A drilling fluid containing a liquid phase, a weighting agent (e.g. barite, calcite, ilmenite), and perlite is described. The drilling fluid may further contain one or more additives including a defoamer, a fluid-loss control agent, a viscosifier, an antiscalant, a deflocculant, a lubricant, a clay stabilizer, a bridging agent, and a surfactant. A process of drilling a subterranean geological formation utilizing the drilling fluid is also specified. The introduction of perlite to the drilling fluid is effective in reducing the thickness and permeability of filter cakes formed during the drilling process.