Abstract
For high permeability sandstone, the invasion of particles and the filtrate of drilling fluids is proven as one of the key factors accounting for reservoir damage. However, it is difficult to determine the invasion depth of particles and the filtrate of drilling fluids by using mathematical model. The novel invasion models of particles and the filtrate of drilling fluids are built up in dynamic condition by the mass conservation equation and radial friction loss equation, especially for the models taking into account the external and internal mud cake at the same time. Parameters of models are determined by experiments of API filter loss and dynamic filtrate loss. The simulating results indicate that the invasion depth of particles is deeper when the core permeability is higher. The invasion depth of the filtrate is influenced seriously by the different pressure, the viscosity of filtrate, the permeability and thickness of external and internal mud cake. Howerver, permeability and fluid viscosity of reservoir have little influence on the filtrate invasion depth.
The zwitterionic polymer drilling fluids are optimized. In an addition, ideal packing approach is applied to the drilling fluids. The instrument of dynamic fluid loss test is used to evaluate return permeability. The test results indicate that the ideal packing approach can reduce the dynamic filtrate loss. It also can improve the return permeability and reduce breakthrough pressure. The predicted results of this model indicate that the invasion depth of particles and filter is deeper without bridging agents. Ideal packing approach can reduce formation damage.
