Optimizing the particle size distribution of drill-in fluids based on fractal characteristics of porous media and solid particles

Drill-in fluid loss will lead to severe formation damage, and the particle size distribution (PSD) of lost circulation material is one of the most essential factors to control the drill-in fluid loss and protect the formation. In this paper, a fractal model for optimal solid PSD in drill-in fluids is developed for porous reservoir protection. The proposed model presents the following features: It demands particle size should be determined based on the “d90 Rule”, it requires the average capillary pressure curve to characterize the whole porous reservoir, and it allows for the microstructure characteristics of porous media and solid particles. The core dynamic damage experiments to verify this fractal model are carried out. Experimental results indicate that the loss of drill-in fluids designed by the proposed fractal model can be controlled within 10 min, and the permeability recovery rate after dynamic damage is above 90%, which means that formation damage is mitigated and well-controlled by the proposed fractal model. It is preliminarily proved that the proposed fractal model is of great validity and more suitable for formation damage control.