Patent ID: 8076269

Claim:
A method associated with drilling a wellbore comprising: determining a pore pressure gradient and a fracture pressure gradient at a selected depth within the wellbore, selecting reusable compressible objects having a shell that encloses an interior region, wherein the compressible objects have an internal pressure at atmospheric external pressure that is in between the pore pressure gradient and fracture pressure gradient at the selected depth and greater than 250 psi, wherein the shell is configured to experience less strain when the external pressure is about equal to the internal pressure than when the external pressure is both above and below the internal pressure of the compressible object, the reusable compressible objects comprising (a) an initial aspect ratio between 3 and 4 in an initial state when an initial state pressure external to the compressible object is substantially equal to an initial state internal pressure in the interior region and the initial state internal pressure is greater than 200 psi and the initial state internal pressure is selected for the shell to compress and expand at a predetermined pressure range, (b) a spherical or near spherical shape in an expanded state when the external pressure is substantially atmospheric pressure, and (c) a compresses state aspect ratio that is higher than the initial aspect ratio when the external pressure is greater than the internal pressure; selecting a drilling fluid; introducing the compressible objects to the drilling fluid to form a variable density drilling mud, wherein the density of the variable density drilling mud varies in a non-linear fashion along at least a portion of the wellbore and the variable density drilling mud provides a density between a pore pressure gradient and a fracture pressure gradient for at least one interval as the variable density drilling mud circulates toward the surface of a well; and drilling the wellbore using the variable density drilling mud.