By smooth fracture plugging experiment, this paper gets some conclusions. When using LCC plugging material to carry on a room temperature static plugging experiment, it is difficult to form a bridge plugging in fracture. And it only forms "front plugging" and "tail plugging". Because the fracture surface is smooth, plugging materials can neither form a stable bridge, nor resist high pressure. When pressure increases, these materials slid to the tail of fracture. If loose "front plugging" forms, the loss of drilling fluid will happen again when the pump works. And if "tail plugging" forms, it indicates that particles invade deep and the plugging does not work.By rough fracture plugging experiment, it is easy to find that LCC plugging material can form a stable bridge plugging within the fracture, and the mixture material works better than single material. Based on research of the different plugging states, which caused by different plugging materials, we find that the ratio of main plugging particle and minor plugging particle is the major control factor. Moreover, the minor plugging particle has the dual function of plugging and filling, which should be given high priority. Finally, this paper optimizes inner-plugging formulas for different fracture width.By researches on the mechanism of the plugging materials, the conclusion that the approximate grain size regularity of inner-plugging bridge material conforms to the D90principle will be gotten.