Research on Mechanism and Countermeasures of Wellbore Instability in Gravel Layer in Tarim Basin

There is a very thick gravel layer in Bozi-Dabei Block of Tarim Basin. Due to the strong heterogeneity of the gravel layer, the complex situations and accidents such as wellbore collapse and stuck pipe are caused. In response to this issue, the horizontal and vertical variation patterns of distribution patterns of gravel particles were first analyzed. Secondly, the geological and mechanical parameters of the block were analyzed and obtained. In-situ stress distribution is obtained by using acoustic emission method combined with field logging data. Test and analyze the influence of immersion in water-based mud on rock mechanics parameters. Completed the testing and analysis of the microstructure and hydration effects of the gravel layer once again. The microstructure and spatial distribution of gravel were analyzed by SEM and casting thin section test, and the influence of water-based mud on mechanical parameters of weak surface of gravel layer was tested to study its influence on rock mechanics properties and wellbore stability. Finally, a simulation study was conducted on the failure mechanism of the surrounding rock of the gravel layer. The research results showed that the main factor affecting the stability of gravel formation wellbore is the cement between the gravel and the gravel. The stronger the cement, the better the stability of the gravel, At the same time, the performance of the drilling fluid should also be matched with the physical and chemical properties of the cement. Based on these measures, optimizing the drilling fluid density and construction process can ensure the stability of the gravel layer wellbore. The above research results have been applied in three wells, and on-site experimental results show that the wellbore diameter remains relatively stable after using the above technology, without any related accident complications.