Oil phase drilling fluid additive, composition and process

Claim 2

The drilling fluid of claim 1 wherein the ratio of said asphalt particles to said resin is about 4-to-1.

Claim 3

In a method of drilling a well into subterranean formations in which a water-in-oil emulsion drilling fluid is circulated into the well, the steps of forming a filter cake on the wall of The well to decrease loss of fluid from the drilling fluid which comprises admixing with said drilling fluid an amount of at least about 1.5 pounds per 42 gallon barrel of (1) a vinyl toluene-acrylate copolymer resin which is obtained by reacting (a) vinyl toluene with (b) an acrylate moiety selected from the class consisting of methyl, ethyl, 2-ethyl-hexyl, butyl and dodecyl acrylates and methacrylates, the weight ratio of said acrylate-to-vinyl toluene being at least about 1.65-to-1, the molecular weight of said resin being at least 200,000, and (2) asphalt particles having a softening point from between 220*F and about 320*F, said particles being small enough to pass through a United States No. 60 standard mesh screen, the ratio of said asphalt particles to said resin being from about 1-to-1 to about 8-to-1, and circulating said drilling fluid in said well.

Claim 4

The method of claim 4 wherein the asphalt particles are air-blown asphalt.

Claim 5

The method of claim 4 wherein the ratio of said asphalt particles to said resin is about 4-to-1.