In early 2008, Total E&P USA sidetracked the Mississippi Canyon 243 #A2 well on its "Matterhorn" tension-leg platform (TLP) in the deepwater Gulf of Mexico. A preproject geomechanics study identified that the mud-weight/fracture-pressure window in the depleted and highly unconsolidated "A" reservoir was very narrow, creating a strong potential for mud losses during drilling and cementing of the 7-in. liner. The risk of losses was a primary concern because the well would be frac packed, and if a competent cement column did not reach a sufficient height, the ability to fracture the reservoir would have been compromised. To mitigate this risk, the decision was made to drill through the depleted reservoir using a flat-rheology synthetic-based fluid, engineered with a high concentration of bridging particles to impart a strengthening effect on the formation.The designer fluid allowed the reservoir to be drilled through successfully and the 7-in. liner to be run and cemented with full returns. Analysis of the frac-pack data showed that the formation-breakdown pressure was lower than the wellbore pressures experienced while drilling and cementing the liner, suggesting that the designer fluid improved the fracture resistance of the formation. The results imply that using such a designer fluid can have a strengthening effect on depleted/unconsolidated formations, in which some operators have had limited success applying wellbore-strengthening techniques.The implication for the industry is that this technique can and should be considered on wells with challenges and risks similar to those of the Matterhorn A2 well. This paper will describe the approach taken in the laboratory for the fluid design, as well as operational practices to apply the treatment on location. A postmortem analysis will compare formation-breakdown pressures taken from the fracturing operations to actual wellbore pressures experienced while drilling and cementing, to demonstrate that a strengthening effect was realized.