Patent ID: 7152697

Claim:
A method of controlling the inversion of a drilling fluid, wherein the drilling fluid includes: an oleaginous fluid; a non-oleaginous fluid; an amine surfactant having the structure wherein R is a C 12 –C 22 aliphatic hydrocarbon; R′ is independently selectable from hydrogen or C 1 to C 3 alkyl; A is NH or O, and 1≦x+y≦3, the method comprising: mixing said drilling fluid with a delayed phase changing agent selected from the group consisting of aliphatic amine acids, salts of aliphatic amine acids and combinations thereof, wherein the delayed phase changing agent is delivered in the form of a pill, the pill comprising a carrier fluid, a viscosifier and the delayed phase changing agent, and wherein the pill is in the form of a slug of fluid that remains generally uniform within the well bore.