Selecting bridging agents properly is a critical factor in designing non-damaging or low-damaging drill-in fluids. Historically, Abrams’ rule has been used for this purpose. However, Abrams’ rule only addresses the size of particle required to initiate a bridge. The rule does not give an optimum size nor an ideal packing sequence for minimizing fluid invasion and optimizing sealing. This paper elaborates an ideal packing approach to solving the sealing problem by sealing pores with different sizes, especially those large pores which usually make dominant contribution to permeability and thereby effectively preventing the solids and filtrate of drill-in fluids from invading into formations, compared with the conventionally used techniques. Practical software has been developed to optimize the blending proportion of several bridging agents, so as to achieve ideal packing effectiveness. The method and its use in selecting the best blending proportion of several bridging agents are also discussed in this paper. A carefully designed drill-in fluid by using the ideal packing technique (named the IPT fluid) for offshore drilling operations at the Weizhou Oilfield, Nanhai West Company, CNOOC is presented. The near 100% return permeabilities from the dynamic damage tests using reservoir cores demonstrated the excellent bridging effect provided by this drill-in fluid. Brid,,, Ab, brid brid brid brid Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting Selecting / This paper does not give an optimum size nor an ideal packing approach for minimizing fluid invasion and optimizing sealing. This paper elaborates an ideal packing approach to solve the sealing problem by sealing pores with different sizes, especially those large pores which usually make a dominant contribution to permeability and thus effectively preventing the solids and filtrate of drill-in fluids from invading into formations, compared with the conventionally used techniques. Practical software has been developed to optimize the blending proportion of several bridging agents, so as to achieve ideal packing effectiveness. The method and its use in selecting the best blending proportion of several bridging agents are also di The scoped in this paper. A carefully designed drill-in fluid by using the ideal packing technique (named the IPT fluid) for offshore drilling operations at the Weizhou Oilfield, Nanhai West Company, CNOOC is presented. The near 100% return permeabilities from the dynamic damage tests using reservoir cores demonstrated the excellent bridging effect provided by this drill-in fluid.