Research Fractured Plugging

Lost circulation is one of the most serious drilling troubles that affect drilling safety, because it not only brings loss to drilling engineering, but also iMPacts exploration and development of oil and gas resources. This paper is concerned with the outstanding problems that exist in lost circulation resistance and control technology during drilling. Lost circulation mechanism, mathematic model and control technology were studied. It proposed a selection procedure suitable for controlling lost circulation in fractured formations.This article focused on the mechanism of lost circulation, analyzed the reasons, conditions and influence factors for lost circulation in fractured formations. It established the relationship between underground fracture parameters, such as fracture width, fracture porosity, fracture permeability, fracture length, and logging parameters. Based on the mechanism of lost circulation, a lost circulation mathematic model was established by continuity equations and Darcy laws. This model considered the coupling relationship among wellbore pressure, fracture flow pressure loss, and formation pressure. The effects of differential pressure, flow index, viscosity, permeability and time on the lost circulation were analyzed by solving this model. Some key issues exist in lost circulation control technology were discussed, and analyzed the impact of lost circulation position, control method and drill string depth to lost circulation control effect. It proposed a selection procedure suitable for controlling lost circulation in fractured formations. According to the analysis and summary of controlling lost circulation cases in six wells, controling lost circulation technologies in fractured formation were recommended.The research showed that the amount of drilling fluid lost circulation increased with the increase of differential pressure. When the distance from the center of borehole increased, it resulted in the decrease of differential pressure. When the time of lost circulation increased, it resulted in the increase of differential pressure. Therefore, it is critical to keep drilling fluid performance and trip speed in drill practice. The radius of lost circulation increased with the decrease of flow index, leaded to more serious lost circulation. So it need to adjust the flow index to a certain range which is helpful to constrain lost circulation during drilling practice. The radius of lost circulation decreased with the increase of viscosity. It is good to increase viscosity for mitigating lost circulation. The lost circulation in great permeability formation is more serious than that of low permeability formation.